Effect of the Lateral Exospheric Transport on the Horizontal Hydrogen Distribution Near the Exobase of Mars

NASA Astrophysics Data System (ADS)

Chaufray, J.-Y.; Yelle, R. V.; Gonzalez-Galindo, F.; Forget, F.; Lopez-Valverde, M.; Leblanc, F.; Modolo, R.

2018-03-01

We simulate the hydrogen density near the exobase of Mars, using the 3-D Martian Global Circulation Model of Laboratoire de Météorologie Dynamique, coupled to an exospheric ballistic model to compute the downward ballistic flux. The simulated hydrogen distribution near the exobase obtained at two different seasons—Ls = 180° and Ls = 270°—is close to Zero Net Ballistic Flux equilibrium. In other words, the hydrogen density near the exobase adjusts to have a balance between the local upward ballistic and the downward ballistic flux due to a short lateral migration time in the exosphere compared to the vertical diffusion time. This equilibrium leads to a hydrogen density n near the exobase directly controlled by the exospheric temperature T by the relation nT5/2 = constant. This relation could be used to extend 1-D hydrogen exospheric model of Mars used to derive the hydrogen density and escape flux at Mars from Lyman-α observations to 3-D model based on observed or modeled exospheric temperature near the exobase, without increasing the number of free parameters.

Tomographic Reconstruction of Mercury's Exosphere from MESSENGER Flyby Data

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; McClintock, William E.; Slavin, James A.; Solomon, Sean C.; Vervack, Ronald J., Jr.

2011-01-01

The exosphere of Mercury is among the best-studied examples of a common type of atmosphere, a surface-bounded exosphere. Mercury's exosphere was probed in 2008-2009 with Ultraviolet and Visible Spectrometer (UVVS) measurements obtained during three planetary flybys by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft [1-3]. The measurements detailed the distribution of two previously known metallic constituents of Mercury's exosphere, Na and Ca, and indicated the presence in the gas phase of yet another metallic species, Mg. Such measurements can answer fundamental scientific questions regarding the relative importance of possible source and loss processes for exospheric species ejected from a surface boundary [4]. The trajectory of MESSENGER during the last of its three flybys provided the best spatial coverage prior to orbit insertion. The measurements by MESSENGER of Na, Ca, and Mg during the third flyby have been analyzed with a novel tomographic method. This approach maximizes the amount of information that can be extracted from line-of-sight measurements because it yields three-dimensional distributions of neutrals consistent with the data.

Seasonal Variations in Mercury's Dayside Calcium Exosphere

NASA Technical Reports Server (NTRS)

Burger, Matthew H.; Killen, Rosemary M.; McClintock, William E.; Merkel, Aimee W.; Vervack, Ronald J., Jr.; Cassidy, Timothy A.; Sarantos, Menelaos

2014-01-01

The Mercury Atmospheric and Surface Composition Spectrometer on the MESSENGER spacecraft has observed calcium emission in Mercury's exosphere on a near-daily basis since March 2011. During MESSENGER's primary and first extended missions (March 2011 - March 2013) the dayside calcium exosphere was measured over eight Mercury years. We have simulated these data with a Monte Carlo model of exospheric source processes to show that (a) there is a persistent source of energetic calcium located in the dawn equatorial region, (b) there is a seasonal dependence in the calcium source rate, and (c) there are no obvious year-to-year variations in the near-surface dayside calcium exosphere. Although the precise mechanism responsible for ejecting the calcium has not yet been determined, the most likely process is the dissociation of Ca-bearing molecules produced in micrometeoroid impact plumes to form energetic, escaping calcium atoms.

Differential equation of exospheric lateral transport and its application to terrestrial hydrogen

NASA Technical Reports Server (NTRS)

Hodges, R. R., Jr.

1973-01-01

The differential equation description of exospheric lateral transport of Hodges and Johnson is reformulated to extend its utility to light gases. Accuracy of the revised equation is established by applying it to terrestrial hydrogen. The resulting global distributions for several static exobase models are shown to be essentially the same as those that have been computed by Quessette using an integral equation approach. The present theory is subsequently used to elucidate the effects of nonzero lateral flow, exobase rotation, and diurnal tidal winds on the hydrogen distribution. Finally it is shown that the differential equation of exospheric transport is analogous to a diffusion equation. Hence it is practical to consider exospheric transport as a continuation of thermospheric diffusion, a concept that alleviates the need for an artificial exobase dividing thermosphere and exosphere.

Insights into the Nature of Mercury's Exosphere: Early Results from the MESSENGER Orbital Mission Phase

NASA Technical Reports Server (NTRS)

McClintock, William E.; Burger, Matthew H.; Killen, Rosemary M.; Merkel, Aimee W.; Sarantos, Menelaos; Sprague, Ann L.; Solomon, Sean C.; Vervack, Ronald J., Jr.

2011-01-01

The Ultraviolet and Visible Spectrometer aboard the MESSENGER spacecraft has been making routine observations of Mercury's exosphere since March 29, 2011. Correlations of the spatial distributions of Ca, Mg, and Na with MESSENGER magnetic field and energetic particle distribution data provide insight into the processes that populate the neutral exosphere

The long egress of GJ 436b's giant exosphere

NASA Astrophysics Data System (ADS)

Lavie, B.; Ehrenreich, D.; Bourrier, V.; Lecavelier des Etangs, A.; Vidal-Madjar, A.; Delfosse, X.; Gracia Berna, A.; Heng, K.; Thomas, N.; Udry, S.; Wheatley, P. J.

2017-09-01

The M dwarf GJ 436 hosts a transiting warm Neptune known to experience atmospheric escape. Previous observations revealed the presence of a giant hydrogen exosphere transiting the star for more than 5 h, and absorbing up to 56% of the flux in the blue wing of the stellar Lyman-α line of neutral hydrogen (H I Lyα). The unexpected size of this comet-like exosphere prevented observing the full transit of its tail. In this Letter, we present new Lyα observations of GJ 436 obtained with the Space Telescope Imaging Spectrograph (STIS) instrument onboard the Hubble Space Telescope. The stability of the Lyα line over six years allowed us to combine these new observations with archival data sets, substantially expanding the coverage of the exospheric transit. Hydrogen atoms in the tail of the exospheric cloud keep occulting the star for 10-25 h after the transit of the planet, remarkably confirming a previous prediction based on 3D numerical simulations with the EVaporating Exoplanet code (EVE). This result strengthens the interpretation that the exosphere of GJ 436b is shaped by both radiative braking and charge exchanges with the stellar wind. We further report flux decreases of 15 ± 2% and 47 ± 10% in the red wing of the Lyα line and in the line of ionised silicon (Si III). Despite some temporal variability possibly linked with stellar activity, these two signals occur during the exospheric transit and could be of planetary origin. Follow-up observations will be required to assess the possibility that the redshifted Lyα and Si III absorption signatures arise from interactions between the exospheric flow and the magnetic field of the star.

Contributions of solar-wind induced potential sputtering to the lunar surface erosion rate and it's exosphere

NASA Astrophysics Data System (ADS)

Alnussirat, S. T.; Barghouty, A. F.; Edmunson, J. E.; Sabra, M. S.; Rickman, D. L.

2018-04-01

Sputtering of lunar regolith by solar-wind protons and heavy ions with kinetic energies of about 1 keV/amu is an important erosive process that affects the lunar surface and exosphere. It plays an important role in changing the chemical composition and thickness of the surface layer, and in introducing material into the exosphere. Kinetic sputtering is well modeled and understood, but understanding of mechanisms of potential sputtering has lagged behind. In this study we differentiate the contributions of potential sputtering from the standard (kinetic) sputtering in changing the chemical composition and erosion rate of the lunar surface. Also we study the contribution of potential sputtering in developing the lunar exosphere. Our results show that potential sputtering enhances the total characteristic sputtering erosion rate by about 44%, and reduces sputtering time scales by the same amount. Potential sputtering also introduces more material into the lunar exosphere.

Synodic and Semiannual Oscillations of Argon-40 in the Lunar Exosphere

NASA Technical Reports Server (NTRS)

Hodges, R. Richard, Jr.; Mahaffy, Paul R.

2016-01-01

The neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft collected a trove of exospheric data, including a set of high-quality measurements of radiogenic Ar-40 over a period of 142 days. Data synthesis studies, using well-established exosphere simulation tools, show that the LADEE argon data are consistent with an exosphere-regolith interaction that is dominated by adsorption and that the desorption process generates the Armand distribution of exit velocities. The synthesis work has uncovered an apparent semiannual oscillation of argon that is consistent with temporal sequestration in the seasonal cold traps created at the poles by the obliquity of the Moon. In addition, the LADEE data provide new insight into the pristine nature of lunar regolith, its spatially varying sorption properties, and the influence of sorption processes on the synodic oscillation of the argon exosphere.

Variability of Europa's Interaction with the Jovian Magnetosphere

NASA Astrophysics Data System (ADS)

Hale, J. M.; Paty, C. S.; Crary, F. J.; Jones, A. J.

2017-12-01

In anticipation of the arrival of the Europa Clipper mission at its destination, this work characterizes the interaction of Europa with the Jovian magnetosphere using a multifluid MHD treatment. In order to accomplish this, the system is simulated in multiple relevant configurations, including cases in which Europa is without an exosphere and cases with an exosphere. While not a reflection of reality, simulations of the system without a Europan exosphere—and ionosphere—allow for quantification of the effects of the induced dipole separate from those of plasma sourced at Europa. In the cases in which an exosphere is simulated, asymmetries due to the sputtering derived nature of the exosphere are included. Ionization of exospheric material is calculated dynamically using electron impact ionization, photoionization, and ion charge exchange. Additionally, changes between when Europa is inside of or outside of the Jovian plasma sheet are investigated, as this may cause significant alteration to the Europan ionosphere between Europa Clipper's various flybys.

A PDS Archive for Observations of Mercury's Na Exosphere

NASA Astrophysics Data System (ADS)

Backes, C.; Cassidy, T.; Merkel, A. W.; Killen, R. M.; Potter, A. E.

2016-12-01

We present a data product consisting of ground-based observations of Mercury's sodium exosphere. We have amassed a sizeable dataset of several thousand spectral observations of Mercury's exosphere from the McMath-Pierce solar telescope. Over the last year, a data reduction pipeline has been developed and refined to process and reconstruct these spectral images into low resolution images of sodium D2 emission. This dataset, which extends over two decades, will provide an unprecedented opportunity to analyze the dynamics of Mercury's mid to high-latitude exospheric emissions, which have long been attributed to solar wind ion bombardment. This large archive of observations will be of great use to the Mercury science community in studying the effects of space weather on Mercury's tenuous exosphere. When completely processed, images in this dataset will show the observed spatial distribution of Na D2 in the Mercurian exosphere, have measurements of this sodium emission per pixel in units of kilorayleighs, and be available through NASA's Planetary Data System. The overall goal of the presentation will be to provide the Planetary Science community with a clear picture of what information and data this archival product will make available.

Seasonal variability of the hydrogen exosphere of Mars

NASA Astrophysics Data System (ADS)

Halekas, J. S.

2017-05-01

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures both the upstream solar wind and collisional products from energetic neutral hydrogen atoms that precipitate into the upper atmosphere after their initial formation by charge exchange with exospheric hydrogen. By computing the ratio between the densities of these populations, we derive a robust measurement of the column density of exospheric hydrogen upstream of the Martian bow shock. By comparing with Chamberlain-type model exospheres, we place new constraints on the structure and escape rates of exospheric hydrogen, derived from observations sensitive to a different and potentially complementary column from most scattered sunlight observations. Our observations provide quantitative estimates of the hydrogen exosphere with nearly complete temporal coverage, revealing order of magnitude seasonal changes in column density and a peak slightly after perihelion, approximately at southern summer solstice. The timing of this peak suggests either a lag in the response of the Martian atmosphere to solar inputs or a seasonal effect driven by lower atmosphere dynamics. The high degree of seasonal variability implied by our observations suggests that the Martian atmosphere and the thermal escape of light elements depend sensitively on solar inputs.

Monte Carlo Model Insights into the Lunar Sodium Exosphere

NASA Technical Reports Server (NTRS)

Hurley, Dana M.; Killen, R. M.; Sarantos, M.

2012-01-01

Sodium in the lunar exosphere is released from the lunar regolith by several mechanisms. These mechanisms include photon stimulated desorption (PSD), impact vaporization, electron stimulated desorption, and ion sputtering. Usually, PSD dominates; however, transient events can temporarily enhance other release mechanisms so that they are dominant. Examples of transient events include meteor showers and coronal mass ejections. The interaction between sodium and the regolith is important in determining the density and spatial distribution of sodium in the lunar exosphere. The temperature at which sodium sticks to the surface is one factor. In addition, the amount of thermal accommodation during the encounter between the sodium atom and the surface affects the exospheric distribution. Finally, the fraction of particles that are stuck when the surface is cold that are rereleased when the surface warms up also affects the exospheric density. In [1], we showed the "ambient" sodium exosphere from Monte Carlo modeling with a fixed source rate and fixed surface interaction parameters. We compared the enhancement when a CME passes the Moon to the ambient conditions. Here, we compare model results to data in order to determine the source rates and surface interaction parameters that provide the best fit of the model to the data.

Applicability of a diffusion model to lateral transport in the terrestrial and lunar exospheres.

NASA Technical Reports Server (NTRS)

Hodges, R. R., Jr.

1972-01-01

Kinetic theory is used to determine a series expansion of the vertical flux of particles in an exosphere in terms of time and space derivatives of particle concentration, exobase velocity, and temperature. For sufficiently large scale variations of these parameters in time and space, the series can be truncated to a form that is similar to a diffusion equation. Owing to this analogy, it is possible to unite the mathematical description of molecular diffusion, which governs thermospheric flow, and the corresponding exospheric equation by using effective transport coefficients which change smoothly with altitude through the transition from thermosphere to exosphere. A new definition of the exobase for lateral flow emerges from the analogy of exospheric and thermospheric diffusion, as the altitude where the horizontal mean free path length equals the mean horizontal extent of ballistic trajectories of the transported gas, as opposed to the scale height of the dominant gas which determines the exobase for escape. It is shown that the approximation of exospheric lateral flow as a diffusion process is applicable to global scale problems concerning terrestrial helium and heavier gases, and lunar gases heavier than helium.

The Effect on the Lunar Exosphere of a Coroual Mass Ejection Passage

NASA Technical Reports Server (NTRS)

Killen, R. M.; Hurley, D. M.; Farrell, W. M.

2011-01-01

Solar wind bombardment onto exposed surfaces in the solar system produces an energetic component to the exospheres about those bodies. The solar wind energy and composition are highly dependent on the origin of the plasma. Using the measured composition of the slow wind, fast wind, solar energetic particle (SEP) population, and coronal mass ejection (CME), broken down into their various components, we have estimated the total sputter yield for each type of solar wind. We show that the heavy ion component, especially the He++ and 0+7 can greatly enhance the total sputter yield during times when the heavy ion population is enhanced. Folding in the flux, we compute the source rate for several species during different types of solar wind. Finally, we use a Monte Carlo model developed to simulate the time-dependent evolution of the lunar exosphere to study the sputtering component of the exosphere under the influence of a CME passage. We simulate the background exosphere of Na, K, Ca, and Mg. Simulations indicate that sputtering increases the mass of those constituents in the exosphere a few to a few tens times the background values. The escalation of atmospheric density occurs within an hour of onset The decrease in atmospheric density after the CME passage is also rapid, although takes longer than the increase, Sputtered neutral particles have a high probability of escaping the moon,by both Jeans escape and photo ionization. Density and spatial distribution of the exosphere can be tested with the LADEE mission.

MESSENGER observations of Mercury's exosphere: detection of magnesium and distribution of constituents.

PubMed

McClintock, William E; Vervack, Ronald J; Bradley, E Todd; Killen, Rosemary M; Mouawad, Nelly; Sprague, Ann L; Burger, Matthew H; Solomon, Sean C; Izenberg, Noam R

2009-05-01

Mercury is surrounded by a tenuous exosphere that is supplied primarily by the planet's surface materials and is known to contain sodium, potassium, and calcium. Observations by the Mercury Atmospheric and Surface Composition Spectrometer during MESSENGER's second Mercury flyby revealed the presence of neutral magnesium in the tail (anti-sunward) region of the exosphere, as well as differing spatial distributions of magnesium, calcium, and sodium atoms in both the tail and the nightside, near-planet exosphere. Analysis of these observations, supplemented by observations during the first Mercury flyby, as well as those by other MESSENGER instruments, suggests that the distinct spatial distributions arise from a combination of differences in source, transfer, and loss processes.

Evidence for a Dynamic Nanodust Cloud Enveloping the Moon

NASA Technical Reports Server (NTRS)

Wooden, D. H.; Cook, A. M.; Colaprete, A.; Glenar, D. A.; Stubbs, T. J.; Shirley, M.

2015-01-01

The exospheres that surround airless bodies such as the Moon are tenuous, atmosphere-like layers whose constituent particles rarely collide with one another. Some particles contained within such exospheres are the product of direct interactions between airless bodies and the space environment, and offer insights into space weathering processes. NASAs Lunar Atmosphere and Dust Environment Explorer (LADEE) mission studied the Moons exospheric constituents in situ and detected a permanent dust exosphere1 of particles with radii as small as 300 nm. Here we present evidence from LADEE spectral data for an additional fluctuating nanodust exosphere at the Moon containing a population of particles sufficiently dense to be detectable via scattered sunlight. We compare two anti-Sun spectral observations: one near the peak of the Quadrantidmeteoroid stream, the other during a period of comparativelyweak stream activity. The former shows a negative spectralslope consistent with backscattering of sunlight by nanodustgrains with radii less than 20 to 30 nm; the latter has a flatterspectral slope. We hypothesize that a spatially and temporallyvariable nanodust exosphere may exist at the Moon, and thatit is modulated by changes in meteoroid impact rates, suchas during encounters with meteoroid streams. The findingssuggest that similar nanodust exospheresand the particle ejection and transport processes that form themmay occurat other airless bodies.

Early MESSENGER Results for Less Abundant or Weakly Emitting Species in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Vervack, Ronald J., Jr.; McClintock, William E.; Killen, Rosemary M.; Sprague, Ann L.; Burger, Matthew H.; Merkel, Aimee W.; Sarantos, Menelaos

2011-01-01

Now that the Messenger spacecraft is in orbit about Mercury, the extended observing time enables searches for exospheric species that are less abundant or weakly emitting compared with those for which emission has previously been detected. Many of these species cannot be observed from the ground because of terrestrial atmospheric absorption. We report here on the status of MESSENGER orbital-phase searches for additional species in Mercury's exosphere.

Exospheric hydrogen above St-Santin /France/

NASA Technical Reports Server (NTRS)

Derieux, A.; Lejeune, G.; Bauer, P.

1975-01-01

The temperature and hydrogen concentration of the exosphere was determined using incoherent scatter measurements performed above St. Santin from 1969 to 1972. The hydrogen concentration was deduced from measurements of the number density of positive hydrogen and oxygen ions. A statistical analysis is given of the hydrogen concentration as a function of the exospheric temperature and the diurnal variation of the hydrogen concentration is investigated for a few selected days of good quality observation. The data averaged with respect to the exospheric temperature without consideration of the local time exhibits a distribution consistent with a constant effective Jeans escape flux of about 9 x 10 to the 7 cu cm/s. The local time variation exhibits a maximum to minimum concentration ratio of at least 3.5.

Dione and Rhea seasonal exospheres revealed by Cassini CAPS and INMS

NASA Astrophysics Data System (ADS)

Teolis, B. D.; Waite, J. H.

2016-07-01

A Dione O2 and CO2 exosphere of similar composition and density to Rhea's is confirmed by Cassini spacecraft Ion Neutral Mass Spectrometer (INMS) flyby data. INMS results from three Dione and two Rhea flybys show exospheric spatial and temporal variability indicative of seasonal exospheres, modulated by winter polar gas adsorption and desorption at the equinoxes. Cassini Plasma Spectrometer (CAPS) pickup ion fluxes also show exospheric structure and evolution at Rhea consistent with INMS, after taking into consideration the anticipated charge exchange, electron impact, and photo-ionization rates. Data-model comparisons show the exospheric evolution to be consistent with polar frost diffusion into the surface regolith, which limits surface exposure and loss of the winter frost cap by sputtering. Implied O2 source rates of ∼45(7) × 1021 s-1 at Dione(Rhea) are ∼50(300) times less than expected from known O2 radiolysis yields from ion-irradiated pure water ice measured in the laboratory, ruling out secondary sputtering as a major exospheric contributor, and implying a nanometer scale surface refractory lag layer consisting of concentrated carbonaceous impurities. We estimate ∼30:1(2:1) relative O2:CO2 source rates at Dione(Rhea), consistent with a stoichiometric bulk composition below the lag layer of 0.01(0.13) C atoms per H2O molecule, deriving from endogenic constituents, implanted micrometeoritic organics, and (in particular at Dione) exogenous H2O delivery by E-ring grains. Impact deposition, gardening and vaporization may thereby control the global O2 source rates by fresh H2O ice exposure to surface radiolysis and trapped oxidant ejection.

On the Origins of Mars' Exospheric Nonthermal Oxygen Component as Observed by MAVEN and Modeled by HELIOSARES

NASA Astrophysics Data System (ADS)

Leblanc, F.; Chaufray, J. Y.; Modolo, R.; Leclercq, L.; Curry, S.; Luhmann, J.; Lillis, R.; Hara, T.; McFadden, J.; Halekas, J.; Schneider, N.; Deighan, J.; Mahaffy, P. R.; Benna, M.; Johnson, R. E.; Gonzalez-Galindo, F.; Forget, F.; Lopez-Valverde, M. A.; Eparvier, F. G.; Jakosky, B.

2017-12-01

The first measurements of the emission brightness of the oxygen atomic exosphere by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission have clearly shown that it is composed of a thermal component produced by the extension of the upper atmosphere and of a nonthermal component. Modeling these measurements allows us to constrain the origins of the exospheric O and, as a consequence, to estimate Mars' present oxygen escape rate. We here propose an analysis of three periods of MAVEN observations based on a set of three coupled models: a hybrid magnetospheric model (LATmos HYbrid Simulation (LatHyS)), an Exospheric General Model (EGM), and the Global Martian Circulation model of the Laboratoire de Météorologie Dynamique (LMD-GCM), which provide a description of Mars' environment from the surface up to the solar wind. The simulated magnetosphere by LatHyS is in good agreement with MAVEN Plasma and Field Package instruments data. The LMD-GCM modeled upper atmospheric profiles for the main neutral and ion species are compared to Neutral Gas and Ion Mass Spectrometer/MAVEN data showing that the LMD-GCM can provide a satisfactory global view of Mars' upper atmosphere. Finally, we were able to reconstruct the expected emission brightness intensity from the oxygen exosphere using EGM. The good agreement with the averaged measured profiles by Imaging Ultraviolet Spectrograph during these three periods suggests that Mars' exospheric nonthermal component can be fully explained by the reactions of dissociative recombination of the O2+ ion in Mars' ionosphere, limiting significantly our ability to extract information from MAVEN observations of the O exosphere on other nonthermal processes, such as sputtering.

MESSENGER Searches for Less Abundant or Weakly Emitting Species in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Vervack, Ronald J., Jr.; McClintock, William E.; Killen, Rosemary M.; Sprague, Ann L.; Burger, Matthew H.; Merkel, Aimee W.; Sarantos, Menelaos

2011-01-01

Mercury's exosphere is composed of material that originates at the planet's surface, whether that material is native or delivered by the solar wind and micrometeoroids. Many exospheric species have been detected by remote sensing, including H and He by Mariner 10, Na, K, and Ca by ground-based observations, and H, Na, Ca, Mg, and Ca+ by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Other exospheric species, including Fe, AI, Si, 0, S, Mn, CI, Ti, OH, and their ions, are expected to be present on the basis of MESSENGER surface measurements and models of Mercury's surface chemistry. Here we report on searches for these species made with the Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). No obvious signatures of the listed species have yet been observed in Mercury's exosphere by the UVVS as of this writing. It is possible that detections are elusive because the optimum regions of the exosphere have not been sampled. The Sun-avoidance constraints on MESSENGER place tight limits on instrument boresight directions, and some regions are probed infrequently. If there are strong spatial gradients in the distribution of weakly emitting species, a high-resolution sampling of specific regions may be required to detect them. Summing spectra over time will also aid in the ability to detect weaker emission. Observations to date nonetheless permit strong upper limits to be placed on the abundances of many undetected species, in some cases as functions of time and space. As those limits are lowered with time, the absence of detections can provide insight into surface composition and the potential source mechanisms of exospheric material.

Observations of Al, Fe and Ca(+) in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Bida, Thomas A.; Killen, Rosemary M.

2011-01-01

We report 5-(sigma) tangent column detections of Al and Fe, and strict 3-(sigma) tangent column upper limits for Ca(+) in Mercury's exosphere obtained using the HIRES spectrometer on the Keck I telescope. These are the first direct detections of Al and Fe in Mercury's exosphere. Our Ca(-) observation is consistent with that reported by The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.

LADEE Search for a Dust Exosphere: A Historical Perspective

NASA Technical Reports Server (NTRS)

Glenar, D. A.; Stubbs, T. J.; Elphic, R.

2014-01-01

The LADEE search for exospheric dust is strongly motivated by putative detections of forward-scattered sunlight from exospheric dust grains which were observed during the Apollo era. This dust population, if it exists, has been associated with charging and transport of dust near the terminators. It is likely that the concentration of these dust grains is governed by a saltation mechanism originated by micrometeoroid impacts, which are the source of the more tenuous ejecta cloud.

Metallic Species, Oxygen and Silicon in the Lunar Exosphere: Upper Limits and Prospects for LADEE Measurements

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; Killen, Rosemary Margaret; Glenar, David A.; Benna, Mehdi; Stubbs, Timothy J.

2012-01-01

The only species that have been so far detected in the lunar exosphere are Na, K, Ar,and He. However, models for the production and loss of species derived from the lunarregolith through micrometeoroid impact vaporization, sputtering, and photon-stimulateddesorption, predict that a host of other species should exist in the lunar exosphere.Assuming that loss processes are limited to ballistic escape, photoionization, and recyclingto the surface, we have computed column abundances and compared them to publishedupper limits for the Moon. Only for Ca do modeled abundances clearly exceed theavailable measurements. This result suggests the relevance of some loss processes thatwere not included in the model, such as the possibility of gas-to-solid phasecondensation during micrometeoroid impacts or the formation of stable metallic oxides.Our simulations and the recalculation of efficiencies for resonant light scattering showthat models for other species studied are not well constrained by existingmeasurements. This fact underlines the need for improved remote and in situmeasurements of the lunar exosphere such as those planned by the Lunar Atmosphereand Dust Environment Explorer (LADEE) spacecraft. Our simulations of the LADEEneutral mass spectrometer and visibleultraviolet spectrometer indicate that LADEE measurements promise to provide definitive observations or set stringent upper limitsfor all regolith-driven exospheric species. We predict that observations by LADEE willconstrain assumed model parameters for the exosphere of the Moon.

Metallic Species, Oxygen and Silicon in the Lunar Exosphere: Upper Limits and Prospects for LADEE Measurements

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; Killen, Rosemary M.; Glenar, David A.; Benna, Mehdi; Stubbs, Timothy J.

2011-01-01

The only species that have been continued in the lunar exosphere are Na, K, Ar, and He. Models for the production and loss of lunar regolith-derived exospheric species from source processes including micrometeoroid impact vaporization, sputtering. and, for Na and K, photon-stimulated desorption, predict a host of other species should exist in the lunar exosphere. Assuming that loss processes are limited to ballistic escape and recycling to the surface, we have computed column abundances and compared them to published upper limits from the Moon and to detected abundances from Mercury. Only for Ca do the available measurements show a clear deficiency compared to the model estimates. This result suggests the importance of loss processes not included in the model, such as the possibility of gas-to-solid phase condensation during micrometeoroid impacts or the formation of stable metallic oxides, and underlines the need for improved spectroscopic measurements of the lunar exosphere. Simulations of the neutral mass (NMS) and visible/ultraviolet spectrometry (UVS) investigations planned by the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft are presented. Our calculations indicate that LADEE measurements promise to make definitive observations or set stringent upper limits for all regolith-driven exospheric species. Our models, along with LADEE observations, will constrain assumed model parameters for the Moon, such as sticking coefficients, source processes. and velocity distributions.

Short-term cyclic variations and diurnal variations of the Venus upper atmosphere

NASA Technical Reports Server (NTRS)

Keating, G. M.; Taylor, F. W.; Nicholson, J. Y.; Hinson, E. W.

1979-01-01

The vertical structure of the nighttime thermosphere and exosphere of Venus was discussed. A comparison of the day and nighttime profiles indicates, contrary to the model of Dickinson and Riley (1977), that densities (principally atomic oxygen) dropped sharply from day to night. It was suggested either that the lower estimates were related to cooler exospheric temperatures at night or that the atomic bulge was flatter than expected at lower altitudes. Large periodic oscillations, in both density and inferred exospheric temperatures, were detected with periods of 5 to 6 days. The possibility that cyclic variations in the thermosphere and stratosphere were caused by planetary-scale waves, propagated upward from the lower atmosphere, was investigated using simultaneous temperature measurements obtained by the Venus radiometric temperature experiment (VORTEX). Inferred exospheric temperatures in the morning were found to be lower than in the evening as if the atmosphere rotated in the direction of the planet's rotation, similar to that of earth. Superrotation of the thermosphere and exosphere was discussed as a possible extension of the 4-day cyclic atmospheric rotation near the cloud tops.

Search for spectroscopical signatures of transiting HD 209458b's exosphere

NASA Astrophysics Data System (ADS)

Moutou, C.; Coustenis, A.; Schneider, J.; St Gilles, R.; Mayor, M.; Queloz, D.; Kaufer, A.

2001-05-01

Following recent attempts to detect the exosphere of the extra-solar planet 51 Pegb in the infrared (Coustenis et al. \\cite{cou97}, \\cite{cou98}; Rauer et al. \\cite{rau00a}), we discuss here a search for optical spectroscopic signatures from a gaseous extended envelope (called exosphere) surrounding the planet HD 209458b. This planet has a demonstrated photometric transit (Charbonneau et al. \\cite{cha00a}; Henry et al. \\cite{hen00}), thus offering an increased probability for the spectroscopic detection of such an envelope. Therefore it is the best known candidate for probing the exospheric composition of a giant planet, orbiting a Sun-like star at a short distance. The observations were performed with UVES at the VLT and cover most of the 328-669 nm range. We did not detect HD 209458b's exosphere at a level of 1%, a value close to the predictions. We discuss here the first results obtained and their limitations, as well as future prospective. Based on public data from the UVES Commissioning at the ESO 8.2~m Kueyen telescope operated on Paranal Observatory, Chile.

Impacts of Geomagnetic Storms on the Terrestrial H-Exosphere Using Twins-Lyman Stereo Data

NASA Astrophysics Data System (ADS)

Nass, U.; Zoennchen, J.; Fahr, H. J.; Goldstein, J.

2015-12-01

Based on continuously monitored Lyman-alpha data registered by the TWINS1/2-LAD instruments we have studied the impact of a weaker and a stronger geomagnetic storm on the exospheric H-density distribution between heights of 3--8 Earth-radii. As is well known, solar Lyman-alpha radiation is resonantly backscattered from geocoronal neutral hydrogen (H). The resulting resonance glow intensity in the optically thin regime is proportional to H column density along the line of sight (LOS). Here we present the terrestrial exospheric response to geomagnetic storms. We quantify the reaction to geomagnetic activity in form of amplitude and temporal response of the H-density, sampled at different geocentric distances. We find that even in case of a weak storm, the exospheric H-density in regions above the exobase reacts with a suprisingly large increase in a remarkably short time period of less than half a day. Careful analysis of this geomagnetic density effect indicates that it is an expansion in the radial scale height of the exospheric H-density, developing from exobasic heights.

The sodium exosphere and magnetosphere of Mercury

NASA Astrophysics Data System (ADS)

Ip, W.-H.

1986-05-01

Following the recent optical discovery of intense sodium D-line emission from Mercury, the scenario of an extended exosphere of sodium and other metallic atoms is explored. It is shown that the strong effect of solar radiation pressure acceleration would permit the escape of Na atoms from Mercury's surface even if they are ejected at a velocity lower than the surface escape velocity. Fast photoionization of the Na atoms is effective in limiting the tailward extension of the sodium exosphere, however. The subsequent loss of the photoions to the magnetosphere could be a significant source of the magnetospheric plasma. The recirculation of the magnetospheric charged particles to the planetary surface could also play an important role in maintaining an extended sodium exosphere as well as a magnetosphere of sputtered metallic ions.

LRO-LAMP Observations of the Lunar Exosphere Coordinated with LADEE

NASA Astrophysics Data System (ADS)

Grava, C.; Retherford, K. D.; Greathouse, T. K.; Gladstone, R.; Hurley, D.; Cook, J. C.; Stern, S. A.; Feldman, P. D.; Kaufmann, D. E.; Miles, P. F.; Pryor, W. R.; Halekas, J. S.

2014-12-01

The polar orbiting Lunar Reconnaissance Orbiter's (LRO) Lyman Alpha Mapping Project (LAMP) carried out an atmospheric campaign during the month of December 2013, at the same time the Lunar Atmospheric and Dust Environment Explorer (LADEE) mission was sampling the lunar exosphere in a retrograde equatorial orbit. Observations of the lunar exosphere were performed by LAMP during a solar "beta-90" geometry, i.e. riding along the lunar terminator. During this geometry, the LAMP nadir-pointed line of sight to the nightside surface also includes illuminated columns of foreground emissions from exospheric species, which is invaluable in the study of the tenuous lunar exosphere. Other types of maneuvers to probe the lunar exosphere were also performed by LAMP/LRO during this campaign. During backward pitch slews, the LRO spacecraft was pitched to look opposite its direction of motion to a point just inside the limb in the nightside region around the polar terminator. Forward pitch slews were also obtained, and the angles of 63 deg or 77 deg from nadir were set depending on the polar region observed. Finally, during lateral roll slews, LRO rotated by ~60 deg towards the nightside limb, maximizing the amount of illuminated atmosphere in the foreground probed by the LAMP field of view. We extract day to day density variations on helium and/or upper limits for numerous other species that were accessible to both LAMP and LADEE (e.g., Ar, Ne, O, and H2). Moreover, constraints on helium density will complement measurements of solar wind alpha particles (He++) from the ARTEMIS (Acceleration, Reconnection, Turbulence, & Electrodynamics of Moon's Interaction with the Sun) mission. This comparison will provide a comprehensive picture of composition, abundance, and spatial and temporal variations of volatiles of the lunar exosphere, combining equatorial (LADEE) and polar (LAMP) measurements for the first time. Volatiles in the lunar exosphere, especially water, are of paramount importance in the context of lunar exploration, since the compelling hypothesis of their storage in Permanently Shaded Regions (PSRs) was advanced in the second half of the last century.

Comparative study of ion cyclotron waves at Mars, Venus and Earth

NASA Astrophysics Data System (ADS)

Wei, H. Y.; Russell, C. T.; Zhang, T. L.; Blanco-Cano, X.

2011-08-01

Ion cyclotron waves are generated in the solar wind when it picks up freshly ionized planetary exospheric ions. These waves grow from the free energy of the highly anisotropic distribution of fresh pickup ions, and are observed in the spacecraft frame with left-handed polarization and a wave frequency near the ion's gyrofrequency. At Mars and Venus and in the Earth's polar cusp, the solar wind directly interacts with the planetary exospheres. Ion cyclotron waves with many similar properties are observed in these diverse plasma environments. The ion cyclotron waves at Mars indicate its hydrogen exosphere to be extensive and asymmetric in the direction of the interplanetary electric field. The production of fast neutrals plays an important role in forming an extended exosphere in the shape and size observed. At Venus, the region of exospheric proton cyclotron wave production may be restricted to the magnetosheath. The waves observed in the solar wind at Venus appear to be largely produced by the solar-wind-Venus interaction, with some waves at higher frequencies formed near the Sun and carried outward by the solar wind to Venus. These waves have some similarity to the expected properties of exospherically produced proton pickup waves but are characterized by magnetic connection to the bow shock or by a lack of correlation with local solar wind properties respectively. Any confusion of solar derived waves with exospherically derived ion pickup waves is not an issue at Mars because the solar-produced waves are generally at much higher frequencies than the local pickup waves and the solar waves should be mostly absorbed when convected to Mars distance as the proton cyclotron frequency in the plasma frame approaches the frequency of the solar-produced waves. In the Earth's polar cusp, the wave properties of ion cyclotron waves are quite variable. Spatial gradients in the magnetic field may cause this variation as the background field changes between the regions in which the fast neutrals are produced and where they are re-ionized and picked up. While these waves were discovered early in the magnetospheric exploration, their generation was not understood until after we had observed similar waves in the exospheres of Mars and Venus.

Thermospheric winds and exospheric temperatures from incoherent scatter radar measurements in four seasons

NASA Technical Reports Server (NTRS)

Antoniadis, D. A.

1976-01-01

The time-dependent equations of neutral air motion are solved subject to three constraints: two of them are the usual upper and lower boundary conditions and the third is the value of the wind-induced ion drift at any given height. Using incoherent radar data, this procedure leads to a fast, direct numerical integration of the two coupled differential equations describing the horizontal wind components and yields time dependent wind profiles and meridional exospheric neutral temperature gradients. The diurnal behavior of the neutral wind system and of the exospheric temperature is presented for two solstice and two equinox days. The data used were obtained by the St. Santin and the Millstone Hill incoherent scatter radars. The derived geographic distributions of the exospheric temperatures are compared with those predicted by the OGO-6 empirical thermospheric model.

Understanding Temporal and Spatial Variability of the Lunar Helium Atmosphere Using Simultaneous Observations from LRO, LADEE, and ARTEMIS

NASA Technical Reports Server (NTRS)

Hurley, Dana M.; Cook, Jason C.; Benna, Mehdi; Halekas, Jasper S.; Feldman, Paul D.; Retherford, Kurt D.; Hodges, R. Richard; Grava, Cesare; Mahaffy, Paul; Gladstone, G. Randall;

Understanding temporal and spatial variability of the lunar helium atmosphere using simultaneous observations from LRO, LADEE, and ARTEMIS

NASA Astrophysics Data System (ADS)

Hurley, Dana M.; Cook, Jason C.; Benna, Mehdi; Halekas, Jasper S.; Feldman, Paul D.; Retherford, Kurt D.; Hodges, R. Richard; Grava, Cesare; Mahaffy, Paul; Gladstone, G. Randall; Greathouse, Thomas; Kaufmann, David E.; Elphic, Richard C.; Stern, S. Alan

2016-07-01

Simultaneous measurements of helium in the exosphere of the Moon are made from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) and the Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS) through the entire 5-month span of the LADEE mission. In addition, the ARTEMIS mission monitored the solar wind alpha particle flux to the Moon. Modeling the lunar helium exosphere, we relate the LAMP polar observations to the LADEE equatorial observations. Further, using the ARTEMIS alpha flux in the Monte Carlo model reproduces the temporal variations in helium density. Comparing the LAMP data to the LADEE data shows excellent agreement. Comparing those with the ARTEMIS data reveals that the solar wind alpha flux is the primary driver to variability in the helium exosphere throughout the LADEE mission. Using a decay time for exospheric helium of 5 days, we determine that the solar wind contributes 64 ± 5% of the helium to the lunar exosphere. The remaining 36 ± 5% is presumed to come from outgassing of radiogenic helium from the interior of the Moon. Furthermore, the model reproduces the measurements if 63 ± 6% of the incident alpha particles are converted to thermalized helium atoms through the interaction between the alphas and the lunar surface. However, these values are dependent on both inferred source rates from LAMP and LADEE observations and on the assumed time constant of the exospheric decay rate.

3D tomographic reconstruction of the terrestrial exosphere and its time-dependent coupling to the magnetospheric ring current

NASA Astrophysics Data System (ADS)

Waldrop, L.; Cucho-Padin, G.; Ilie, R.

2017-12-01

Charge exchange collisions between ring current ions and hydrogen (H) atoms in the outer exosphere serve to dissipate magnetospheric energy, particularly during the slow recovery phase of geomagnetic storms, through the generation of energetic neutral atoms (ENAs) which escape the system. As a result, knowledge of the spatial distribution and temporal variability of exospheric H density is critical for reliable interpretation of ENA flux measurements as well as for accurate modeling of the ring current. Although numerous theoretical, numerical, and empirical H distributions have been used for such analyses, their reliance on ad hoc or unphysical assumptions, together with their inherently static formulations, is a source of significant uncertainty. Our recent development of a robust tomographic technique for the model-independent estimation of global exospheric H density from optical remote sensing data overcomes the limitations of past analysis and enables an unprecedented investigation of global exospheric and ring current dynamics. Here, we present sample results of our 3D, time-dependent reconstructions of exospheric structure, derived from measurements of resonantly scattered solar Lyman-alpha (121.6 nm) photons acquired by the Lyman-alpha detectors (LADs) onboard NASA's Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission. We use the Hot Electron and Ion Drift Integrator (HEIDI) kinetic model of the ring current to investigate the charge exchange interactions between the resulting H density distribution and ring current ions and generate synthetic images of ENA flux for comparison with those measured by TWINS.

Solar cycle variation of Mars exospheric temperatures: Critical review of available dayside measurements and recent model simulations

NASA Astrophysics Data System (ADS)

Bougher, Stephen; Huestis, David

The responses of the Martian dayside thermosphere to solar flux variations (on both solar rotation and solar cycle timescales) have been the subject of considerable debate and study for many years. Available datasets include: Mariner 6,7,9 (UVS dayglow), Viking Lander 1-2 (UAMS densities upon descent), several aerobraking campaigns (MGS, Odyssey, MRO densities), and Mars Express (SPICAM dayglow). Radio Science derived plasma scale heights near the ionospheric peak can be used to derive neutral temperatures in this region (only); such values are not applicable to exobase heights (e.g. Forbes et al. 2008; Bougher et al. 2009). Recently, densities and temperatures derived from precise orbit determination of the MGS spacecraft (1999-2005) have been used to establish the responses of Mars' exosphere to long-term solar flux variations (Forbes et al., 2008). From this multi-year dataset, dayside exospheric temperatures weighted toward moderate southern latitudes are found to change by about 120 K over the solar cycle. However, the applicability of these drag derived exospheric temperatures to near solar minimum conditions is suspect (e.g Bruinsma and Lemoine, 2002). Finally, re-evaluation of production mechanisms for UV dayglow emissions implies revised values for exospheric temperatures (e.g. Simon et al., 2009; Huestis et al. 2010). Several processes are known to influence Mars' exospheric temperatures and their variability (Bougher et al., 1999; 2000; 2009). Solar EUV heating and its variations with solar fluxes received at Mars, CO2 15-micron cooling, molecular thermal conduction, and hydrodynamic heating/cooling associated with global dynamics all contribute to regulate dayside thermo-spheric temperatures. Poorly measured dayside atomic oxygen abundances render CO2 cooling rates uncertain at the present time. However, global thermospheric circulation models can be exercised for conditions spanning the solar cycle and Mars seasons to address the relative roles of these processes in driving observed variations in dayside exospheric temperatures. Mars Thermospheric General Circulation Model (MTGCM) simulations and resulting exo-spheric temperatures will be presented and compared with assimilated temperatures collected from all these available measurements over the solar cycle. It is important to match measure-ments at dayside local times and latitudes for specific seasons with corresponding MTGCM simulated outputs. Calculated local heat budgets and their variations illustrate the changes required to reproduce solar cycle variations in exospheric temperatures. The ability to success-fully predict solar cycle responses of the Martian upper atmosphere is important for simulations of present-day Mars volatile escape rates.

Coronagraphic Observations of the Lunar Sodium Exosphere Near the Lunar Surface

NASA Technical Reports Server (NTRS)

Potter, A. E.; Morgan, T. H.

1998-01-01

The sodium exosphere of the Moon was observed using a solar coronagraph to occult the illuminated surface of the Moon. Exceptionally dust-free atmospheric conditions were required to allow the faint emission from sunlight scattered by lunar sodium atoms to be distinguished from moonlight scattered from atmospheric dust. At 0300 UT on April 22, 1994, ideal conditions prevailed for a few hours, and one excellent image of the sodium exosphere was measured, with the Moon at a phase angle of 51 deg, 81 % illuminated. Analysis of the image data showed that the weighted mean temperature of the exosphere was 1280 K and that the sodium column density varied approximately as cosine-cubed of the latitude. A cosine-cubed variation is an unexpected result, since the flux per unit area of solar photons and solar particles varies as the cosine of latitude. It is suggested that this can be explained by a temperature dependence for the sputtering of sodium atoms from the surface. This is a characteristic feature of chemical sputtering, which has been previously proposed to explain the sodium exosphere of Mercury. A possible interaction between chemical sputtering and solar photons is suggested.

Mercury's Seasonal Sodium Exosphere: MESSENGER Orbital Observations

NASA Technical Reports Server (NTRS)

Cassidy, Timothy A.; Merkel, Aimee W.; Burger, Matthew H.; Sarantos, Menelaos; Killen, Rosemary M.; McClintock, William E.; Vervack, Ronald J., Jr.

2014-01-01

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Ultraviolet and Visible Spectrometer (UVVS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft now orbiting Mercury provides the first close-up look at the planet's sodium exosphere. UVVS has observed the exosphere from orbit almost daily for over 10 Mercury years. In this paper we describe and analyze a subset of these data: altitude profiles taken above the low-latitude dayside and south pole. The observations show spatial and temporal variation but there is little or no year-to-year variation; we do not see the episodic variability reported by ground-based observers. We used these altitude profiles to make estimates of sodium density and temperature. The bulk of the exosphere is about 1200 K, much warmer than Mercury's surface. This value is consistent with some ground-based measurements and suggests that photon-stimulated desorption is the primary ejection process. We also observe a tenuous energetic component but do not see evidence of the predicted thermalized (or partially thermalized) sodium near Mercury's surface temperature. Overall we do not see the variable mixture of temperatures predicted by most Monte Carlo models of the exosphere.

Mercury's Seasonal Sodium Exosphere: MESSENGER Orbital Observations

NASA Technical Reports Server (NTRS)

Cassidy, Timothy A.; Merkel, Aimee W.; Burger, Matthew H.; Killen, Rosemary M.; McClintock, William E.; Vervack, Ronald J., Jr.; Sarantos, Menelaos

2014-01-01

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Ultraviolet and Visible Spectrometer (UVVS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft now orbiting Mercury provides the first close-up look at the planet's sodium exosphere. UVVS has observed the exosphere from orbit almost daily for over 10 Mercury years. In this paper we describe and analyze a subset of these data: altitude profiles taken above the low-latitude dayside and south pole. The observations show spatial and temporal variations, but there are no obvious year-to-year variations in most of the observations. We do not see the episodic variability reported by some ground-based observers. We used these altitude profiles to make estimates of sodium density and temperature. The bulk of the exosphere, at about 1200 K, is much warmer than Mercury's surface. This value is consistent with some ground-based measurements and suggests that photon-stimulated desorption is the primary ejection process. We also observe a tenuous energetic component but do not see evidence of the predicted thermalized (or partially thermalized) sodium near Mercury's surface temperature. Overall we do not see the variable mixture of temperatures predicted by most Monte Carlo models of the exosphere.

Pickup Ion Distributions from Three Dimensional Neutral Exospheres

NASA Technical Reports Server (NTRS)

Hartle, R. E.; Sarantos, M.; Sittler, E. C., Jr.

2011-01-01

Pickup ions formed from ionized neutral exospheres in flowing plasmas have phase space distributions that reflect their source's spatial distributions. Phase space distributions of the ions are derived from the Vlasov equation with a delta function source using three.dimensional neutral exospheres. The ExB drift produced by plasma motion picks up the ions while the effects of magnetic field draping, mass loading, wave particle scattering, and Coulomb collisions near a planetary body are ignored. Previously, one.dimensional exospheres were treated, resulting in closed form pickup ion distributions that explicitly depend on the ratio rg/H, where rg is the ion gyroradius and H is the neutral scale height at the exobase. In general, the pickup ion distributions, based on three.dimensional neutral exospheres, cannot be written in closed form, but can be computed numerically. They continue to reflect their source's spatial distributions in an implicit way. These ion distributions and their moments are applied to several bodies, including He(+) and Na(+) at the Moon, H(+2) and CH(+4) at Titan, and H+ at Venus. The best places to use these distributions are upstream of the Moon's surface, the ionopause of Titan, and the bow shock of Venus.

Lunar Hydrospheric Explorer (HYDROX)

NASA Technical Reports Server (NTRS)

Cooper, J. F.; Paschalidis, N.; Sittler, E. C., Jr.; Jones, S. L.; Stubbs, T. J.; Sarantos, M.; Khurana, K. K.; Angelopoulos, V.; Jordan, A. P.; Schwadron, N. A.

2015-01-01

The Lunar Hydrospheric Explorer (HYDROX) is a 6U CubeSat designed to further confirm the existence of lunar exospheric water, and to determine source processes and surface sites, through ion mass spectrometer measurements of water group (O+, OH+, H2O+) and related ions at energy charge up to 2 keV/e. and mass/charge 1-40amu/e. HYDROX would follow up on the now-concluded exospheric compositional measurements by the Neutral Mass Spectrometer on the NASA LADEE mission and on other remote sensing surface and exospheric measurements (LADEE,LRO, etc.).

Modeling Mercury

NASA Astrophysics Data System (ADS)

Burger, M. H.; Killen, R. M.; M, N.; Sarantos, M.; Crider, D. H.; Vervak, R. J.

2009-04-01

Mercury has a tenuous exosphere created by the combined effects of solar radiation and micrometeoroid bombardment on the surface and the interaction of the solar wind with Mercury's magnetic field and surface. Observations of this exosphere provide essential data necessary for understanding the composition and evolution of Mercury's surface, as well as the interaction between Mercury's magnetosphere with the solar wind. The sodium component of the exosphere has been well observed from the ground (see review by Killen et al., 2007). These observations have revealed a highly variable and inhomogeneous exosphere with emission often peaking in the polar regions. Radiation acceleration drives exospheric escape producing a sodium tail pointing away from the sun which has been detected up to 1400 Mercury radii from the planet (Potter et al. 2002; Baumgardner et al. 2008). Calcium has also been observed in Mercury's exosphere showing a distribution distinct from sodium, although also variable (Killen et al. 2005). During the first two encounters with Mercury by MESSENGER, observations of the exosphere were made by the UltraViolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). Sodium and calcium emission were detected during both flybys, and magnesium was detected for the first time in Mercury's exosphere during the second flyby. The spatial distributions of these species showed significant, unexpected differences which suggest differences in the mechanisms responsible for releasing them from the surface. We present a Monte-Carlo model of sodium, magnesium, and calcium in Mercury's exosphere. The important source mechanisms for ejecting these species from the surface are sputtering by solar wind ions, photon-stimulated desorption, and micrometeoroid impact vaporization. Thermal desorption on the dayside does not supply enough energy to significantly populate the exosphere, although it does play a role in redistributing volatiles over the surface. In addition, atomic calcium can be produced from the dissociation of Ca-bearing molecules, such as CaO, which can be formed in impact vapors. The primary loss processes are the escape of neutrals ejected with sufficient energy and photoionization. The former process is supplemented by radiation pressure which accelerates neutrals anti-sunward such that escaping neutrals form a tail pointing away from the sun. Because Mercury's heliocentric distance and radial velocity vary during its orbit, both loss processes are functions of Mercury's true anomaly. We also consider the spatial distribution of the surface source. Impact vaporization is roughly isotropic over the surface, although there may be a leading/trailing asymmetry in the impact rate due to Mercury's orbital motion. Sputtering is confined to regions where the solar wind can impact the surface, which is shielded somewhat by the internal magnetic field. The surface regions vulnerable depend on the solar wind conditions. References: Baumgardner et al., GRL, 35, L03201, 2008. Killen, R.M. et al., Space Sci. Rev. 132, 433-509, 2007. Killen, R.M. et al., Icarus, 173, 300-311, 2005. Potter et al., Meteoritics & Planetary Sci., 37, 1165, 2002.

Calcium in Mercury's Exosphere: Modeling MESSENGER Data

NASA Technical Reports Server (NTRS)

Burger, Matthew H.; Killen, Rosemary M.; McClintock, William E.; Merkel, Aimee; Vervack, Ronald J.; Sarantos, Menelaos; Sprague, Ann L.

2011-01-01

Mercury is surrounded by a surface-bounded exosphere comprised of atomic species including hydrogen, sodium, potassium, calcium, magnesium, and likely oxygen. Because it is collisionless. the exosphere's composition represents a balance of the active source and loss processes. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface. Space ENvironment. GEochemistry. and Ranging (MESSENGER) spacecraft has made high spatial-resolution observations of sodium, calcium, and magnesium near Mercury's surface and in the extended, anti-sunward direction. The most striking feature of these data has been the substantial differences in the spatial distribution of each species, Our modeling demonstrates that these differences cannot be due to post-ejection dynamics such as differences in photo-ionization rate and radiation pressure. but instead point to differences in the source mechanisms and regions on the surface from which each is ejected. The observations of calcium have revealed a strong dawn/dusk asymmetry. with the abundance over the dawn hemisphere significantly greater than over the dusk. To understand this asymmetry, we use a Monte Carlo model of Mercury's exosphere that we developed to track the motions of exospheric neutrals under the influence of gravity and radiation pressure. Ca atoms can be ejected directly from the surface or produced in a molecular exosphere (e.g., one consisting of CaO). Particles are removed from the system if they stick to the surface or escape from the model region of interest (within 15 Mercury radii). Photoionization reduces the final weighting given to each particle when simulating the Ca radiance. Preliminary results suggest a high temperature ( I-2x 10(exp 4) K) source of atomic Ca concentrated over the dawn hemisphere. The high temperature is consistent with the dissociation of CaO in a near-surface exosphere with scale height <= 100 km, which imparts 2 eV to the freshly produced Ca atom. This source region and energy are consistent with data from the three MESSENGER flybys; whether this holds true for the data obtained in orbit is under investigation.

Mercury Sodium Exospheric Emission as a Proxy for Solar Perturbations Transit

NASA Astrophysics Data System (ADS)

Orsini, S.; Mangano, V.; Milillo, A.; Plainaki, C.; Mura, A.; Raines, J. M.; Laurenza, M.; De Angelis, E.; Rispoli, R.; Lazzarotto, F.; Aronica, A.

2018-05-01

We report about recent results published on Scientific Reports @nature.com showing the first evidence of direct relationship between exosphere Na dynamics observed from ground and ICME transit at Mercury, as detected by MESSENGER.

MESSENGER MASCS/UVVS Observations of Cold Exospheric Calcium

NASA Astrophysics Data System (ADS)

Cassidy, T. A.

2018-05-01

Exospheric calcium is primarily ejected by a high energy process on the dawn hemisphere. UVVS data also show a sporadic cold component at low altitudes. Its temperature is consistent with laboratory measurements of photodesorption of calcium sulfide.

Pickup Ion Mass Spectrometry for Surface Bounded Exospheres and Composition Mapping of Lunar and Planetary Surfaces

NASA Technical Reports Server (NTRS)

Keller, J. W.; Zurbuchen, T. H.; Baragiola, R. A.; Cassidy, T. A.; Chornay, D. J.; Collier, M. R.; Hartle, R. E.; Johnson, R. E.; Killen, R. M.; Koehn, P.

2005-01-01

Many of the small to medium sized objects in the solar system can be characterized as having surface bounded exospheres, or atmospheres so tenuous that scale lengths for inter-particle collisions are much larger than the dimensions of the objects. The atmospheres of these objects are the product of their surfaces, both the surface composition and the interactions that occur on them and also their interiors when gases escape from there. Thus by studying surface bounded exospheres it is possible to develop insight into the composition and processes that are taking place on the surface and interiors of these objects. The Moon and Mercury are two examples of planetary bodies with surface bounded exospheres that have been studied through spectroscopic observations of sodium, potassium, and, on the moon, mass spectrometric measurements of lunar gases such as argon and helium.

Diagnostic Simulations of the Lunar Exosphere using Coma and Tail

NASA Astrophysics Data System (ADS)

Lee, Dong Wook; Kim, Sang J.

2017-10-01

The characteristics of the lunar exosphere can be constrained by comparing simulated models with observational data of the coma and tail (Lee et al., JGR, 2011); and thus far a few independent approaches on this issue have been performed and presented in the literature. Since there are two-different observational constraints for the lunar exosphere, it is interesting to find the best exospheric model that can account for the observed characteristics of the coma and tail. Considering various initial conditions of different sources and space weather, we present preliminary time-dependent simulations between the initial and final stages of the development of the lunar tail. Based on an updated 3-D model, we are planning to conduct numerous simulations to constrain the best model parameters from the coma images obtained from coronagraph observations supported by a NASA monitoring program (Morgan, Killen, and Potter, AGU, 2015) and future tail data.

Anisotropic Solar Wind Sputtering of the Lunar Surface Induced by Crustal Magnetic Anomalies

NASA Technical Reports Server (NTRS)

Poppe, A. R.; Sarantos, M.; Halekas, J. S.; Delory, G. T.; Saito, Y.; Nishino, M.

2014-01-01

The lunar exosphere is generated by several processes each of which generates neutral distributions with different spatial and temporal variability. Solar wind sputtering of the lunar surface is a major process for many regolith-derived species and typically generates neutral distributions with a cosine dependence on solar zenith angle. Complicating this picture are remanent crustal magnetic anomalies on the lunar surface, which decelerate and partially reflect the solar wind before it strikes the surface. We use Kaguya maps of solar wind reflection efficiencies, Lunar Prospector maps of crustal field strengths, and published neutral sputtering yields to calculate anisotropic solar wind sputtering maps. We feed these maps to a Monte Carlo neutral exospheric model to explore three-dimensional exospheric anisotropies and find that significant anisotropies should be present in the neutral exosphere depending on selenographic location and solar wind conditions. Better understanding of solar wind/crustal anomaly interactions could potentially improve our results.

An Exospheric Temperature Model Based On CHAMP Observations and TIEGCM Simulations

NASA Astrophysics Data System (ADS)

Ruan, Haibing; Lei, Jiuhou; Dou, Xiankang; Liu, Siqing; Aa, Ercha

2018-02-01

In this work, thermospheric densities from the accelerometer measurement on board the CHAMP satellite during 2002-2009 and the simulations from the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) are employed to develop an empirical exospheric temperature model (ETM). The two-dimensional basis functions of the ETM are first provided from the principal component analysis of the TIEGCM simulations. Based on the exospheric temperatures derived from CHAMP thermospheric densities, a global distribution of the exospheric temperatures is reconstructed. A parameterization is conducted for each basis function amplitude as a function of solar-geophysical and seasonal conditions. Thus, the ETM can be utilized to model the thermospheric temperature and mass density under a specified condition. Our results showed that the averaged standard deviation of the ETM is generally less than 10% than approximately 30% in the MSIS model. Besides, the ETM reproduces the global thermospheric evolutions including the equatorial thermosphere anomaly.

LADEE Test

NASA Image and Video Library

2017-12-08

Engineers at NASA's Ames Research Center, Moffett Field, Calif., prepare NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) Observatory for acoustic environmental testing. Credit: NASA/Ames ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

LADEE Preparations

NASA Image and Video Library

2013-09-04

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft being prepared in the clean room at Wallops Flight Facility. Credit: NASA ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Constraints on water vapor and sulfur dioxide at Ceres: Exploiting the sensitivity of the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Roth, Lorenz

2018-05-01

Far-ultraviolet observations of dwarf-planet (1) Ceres were obtained on several occasions in 2015 and 2016 by the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS), both on board the Hubble Space Telescope (HST). We report a search for neutral gas emissions at hydrogen, oxygen and sulfur lines around Ceres from a potential teneous exosphere. No detectable exosphere emissions are present in any of the analyzed HST observations. We apply analytical models to relate the derived upper limits for the atomic species to a water exosphere (for H and O) and a sulfur dioxide exosphere (for S and O), respectively. The H and O upper limits constrain the H2O production rate at the surface to (2 - 4) ×1026 molecules s-1 or lower, similar to or slightly larger than previous detections and upper limits. With low fluxes of energetic protons measured in the solar wind prior to the HST observations and the obtained non-detections, an assessment of the recently suggested sputter-generated water exosphere during solar energetic particle events is not possible. Investigating a sulfur dioxide-based exosphere, we find that the O and S upper limits constrain the SO2 density at the surface to values ∼ 1010 times lower than the equilibrium vapor pressure density. This result implies that SO2 is not present on Ceres' sunlit surface, contrary to previous findings in HST ultraviolet reflectance spectra but in agreement with the absence of SO2 infrared spectral features as observed by the Dawn spacecraft.

MESSENGER Orbital Observations of Mercury's Hydrogen Exosphere

NASA Astrophysics Data System (ADS)

Vervack, R. J.; Hurley, D. M.; Pryor, W.; Killen, R. M.

2018-05-01

We present a complete analysis of the MESSENGER H Lyman alpha altitude profiles. These data confirm the two-temperature nature of the Mariner 10 observations of H and address long-outstanding questions on the origin of Mercury's H exosphere.

Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e

NASA Astrophysics Data System (ADS)

Ridden-Harper, A. R.; Snellen, I. A. G.; Keller, C. U.; de Kok, R. J.; Di Gloria, E.; Hoeijmakers, H. J.; Brogi, M.; Fridlund, M.; Vermeersen, B. L. A.; van Westrenen, W.

2016-10-01

Context. The atmospheric and surface characterization of rocky planets is a key goal of exoplanet science. Unfortunately, the measurements required for this are generally out of reach of present-day instrumentation. However, the planet Mercury in our own solar system exhibits a large exosphere composed of atomic species that have been ejected from the planetary surface by the process of sputtering. Since the hottest rocky exoplanets known so far are more than an order of magnitude closer to their parent star than Mercury is to the Sun, the sputtering process and the resulting exospheres could be orders of magnitude larger and potentially detectable using transmission spectroscopy, indirectly probing their surface compositions. Aims: The aim of this work is to search for an absorption signal from exospheric sodium (Na) and singly ionized calcium (Ca+) in the optical transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the current best-fitting models to the planet mass and radius require a possible atmospheric component, uncertainties in the radius exist, making it possible that 55 Cancri e could be a hot rocky planet without an atmosphere. Methods: High resolution (R ~ 110 000) time-series spectra of five transits of 55 Cancri e, obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6 m and HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and K lines, the potential planet exospheric signal was filtered out from the much stronger stellar and telluric signals, making use of the change of the radial component of the orbital velocity of the planet over the transit from -57 to +57 km s-1. Results: Combining all five transit data sets, we detect a signal potentially associated with sodium in the planet exosphere at a statistical significance level of 3σ. Combining the four HARPS transits that cover the calcium H and K lines, we also find a potential signal from ionized calcium (4.1σ). Interestingly, this latter signal originates from just one of the transit measurements - with a 4.9σ detection at this epoch. Unfortunately, due to the low significance of the measured sodium signal and the potentially variable Ca+ signal, we estimate the p-values of these signals to be too high (corresponding to <4σ) to claim unambiguous exospheric detections. By comparing the observed signals with artificial signals injected early in the analysis, the absorption by Na and Ca+ are estimated to be at a level of ~2.3 × 10-3 and ~7.0 × 10-2 respectively, relative to the stellar spectrum. Conclusions: If confirmed, the 3σ signal would correspond to an optically thick sodium exosphere with a radius of 5 R⊕, which is comparable to the Roche lobe radius of the planet. The 4.9σ detection of Ca+ in a single HARPS data set would correspond to an optically thick Ca+ exosphere approximately five times larger than the Roche lobe radius. If this were a real detection, it would imply that the exosphere exhibits extreme variability. Although no formal detection has been made, we advocate that probing the exospheres of hot super-Earths in this way has great potential, also knowing that Mercury's exosphere varies significantly over time. It may be a fast route towards the first characterization of the surface properties of this enigmatic class of planets. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 092.C-0178 and 288.C-5010 and the Telescopio Nazionale Galileo under programme CAT13B_33.

Mercury's Exosphere: Ground Based Observations as a Support to the Forthcoming Bepi-Colombo

NASA Astrophysics Data System (ADS)

Leblanc, F.; Chaufray, J. Y.

2018-05-01

We will summarize the still open questions regarding Mercury's exosphere, highlighting which new topics Bepi-Colombo set of instruments might be able to address and how ground based observations should contribute to further improve our understanding.

Mercury's Sodium Exosphere: Observations during the MESSENGER Orbital Phase

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; Cassidy, Timothy A.; Vervack, Ronald J., Jr.; Burger, Matthew H.; Merkel, Aimee W.; Sarantos, Menelaos; Sprague, Ann L.; McClintock, William E.; Benna, Mehdi; Solomon, Sean C.

2012-01-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft entered into orbit about Mercury on March 18,2011. We now have approximately five Mercury years of data from orbit. Prior to the MESSENGER mission, Mercury's surface-bounded exosphere was known to contain H, He, Na. K, and Ca. The Ultraviolet and Visible Spectrometer (UVVS) began routine orbital observations of both the dayside and nightside exosphere on March 29. 2011, measuring altitude profiles for all previously detected neutral species except for He and K. We focus here on what we have learned about the sodium exosphere: its spatial, seasonal, and sporadic variation. Observations to date permit delineation of the relative roles of photon-stimulated desorption (PSD) and impact vaporization (IV) from seasonal and spatial effects, as well as of the roles of ions both as sputtering agents and in their possible role to enhance the efficiency of PSD. Correlations of Mercury's neutral sodium exosphere with measurements from MESSENGER's Magnetometer (MAG) and Energetic Particle and Plasma Spectrometer (EPPS) provide insight into the roles of ions and electrons. Models incorporating MAG observations provide a basis for identifying the location and area of the surface exposed to solar wind plasma, and EPPS observations reveal episodic populations of energetic electrons in the magnetosphere and the presence of planetary He(+), 0(+), and Na(+),

LADEE Encapsulated in the Fairing

NASA Image and Video Library

2013-09-04

Engineers at NASA's Wallops Flight Facility in Virginia prepare to encapsulate the LADEE spacecraft into the fairing of the Minotaur V launch vehicle nose-cone. Credit: NASA/Wallops/Terry Zaperach ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

LADEE in Lunar Orbit

NASA Image and Video Library

2013-09-04

An artist's concept showing the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft is seen orbiting the moon as it prepares to fire its maneuvering thrusters to maintain a safe orbital altitude. Credit: NASA Ames / Dana Berry ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

LADEE Fires Thrusters Artist's Concept

NASA Image and Video Library

2013-09-04

An artist's concept of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft firing its maneuvering thrusters in order to maintain a safe altitude as it orbits the moon. Credit: NASA Ames / Dana Berry ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Exospheric Neutral Density at the Earth's subsolar magnetopause deduced from the XMM-Newton X-ray observations

NASA Astrophysics Data System (ADS)

Connor, H. K.; Carter, J. A.

2017-12-01

Soft X-rays can be emitted when highly charged solar wind ions and exospheric neutrals exchange electrons. Astrophysics missions, such as XMM-Newton and ROSAT X-ray telescopes, have found that such solar wind charge exchange happens at the Earth's exosphere. The Earth's magnetosphere can be imaged via soft X-rays in order to understand its interaction with solar wind. Consequently, two soft X-ray telescope missions (CuPID and SMILE) are scheduled to launch in 2019 and 2021. They will provide wide field-of-view soft X-ray images of the Earth's dayside magnetosphere. The imagers will track the location and movement of the cusps, magnetopause, and bow shock in response to solar wind variations. To support these missions, an understanding of exospheric neutral density profile is needed. The neutral density is one of the controlling factors of soft X-ray signals. Strong neutral density can help to obtain high-resolution and high-cadence of soft X-ray images. In this study, we estimate the exospheric neutral density at 10 RE subsolar point using XMM X-ray observations, Cluster plasma observations, and OpenGGCM global magnetosphere - ionosphere MHD model. XMM-Newton observes line-of-sight, narrow field-of-view, integrated soft X-ray emissions when it looks through the dayside magnetosphere. OpenGGCM reproduces soft X-ray signals seen by the XMM spacecraft, assuming exospheric neutral density as a function of the neutral density at the 10RE subsolar point and the radial distance. Cluster observations are used to confirm OpenGGCM plasma results. Finally, we deduce the neutral density at 10 RE subsolar point by adjusting the model results to the XMM-Newton soft X-ray observations.

Probing of Hermean Exosphere by ultraviolet spectroscopy: Instrument presentation, calibration philosophy and first lights results

NASA Astrophysics Data System (ADS)

Mariscal, J. F.; Rouanet, N.; Maria, J. L.; Quémerais, E.; Mine, P. O.; Zuppella, P.; Suman, M.; Nicolosi, P.; Pelizzo, M. G.; Yoshikawa, I.; Yoshioka, K.; Murakami, G.

2017-11-01

PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) is a double spectrometer for the Extreme Ultraviolet range (55-155 nm) and the Far Ultraviolet range (145-315 nm) dedicated to the characterization of Mercury's exosphere composition and dynamics, and surface-exosphere connections. PHEBUS is part of the ESA BepiColombo cornerstone mission payload devoted to the study of Mercury. The BepiColombo mission consists of two spacecrafts: the Mercury Magnetospheric Orbiter (MMO) and the Mercury Planetary Orbiter (MPO) on which PHEBUS will be mounted. PHEBUS is a French-led instrument implemented in a cooperative scheme involving Japan (detectors), Russia (scanner) and Italy (ground calibration). Before launch, PHEBUS team want to perform a full absolute calibration on ground, in addition to calibrations which will be made in-flight, in order to know the instrument's response as precisely as possible. Instrument overview and calibration philosophy are introduced along with the first lights results observed by a first prototype.

Early Results from the Lunar Atmosphere and Dust Environment Explorer (LADEE)

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Hine, B.; Delory, G. T.; Mahaffy, Paul; Benna, Mehdi; Horanyi, Mihaly; Colaprete, Anthony; Noble, Sarah

2014-01-01

On 6 September, 2013, a near-perfect launch of the first Minotaur V rocket successfully carried NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) into a high-eccentricity geocentric orbit. After 30 days of phasing, LADEE arrived at the Moon on 6 October, 2013. LADEE's science objectives are twofold: (1) Determine the composition of the lunar atmosphere, investigate processes controlling its distribution and variability, including sources, sinks, and surface interactions; (2) Characterize the lunar exospheric dust environment, measure its spatial and temporal variability, and effects on the lunar atmosphere, if any. After a successful commissioning phase, the three science instruments have made systematic observations of the lunar dust and exospheric environment. These include initial observations of argon, neon and helium exospheres, and their diurnal variations; the lunar micrometeoroid impact ejecta cloud and its variations; spatial and temporal variations of the sodium exosphere; and the search for sunlight extinction caused by dust. LADEE also made observations of the effects of the Chang'e 3 landing on 14 December 2013.

Non-detection of a Helium Exosphere for the Hot Jupiter WASP-12b

NASA Astrophysics Data System (ADS)

Kreidberg, Laura; Oklopčić, Antonija

2018-06-01

An exosphere was recently detected around the exoplanet WASP-107b, a low-density, warm Neptune, based on an absorption feature from metastable helium (which has a vacuum wavelength of 10833 \\AA). Inspired by the WASP-107b detection, we reanalyzed archival HST observations of another evaporating exoplanet, WASP-12b, to search for signs of helium in its exosphere. We find no significant increase in transit depth at 10833 \\AA. We compare this result to theoretical predictions from a 1D model, and find that the expected helium feature amplitude is small, in agreement with the observed non-detection. We discuss possible explanations for why the helium feature is weaker for WASP-12b than WASP-107b, and conclude that the amplitude of the signal is highly sensitive to the stellar spectrum and the geometry of the evaporating gas cloud. These considerations should be taken into account in the design of future searches for helium exospheres.

Thermospheric temperature, density, and composition: New models

NASA Technical Reports Server (NTRS)

Jacchia, L. G.

1977-01-01

The models essentially consist of two parts: the basic static models, which give temperature and density profiles for the relevant atmospheric constituents for any specified exospheric temperature, and a set of formulae to compute the exospheric temperature and the expected deviations from the static models as a result of all the recognized types of thermospheric variation. For the basic static models, tables are given for heights from 90 to 2,500 km and for exospheric temperatures from 500 to 2600 K. In the formulae for the variations, an attempt has been made to represent the changes in composition observed by mass spectrometers on the OGO 6 and ESRO 4 satellites.

Investigation of the atmospheres of Europa, Ganymede, and Callisto with PEP/JUICE

NASA Astrophysics Data System (ADS)

Wurz, Peter; Tulej, Marek; Vorburger, Audrey; Thomas, Nicolas; Barabash, Stas; Wieser, Martin; Lammer, Helmut

2013-04-01

The Particle Environment Package (PEP) suite of instruments has been proposed for the JUICE mission, which contains sensors for the comprehensive measurements of electrons, ions and neutrals. One of the instruments for neutral particles is the Neutral and Ion Mass spectrometer instrument (NIM). NIM is a time-of-flight neutral gas and thermal ion mass spectrometer and is optimised for exospheric investigations. Full mass spectra (1 - 1000 amu, m/Δm = 1100) are recorded with high cadence, typically every 100 s, and during flybys even at 1 s cadence. In a 5-s spectrum the detection threshold is 10-16 mbar (about 1 cm-3). Various physical processes are acting on the surfaces of Jupiter's icy moons (Europa, Ganymede, Callisto) to promote material from the surface into the exosphere. These are thermal desorption (sublimation), photon stimulated desorption, ion-induced sputtering, and micro-meteorite impact vaporisation (Wurz and Lammer, 2003; Wurz et al., 2010). At Europa, sputtering is the most important surface release process (Johnson et al., 2009), which releases all species present on the surface more or less stoichiometrically into the exosphere, allowing to derive the chemical composition of the surface from the exospheric measurements. However, the chemical composition of the surface is modified by the bombardment of energetic electrons and ions, and the ultraviolet radiation. For example, species like H2, O2, H2O2 or O3 begin to be produced in the top surface layer and are later released into the exosphere by various means. Also, the co-rotation plasma's electrons and to a smaller extent the UV photons cause fragmentation and ionisation of molecules at some locations in these exospheres. We calculated the expected densities for established and expected species in Jupiter's icy moons exospheres. We find that for the planned JUICE trajectories near these moons that NIM will record most known species because of NIM's high sensitivity, even in the presence of the severe radiation environment at Europa. With NIM's dynamic range of 105 one can measure even the D/H ratios during flybys. NIM offers the possibility of detection of yet undiscovered species, with the likely candidates from the non-ice materials Mg, Al, Si, and Ca, that will help understand the mineralogical composition of the surfaces of the moons. NIM's high mass resolution, range and sensitivity are critical in contributing to the habitability assessment of Europa by being able to investigate localised patchy regions of the exosphere indicative of sub-surface venting and to resolve chemical composition.

Monte Carlo Simulation of Callisto's Exosphere

NASA Astrophysics Data System (ADS)

Vorburger, Audrey; Wurz, Peter; Galli, André; Mousis, Olivier; Barabash, Stas; Lammer, Helmut

2014-05-01

Whereas Callisto's surface has been mapped as early as in 1980 by the two Voyager missions, Callisto's tenuous atmosphere, also called an exosphere, was not directly observed until the Galileo mission in 1999. The Galileo Near-Infrared Mapping Spectrometer detected a CO2 signal up to 100 km above the surface [Carlson, Science, 1999]. Radio occultation measurements, also conducted by Galileo, led to the detection of an ionosphere with inferred densities much higher than can be explained by the measured CO2 exosphere, though [Kliore et al., J. Geophys. Res, 2002]. Insight about Callisto's exosphere is expected to be boosted by the Neutral Ion Mass Spectrometer (NIM) of the Particle Environment Package (PEP) on board the planned JUpiter ICy moons Explorer (JUICE) mission, which will conduct the first-ever direct sampling of the exospheres of Europa, Ganymede, and Callisto. To ensure that NIM's mass resolution and mass range will be sufficient for NIM to detect most expected species in Callisto's exosphere, we model said exosphere ab initio. Since Callisto is thought to consist to about equal parts of both icy and rocky components [Showman and Malhotra, Science, 1999], we model particle release from an icy as well as from a mineral surface separately. For the ice component, we investigate two different compositions, for reducing and oxidising conditions, which find analogy in the initial gas phase conditions in the solar nebula [Mousis et al., Planet. Space Sci., submitted]. For the non-ice material, the mineral surface, we investigate surfaces with compositions similar to CI chondrites and L/LL type chondrites, both of which have been suggested to represent Callisto's non-ice material best [Kuskov and Kronrod, Icarus, 2005 and Moore et al., Cambridge University Press, 2004]. For all mentioned materials, we compute density profiles for particles released by either surface sublimation or ion induced sputtering up to an altitude of 100'000 km. Our results show that close to the surface the sublimated particles dominate the day-side exosphere, however, their density profiles (with the exception of H and H2) decrease much more rapidly with altitude than those of the sputtered particles, thus, the latter particles start to dominate at altitudes above ~1000 km. Since the JUICE flybys are as low as 200 km above Callisto's surface, NIM is expected to register both the sublimated as well as sputtered particle populations. Our simulations show that NIM's sensitivity is high enough to allow the detection of particles sputtered from the icy as well as the mineral surfaces, and to distinguish between the different composition models.

Contributions of solar wind and micrometeoroids to molecular hydrogen in the lunar exosphere

NASA Astrophysics Data System (ADS)

Hurley, Dana M.; Cook, Jason C.; Retherford, Kurt D.; Greathouse, Thomas; Gladstone, G. Randall; Mandt, Kathleen; Grava, Cesare; Kaufmann, David; Hendrix, Amanda; Feldman, Paul D.; Pryor, Wayne; Stickle, Angela; Killen, Rosemary M.; Stern, S. Alan

2017-02-01

We investigate the density and spatial distribution of the H2 exosphere of the Moon assuming various source mechanisms. Owing to its low mass, escape is non-negligible for H2. For high-energy source mechanisms, a high percentage of the released molecules escape lunar gravity. Thus, the H2 spatial distribution for high-energy release processes reflects the spatial distribution of the source. For low energy release mechanisms, the escape rate decreases and the H2 redistributes itself predominantly to reflect a thermally accommodated exosphere. However, a small dependence on the spatial distribution of the source is superimposed on the thermally accommodated distribution in model simulations, where density is locally enhanced near regions of higher source rate. For an exosphere accommodated to the local surface temperature, a source rate of 2.2 g s-1 is required to produce a steady state density at high latitude of 1200 cm-3. Greater source rates are required to produce the same density for more energetic release mechanisms. Physical sputtering by solar wind and direct delivery of H2 through micrometeoroid bombardment can be ruled out as mechanisms for producing and liberating H2 into the lunar exosphere. Chemical sputtering by the solar wind is the most plausible as a source mechanism and would require 10-50% of the solar wind H+ inventory to be converted to H2 to account for the observations.

Theory for planetary exospheres: III. Radiation pressure effect on the Circular Restricted Three Body Problem and its implication on planetary atmospheres

NASA Astrophysics Data System (ADS)

Beth, A.; Garnier, P.; Toublanc, D.; Dandouras, I.; Mazelle, C.

2016-12-01

The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the stellar radiation pressure on planetary exospheres. In a series of papers, we present with a Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain [1989] Icarus, 81, 145-163. In this third paper, we investigate the effect of the stellar radiation pressure on the Circular Restricted Three Body Problem (CR3BP), called also the photogravitational CR3BP, and its implication on the escape and the stability of planetary exospheres, especially for hot Jupiters. In particular, we describe the transformation of the equipotentials and the location of the Lagrange points, and we provide a modified equation for the Hill sphere radius that includes the influence of the radiation pressure. Finally, an application to the hot Jupiter HD 209458b and hot Neptune GJ 436b reveals the existence of a blow-off escape regime induced by the stellar radiation pressure.

Contributions of Solar Wind and Micrometeoroids to Molecular Hydrogen in the Lunar Exosphere

NASA Technical Reports Server (NTRS)

Hurley, Dana M.; Cook, Jason C.; Retherford, Kurt D.; Greathouse, Thomas; Gladstone, G. Randall; Mandt, Kathleen; Grava, Cesare; Kaufmann, David; Hendrix, Amanda; Feldman, Paul D.;

Long-Range Transhorizon Lunar Surface Radio Wave Propagation in the Presence of a Regolith and a Sparse Exospheric Plasma

NASA Technical Reports Server (NTRS)

Manning, Robert M.

2008-01-01

Long-range, over-the-horizon (transhorizon) radio wave propagation is considered for the case of the Moon. In the event that relay satellites are not available or otherwise unwarranted for use, transhorizon communication provides for a contingency or backup option for non line-of-sight lunar surface exploration scenarios. Two potential low-frequency propagation mechanisms characteristic of the lunar landscape are the lunar regolith and the photoelectron induced plasma exosphere enveloping the Moon. Although it was hoped that the regolith would provide for a spherical waveguide which could support a trapped surface wave phenomena, it is found that, in most cases, the regolith is deleterious to long range radio wave propagation. However, the presence of the plasma of the lunar exosphere supports wave propagation and, in fact, surpasses the attenuation of the regolith. Given the models of the regolith and exosphere adopted here, it is recommended that a frequency of 1 MHz be considered for low rate data transmission along the lunar surface. It is also recommended that further research be done to capture the descriptive physics of the regolith and the exospheric plasma so that a more complete model can be obtained. This comprehensive theoretical study is based entirely on first principles and the mathematical techniques needed are developed as required; it is self-contained and should not require the use of outside resources for its understanding.

Radiation pressure dynamics in planetary exospheres - A 'natural' framework

NASA Technical Reports Server (NTRS)

Bishop, James; Chamberlain, Joseph W.

1989-01-01

Exospheric theory is reformulated to provide for the analysis of dynamical underpinning of exospheric features. The formulation is based on the parabolic-cylindrical separability of the Hamiltonian that describes particle motions in the combined fields of planetary gravity and solar radiation pressure. An approximate solution for trajectory evolution in terms of orbital elements is derived and the role of the exopause in the tail phenomenon is discussed. Also, an expression is obtained for the bound constituent atom densities at outer planetocoronal positions along the planet-sun axis for the case of an evaporative, uniform exobase. This expression is used to estimate midnight density enhancements as a function of radial distance for the terrestrial planets.

A Combined Experimental and Modeling Program to Study the Impact of Solar Wind Ions on the Surface and Exosphere of Mercury

NASA Astrophysics Data System (ADS)

Savin, D. W.; Bostick, B. C.; Domingue, D. L.; Ebel, D. S.; Harlow, G. E.; Killen, R. M.

2018-05-01

We aim to improve the interpretation of in-situ and remote-sensing data of Mercury. We will use updated exosphere and spectrophotometric models incorporating new data from lab simulations of solar wind ion irradiation of Mercury’s regolith surface.

Hydrogen Bearing Material in the Lunar Exosphere

NASA Astrophysics Data System (ADS)

Hurley, D.; Benna, M.; Colaprete, A.; Retherford, K. D.; Cook, J. C.; Elphic, R. C.; Farrell, W. M.; Killen, R. M.; Sarantos, M.

2015-12-01

We report on observations of water and its daughters in the lunar exosphere. Data from LADEE NMS, LADEE UVS, and LRO LAMP indicating the presence of H, H2, OH, and H2O are presented in terms of their relationship to external drivers. These observations point to the roles of solar wind and micrometeoroids in the source and release of hydrogen-bearing atoms and molecules in the exosphere. In particular, the implantation of H via solar wind is found to be the largest contributor to H2 in the moon's exosphere. However, the spatial distribution is more consistent with a release mechanism centered on the morning hemisphere. Thus the data are consistent with H2 created through a 2-step process involving the implantation of solar wind and subsequent release by micrometeoroids. This accounts for >12% of the solar wind H budget, leaving < 50% of the solar wind proton budget unobserved. LADEE data are consistent with water mainly being released by micrometeoroids. We present an overall picture of the present-day water cycle occurring on the Moon.

NASA's First Laser Communication System

NASA Image and Video Library

2017-12-08

A new NASA-developed, laser-based space communication system will enable higher rates of satellite communications similar in capability to high-speed fiber optic networks on Earth. The space terminal for the Lunar Laser Communication Demonstration (LLCD), NASA's first high-data-rate laser communication system, was recently integrated onto the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. LLCD will demonstrate laser communications from lunar orbit to Earth at six times the rate of the best modern-day advanced radio communication systems. Credit: NASA ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

First in-situ observations of exospheric response to CME impact at Mercury

NASA Astrophysics Data System (ADS)

Raines, J. M.; Wallace, K. L.; Sarantos, M.; Jasinski, J. M.; Tracy, P.; Dewey, R. M.; Weberg, M. J.; Slavin, J. A.

2017-12-01

We present the first in-situ observations of enhancements to Mercury's He exosphere generated by CME impact. We analyzed both plasma and magnetic field measurements from the Mercury Surface Space Environment, Geochemistry and Mapping (MESSENGER) spacecraft over a 60-hour period as a coronal mass ejection (CME) passed by the planet. We identified the shock, magnetic cloud and cavity regions of the moderate intensity CME while MESSENGER was in the solar wind. Inside the magnetosphere just after the CME shock passage, we observed a very active dayside magnetosphere, as evident from the high flux plasma parcels passing through the dayside and a broad northern magnetospheric cusp with exceptionally high planetary ion content. All of these signatures indicate substantial reconnection at the dayside magnetopause, making conditions that were excellent for solar wind access to Mercury's surface. The CME appeared to have been particularly enriched in He2+, causing the observed density of solar wind He2+ in the cusp to rise above 0.1 cm-3 and putting it in the top 1% of the over 3200 cusps analyzed. As the low-density CME cavity passed over the planet on the next orbit, the magnetosphere appeared much quieter, with smoother magnetic fields and a smaller, less intense northern cusp but with greatly enhanced He+ content. The elevated He+ observed density continued to increase on subsequent cusp crossings, peaking at 0.1 cm-3 36 hours after CME impact, the highest observed throughout the entire MESSENGER mission. We suggest that the enhancement in He+ indicates an increase to the neutral He exosphere density from the He-enriched CME, a phenomenon observed at the moon, possibly acting as follows: Increased access to the surface from CME-enhanced reconnection, combined with high He2+ flux, enhanced surface implantation. Neutral He atoms were then liberated at an increased rate by surface processes supplying the exosphere, causing a gradual increase in He exosphere density. This led to an increase in He+ abundance through photoionization and charge exchange, which, after acceleration on the dayside, was measured by MESSENGER. These first in-situ observations of exospheric response to CME impact at Mercury have implications for understanding exosphere generation and loss processes, as well space weathering of the planet's surface.

Twilight and nighttime ionospheric temperatures from oxygen 6300- and 5577-A spectral-line profiles.

NASA Technical Reports Server (NTRS)

Feibelman, W. A.; Hake, R. D., Jr.; Sipler, D. P.; Biondi , M. A.

1972-01-01

Use of Fabry-Perot interferometer measurements of atomic-oxygen 6300- and 5577-A line profiles from twilight and nightglow to determine the neutral temperatures in the F2 and E regions of the earth's ionosphere. The exospheric temperatures determined from the 6300-A profiles are usually somewhat higher than the temperatures calculated from Jacchia's model, and differences as large as about 300 K are noted when the exospheric temperature equals 1500 to 1600 K. The postsunset and predawn rate of change of the exospheric temperature is often substantially larger than the Jacchia prediction. The 5577-A (E region) measured temperatures range from 200 to 220 K on quiet nights to 500 to 600 K during geomagnetic storms.

Observations of Metallic Species in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; Potter, Andrew E.; Vervack, Ronald J., Jr.; Bradley, E. Todd; McClintock, William E.; Anderson, Carrie M.; Burger, Matthew H.

2010-01-01

From observations of the metallic species sodium (Na), potassium (K), and magnesium (Mg) in Mercury's exosphere, we derive implications for source and loss processes. All metallic species observed exhibit a distribution and/or line width characteristic of high to extreme temperature - tens of thousands of degrees K. The temperatures of refractory species, including magnesium and calcium, indicate that the source process for the atoms observed in the tail and near-planet exosphere are consistent with ion sputtering and/or impact vaporization of a molecule with subsequent dissociation into the atomic form. The extended Mg tail is consistent with a surface abundance of 5-8% Mg by number, if 30% of impact-vaporized Mg remains as MgO and half of the impact vapor condenses. Globally, ion sputtering is not a major source of Mg, but locally the sputtered source can be larger than the impact vapor source. We conclude that the Na and K in Mercury's exosphere can be derived from a regolith composition similar to that of Luna 16 soil (or Apollo 17 orange glass), in which the abundance by number is 0.0027 (0.0028) for Na and 0.0006 (0.0045) for K.

Modeling MESSENGER Observations of Calcium in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Burger, Matthew Howard; Killen, Rosemary M.; McClintock, William E.; Vervack, Ronald J., Jr.; Merkel, Aimee W.; Sprague, Ann L.; Sarantos, Menelaos

2012-01-01

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MESSENGER spacecraft has made the first high-spatial-resolution observations of exospheric calcium at Mercury. We use a Monte Carlo model of the exosphere to track the trajectories of calcium atoms ejected from the surface until they are photoionized, escape from the system, or stick to the surface. This model permits an exploration of exospheric source processes and interactions among neutral atoms, solar radiation, and the planetary surface. The MASCS data have suggested that a persistent, high-energy source of calcium that was enhanced in the dawn, equatorial region of Mercury was active during MESSENGER's three flybys of Mercury and during the first seven orbits for which MASCS obtained data. The total Ca source rate from the surface varied between 1.2x10(exp 23) and 2.6x10(exp 23) Ca atoms/s, if its temperature was 50,000 K. The origin of this high-energy, asymmetric source is unknown, although from this limited data set it does not appear to be consistent with micrometeoroid impact vaporization, ion sputtering, electron-stimulated desorption, or vaporization at dawn of material trapped on the cold nightside.

The effect of the charge exchange source on the velocity and 'temperature' distributions and their anisotropies in the earth's exosphere

NASA Technical Reports Server (NTRS)

Hodges, R. R., Jr.; Rohrbaugh, R. P.; Tinsley, B. A.

1981-01-01

The velocity distribution of atomic hydrogen in the earth's exosphere is calculated as a function of altitude and direction taking into account both the classic exobase source and the higher-altitude plasmaspheric charge exchange source. Calculations are performed on the basis of a Monte Carlo technique in which random ballistic trajectories of individual atoms are traced through a three-dimensional grid of audit zones, at which relative concentrations and momentum or energy fluxes are obtained. In the case of the classical exobase source alone, the slope of the velocity distribution is constant only for the upward radial velocity component and increases dramatically with altitude for the incoming radial and transverse velocity components, resulting in a temperature decrease. The charge exchange source, which produces the satellite hydrogen component and the hot ballistic and escape components of the exosphere, is found to enhance the wings of the velocity distributions, however this effect is not sufficient to overcome the temperature decreases at altitudes above one earth radius. The resulting global model of the hydrogen exosphere may be used as a realistic basis for radiative transfer calculations.

Magnetosphere-Regolith/Exosphere Coupling: Differences and Similarities to the Earth Magnetosphere-Ionosphere Coupling

NASA Technical Reports Server (NTRS)

Gjerleov, J. W.; Slavin, J. A.

2001-01-01

Of the three Mercury passes made by Mariner 10, the first and third went through the Mercury magnetosphere. The third encounter which occurred during northward IMF (interplanetary magnetic field) showed quiet time magnetic fields. In contrast the third encounter observed clear substorm signatures including dipolarization, field-aligned currents (FACs) and injection of energetic electrons at geosynchronous orbit. However, the determined cross-tail potential drop and the assumed height integrated conductance indicate that the FAC should be 2-50 times weaker than observed. We address this inconsistency and the fundamental problem of FAC closure whether this takes place in the regolith or in the exosphere. The current state of knowledge of the magnetosphere-exosphere/regolith coupling is addressed and similarities and differences to the Earth magnetosphere-ionosphere coupling are discussed.

The Unknown Hydrogen Exosphere: Space Weather Implications

NASA Astrophysics Data System (ADS)

Krall, J.; Glocer, A.; Fok, M.-C.; Nossal, S. M.; Huba, J. D.

2018-03-01

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere-Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

Mercury's Weather-Beaten Surface: Understanding Mercury in the Context of Lunar and Asteroid Space Weathering Studies

NASA Technical Reports Server (NTRS)

Dominque, Deborah L.; Chapman, Clark R.; Killen, Rosemary M.; Zurbuchen, Thomas H.; Gilbert, Jason A.; Sarantos, Menelaos; Benna, Mehdi; Slavin, James A.; Orlando, Thomas M.; Schriver, David;

Titan's ion exosphere observed from Voyager 1

NASA Technical Reports Server (NTRS)

Hartle, R. E.; Sittler, E. C., Jr.; Ogilvie, K. W.; Scudder, J. D.; Lazarus, A. J.; Atreya, S. K.

1982-01-01

The plasma wake surrounding Titan in Saturn's rotating magnetosphere is characterized by a plasma which is denser and cooler than the surrounding subsonic magnetospheric plasma, and which is produced by the deflection of magnetospheric plasma around Titan and the addition of exospheric ions picked up by the rotating magnetosphere. A resemblance to the interaction between the solar wind and Venus is shown for the case of ion pickup in the ion exosphere outside Titan's magnetic tail and ion flow within the boundaries of the tail as Saturn's rotating magnetosphere interacts with Titan. The boundary of the tail is indicated by a sharp reduction in the flux of high-energy electrons, which are removed by inelastic scattering with the atmosphere and centrifugal drift produced when the electrons traverse the magnetic field draped around Saturn.

How Surface Composition and Meteoroid Impacts Mediate Sodium and Potassium in the Lunar Exosphere

NASA Technical Reports Server (NTRS)

Colaprete, A.; Sarantos, M.; Wooden, D. H.; Stubbs, T. J.; Cook, A. M.; Shirley, M.

2016-01-01

Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.

Small meteoroids' major contribution to Mercury's exosphere

NASA Astrophysics Data System (ADS)

Grotheer, E. B.; Livi, S. A.

2014-01-01

The contribution of the meteoroid population to the generation of Mercury's exosphere is analyzed to determine which segment contributes most greatly to exospheric refilling via the process of meteoritic impact vaporization. For the meteoroid data, a differential mass distribution based on work by Grün et al. (Grün, E., Zook, H.A., Fechtig, H., Giese, R.H. [1985]. Icarus 62(2), 244-272) and a differential velocity distribution based on the work of Zook (Zook, H.A. [1975]. In: 6th Lunar Science Conference, vol. 2. Pergamon Press, Inc., Houston, TX, pp. 1653-1672) is used. These distributions are then evaluated using the method employed by Cintala (Cintala, M.J. [1992]. J. Geophys. Res. 97(E1), 947-974) to determine impact rates for selected mass and velocity segments of the meteoroid population.

Chemistry of impact events on Mercury

NASA Astrophysics Data System (ADS)

Berezhnoy, Alexey A.

2018-01-01

Based on the equilibrium thermochemical approach and quenching theory, formation of molecules and dust grains in impact-produced clouds formed after collisions between meteoroids and Mercury is considered. Based on observations of Al, Fe, and Mn atoms in the exosphere of Mercury and new results of studies of the elemental composition of the surface of Mercury, quenching temperatures and pressures of main chemical reactions and condensation of dust particles were estimated. The behavior of the main Na-, K-, Ca-, Fe-, Al-, Mn-, Mg-, Si-, Ti, Ni-, Cr-, Co, Zn-, O-, H-, S-, C-, Cl-, N-, and P-containing species delivered to the Hermean exosphere during meteoroid impacts was studied. The importance of meteoroid bombardment as a source of Na, K, Ca, Fe, Al, Mn, Mg, and O atoms in the exosphere of Mercury is discussed.

Ratio of Sodium to Potassium in the Mercurian Exosphere

NASA Technical Reports Server (NTRS)

Potter, A. E.; Anderson, C. M.; Killen, R. M.; Morgan, T. H.

2001-01-01

Sodium (Na) and Potassium (K) atoms can be seen in the exosphere of Mercury and the Moon because they are extremely efficient at scattering sunlight. These species must be derived from surface materials, so that we might expect the ratio of sodium to potassium to reflect the ratio of these elements in the surface crust. This expectation is approximately born out for the Moon, where the ratio of sodium to potassium in the lunar exosphere averages to be about 6, not too far from the ratio in lunar rocks of 2 to 7. However, the ratio in the Mercury exosphere was found to be in the range 80 to 190, and at least once, as high as 400. The sodium and potassium atoms seen in the Mercury exosphere represent a balance between production from the surface and loss to space. Only if the production efficiencies and loss rates for Na and K were equal, would the ratio of Na to K in the exosphere reflect the ratio in the surface rocks. Since a value of 100 or more for the ratio of sodium to potassium in the surface rocks seems very unlikely, the high values of the observed ratios suggests that either production efficiencies or loss processes for the two elements are not equivalent. It does not seem likely that source processes should be different on the Moon and Mercury by an order of magnitude. This suggests that loss processes rather than source processes are the cause of the difference between the two. The major loss processes for sodium and potassium on Mercury are radiation pressure and trapping of photoions by the solar wind. Radiation pressure can reach 50-70% of surface gravity, and can sweep sodium and potassium atoms off the planet, provided they are sufficiently hot. Photoionization followed by trapping of the ions in the solar wind is the other major loss process. Photoions are accelerated to keV energies in the magnetosphere, and may either intercept the magnetopause, and be lost from the planet, or impact the planetary surface. Ions that impact the surface are neutralized, and are then available for resupply to the exosphere. The loss efficiency depends on characteristics of the magnetosphere that determine the fraction of the ions that are recycled by neutralization on the surface. Over the preceding decade, we have collected sodium and potassium data for Mercury at irregular intervals. We analyzed these data to extract values for the Na/K ratio at a variety of conditions on Mercury. Additional information is contained in the original extended abstract.

The Lunar Atmosphere and Dust Environment Explorer (LADEE): Initial Science Results

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Hine, B.; Delory, G. T.; Salute, J. S.; Noble, S.; Colaprete, A.; Horanyi, M.; Mahaffy, P.

2014-01-01

On September 6, 2013, a near-perfect launch of the first Minotaur V rocket successfully carried NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) into a high-eccentricity geocentric orbit. LADEE arrived at the Moon on October 6, 2013, dur-ing the government shutdown. The spacecraft impact-ed the lunar surface on April 18, 2014, following a completely successful mission. LADEE's science objectives were twofold: (1) De-termine the composition and variability of the lunar atmosphere; (2) Characterize the lunar exospheric dust environment, and its variability. The LADEE science payload consisted of the Lunar Dust Experiment (LDEX), which sensed dust impacts in situ, for parti-cles between 100 nm and 5 micrometers; a neutral mass spectrometer (NMS), which sampled lunar exo-spheric gases in situ, over the 2-150 Dalton mass range; an ultraviolet/visible spectrometer (UVS) ac-quired spectra of atmospheric emissions and scattered light from tenuous dust, spanning a 250-800 nm wave-length range. UVS also performed dust extinction measurements via a separate solar viewer optic. The following are preliminary results for the lunar exosphere: (1) The helium exosphere of the Moon, first observed during Apollo, is clearly dominated by the delivery of solar wind He++. (2) Neon 20 is clearly seen as an important constituent of the exosphere. (3) Argon 40, also observed during Apollo and arising from interior outgassing, exhibits variations related to surface temperature-driven condensation and release, and is also enhanced over specific selenographic longi-tudes. (4) The sodium abundance varies with both lu-nar phase and with meteoroid influx, implicating both solar wind sputtering and impact vaporization process-es. (5) Potassium was also routinely monitored and exhibits some of the same properties as sodium. (6) Other candidate species were seen by both NMS and UVS, and await confirmation. Dust measurements have revealed a persistent "shroud" of small dust particles between 0.7 and sev-eral micrometers in size, present over the pre-dawn and morning sector of the Moon. This tenuous dust exosphere, with densities of approximately 10(exp -5) m(exp -3), appears to be sustained by the ejecta of micrometeoroid impacts.

Ceres' darkest secret and its putative exosphere

NASA Astrophysics Data System (ADS)

Schorghofer, N.; Mazarico, E.; Platz, T.; Schroeder, S.; Byrne, S.; Carsenty, U.; Combe, J. P.; Ermakov, A.; McFadden, L. A.; Prettyman, T. H.; Preusker, F.; Raymond, C. A.; Russell, C. T.

2016-12-01

Craters near Ceres' rotational poles can be shadowed year-round and trap volatiles. The persistently shadowed regions (PSRs) have been mapped in the northern hemisphere in two ways: by illumination modeling based on the topography and by stacking of images acquired near summer solstice. Scattered light reveals bright crater floor deposits (BCFDs) in a few PSRs. The lack of BCFDs in most PSRs can in part be explained by changes in Ceres' obliquity (axis tilt). At least one BCFD is illuminated and spectroscopically identified as H2O ice; this deposit is exceptionally bright and unusual morphologically. The BCFDs are likely water ice, either delivered through the exosphere or exposed ground ice. The remarkably shallow depths at which water ice is encountered on Ceres, on a global scale, imply that only a small amount of H2O was supplied to its water exosphere from this endogenic source. Ice that accumulated in the PSRs is hence easily dominated by other sources. The lack of optically thick ice deposits in most PSRs provides an upper bound on the exogenic delivery of water to Ceres, estimated as <109 kg since the most recent obliquity maximum 14 kyr ago. Water molecules are only barely gravitationally bound to Ceres at thermal speeds, but heavier species can be long-lived in the exosphere due to the low photo-destruction rates. Nevertheless, there is no observational evidence of other exospheric species yet. These results are based on observations by the FC (Framing Camera), VIR (Visible and Infrared Spectrometer), GRaND (Gamma-Ray and Neutron Spectrometer), and Gravity Science investigation of the Dawn spacecraft, which continues to advance our understanding not only of Ceres but of processes relevant to other Solar System bodies as well.

Constraints on Mercury's Na Exosphere: Combined MESSENGER and Ground-Based Data

NASA Technical Reports Server (NTRS)

Mouawad, Nelly; Burger, Matthew H.; Killen, Rosemary M.; Potter, Andrew E.; McClintock, William E.; Vervack, Ronald J., Jr.; Bradley, E. Todd; Benna, Mehdi; Naidu, Shantanu

2010-01-01

We have used observations of sodium emission obtained with the McMath-Pierce solar telescope and MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer (MASCS) to constrain models of Mercury's sodium exosphere, The distribution of sodium in Mercury's exosphere during the period January 12-15. 2008. was mapped using the McMath-Pierce solar telescope with the 5" X 5" image slicer to observe the D-line emission. On January 14, 2008, the Ultraviolet and Visible Spectrometer (UVVS) channel on MASCS sampled the sodium in Mercury's anti-sunward tail region. We find that the bound exosphere has an equivalent temperature of 900-1200 K, and that this temperature can be achieved if the sodium is ejected either by photon-stimulated desorption (PSD) with a 1200 K Maxwellian velocity distribution, or by thermal accommodation of a hotter source. We were not able to discriminate between the two assumed velocity distributions of the ejected particles for the PSD. but the velocity distributions require different values of the thermal accommodation coefficient and result in different upper limits on impact vaporization, We were able to place a strong constraint on the impact vaporization rate that results in the release of neutral Na atoms with an upper limit of 2.1 x 10(exp 6) sq cm/s, The variability of the week-long ground-based observations can be explained by variations in the sources, including both PSD and ion-enhanced PSD, as well as possible temporal enhancements in meteoroid vaporization. Knowledge of both dayside and anti-sunward tail morphologies and radiances are necessary to correctly deduce the exospheric source rates, processes, velocity distribution, and surface interaction.

Pickup Ion Velocity Distributions at Titan: Effects of Spatial Gradients

NASA Technical Reports Server (NTRS)

Hartle, R. E.; Sittler, E. C.

2004-01-01

The principle source of pickup ions at Titan is its neutral exosphere, extending well above the ionopause into the magnetosphere of Saturn or the solar wind, depending on the moon's orbital position. Thermal and nonthermal processes in the thermosphere generate the distribution of neutral atoms and molecules in the exosphere. The combination of these processes and the range of mass numbers, 1 to over 28, contribute to an exospheric source structure that produces pickup ions with gyroradii that are much larger or smaller than the corresponding scale heights of their neutral sources. The resulting phase space distributions are dependent on the spatial structure of the exosphere as well as that of the magnetic field and background plasma. When the pickup ion gyroradius is less than the source gas scale height, the pickup ion velocity distribution is characterized by a sharp cutoff near the maximum speed, which is twice that of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. This was the case for pickup H(sup +) ions identified during the Voyager 1 flyby. In contrast, as the gyroradius becomes much larger than the scale height, the peak of the velocity distribution in the source region recedes from the maximum speed. Iri addition, the amplitude of the distribution near the maximum speed decreases. These more beam like distributions of heavy ions were not observed from Voyager 1 , but should be observable by more sensitive instruments on future spacecraft, including Cassini. The finite gyroradius effects in the pickup ion velocity distributions are studied by including in the analysis the possible range of spatial structures in the neutral exosphere and background plasma.

High-Resolution Spectroscopic Observations of Potassium Emissions in the Lunar Exosphere

NASA Astrophysics Data System (ADS)

Robertson, S. D.; Oliversen, R. J.; Mierkiewicz, E. J.; Kuruppuaratchi, D. C. P.; Derr, N. J.; Gallant, M. A.; McFarland, C. G.; Sarantos, M.

2017-12-01

We investigate lunar exospheric potassium D1 emissions (7698.9646 Å) using a high-resolution (R = 180,000 or 1.7 km/s) spectroscopy with our dual-etalon Fabry-Perot instrument to measure line widths and radial velocities. The Field of View (FOV) is 2 arcmin ( 224 km at the mean lunar distance of 384,400 km) positioned tangent to the sunlit limb. The FOV placements are at cardinal directions from a variety of reference craters. All observations are collected at the National Solar Observatory McMath-Pierce Telescope in Kitt Peak, Arizona. The data are from monthly observing runs in 2017 from January to June excluding February. Results are produced via a newly created automated data reduction using Python. Python was chosen as an open-source alternative to the previously used IDL and MATLAB scripts to decrease the cost of software licenses and maintenance. The potassium spectral line profiles provide a direct method to track exospheric effective temperatures and velocities. By monitoring the state of the potassium emissions over different lunar phases, solar activity, and influx of meteor streams, we can constrain physical processes of sources and sinks at the lunar surface. Mechanisms that create the exosphere include photon-stimulated desorption, thermal evaporation, meteoroid impact vaporization, and ion sputtering via solar wind. Whereas the exosphere is diminished due to the low lunar escape velocity, solar radiation pressure, and neutral gas being ionized and swept away by the interplanetary and terrestrial magnetic field. Preliminary analysis indicates an average potassium temperature of 1140 K but varying over the range of 550 K to 2000 K. Further analysis is expected for data from 2014 to 2017 to make month to month, as well as annual, comparisons of potassium emissions.

In-situ observation of Martian neutral exosphere: Results from MENCA aboard Indian Mars Orbiter Mission (MOM)

NASA Astrophysics Data System (ADS)

Bhardwaj, Anil; Pratim Das, Tirtha; Dhanya, M. B.; Thampi, Smitha V.

2016-07-01

Till very recently, the only in situ measurements of the Martian upper atmospheric composition was from the mass spectrometer experiments aboard the two Viking landers, which covered the altitude region from 120 to 200 km. Hence, the exploration by the Mars Exospheric Neutral Composition Analyser (MENCA) aboard the Mars Orbiter Mission (MOM) spacecraft of ISRO and the Neutral Gas and Ion Mass Spectrometer (NGIMS) experiment aboard the Mars Atmosphere and Volatile ENvironment (MAVEN) mission of NASA are significant steps to further understand the Martian neutral exosphere and its variability. MENCA is a quadrupole based neutral mass spectrometer which observes the radial distribution of the Martian neutral exosphere. The analysis of the data from MENCA has revealed unambiguous detection of the three major constituents, which are amu 44 (CO2), amu 28 (contributions from CO and N2) and amu 16 (atomic O), as well as a few minor species. Since MOM is in a highly elliptical orbit, the MENCA observations pertain to different local times, in the low-latitude region. Examples of such observations would be presented, and compared with NGIMS results. Emphasis would be given to the observations pertaining to high solar zenith angles and close to perihelion period. During the evening hours, the transition from CO2 to O dominated region is observed near 270 km, which is significantly different from the previous observations corresponding to sub-solar point and SZA of ~45°. The mean evening time exospheric temperature derived using these observations is 271±5 K. These are the first observations corresponding to the Martian evening hours, which would help to provide constraints to the thermal escape models.

First optical observation of the Moon's sodium exosphere from the lunar orbiter SELENE (Kaguya)

NASA Astrophysics Data System (ADS)

Kagitani, M.; Taguchi, M.; Yamazaki, A.; Yoshikawa, I.; Murakami, G.; Yoshioka, K.; Kameda, S.; Ezawa, F.; Toyota, T.; Okano, S.

2009-08-01

The first successful observations of resonant scattering emission from the lunar sodium exosphere were made from the lunar orbiter SELENE (Kaguya) using TVIS instruments during the period 17-19 December, 2008. The emission intensity of the NaD-line decreased by 12±6%, with an average value of 5.4 kR (kilorayleighs) in this period, which was preceded, by 1 day, by enhancement of the solar proton flux associated with a corotating interaction region. The results suggest that solar wind particles foster the diffusion of sodium atoms or ions in the lunar regolith up to the surface and that the time scale of the diffusion is a few tens of hours. The declining activity of the Geminid meteor shower is also one possible explanation for the decreasing sodium exosphere.

Lunar atmosphere. How surface composition and meteoroid impacts mediate sodium and potassium in the lunar exosphere.

PubMed

Colaprete, A; Sarantos, M; Wooden, D H; Stubbs, T J; Cook, A M; Shirley, M

2016-01-15

Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition. Copyright © 2016, American Association for the Advancement of Science.

Global Distribution of Mercury's Neutrals from MESSENGER Measurements Combined with a Tomographic Method

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; McClintock, Bill; Vervack, Ron, Jr.; Killen, Rosemary; Merkel, Aimee; Slavin, James; Solomon, Sean C.

2011-01-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft entered orbit about Mercury on March 18, 2011. Since then, the Ultraviolet and Visible Spectrometer (UVVS) onboard this spacecraft has been observing Mercury's collisionless exosphere. We present measurements by MESSENGER UVVS of the sodium, calcium, and magnesium distributions that were obtained during multiple passes through the tail over a period of one month. Global maps of the exosphere were constructed daily from such measurements using a recently developed tomographic technique. During this period, Mercury moved towards the Sun from being about 0.44 astronomical units (AU) to approximately 0.32 AU from the Sun. Hence, our reconstructions provide information about the three-dimensional structure of the exosphere, the source processes for these species, and their dependence with orbital distance during the entire in-leg of Mercury's orbit.

Venus thermosphere and exosphere - First satellite drag measurements of an extraterrestrial atmosphere

NASA Technical Reports Server (NTRS)

Keating, G. M.; Tolson, R. H.; Hinson, E. W.

1979-01-01

Atmospheric drag measurements obtained from the study of the orbital decay of Pioneer Venus I indicate that atomic oxygen predominates in the Venus atmosphere above 160 kilometers. Drag measurements give evidence that conditions characteristic of a planetary thermosphere disappear near sundown, with inferred exospheric temperatures sharply dropping from approximately 300 K to less than 150 K. Observed densities are generally lower than given by theoretical models.

Lunar Riometry

NASA Astrophysics Data System (ADS)

Lazio, J.; Jones, D. L.; MacDowall, R. J.; Burns, J. O.; Kasper, J. C.

2011-12-01

The lunar exosphere is the exemplar of a plasma near the surface of an airless body. Exposed to both the solar and interstellar radiation fields, the lunar exosphere is mostly ionized, and enduring questions regarding its properties include its density and vertical extent and its behavior over time, including modification by landers. Relative ionospheric measurements (riometry) are based on the simple physical principle that electromagnetic waves cannot propagate through a partially or fully ionized medium below the plasma frequency, and riometers have been deployed on the Earth in numerous remote and hostile environments. A multi-frequency riometer on the lunar surface would be able to monitor, in situ, the peak plasma density of the lunar exosphere over time. We describe a concept for a riometer implemented as a secondary science payload on future lunar landers, such as those recommended in the recent Planetary Sciences Decadal Survey report. While the prime mission of such a riometer would be probing the lunar exosphere, our concept would also be capable to measuring the properties of nanometer- to micron-scale dust. The LUNAR consortium is funded by the NASA Lunar Science Institute to investigate concepts for astrophysical observatories on the Moon. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

SELMA mission: revealing the origin of lunar water

NASA Astrophysics Data System (ADS)

Barabash, Stas; Selma Team

2013-04-01

We propose a very low cost lunar mission to cover a poorly investigated inter-disciplinary area in the lunar science. The mission SELMA (Surface, Environment, and Lunar Magnetic Anomalies) investigates the interaction of the neutral and plasma environment with the lunar surface and the impact of this interaction on the surface composition, in the first hand, on the presence of water. The mission focuses on the fundamental question: What is the origin of the water in the lunar soil? The mission also addresses the questions: What are the lunar exosphere content and composition and how does the exosphere interact with the surface? How do the lunar magnetic anomalies interact with the solar wind and affect the surface? SELMA investigates the origin of the water in the lunar soil via simultaneous measurements of the OH/H2O abundance in the soil, the proton flux deposited to the surface, and transient changes in the exospheric gas content and composition. The water content in the surface is mapped via measurements of the 2700 - 3300 nm OH/H2O/ice absorption lines. The proton flux at the surface is measured remotely via backscattered hydrogen flux (energetic neutral atoms, ENAs). The exospheric gas content and composition and possible transient changes due to micrometeoroid influx or outgassing are monitored by a neutral gas mass spectrometer. Little is known about the tenuous lunar exosphere, its composition, structure, and relation to the plasma environment. The reasons for the present poor knowledge of the lunar exosphere is the difficulty of observations due to the low number densities, and the complexity of models due to the multiplicity of the mechanisms responsible for the input and loss of exospheric species. To investigate the lunar exosphere SELMA is equipped with state-of-the-art time-of-flight neutral gas mass spectrometer with unprecedented sensitivity and mass resolution. The Moon does not have a global magnetic field but possesses local magnetizations. The magnetizations interact with the solar wind plasma creating highly variable mini-magnetospheres affecting, through an as yet unknown mechanism, the surface visible albedo. The electrodynamical interaction is very complex being one of the fundamental solar wind interactions in the solar system. SELMA studies how the magnetic anomaly interact with the solar wind and surface via simultaneous measurements of 3D ion and electron distribution functions, the local magnetic field, solar wind flux variations on the surface through ENA imaging of the backscattered hydrogen flux, imaging in the visible range, and measuring the surface IR spectrum. The SELMA results will be of critical importance for the interpretation of data from Mercury to be collected by the ESA BepiColombo mission in 2020 - 2022. To address its scientific objectives SELMA carries a highly focused suite of instruments including an IR spectrometer, an ENA telescope, an ion and electron spectrometer, a neutral gas mass spectrometer, a magnetometer, and a visible camera. SELMA is a spinning platform to be inserted on a low maintenance quasi-frozen polar orbit of 30 km x 216 km by a dedicated launch and a solid state fuel kick stage. SELMA was proposed to ESA as a candidate for the S-class mission.

Feasibility of hydrogen density estimation from tomographic sensing of Lyman alpha emission

NASA Astrophysics Data System (ADS)

Waldrop, L.; Kamalabadi, F.; Ren, D.

2015-12-01

In this work, we describe the scientific motivation, basic principles, and feasibility of a new approach to the estimation of neutral hydrogen (H) density in the terrestrial exosphere based on the 3-D tomographic sensing of optically thin H emission at 121.6 nm (Lyman alpha). In contrast to existing techniques, Lyman alpha tomography allows for model-independent reconstruction of the underlying H distribution in support of investigations regarding the origin and time-dependent evolution of exospheric structure. We quantitatively describe the trade-off space between the measurement sampling rate, viewing geometry, and the spatial and temporal resolution of the reconstruction that is supported by the data. We demonstrate that this approach is feasible from either earth-orbiting satellites such as the stereoscopic NASA TWINS mission or from a CubeSat platform along a trans-exosphere trajectory such as that enabled by the upcoming Exploration Mission 1 launch.

MESSENGER observations of the composition of Mercury's ionized exosphere and plasma environment.

PubMed

Zurbuchen, Thomas H; Raines, Jim M; Gloeckler, George; Krimigis, Stamatios M; Slavin, James A; Koehn, Patrick L; Killen, Rosemary M; Sprague, Ann L; McNutt, Ralph L; Solomon, Sean C

2008-07-04

The region around Mercury is filled with ions that originate from interactions of the solar wind with Mercury's space environment and through ionization of its exosphere. The MESSENGER spacecraft's observations of Mercury's ionized exosphere during its first flyby yielded Na+, O+, and K+ abundances, consistent with expectations from observations of neutral species. There are increases in ions at a mass per charge (m/q) = 32 to 35, which we interpret to be S+ and H2S+, with (S+ + H2S+)/(Na+ + Mg+) = 0.67 +/- 0.06, and from water-group ions around m/q = 18, at an abundance of 0.20 +/- 0.03 relative to Na+ plus Mg+. The fluxes of Na+, O+, and heavier ions are largest near the planet, but these Mercury-derived ions fill the magnetosphere. Doubly ionized ions originating from Mercury imply that electrons with energies less than 1 kiloelectron volt are substantially energized in Mercury's magnetosphere.

Observations of Lunar Exospheric Helium with LAMP UV Spectrograph onboard the Lunar Reconnaissance Orbiter

NASA Astrophysics Data System (ADS)

Grava, Cesare; Hurley, Dana M.; Retherford, Kurt D.; Gladstone, G. Randall; Feldman, Paul D.; Pryor, Wayne R.; Greathouse, Thomas K.; Mandt, Kathleen E.

2017-04-01

Helium was one of the first elements discovered in the lunar exosphere, being detected by the mass spectrometer LACE (Lunar Atmosphere Composition Experiment) deployed at the lunar surface during the Apollo 17 mission. Most of it comes from neutralization of solar wind alpha particles impinging on the lunar surface, but there is increasing evidence that a non-negligible fraction of it diffuses from the interior of the Moon, as a result of radioactive decay of thorium and uranium. Therefore, pinpointing the amount of endogenic helium can constrain the abundance of these two elements in the crust, with implication for the formation of the Moon. The Lyman-Alpha Mapping Project (LAMP) far-UV spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) carried out an atmospheric campaign to study the lunar exospheric helium. The spacecraft was pitched along the direction of motion to look through a longer illuminated column of gas, compared to the usual nadir-looking mode, and therefore enhancing the brightness of the emission line at 58.4 nm of helium atoms resonantly scattering solar photons. The lines of sight of the observations spanned a variety of local times, latitudes, longitudes, and altitudes, allowing us to reconstruct the temporal and spatial distribution of helium and its radial density profile with the help of an exospheric model. Moreover, correlating the helium density inferred by LAMP with the flux of solar wind alpha particles (the main source of lunar helium) measured from the twin ARTEMIS spacecraft, it is possible to constrain the amount of helium which comes from the interior of the Moon via outgassing. While most of the observations can be explained by the exospheric model, we have found discrepancies between the model and LAMP observations, with the former underestimating the latter, especially at northern selenographic latitudes, when LRO altitude is maximum. Such discrepancies suggest that the vertical distribution of helium differs from a Chamberlain exospheric model, an interesting result considered that helium does not interact with the lunar surface, and may be indicative of a different thermal population of helium atoms. We present results from over 150 observations performed routinely from 2013 to 2016 to look for trends in the spatial and temporal distribution of helium and to constrain the fraction of endogenous helium compared to the solar wind contribution.

The Mercury exosphere after MESSENGER

NASA Astrophysics Data System (ADS)

Killen, Rosemary; McClintock, William; Vervack, Ronald; Merkel, Aimee; Burger, Matthew; Cassidy, Timothy; Sarantos, Menelaos

2016-07-01

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft observed sodium, calcium and magnesium emisison in Mercury's exosphere on a near-daily basis for >16 Mercury years. The MASCS observations showed that calcium in Mercury's exosphere is persistently concentrated in the dawn hemisphere and is of extreme temperature (>50,000 K). The column abundance varies seasonally, and is extremely repeatable each Mercury year. In addition, the calcium exhibits a persistent maximum not at perihelion but 20° after perihelion, an enhancement that was shown to be coincident with the probable intersection of Mercury's orbit with a dust stream originating at Comet Encke. Any mechanism producing the Mercurian Ca exosphere must explain the facts that the Ca is extremely hot, that it is seen almost exclusively on the dawnside of the planet, and that its content varies seasonally, not sporadically. Energization of the Ca atoms was suggested to originate through dissociation of Ca-bearing molecules ejected by meteoritic impacts. Magnesium was also observed on a daily basis throughout the MESSENGER orbital phase. Mg has its own spatial and temporal pattern, peaking at mid-morning instead of early morning like Ca, and exhibiting a warm thermal profile, about 5000 K, unlike the extreme temperature of Ca which is an order of magnitude hotter. Although Mercury's sodium exosphere has been observed from the ground for many decades, the MASCS observations showed that, like calcium, the sodium exosphere is dominated by seasonal variations, not sporadic variations. However a conundrum exists as to why ground-based observations show highly variable high-latitude variations that eluded the MASCS. The origin of a persistent south polar enhancement has not been explained. The more volatile element, Na, is again colder, about 1200 K, but not thermally accommodated to the surface temperature. A combination of source processes is surmised for this element, dominated by photon-stimulated desorption. Sporadic and high latitude enhancements persistently seen from the Earth have eluded measurement from orbit, possibly due to the geometry of the observations. One discovery still not fully explained is the observation that ionized calcium is almost as dense in the anti-sunward near tail as neutral calcium. The reason is most probably due to magnetospheric convection, but further work is needed to confirm this. Other weakly emitting species such as aluminum were observed sporadically, but most often near the dawn terminator.

Quasi-exospheric heat flux of solar-wind electrons

NASA Technical Reports Server (NTRS)

Eviatar, A.; Schultz, M.

1975-01-01

Density, bulk-velocity, and heat-flow moments are calculated for truncated Maxwellian distributions representing the cool and hot populations of solar-wind electrons, as realized at the base of a hypothetical exosphere. The electrostatic potential is thus calculated by requiring charge quasi-neutrality and the absence of electrical current. Plasma-kinetic coupling of the cool-electron and proton bulk velocities leads to an increase in the electrostatic potential and a decrease in the heat-flow moment.

On charge exchange and knock-on processes in the exosphere of Io

NASA Technical Reports Server (NTRS)

Ip, W.-H.

1982-01-01

One direct consequence of magnetospheric interaction of Io is the strong dynamical coupling of its neutral atmosphere with the corotating plasma. The absorption of the thermal ions and the associated neutral injection is an improtant issue not yet explored. As far as nonthermal escape of the neutral atmosphere is concerned, three processes stand out. That is, apart from sputtering, exospheric interactions like atom-ion knock-on collision and charge exchange recombination could be a significant source of the neutral clouds in the Jovian system. Using a current electrodynamic model of Io, both the absorption rate of the corotating thermal plasma and the production rates of new exospheric ions and the fast neutrals are considered. It is found that the source strength of the neutral atoms and molecules with speeds of about 100 km/sec could amount to 10 to the 26th/sec whereas exospheric neutrals emitted at lower speed (of about 10 km/sec) amounts to 4 x 10 to the 25th/sec. The generation of the new ions in connection with the streaming of the magnetospheric plasma around Io could also produce an asymmetric sputtering with a neutral flux of about 10 to the 27th/sec emitted from the region of Io which faces Jupiter. These results may be related to a number of sodium observations.

LADEE UVS (UltraViolet Visible Spectrometer) and the Search for Lunar Exospheric Dust: A Detailed Spectral Analysis

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Cook, Amanda; Colaprete, Anthony; Shirley, Mark; Vargo, Kara; Elphic, Richard C.; Hermalyn, Brendan; Stubbs, Timothy John; Glenar, David A.

2014-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) executed science observations in lunar orbit spanning 2013-Oct-16- 2014-04-18 UT. LADEE's Ultraviolet/Visible Spectrometer (UVS) studies the composition and temporal variations of the tenuous lunar exosphere and dust environment, utilizing two sets of optics: a limb-viewing telescope, and a solar-viewer. The limb-viewing telescope observes illuminated dust and emitting gas species while the Sun is just behind the lunar limb. The solar viewer, with its diffuser, allows UVS to also stare directly at the solar disk as it approaches the limb, sampling progressively lower exosphere altitudes. Solar viewer "Occultation" activities occur at the lunar sunrise limb, as the LADEE spacecraft passes into the lunar night side, facing the Sun (the spacecraft orbit is near-equatorial retrograde). A loss of transmission of sunlight occurs by the occultation of dust grains along the line-of-sight. So-called "Inertial Limb" activities have the limb-viewing telescope pointed at the lit exosphere just after the Sun has set. Inertial Limb activities follow a similar progression of diminishing sampling altitudes but hold the solar elongation angle constant so the zodiacal light contribution remains constant while seeking to observe the weak lunar horizon glow. On the dark side of the moon, "Sodium Tail" activities pointed the limb-viewing telescope in the direction of the Moon's sodium tail (similar to anti-sunward), during different lunar phases. Of the UVS data sets, these show the largest excess of scattered blue light, indicative of the presence of small (approximately 100 nm) dust grains in the tail. Correlations are sought between dust in the sodium tail and meteor streams and magnetotail crossings to investigate impact- versus electrostatic-lofting. Once lofted, nanoparticles can become charged and picked up by the solar wind. The LADEE UVS Occultation, Inertial Limb, and Sodium Tail spectral datasets provide evidence of a lunar dust exosphere.

MAVEN Pickup Ion Constraints on Mars Neutral Escape

NASA Astrophysics Data System (ADS)

Rahmati, A.; Larson, D. E.; Cravens, T.; Lillis, R. J.; Dunn, P.; Halekas, J. S.; McFadden, J. P.; Mitchell, D. L.; Thiemann, E.; Connerney, J. E. P.; DiBraccio, G. A.; Espley, J. R.; Eparvier, F. G.

2017-12-01

Mars is currently losing its atmosphere mainly due to the escape of neutral hydrogen and oxygen. Directly measuring the rate of escaping neutrals is difficult, because the neutral density in the Mars exosphere is dominated, up to several Martian radii, by atoms that are gravitationally bound to the planet. Neutral atoms in the Martian exosphere, however, can get ionized, picked up, and accelerated by the solar wind motional electric field and energized to energies high enough for particle detectors to measure them. The MAVEN SEP instrument detects O+ pickup ions that are created at altitudes where the escaping part of the exosphere is dominant. Fluxes of these ions reflect neutral densities in the distant exosphere of Mars, allowing us to constrain neutral oxygen escape rates. The MAVEN SWIA and STATIC instruments measure pickup H+ and O+ created closer to Mars; comparisons of these data with models can be used to constrain exospheric hot O and thermal H densities and escape rates. In this work, pickup ion measurements from SEP, SWIA, and STATIC, taken during the first 3 Earth years of the MAVEN mission, are compared to the outputs of a pickup ion model to constrain the variability of neutral escape at Mars. The model is based on data from six MAVEN instruments, namely, MAG providing magnetic field used in calculating pickup ion trajectories, SWIA providing solar wind velocity as well as 3D pickup H+ and O+ spectra, SWEA providing solar wind electron spectrum used in electron impact ionization rate calculations, SEP providing pickup O+ spectra, STATIC providing mass resolved 3D pickup H+ and O+ spectra, and EUVM providing solar EUV spectra used in photoionization rate calculations. A variability of less than a factor of two is observed in hot oxygen escape rates, whereas thermal escape of hydrogen varies by an order of magnitude with Mars season. This hydrogen escape variability challenges our understanding of the H cycle at Mars, but is consistent with other recent measurements.

High-Resolution Spectroscopic Observations of Potassium Emissions in the Lunar Exosphere

NASA Astrophysics Data System (ADS)

Robertson, Sarena D.; Oliversen, Ronald J.; Mierkiewicz, Edwin J.; Kuruppuaratchi, Dona Chathuni P.; Derr, Nicholas James; Gallant, Margaret A.; McFarland, Christina G.; Sarantos, Menelaos

2018-01-01

We investigate lunar exospheric potassium D1 emissions (7698.9646 Å) using high-resolution (R = 180,000 or 1.7 km/s) spectroscopy with our dual-etalon Fabry-Perot instrument to measure line widths and radial velocities. The Field of View (FOV) is 2 arcmins (~224 km at the mean lunar distance of 384,400 km) positioned tangent to the sunlit limb. The FOV placements are at cardinal directions from a variety of reference craters. All observations are collected at the National Solar Observatory McMath-Pierce Telescope in Kitt Peak, Arizona. The data are from several observations from 2014 through 2017 at various times of the year. Results are produced via a newly created automated data reduction using Python. Python was chosen as an open-source alternative to the previously used IDL and MATLAB scripts to decrease the cost of software licenses and maintenance. The potassium spectral line profiles provide a direct method to track exospheric effective temperatures and velocities. By monitoring the state of the potassium emissions over different lunar phases, solar activity, and the influx of meteor streams, we can constrain physical processes of sources and sinks at the lunar surface. Mechanisms that create the exosphere include photon-stimulated desorption, thermal evaporation, meteoroid impact vaporization, and ion sputtering via solar wind. In contrast, the exosphere is diminished due to the low lunar escape velocity, solar radiation pressure, and neutral gas being ionized and swept away by the interplanetary and terrestrial magnetic field. Preliminary analysis of 2017 data (January through June, excluding February) indicates an average potassium temperature of 1140 K but varying over the range of 550 K to 2000 K. Preliminary results from 2014 data depict a similar range of temperatures to that of 2017. Further analysis is expected for additional data from 2014 to later observations in 2017 that were not included in the initial set of models.

Viewing Mercury's Surface-bound Exosphere from Orbit: Eighteen Months of Observations by the Mercury Atmospheric and Surface Composition Spectrometer aboard the MESSENGER Spacecraft

NASA Astrophysics Data System (ADS)

McClintock, W. E.; Benna, M.; Burger, M. H.; Cassidy, T.; Killen, R. M.; Merkel, A. W.; Sarantos, M.; Solomon, S. C.; Sprague, A. L.; Vervack, R. J.

2012-12-01

Prior to the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, Mercury's surface-bounded exosphere was known to contain H and He, observed by Mariner 10, as well as Na, K, and Ca, observed from the ground. The exosphere is the interface between the planet's surface and the surrounding space environment. Its composition and structure are controlled by interactions among the surface, magnetosphere, solar wind, sunlight, and impacting meteoroids. When species are liberated from the surface with sufficient energy, they can be accelerated by solar radiation pressure to form an anti-sunward tail. During three flybys en route to orbit, the Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) aboard MESSENGER discovered Mg in the tail and detected Ca+ in a narrow region centered ~ 2.5 Mercury radii anti-sunward of the planet's terminator. UVVS began routine orbital observations of both the dayside and nightside exosphere on March 29, 2011. It regularly measures altitude profiles for all previously detected neutral species with the exception of He and K. The former has no emission features within the UVVS wavelength range (115-600 nm), and the latter has only one relatively weak feature there. A single component of Ca is usually observed at lower altitudes (~2000 km) and exhibits the strong equatorial, dawn enhancement observed during the flybys. Mg distributions exhibit two components. The more energetic component has been detected at high altitudes, up to 4000 km above the surface on both the dayside and nightside, and shows a dawn enhancement similar to Ca. Dayside distributions of Na exhibit two components with e-folding heights comparable to profiles above the poles obtained during the third flyby. Concentrations of all three species exhibit seasonal variability. The best studied of these is Na, for which maximum dayside density occurs at a Mercury true anomaly angle of 180°. UVVS also observes H. It is less well studied than Ca, Mg, and Na because signal from the exospheric H is often contaminated by emission from interplanetary hydrogen and sunlight reflected from the surface. O has also been detected near the subsolar point, but its emission is too weak for routine study. UVVS observations also include wavelength scans for neutral species that are known or are predicted to be present in the surface materials (e.g., Si, Al, S, Mn, Fe, and OH), but emissions from these species are not sufficiently bright for detection with current operational scenarios. The UVVS team uses a variety of techniques to relate exosphere composition and structure to source processes, including tomographic inversion and Monte Carlo modeling. Correlations of Mercury's neutral exosphere composition and structure with direct measurements of the space environment from MESSENGER's Magnetometer (MAG) and Energetic Particle and Plasma Spectrometer (EPPS) provide further insight into source processes.

Neutral sodium atoms extraction by micrometeoroid impacts on the surface of Mercury

NASA Astrophysics Data System (ADS)

Cremonese, G.; Orsini, S.; Capria, M. T.; Milillo, A.; Mura, A.; Mangano, V.; Carbognani, A.

2003-04-01

The Mercury's exosphere is more dependent on the micrometeoroid impacts than the lunar exosphere and we have applied an order-to-magnitude calculation on the physical conditions of the sodium atoms during these events. This calculation shows the different ionization degree of sodium atoms depending on the meteoroid impact velocity and the related emission enhancements we may have observing the exosphere. We have applied the same calculation to the visible and UV doublets showing the large difference, a factor 5, between the two emission intensities only taking into account the same micrometeoroids contribution. Furthermore we provide a rough estimate for the impact magnitude in sodium light if we observe the night side of the Mercury's surface from the orbit of the ESA mission BepiColombo. Assuming a specific energy distribution of the emitted neutrals, we simulate the characteristics of the low-energy neutral atom fluxes as observable by the SERENA/ELENA instrument proposed on board the ESA BepiColombo Planetary Orbiter.

Collision cross sections and diffusion parameters for H and D in atomic oxygen. [in upper earth and Venus atmospheres

NASA Technical Reports Server (NTRS)

Hodges, R. R., Jr.

1993-01-01

Modeling the behavior of H and D in planetary exospheres requires detailed knowledge of the differential scattering cross sections for all of the important neutral-neutral and ion-neutral collision processes affecting these species over their entire ranges of interaction energies. In the upper atmospheres of Earth, Venus, and other planets as well, the interactions of H and D with atomic oxygen determine the rates of diffusion of escaping hydrogen isotopes through the thermosphere, the velocity distributions of exospheric atoms that encounter the upper thermosphere, the lifetimes of exospheric orbiters with periapsides near the exobase, and the transfer of momentum in collisions with hot O. The nature of H-O and D-O collisions and the derivation of a data base consisting of phase shifts and the differential, total, and momentum transfer cross sections for these interactions in the energy range 0.001 - 10 eV are discussed. Coefficients of mutual diffusion and thermal diffusion factors are calculated for temperatures of planetary interest.

Effect on the Lunar Exosphere of a CME Passage

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; Hurley, Dana M.; Farrell, William M.; Sarantos, Menelaos

2011-01-01

It has long been recognized that solar wind bombardment onto exposed surfaces in the solar system will produce an energetic component to the exospheres about those bodies. Laboratory experiments have shown that the sputter yield can be noticeably increased in the case of a good insulating surface. It is now known that the solar wind composition is highly dependent on the origin of the particular plasma. Using the measured composition of the slow wind, fast wind, solar energetic particle (SEP) population, and coronal mass ejection (CME), broken down into its various components, we have estimated the total sputter yield for each type of solar wind. The heavy ion component, especially the He++ component, greatly enhances the total sputter yield during times when the heavy ion population is enhanced, most notably during a coronal mass ejection. To simulate the effect on the lunar exosphere of a CME passage past the Moon, we ran a Monte Carlo code for the species Na, K, Mg and Ca.

Sputtering of sodium and potassium from nepheline: Secondary ion yields and velocity spectra

NASA Astrophysics Data System (ADS)

Martinez, R.; Langlinay, Th.; Ponciano, C. R.; da Silveira, E. F.; Palumbo, M. E.; Strazzulla, G.; Brucato, J. R.; Hijazi, H.; Agnihotri, A. N.; Boduch, P.; Cassimi, A.; Domaracka, A.; Ropars, F.; Rothard, H.

2017-09-01

Silicates are the dominant surface material of many Solar System objects, which are exposed to ion bombardment by solar wind ions and cosmic rays. Induced physico-chemical processes include sputtering which can contribute to the formation of an exosphere. We have measured sputtering yields and velocity spectra of secondary ions ejected from nepheline, an aluminosilicate thought to be a good analogue for Mercury's surface, as a laboratory approach to understand the evolution of silicate surfaces and the presence of Na and K vapor in the exosphere. Experiments were performed with highly charged ion beams (keV/u-MeV/u) delivered by GANIL using an imaging XY-TOF-SIMS device under UHV conditions. The fluence dependence of sputtering yields gives information about the evolution of surface stoichiometry during irradiation. From the energy distributions N(E) of sputtered particles, the fraction of particles which could escape from the gravitational field of Mercury, and of those falling back and possibly contributing to populate the exosphere can be roughly estimated.

Elemental Mercury Diffusion Processes and Concentration at the Lunar Poles

NASA Technical Reports Server (NTRS)

Moxley, Frederick; Killen, Rosemary M.; Hurley, Dana M.

2011-01-01

In 2009, the Lyman Alpha Mapping Project (LAMP) spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft made the first detection of element mercury (Hg) vapor in the lunar exosphere after the Lunar Crater Observing and Sensing Satellite (LCROSS) Centaur rocket impacted into the Cabeus crater in the southern polar region of the Moon. The lunar regolith core samples from the Apollo missions determined that Hg had a devolatilized pattern with a concentration gradient increasing with depth, in addition to a layered pattern suggesting multiple episodes of burial and volatile loss. Hg migration on the lunar surface resulted in cold trapping at the poles. We have modeled the rate at which indigenous Hg is lost from the regolith through diffusion out of lunar grains. We secondly modeled the migration of Hg vapor in the exosphere and estimated the rate of cold-trapping at the poles using a Monte Carlo technique. The Hg vapor may be lost from the exosphere via ionization, Jeans escape, or re-impact into the surface causing reabsorption.

Quantifying Sources, Sinks and Gas-surface Interactions on the Moon from LADEE Measurements of Exospheric Na and K

NASA Astrophysics Data System (ADS)

Colaprete, A.; Sarantos, M.; Poppe, A. R.; Bennett, C.; Orlando, T. M.

2015-12-01

We present numerical simulations of the generation and loss of the sodium (Na) and potassium (K) exospheres of the Moon and compare these results to recent LADEE observations. While both species appear to migrate towards the poles like other volatiles, Na resides on the soil and exosphere for one to two months before getting lost to the solar wind or the subsurface. K exhibits a different evolutionary trend: it is lost much more quickly than ionization and sputtering rates allow for, suggesting that it is lost to the ground in just a few bounces. Thus, the two alkalis exhibit very different interactions with the lunar surface. Reproducing the monthly variation exhibited by Na requires higher source rates at Mare, or higher sink rates at Highlands, or a combination of both. The very different behavior of Na on Mare and Highlands soils is reminiscent of laboratory experiments of water binding on Apollo fine soils.

On the Role of Dust in the Lunar Ionosphere

NASA Technical Reports Server (NTRS)

Stubbs, Timothy J.; Glenar, D. A.; Collier, M. R.; Farrell, W. M.; Halekas, J S.; Delory, G. T.; Vondrak, R. R.

2011-01-01

Evidence suggests that electron concentrations above the dayside lunar surface can be significantly higher than expected from either the photo-ionization of exospheric neutrals or any other well-known process. The Luna 19 mission performed dual-frequency radio occultation experiments in order to determine electron column concentrations above the lunar limb as a function of tangent height (shown in the figure below), The resulting electron concentration profiles surprisingly indicated a peak of approx.500-1000/cu cm and scale heights of approx. 10-30 km. It has been suggested that electrically charged exospheric dust could contribute to these electron cnhancemcnts2 , Here we describe how to estimate the electrons produced by photo-charged dust, which is then used to predict electron concentrations from exospheric dust distribution models that are based on the "excess brightness" observed in Apollo 15 coronal photographs. The results indicate that radio occultation measurements likely provide a valuable perspective on the role of dust in the lunar environment.

Absence of a detectable lunar nanodust exosphere during a search with LRO's LAMP UV imaging spectrograph

NASA Astrophysics Data System (ADS)

Grava, C.; Stubbs, T. J.; Glenar, D. A.; Retherford, K. D.; Kaufmann, D. E.

2017-05-01

The Lyman-Alpha Mapping Project (LAMP) UV spectrograph on board the Lunar Reconnaissance Orbiter (LRO) performed a campaign to observe the Moon's nanodust exosphere, evidence for which was provided by the Lunar Atmosphere and Dust Environment Explorer (LADEE) Ultraviolet and Visible Spectrometer (UVS) during the 2014 Quadrantid meteoroid stream. These LADEE/UVS observations were consistent with a nanodust exosphere modulated by meteoroid impacts. LRO performed off-nadir maneuvers around the peak of the 2016 Quadrantids, in order to reproduce, as closely as possible, the active meteoroid environment and observing geometry of LADEE/UVS. We analyzed LAMP spectra to search for sunlight backscattering from nanodust. No brightness enhancement attributable to dust, of any size, was observed. We determine an upper limit for dust column concentration of 105 cm-2 for grains of radius 25 nm, and an upper limit for dust column mass of 10-11 g cm-2, nearly independent of grain size for radii <100 nm.

Mercury Na exospheric emission related to solar disturbances

NASA Astrophysics Data System (ADS)

Orsini, S.; Mangano, V.; Milillo, A.; Plainaki, C.; Mura, A.; Massetti, S.; Raines, J. M.; De Angelis, E.; Rispoli, R.; Lazzarotto, F.; Aronica, A.

2017-09-01

A first attempt to use Na exospheric emission at Mercury as a proxy of CME transit is presented, in a kind of planetary space weather. The link existing between the dayside exosphere Na pattern at Mercury and the solar wind-magnetosphere-surface interactions is investigated. This goal is pursued by analyzing the Na hourly average distributions, as observed by the ground-based THEMIS solar telescope during 10 selected periods between 2012 and 2013 (seeing <2"), when also data from MESSENGER were available. Very often a two-peak pattern of variable intensity is observed, symmetrically located at high latitudes in both hemispheres. Occasionally, the signal is instead diffused above the sub-solar region. We compare these different Na emission patterns with the time profiles of proton fluxes and magnetic field data, as measured in-situ by MESSENGER. Among these 10 cases, only in one occasion the Na signal is all the time diffused above the subsolar region, and only in this case the MESSENGER data indicate the occurrence of significant solar CME perturbations.

The Dependence of the Cerean Exosphere on Solar Energetic Particle Events

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villarreal, M. N.; Russell, C. T.; Luhmann, J. G.

2017-03-20

Observations from Earth-based ground and orbiting telescopes indicate that the Ceres’s exosphere has a time-varying water component. Evidence of a transient atmosphere was also detected by Dawn upon its arrival, inferred from the response on the Gamma Ray and Neutron Detector. That atmosphere appeared shortly after the passage of a large enhancement in the local flux of high-energy solar protons. Solar proton events have highly variable fluxes over a range of proton energies from 10 s of keV to over 100 MeV and are capable of sputtering water ice at or near the surface. Herein, we examine the fluxes ofmore » solar energetic protons measured during Earth-based attempts to detect water vapor and OH in the Ceres’ atmosphere. We find that the presence of the cerean exosphere is correlated with the inferred presence of solar energetic protons at Ceres, consistent with the event detected by Dawn.« less

On Lunar Exospheric Column Densities and Solar Wind Access Beyond the Terminator from ROSAT Soft X-Ray Observations of Solar Wind Charge Exchange

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Snowden, S. L.; Sarantos, M.; Benna, M.; Carter, J. A.; Cravens, T. E.; Farrell, W. M.; Fatemi, S.; Hills, H. Kent; Hodges, R. R.;

Measurement of visible and UV emission from Energetic Neutral Atom Precipitation (ENAP), on Spacelab

NASA Technical Reports Server (NTRS)

Tinsley, B. A.

1980-01-01

The charge exchange of plasmaspheric ions and exospheric H and O and of solar wind ions with exospheric and interplanetary H are sources of precipitating neutrals whose faint emission may be observed by the imaging spectrometric observatory during dark periods of the SL-1 orbit. Measurements of the interactions of these precipitating atoms with the thermosphere are needed to evaluate the heating and ionization effects on the atmosphere as well as the selective loss of i energetic ions from the sources (predominantly the ring current).

Mercury's complex exosphere: results from MESSENGER's third flyby.

PubMed

Vervack, Ronald J; McClintock, William E; Killen, Rosemary M; Sprague, Ann L; Anderson, Brian J; Burger, Matthew H; Bradley, E Todd; Mouawad, Nelly; Solomon, Sean C; Izenberg, Noam R

2010-08-06

During MESSENGER's third flyby of Mercury, the Mercury Atmospheric and Surface Composition Spectrometer detected emission from ionized calcium concentrated 1 to 2 Mercury radii tailward of the planet. This measurement provides evidence for tailward magnetospheric convection of photoions produced inside the magnetosphere. Observations of neutral sodium, calcium, and magnesium above the planet's north and south poles reveal altitude distributions that are distinct for each species. A two-component sodium distribution and markedly different magnesium distributions above the two poles are direct indications that multiple processes control the distribution of even single species in Mercury's exosphere.

Spectral line profiles for a planetary corona

NASA Technical Reports Server (NTRS)

Chamberlain, J. W.

1976-01-01

The Lyman and Balmer emissions of a planetary corona depend on the exospheric temperature, the integrated column density of solar-illuminated hydrogen, and the region of phase space occupied by particles. Measurements of the intensity alone are incapable of defining the exosphere unambiguously. Line profiles with high spectral resolution can show whether a nonthermal component of the escaping hydrogen is present and can indicate at what altitude orbits of hydrogen atoms are depleted. It is necessary, however, to plan the observations carefully if they are to be fitted usefully to a model.

Probing the Martian Exosphere and Neutral Escape Using Pickup Ions Measured by MAVEN

NASA Astrophysics Data System (ADS)

Rahmati, A.; Larson, D. E.; Cravens, T.; Halekas, J. S.; Lillis, R. J.; McFadden, J. P.; Mitchell, D. L.; Thiemann, E.; Connerney, J. E. P.; Dunn, P.; DiBraccio, G. A.; Espley, J. R.; Eparvier, F. G.; Jakosky, B. M.

2016-12-01

Soon after the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft started orbiting Mars in September 2014, the SEP (Solar Energetic Particle), SWIA (Solar Wind Ion Analyzer), and STATIC (Supra-Thermal and Thermal Ion Composition) instruments onboard the spacecraft started detecting planetary pickup ions. SEP can measure energetic (>50 keV) oxygen pickup ions, the source of which is the extended hot oxygen exosphere of Mars. Model results show that these pickup ions originate from tens of Martian radii upstream of Mars and are energized by the solar wind motional electric field as they gyrate back towards Mars. SEP is blind to pickup hydrogen, as the low energy threshold for detection of hydrogen in SEP is 20 keV; well above the maximum pickup hydrogen energy, which is four times the solar wind proton energy. SWIA and STATIC, on the other hand, can detect both pickup oxygen and pickup hydrogen with energies below 30 keV and created closer to Mars. During the times when MAVEN is outside the Martian bow shock and in the upstream undisturbed solar wind, the solar wind velocity measured by SWIA and the solar wind (or interplanetary) magnetic field measured by the MAG (magnetometer) instrument can be used to model pickup oxygen and hydrogen fluxes near Mars. Solar wind flux measurements of the SWIA instrument are used in calculating charge-exchange frequencies, and data from the EUVM (Extreme Ultraviolet Monitor) and SWEA (Solar Wind Electron Analyzer) instruments are also used in calculating photo-ionization and electron impact frequencies of neutral species in the Martian exosphere. By comparing SEP, SWIA, and STATIC measured pickup ion fluxes with model results, the Martian thermal hydrogen and hot oxygen neutral densities can be probed outside the bow shock, which would place constraints on estimates of oxygen and hydrogen neutral escape rates. We will present model-data comparisons of pickup ions measured outside the Martian bow shock. Our analysis reveals an order of magnitude density change with Mars season in the hydrogen exosphere, whereas the hot oxygen exosphere densities vary less than a factor of 2.

Lunar Riometry: Proof-of-Concept Instrument Package

NASA Astrophysics Data System (ADS)

Lazio, J.; Jones, D. L.; MacDowall, R. J.; Stewart, K.; Giersch, L.; Burns, J. O.; Farrell, W. M.; Kasper, J. C.; O'Dwyer, I.; Hartman, J.

2012-12-01

The lunar exosphere is the exemplar of a plasma near the surface of an airless body. Exposed to both the solar and interstellar radiation fields, the lunar exosphere is mostly ionized, and enduring questions regarding its properties include its density and vertical extent, the extent of contributions from volatile outgassing from the Moon, and its behavior over time, including response to the solar wind and modification by landers. Relative ionospheric measurements (riometry) is based on the simple physical principle that electromagnetic waves cannot propagate through a partially or fully ionized medium below the plasma frequency, and riometers have been deployed on the Earth in numerous remote and hostile environments. A multi-frequency riometer on the lunar surface would be able to monitor, in situ, the vertical extent of the lunar exosphere over time. We describe a concept for a riometer implemented as a secondary science payload on future lunar landers, such as those recommended in the recent Planetary Sciences Decadal Survey report. The instrument concept is simple, consisting of an antenna implemented as a metal deposited on polyimide film and receiver. We illustrate various deployment mechanisms and performance of a prototype in increasing lunar analog conditions. While the prime mission of such a riometer would be probing the lunar exosphere, our concept would also be capable to measuring the properties of dust impactors. The Lunar University Network for Astrophysical Research consortium is funded by the NASA Lunar Science Institute to investigate concepts for astrophysical observatories on the Moon. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Mercury sodium exospheric emission as a proxy for solar perturbations transit

NASA Astrophysics Data System (ADS)

Orsini, S.; Mangano, V.; Milillo, A.; Plainaki, C.; Mura, A.; Raines, J. M.; Laurenza, M.; De Angelis, E.; Rispoli, R.; Lazzarotto, F.; Aronica, A.

2017-12-01

The first evidence at Mercury of direct relation between ICME transit and Na exosphere dynamics is presented, suggesting that Na emission, observed from ground, could be a proxy of planetary space weather at Mercury. The link existing between the dayside exosphere Na patterns and the solar wind-magnetosphere-surface interactions is investigated. This goal is pursued by analyzing the Na intensity hourly images, as observed by the ground-based THEMIS solar telescope (Mangano et al., 2015*) during 10 selected periods between 2012 and 2013 (with seeing, σ <2"), when also MESSENGER data were available. Frequently, two-peak patterns of variable intensity are observed, located at high latitudes in both hemispheres. Occasionally, Na signal is instead diffused above the sub-solar region. We compare these different patterns with the in-situ time profiles of proton fluxes and magnetic field data from MESSENGER. Among these 10 cases, only in one occasion the Na signal is diffused above the subsolar region, when the MESSENGER data detect the transit of two ICMEs. The selected cases suggest that the Na emission patterns are well related to the solar wind conditions at Mercury. For corroborating such a result, the ICME propagation from the Sun has been modeled at Mercury location, and space plasma parameters profiles are compared to the observed Na emission. Finally, we conclude that the exospheric Na emission patterns, observed from ground, can be considered as a `natural monitor' of solar disturbances when transiting near Mercury. (*) Mangano, et al., PSS, 115, 102-109, doy: 10.1016/j.pss.2015.04.001, 2015.

Limits to Mercury's Magnesium Exosphere from MESSENGER Second Flyby Observations

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; Killen, Rosemary M.; McClintock, William E.; Bradley, E. Todd; Vervack, Ronald J., Jr.; Benna, Mehdi; Slavin, James A.

2011-01-01

The discovery measurements of Mercury's exospheric magnesium, obtained by the MErcury Surface. Space ENvironment, GEochemistry. and Ranging (MESSENGER) probe during its second Mercury flyby, are modeled to constrain the source and loss processes for this neutral species. Fits to a Chamberlain exosphere reveal that at least two source temperatures are required to reconcile the distribution of magnesium measured far from and near the planet: a hot ejection process at the equivalent temperature of several tens of thousands of degrees K, and a competing, cooler source at temperatures as low as 400 K. For the energetic component, our models indicate that the column abundance that can be attributed to sputtering under constant southward interplanetary magnetic field (IMF) conditions is at least a factor of five less than the rate dictated by the measurements, Although highly uncertain, this result suggests that another energetic process, such as the rapid dissociation of exospheric MgO, may be the main source of the distant neutral component. If meteoroid and micrometeoroid impacts eject mainly molecules, the total amount of magnesium at altitudes exceeding approximately 100 km is found to be consistent with predictions by impact vaporization models for molecule lifetimes of no more than two minutes. Though a sharp increase in emission observed near the dawn terminator region can be reproduced if a single meteoroid enhanced the impact vapor at equatorial dawn, it is much more likely that observations in this region, which probe heights increasingly near the surface, indicate a reservoir of volatile Mg being acted upon by lower-energy source processes.

Short-term observations of double-peaked Na emission from Mercury's exosphere

NASA Astrophysics Data System (ADS)

Massetti, S.; Mangano, V.; Milillo, A.; Mura, A.; Orsini, S.; Plainaki, C.

2017-04-01

We report the analysis of short-term ground-based observations of the exospheric Na emission (D1 and D2 lines) from Mercury, which was characterized by two high-latitude peaks confined near the magnetospheric cusp footprints. During a series of scheduled observations from the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS) telescope, achieved by scanning the whole planet, we implemented a series of extra measurements by recording the Na emission from a narrow north-south strip only, centered above the two emission peaks. Our aim was to inspect the existence of short-term variations, which were never analyzed before from ground-based observations, and their possible correlation with interplanetary magnetic field variations. Though Mercury possesses a miniature magnetosphere, characterized by fast reconnection events that develop on a timescale of few minutes, ground-based observations show that the exospheric Na emission pattern can be globally stable for a prolonged period (some days) and also exhibits fluctuations in the time range of tens of minutes.

Cassini CAPS Identification of Pickup Ion Compositions at Rhea

NASA Astrophysics Data System (ADS)

Desai, R. T.; Taylor, S. A.; Regoli, L. H.; Coates, A. J.; Nordheim, T. A.; Cordiner, M. A.; Teolis, B. D.; Thomsen, M. F.; Johnson, R. E.; Jones, G. H.; Cowee, M. M.; Waite, J. H.

2018-02-01

Saturn's largest icy moon, Rhea, hosts a tenuous surface-sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO2+ during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along-track densities of ˜2 × 10-3 cm-3. Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 ± 3 u which we suggest are carbon-based compounds, such as CN-, C2H-, C2-, or HCO-, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along-track densities of ˜5 × 10-4 cm-3 and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO2 exosphere and surprisingly low O2 sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics.

Seasonal variations of Mercury's magnesium dayside exosphere from MESSENGER observations

NASA Astrophysics Data System (ADS)

Merkel, Aimee W.; Cassidy, Timothy A.; Vervack, Ronald J.; McClintock, William E.; Sarantos, Menelaos; Burger, Matthew H.; Killen, Rosemary M.

2017-01-01

The Ultraviolet and Visible Spectrometer channel of the Mercury Atmospheric and Surface Composition Spectrometer instrument aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft made near-daily observations of solar-scattered resonant emission from magnesium in Mercury's exosphere during the mission's orbital phase (March 2011-April 2015, ∼17 Mercury years). In this paper, a subset of these data (March 2013-April 2015) is described and analyzed to illustrate Mg's spatial and temporal variations. Dayside altitude profiles of emission are used to make estimates of the Mg density and temperature. The main characteristics of the Mg exosphere are (a) a predominant enhancement of emission in the morning (6 am-10 am) near perihelion, (b) a bulk temperature of ∼6000 K, consistent with impact vaporization as the predominant ejection process, (c) a near-surface density that varies from 5 cm-3 to 50 cm-3 and (d) a production rate that is strongest in the morning on the inbound leg of Mercury's orbit with rates ranging from 1 × 105 cm-2 s-1 to 8 × 105 cm-2 s-1.

Seasonal Variations of Mercury's Magnesium Dayside Exosphere from MESSENGER Observations

NASA Technical Reports Server (NTRS)

Merkel, Aimee W.; Cassidy, Timothy A.; Vervack, Ronald J., Jr.; McClintock, William E.; Sarantos, Menelaos; Burger, Matthew H.; Killen, Rosemary M.

2017-01-01

The Ultraviolet and Visible Spectrometer channel of the Mercury Atmospheric and Surface Composition Spectrometer instrument aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft made near-daily observations of solar-scattered resonant emission from magnesium in Mercury's exosphere during the mission's orbital phase (March 2011-April 2015, approx.17 Mercury years). In this paper, a subset of these data (March 2013-April 2015) is described and analyzed to illustrate Mg's spatial and temporal variations. Dayside altitude profiles of emission are used to make estimates of the Mg density and temperature. The main characteristics of the Mg exosphere are (a) a predominant enhancement of emission in the morning (6 am-10 am) near perihelion, (b) a bulk temperature of approx. 6000 K, consistent with impact vaporization as the predominant ejection process, (c) a near-surface density that varies from 5/cu cm to 50/cu cm and (d) a production rate that is strongest in the morning on the inbound leg of Mercury's orbit with rates ranging from 1×10(exp 5)/sq cm/s to 8×10(exp 5)/sq cm/s.

A model of the SO2 atmosphere and ionosphere of Io

NASA Technical Reports Server (NTRS)

Kumar, S.

1980-01-01

The calculations of thermal structure for an SO2 atmosphere of Io lead to exospheric temperatures in 800-1200 K range. The Pioneer 10 electron density profiles can be fit with an SO2 surface density of 1.2 x 10 to the 11th per cu cm at 5:30 pm local time and exosphere temperature of 1030 K. Low energy electrons provide the major ionization source but the solar UV absorption dominates the heating of the atmosphere due to the long wavelength absorption threshold of SO2 and large absorption cross sections.

LADEE Spin Test

NASA Image and Video Library

2017-12-08

During preparations for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) observatory launch on Sept. 6, 2013, the spacecraft went through final preparations and close-outs, which included checking alignment after its cross-country shipment, checking the propulsion system for leaks, inspecting and repairing solar panels, and final electrical tests. After these activities were completed, more challenging portions of the launch preparations began: spin testing and fueling. To make sure that the spacecraft is perfectly balanced for flight, engineers mounted it onto a spin table and rotate it at high speeds, approximately one revolution per second. The team measured any offsets during the spinning, and then added small weights to the spacecraft to balance it. Once the spacecraft was balanced dry, the team loaded the propulsion tanks with fuel, oxidizer, and pressurant. The spin testing was performed again "wet," or with fuel, in order to see if the balance changed with the full fuel tanks. Engineers from NASA's Ames Research Center in Moffett Field, Calif., have now successfully completed launch preparation activities for LADEE, which has been encapsulated into the nose-cone of the Minotaur V rocket at NASA's Wallops Flight Facility in Virginia. LADEE is ready to launch when the window opens on Friday. Image Credit: NASA ----- What is LADEE? The Lunar Atmosphere and Dust Environment Explorer (LADEE) is designed to study the Moon's thin exosphere and the lunar dust environment. An "exosphere" is an atmosphere that is so thin and tenuous that molecules don't collide with each other. Studying the Moon's exosphere will help scientists understand other planetary bodies with exospheres too, like Mercury and some of Jupiter's bigger moons. The orbiter will determine the density, composition and temporal and spatial variability of the Moon's exosphere to help us understand where the species in the exosphere come from and the role of the solar wind, lunar surface and interior, and meteoric infall as sources. The mission will also examine the density and temporal and spatial variability of dust particles that may get lofted into the atmosphere. The mission also will test several new technologies, including a modular spacecraft bus that may reduce the cost of future deep space missions and demonstrate two-way high rate laser communication for the first time from the Moon. LADEE now is ready to launch when the window opens on Sept. 6, 2013. Read more: www.nasa.gov/ladee NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Plasma precipitation on Mercury's nightside and its implications for magnetospheric convection and exosphere generation.

NASA Astrophysics Data System (ADS)

Raines, J. M.; Slavin, J. A.; Tracy, P.; Gershman, D. J.; Zurbuchen, T.; Korth, H.; Anderson, B. J.; Solomon, S. C.

2015-12-01

Plasma impact onto Mercury's surface can be an important contributor to Mercury's exosphere through the process of ion sputtering. Under some circumstances, this process can produce a substantial fraction of the exosphere. When the impacting plasma originates from the magnetosphere itself, this sputtering process can conversely be considered as a sink for the plasma of the Mercury magnetosphere, providing evidence for the processes at work in that system. One such process is reconnection in Mercury's magnetotail, which can accelerate ions and electrons from the central plasma sheet toward the nightside of the planet. By analogy with processes at Earth, it is hypothesized that as these flows approach the planet, much of the plasma is diverted from impact onto the surface by the increasingly strong planetary magnetic field closer to the planet. The remainder of the plasma is expected to follow nearly dipolar field lines, impacting the nightside surface and potentially contributing to field-aligned currents. We present the first direct evidence that this process is operating at Mercury. We examine ion precipitation events on Mercury's nightside with the Fast Imaging Plasma Spectrometer (FIPS) on the MESSENGER spacecraft, which orbited Mercury from 2011 to 2015. We characterize the energy distributions of these events and their extent in latitude and local time. We use these observations to predict the precipitating proton flux from altitudes as low as 11 km. We use this information to bound the region of Mercury's surface that remains protected from plasma bombardment by the planetary dipole magnetic field, and to explore the implications of this information for magnetospheric convection and exosphere generation at Mercury.

Plasma precipitation on Mercury's nightside and its implications for magnetospheric convection and exosphere generation.

NASA Astrophysics Data System (ADS)

Raines, J. M.; Slavin, J. A.; Tracy, P.; Gershman, D. J.; Zurbuchen, T.; Dewey, R. M.; Sarantos, M.

2016-12-01

Plasma impact onto Mercury's surface can be an important contributor to Mercury's exosphere through the process of ion sputtering. Under some circumstances, this process can produce a substantial fraction of the exosphere. When the impacting plasma originates from the magnetosphere itself, this sputtering process can conversely be considered as a sink for the plasma of the Mercury magnetosphere, providing evidence for the processes at work in that system. One such process is reconnection in Mercury's magnetotail, which can accelerate ions and electrons from the central plasma sheet toward the nightside of the planet. By analogy with processes at Earth, it is hypothesized that as these flows approach the planet, much of the plasma is diverted from impact onto the surface by the increasingly strong planetary magnetic field closer to the planet. The remainder of the plasma is expected to follow nearly dipolar field lines, impacting the nightside surface and potentially contributing to field-aligned currents. We present the first direct evidence that this process is operating at Mercury. We examine ion precipitation events on Mercury's nightside with the Fast Imaging Plasma Spectrometer (FIPS) on the MESSENGER spacecraft, which orbited Mercury from 2011 to 2015. We characterize the energy distributions of these events and their extent in latitude and local time. We use these observations to predict the precipitating proton flux from altitudes as low as 11 km. We use this information to bound the region of Mercury's surface that remains protected from plasma bombardment by the planetary dipole magnetic field, and to explore the implications of this information for magnetospheric convection and exosphere generation at Mercury.

Analysis of Lyman {alpha} and He I 584-{Angstrom} airglow measurements using a spherical radiative transfer model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bush, B.C.; Chakrabarti, S.

1995-10-01

The authors report on the scattering and excitation mechanisms of the terrestrial exospheric H I 1216-{Angstrom} airglow emissions by comparing simulations from a radiative transfer model with spectroscopic measurements from an Earth-orbiting satellite. The purpose of these comparisons are twofold: to assess the sensitivity of the input parameters to the model results and to test the applicability of the model to airglow analysis. The model incorporates a spherically oriented atmosphere to account for the extended scale heights of the exospheric scatterers as well as to properly mimic scattering across the terminator region from the dayside to the nightside hemispheres. Spectroscopicmore » Lyman {alpha} and He I 584 {Angstrom} data were obtained by the STP78-1 satellite that circumnavigated the Earth in a noon/midnight orbit at an altitude of 600 km. The {open_quotes}best fit{close_quotes} analysis of the Lyman {alpha} data acquired on March 25, 1979, requires scaling the hydrogen density distribution obtained from the MSIS-90 (Hedin) atmospheric model by 45-50%, the exospheric temperature by 90-100%, and the Lyman {alpha} solar flux predicted by EUV91 model (Tobiska) by 1.9-2.0. Similar analysis of the He I 584 {Angstrom} data acquired on March 5, 1979, requires scaling the helium density distribution obtained from the MSIS-90 (Hedin) atmospheric model by 60-80% and the exospheric temperature by 105-115% while using a line center 584-{Angstrom} solar flux of 1.44x10{sup 10} photons cm{sup {minus}2}s{sup {minus}1} {Angstrom}{sup {minus}1}. 46 refs., 22 figs., 5 tabs.« less

Lunar Atmosphere Probe Station: A Proof-of-Concept Instrument Package for Monitoring the Lunar Atmosphere

NASA Astrophysics Data System (ADS)

Lazio, J.; Jones, D. L.; MacDowall, R. J.; Stewart, K. P.; Burns, J. O.; Farrell, W. M.; Giersch, L.; O'Dwyer, I. J.; Hicks, B. C.; Polisensky, E. J.; Hartman, J. M.; Nesnas, I.; Weiler, K.; Kasper, J. C.

2013-12-01

The lunar exosphere is the exemplar of a plasma near the surface of an airless body. Exposed to both the solar and interstellar radiation fields, the lunar exosphere is mostly ionized, and enduring questions regarding its properties include its density and vertical extent, the extent of contributions from volatile outgassing from the Moon, and its behavior over time, including response to the solar wind and modification by landers. Relative ionospheric measurements (riometry) are based on the simple physical principle that electromagnetic waves cannot propagate through a partially or fully ionized medium below the plasma frequency, and riometers have been deployed on the Earth in numerous remote and hostile environments. A multi-frequency riometer on the lunar surface would be able to monitor, *in situ*, the vertical extent of the lunar exosphere over time. We provide an update on a concept for a riometer implemented as a secondary science payload on future lunar landers, such as those recommended in the recent Planetary Sciences Decadal Survey report or commercial ventures. The instrument concept is simple, consisting of an antenna implemented as a metal deposited on polyimide film and receiver. We illustrate various deployment mechanisms and performance of a prototype in increasing lunar analog conditions. While the prime mission of such a riometer would be probing the lunar exosphere, our concept would also be capable to measuring the properties of dust impactors. The Lunar University Network for Astrophysical Research consortium is funded by the NASA Lunar Science Institute to investigate concepts for astrophysical observatories on the Moon. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Artist's impression of the Lunar Atmosphere Probe Station.

Lunar Dust: Properties and Investigation Techniques

NASA Astrophysics Data System (ADS)

Kuznetsov, I. A.; Zakharov, A. V.; Dolnikov, G. G.; Lyash, A. N.; Afonin, V. V.; Popel, S. I.; Shashkova, I. A.; Borisov, N. D.

2017-12-01

Physical conditions in the near-surface layer of the Moon are overviewed. This medium is formed in the course of the permanent micrometeoroid bombardment of the lunar regolith and due to the exposure of the regolith to solar radiation and high-energy charged particles of solar and galactic origin. During a considerable part of a lunar day (more than 20%), the Moon is passing through the Earth's magnetosphere, where the conditions strongly differ from those in the interplanetary space. The external effects on the lunar regolith form the plasma-dusty medium above the lunar surface, the so-called lunar exosphere, whose characteristic altitude may reach several tens of kilometers. Observations of the near-surface dusty exosphere were carried out with the TV cameras onboard the landers Surveyor 5, 6, and 7 (1967-1968) and with the astrophotometer of Lunokhod-2 (1973). Their results showed that the near-surface layer glows above the sunlit surface of the Moon. This was interpreted as the scattering of solar light by dust particles. Direct detection of particles on the lunar surface was made by the Lunar Ejects and Meteorite (LEAM) instrument deployed by the Apollo 17 astronauts. Recently, the investigations of dust particles were performed by the Lunar Atmosphere and Dust Environment Explorer (LADEE) instrument at an altitude of several tens of kilometers. These observations urged forward the development of theoretical models for the lunar exosphere formation, and these models are being continuously improved. However, to date, many issues related to the dynamics of dust and the near-surface electric fields remain unresolved. Further investigations of the lunar exosphere are planned to be performed onboard the Russian landers Luna-Glob and Luna-Resurs.

Structure and Composition of the Distant Lunar Exosphere: Constraints from ARTEMIS Observations of Ion Acceleration in Time-Varying Fields

NASA Technical Reports Server (NTRS)

Halekas, J. S.; Poppe, A. R.; Farrell, W. M.; McFadden, J. P.

2016-01-01

By analyzing the trajectories of ionized constituents of the lunar exosphere in time-varying electromagnetic fields, we can place constraints on the composition, structure, and dynamics of the lunar exosphere. Heavy ions travel slower than light ions in the same fields, so by observing the lag between field rotations and the response of ions from the lunar exosphere, we can place constraints on the composition of the ions. Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) provides an ideal platform to utilize such an analysis, since its two-probe vantage allows precise timing of the propagation of field discontinuities in the solar wind, and its sensitive plasma instruments can detect the ion response. We demonstrate the utility of this technique by using fully time-dependent charged particle tracing to analyze several minutes of ion observations taken by the two ARTEMIS probes 3000-5000 km above the dusk terminator on 25 January 2014. The observations from this time period allow us to reach several interesting conclusions. The ion production at altitudes of a few hundred kilometers above the sunlit surface of the Moon has an unexpectedly significant contribution from species with masses of 40 amu or greater. The inferred distribution of the neutral source population has a large scale height, suggesting that micrometeorite impact vaporization and/or sputtering play an important role in the production of neutrals from the surface. Our observations also suggest an asymmetry in ion production, consistent with either a compositional variation in neutral vapor production or a local reduction in solar wind sputtering in magnetic regions of the surface.

The impact of exospheric neutral dynamics on ring current decay

NASA Astrophysics Data System (ADS)

Ilie, R.; Liemohn, M. W.; Skoug, R. M.; Funsten, H. O.; Gruntman, M.; Bailey, J. J.; Toth, G.

2015-12-01

The geocorona plays an important role in the energy budget of the Earth's inner magnetosphere since charge exchange of energetic ions with exospheric neutrals makes the exosphere act as an energy sink for ring current particles. Long-term ring current decay following a magnetic storm is mainly due to these electron transfer reactions, leading to the formation energetic neutral atoms (ENAs) that leave the ring current system on ballistic trajectories. The number of ENAs emitted from a given region of space depends on several factors, such as the energy and species of the energetic ion population in that region and the density of the neutral gas with which the ions undergo charge exchange. However, the density and structure of the exosphere are strongly dependent on changes in atmospheric temperature and density as well as charge exchange with the ions of plasmaspheric origin, which depletes the geocorona (by having a neutral removed from the system). Moreover, the radiation pressure exerted by solar far-ultraviolet photons pushes the geocoronal hydrogen away from the Earth in an anti-sunward direction to form a tail of neutral hydrogen. TWINS ENA images provide a direct measurement of these ENA losses and therefore insight into the dynamics of the ring current decay through interactions with the geocorona. We assess the influence of geocoronal neutrals on ring current formation and decay by analysis of the predicted ENA emissions using 6 different geocoronal models and simulations from the HEIDI ring current model during storm time. Comparison with TWINS ENA images shows that the location of the peak ENA enhancements is highly dependent on the distribution of geocoronal hydrogen density. We show that the neutral dynamics has a strong influence on the time evolution of the ring current populations as well as on the formation of energetic neutral atoms.

The influence of surface roughness on volatile transport on the Moon

NASA Astrophysics Data System (ADS)

Prem, P.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.

2018-01-01

The Moon and other virtually airless bodies provide distinctive environments for the transport and sequestration of water and other volatiles delivered to their surfaces by various sources. In this work, we conduct Monte Carlo simulations of water vapor transport on the Moon to investigate the role of small-scale roughness (unresolved by orbital measurements) in the migration and cold-trapping of volatiles. Observations indicate that surface roughness, combined with the insulating nature of lunar regolith and the absence of significant exospheric heat flow, can cause large variations in temperature over very small scales. Surface temperature has a strong influence on the residence time of migrating water molecules on the lunar surface, which in turn affects the rate and magnitude of volatile transport to permanently shadowed craters (cold traps) near the lunar poles, as well as exospheric structure and the susceptibility of migrating molecules to photodestruction. Here, we develop a stochastic rough surface temperature model suitable for simulations of volatile transport on a global scale, and compare the results of Monte Carlo simulations of volatile transport with and without the surface roughness model. We find that including small-scale temperature variations and shadowing leads to a slight increase in cold-trapping at the lunar poles, accompanied by a slight decrease in photodestruction. Exospheric structure is altered only slightly, primarily at the dawn terminator. We also examine the sensitivity of our results to the temperature of small-scale shadows, and the energetics of water molecule desorption from the lunar regolith - two factors that remain to be definitively constrained by other methods - and find that both these factors affect the rate at which cold trap capture and photodissociation occur, as well as exospheric density and longevity.

Memoris, A Wide Angle Camera For Bepicolombo

NASA Astrophysics Data System (ADS)

Cremonese, G.; Memoris Team

In order to answer to the Announcement of Opportunity of ESA for the BepiColombo payload, we are working on a wide angle camera concept named MEMORIS (MEr- cury MOderate Resolution Imaging System). MEMORIS will performe stereoscopic images of the whole Mercury surface using two different channels at +/- 20 degrees from the nadir point. It will achieve a spatial resolution of 50m per pixel at 400 km from the surface (peri-Herm), corresponding to a vertical resolution of about 75m with the stereo performances. The scientific objectives will be addressed by MEMORIS may be identified as follows: Estimate of surface age based on crater counting Crater morphology and degrada- tion Stratigraphic sequence of geological units Identification of volcanic features and related deposits Origin of plain units from morphological observations Distribution and type of the tectonic structures Determination of relative age among the structures based on cross-cutting relationships 3D Tectonics Global mineralogical mapping of main geological units Identification of weathering products The last two items will come from the multispectral capabilities of the camera utilizing 8 to 12 (TBD) broad band filters. MEMORIS will be equipped by a further channel devoted to the observations of the tenuous exosphere. It will look at the limb on a given arc of the BepiColombo orbit, in so doing it will observe the exosphere above a surface latitude range of 25-75 degrees in the northern emisphere. The exosphere images will be obtained above the surface just observed by the other two channels, trying to find possible relantionship, as ground-based observations suggest. The exospheric channel will have four narrow-band filters centered on the sodium and potassium emissions and the adjacent continua.

Mercury's Exosphere During MESSENGER's Second Flyby: Detection of Magnesium and Distinct Distributions of Neutral Species

NASA Technical Reports Server (NTRS)

McClintock, William E.; Vervack, Ronald J., Jr.; Bradley, E. Todd; Killen, Rosemary M.; Mouawad, Nelly; Sprague, Ann L.; Burger, Matthew H.; Solomon, Sean C.; Izenberg, Noam R.

2009-01-01

During MESSENGER's second Mercury flyby, the Mercury Atmospheric and Surface Composition Spectrometer observed emission from Mercury's neutral exosphere. These observations include the first detection of emission from magnesium. Differing spatial distributions for sodium, calcium, and magnesium were revealed by observations beginning in Mercury's tail region, approximately 8 Mercury radii anti-sunward of the planet, continuing past the nightside, and ending near the dawn terminator. Analysis of these observations, supplemented by observations during the first Mercury flyby as well as those by other MESSENGER instruments, suggests that the distinct spatial distributions arise from a combination of differences in source, transfer, and loss processes.

The gas-surface interaction of a human-occupied spacecraft with a near-Earth object

NASA Astrophysics Data System (ADS)

Farrell, W. M.; Hurley, D. M.; Poston, M. J.; Zimmerman, M. I.; Orlando, T. M.; Hibbitts, C. A.; Killen, R. M.

2016-11-01

NASA's asteroid redirect mission (ARM) will feature an encounter of the human-occupied Orion spacecraft with a portion of a near-Earth asteroid (NEA) previously placed in orbit about the Moon by a capture spacecraft. Applying a shuttle analog, we suggest that the Orion spacecraft should have a dominant local water exosphere, and that molecules from this exosphere can adsorb onto the NEA. The amount of adsorbed water is a function of the defect content of the NEA surface, with retention of shuttle-like water levels on the asteroid at 1015 H2O's/m2 for space weathered regolith at T ∼ 300 K.

A dynamo theory prediction for solar cycle 22: Sunspot number, radio flux, exospheric temperature, and total density at 400 km

NASA Technical Reports Server (NTRS)

Schatten, K. H.; Hedin, A. E.

1986-01-01

Using the dynamo theory method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent.

SERENA: A Neutral Atoms Detector to be proposed for the ESA's BepiColombo Planetary Orbiter

NASA Astrophysics Data System (ADS)

di Lellis, A.; Orsini, S.; Livi, S.; Wurz, P.; Milillo, A.; Barabash, S.

2003-04-01

A comprehensive suite for the neutral particles detection in the Mercury environment is under development and it will be proposed in the frame of the ESA cornerstone’s BepiColombo mission. The package, namely NPA - SERENA (Neutral Particle Analyser - Searching for Exospheric Refilling and Emitted Neutral Abundances), consists of three dedicated spectrometers (MAIA, ELENA, and M/H-ENA) identifying and measuring the particles and their energies, namely from fraction of eV to tens of keV. The proposed sensors will observe and analyse the bulk of the sub-thermal / thermal exospheric (0-50 eV) gas along the ram direction (MAIA), the sputtering emission (E min < 100eV; E max > 1 keV) within 1-D (2 deg x 60 deg) nadir cross track slices from the planet surface (ELENA), and the charge exchange between ions and exospheric gas (E min < 5 keV; E max > 30 keV) in order to monitor the Mercury’s magnetosphere dynamics (M/H-ENA). The paper describes the progress achieved in the system and sensor level design and provides a summary report on the laboratory test of the investigated techniques and of the expected performances of the ELENA detector head.

Dusty plasmas in the lunar exosphere: Effects of meteoroids

NASA Astrophysics Data System (ADS)

Popel, S. I.; Golub', A. P.; Zelenyi, L. M.; Horányi, M.

2018-01-01

A possibility of the formation in the lunar exosphere of dust cloud due to meteoroid impacts onto the lunar surface is studied. The main attention is paid to the high altitudes over the lunar surface including the range of the altitudes between 30 and 110 km where the measurements of dust were performed within the NASA LADEE mission. From the viewpoint of the formation of dust cloud at high altitudes over the Moon, the most important zone formed by the meteoroid impact is the zone of melting of substance. Only the droplets originated from this zone have the speeds between the first and second astronautical velocities (for the Moon). Correspondingly, only such droplets can perform finite movement around the Moon. The liquid droplets harden when rising over the lunar surface. Furthermore, they aquire electric charges due to the action, in particular, of the solar wind electrons and ions, as well as of the solar radiation. Thus dusty plasmas exist in the lunar exosphere with the characteristic number density ≲ 10-2 m-3 of dust particles with the sizes from 300 nm to 1 μm which is in accordance with the results of measurements performed by LADEE.

Exploring Mercury Tail

NASA Image and Video Library

2008-08-26

As the MESSENGER spacecraft approached Mercury, the UVVS field of view was scanned across the planet's exospheric "tail," which is produced by the solar wind pushing Mercury's exosphere (the planet's extremely thin atmosphere) outward. This figure, recently published in Science magazine, shows a map of the distribution of sodium atoms as they stream away from the planet (see PIA10396); red and yellow colors represent a higher abundance of sodium than darker shades of blue and purple, as shown in the colored scale bar, which gives the brightness intensity in units of kiloRayleighs. The escaping atoms eventually form a comet-like tail that extends in the direction opposite that of the Sun for many planetary radii. The small squares outlined in black correspond to individual measurements that were used to create the full map. These measurements are the highest-spatial-resolution observations ever made of Mercury's tail. In less than six weeks, on October 6, 2008, similar measurements will be made during MESSENGER's second flyby of Mercury. Comparing the measurements from the two flybys will provide an unprecedented look at how Mercury's dynamic exosphere and tail vary with time. Date Acquired: January 14, 2008. http://photojournal.jpl.nasa.gov/catalog/PIA11076

The Exosphere of Ceres Generated by Photolysis and Radiolysis

NASA Astrophysics Data System (ADS)

Tseng, W. L.; Ip, W. H.; Kuan, Y. J.

2016-12-01

Ceres is the largest object (with a diameter of 950 km) among the main-belt asteroids. The OH cloud, the photodissociated products of H2O, was suggested by the IUE (International Ultraviolet Explorer) observations to be present around Ceres (A'Hearn and Feldman, 1992). Recently, Kuppers et al. (2014) reported a direct detection of water vapor by Herschel that > 1026 molecules s-1was produced from localized sources on Ceres' surface. Most excitingly, the Dawn images showed that a haze layer consisting of water-ice particles and dust was found above the Occator crater (Nathues et al., 2015). The haze was also shown to have a diurnal change of brightness, indicating a comet-like sublimation activity. In addition, subsurface outgassing (e.g., cryovolcanism and/or the plume activity similar to that found in Enceladus) is another possible source mechanism, which is not fully understood yet. Following the Ceres' exospheric model of Tu et al. (2014), here we focus on O2, O3 and H2O2 molecules, which are the primary products of radiolytic and photolytic decomposition of water ice, and possibly the CO2 and SO2 molecules produced from the impurities. We will compute the source rates from various production mechanisms and simulate the cloud morphologies. Then we will compare with the available data (e.g., the atomic oxygen emission observed by HST from Roth et al., 2016) and seek for any evidence in the ground-based millimeter/submillimeter observations. Understanding the chemical composition of Ceres and its evolved exosphere, in analogy to comets and the icy satellites, would reveal the secret of the origin and evolution of the solar system. 1. A'Hearn, M.F., Feldman, P.D., (1992) Water vaporization on Ceres. Icarus 98, 389-407. 2. Küppers, M., et al., (2014) Localized sources of water vapour on the dwarf planet (1) Ceres. Nature 505, 525-527. 3. Nathues, A., et al. (2015), Sublimation in bright spots on (1) Ceres, Nature, 528(7581), 237-240. 4. Tu, L., W.-H. Ip, and Y.-C. Wang (2014), A sublimation-driven exospheric model of Ceres, Planet. Space Sci., 104, 157-162. 5. Roth, L., et al. (2016), Constraints on an exosphere at Ceres from Hubble Space Telescope observations, Geophys. Res. Lett., 43, 2465-2472.

Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones.

PubMed

Lammer, Helmut; Lichtenegger, Herbert I M; Kulikov, Yuri N; Griessmeier, Jean-Mathias; Terada, N; Erkaev, Nikolai V; Biernat, Helfried K; Khodachenko, Maxim L; Ribas, Ignasi; Penz, Thomas; Selsis, Franck

2007-02-01

Atmospheric erosion of CO2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ionization processes due to exothermic chemical reactions and cooling by the CO2 infrared radiation in the 15 microm band. Our study shows that intense XUV radiation of active M stars results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O ion pick up at orbital distances

Exploring Mercury's Surface-Bound Exosphere with the Mercury Atmospheric and Surface Composition Spectrometer: AN Overview of Observations during the First Messenger Flyby

NASA Astrophysics Data System (ADS)

McClintock, W. E.; Bradley, E. T.; Izenberg, N. R.; Killen, R. M.; Kochte, M. C.; Lankton, M. R.; Mouawad, N.; Sprague, A. L.; Vervack, R. J.

2008-12-01

Mercury's surface-bound exosphere is the interface between the planet's surface and the external stimuli that interact with it. Its composition and structure are controlled by surface, magnetosphere, and solar-wind processes. Prior to the MESSENGER mission the exosphere was known to contain H, He, and O from Mariner 10 observations, as well as Na, K, and Ca that were discovered during ground-based observations. Na has been extensively studied since its discovery in 1985, including observations of a neutral Na tail first reported in 2002. Undetected species, including Mg, Fe, Al, and S, are also expected to exist in the exosphere. MESSENGER's initial flyby of Mercury, which occurred on January 14, 2008, offered the first opportunity to measure the planet's neutral tail from space. As the spacecraft approached the planet from the nightside, the UltraViolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) scanned the tail beginning at altitudes of 24,500 km behind Mercury's nightside surface and covering a region of space approximately three planet diameters tall and centered on the Sun-Mercury line. The UVVS measured emissions from Na during the entire observation. It also observed neutral hydrogen beginning approximately 5,000 km above the nightside surface. The spatial distributions of both species were seen to be asymmetric, with enhanced densities occurring in the northern hemisphere. UVVS observations of Ca, which were made as the spacecraft traversed the nightside exosphere, exhibited enhanced emission toward the dawn terminator, with north-south behavior similar to that of Na and H. These observations suggest that the relatively high-energy source processes that give rise to species observed in the tail were localized near the northern and morning hemispheres during the flyby. This inference is supported by magnetic field observations made with the MESSENGER Magnetometer, which observed a strong radial component of the interplanetary magnetic field (Bx) directed antisunward after MESSENGER passed outside the magnetosphere. This magnetic field orientation is expected to result in a greater number of open field lines in the northern hemisphere, preferentially allowing solar wind plasma to impinge upon the surface in that region.

Exospheric temperatures deduced from 7320- to 7330-A /O/+//2P/ - O/+//2D// twilight observations

NASA Technical Reports Server (NTRS)

Yee, J. H.; Abreu, V. J.

1982-01-01

A technique developed to deduce exospheric temperatures from the 7320- to 7330-A emission measured by the visible airglow experiment on board the AE-E satellite is considered. An excess emission in the measured 7320- to 7330-A brightness is noticed as a result of the interaction between the spacecraft and the atmosphere. The observed brightnesses are corrected for this effect. The galactic background emission is also carefully subtracted. The deduced temperatures exhibit a positive correlation with solar activity. It varies from approximately 700 K in late 1976 to approximately 1700 K at the peak of this solar cycle. The presence of a nonthermal oxygen corona is considered inconclusive.

Reconciling the Dawn-Dusk Asymmetry in Mercury’s Exosphere with the Micrometeoroid Impact Directionality

NASA Astrophysics Data System (ADS)

Pokorný, Petr; Sarantos, Menelaos; Janches, Diego

2017-06-01

Combining dynamical models of dust from Jupiter-family comets and Halley-type comets, we demonstrate that the seasonal variation of the dust/meteoroid environment at Mercury is responsible for producing the dawn-dusk asymmetry in Mercury’s exosphere observed by the MESSENGER spacecraft. Our latest models, calibrated recently from ground-based and space-borne measurements, provide unprecedented statistics that enable us to study the longitudinal and latitudinal distribution of meteoroids impacting Mercury’s surface. We predict that the micrometeoroid impact vaporization source is expected to undergo significant motion on Mercury’s surface toward the nightside during Mercury’s approach to aphelion and toward the dayside when the planet is approaching the Sun.

Observations at venus encounter by the plasma science experiment on mariner 10.

PubMed

Bridge, H S; Lazarus, A J; Scudder, J D; Ogilvie, K W; Hartle, R E; Asbridge, J R; Bame, S J; Feldman, W C; Siscoe, G L

1974-03-29

Preliminary results from the rearward-looking electrostatic analyzer of the plasma science experiment during the Mariner 10 encounter with Venus are described. They show that the solar-wind interaction with the planet probably involves a bow shock rather than an extended exosphere, but that this is not a thin boundary at the point where it was crossed by Mariner 10. An observed reduction in the flux of electrons with energies greater than 100 electron volts is interpreted as evidence for somne direct interaction with the exosphere. Unusual intermittent features observed downstream of the planet indicate the presence of a comet-like tail hundreds of scale lengths in length.

CONSTRUCTION OF A SMALL AUTOMATED CORONAGRAPH FOR OBSERVATIONS OF THE LUNAR Na EXOSPHERE

NASA Astrophysics Data System (ADS)

Tucker, Roy; Morgan, T. H.; Killen, R. M.

2013-10-01

We report on the final optical and mechanical design and the construction and initial testing of a small coronagraph at the Winer Observatory, near Sonoita, Arizona. The coronagraph includes a narrow band filter and low-light level camera to observe lunar exospheric sodium in the resonance lines of that element near 590 nm. Without the use of a coronagraph, the signal from sodium would be lost against light scattered by the Earth’s atmosphere and scattered light in the telescope. The design uses Commercial Off the Shelf Technology (COTS), and our goal is to obtain observations while the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission is still in orbit.

Solar Wind Implantation into Lunar Regolith II: Monte Carlo Simulations of Hydrogen Retention in a Surface with Defects and the Hydrogen (H, H2) Exosphere

NASA Technical Reports Server (NTRS)

Tucker, O. J.; Farrell, W. M.; Killen, R. M.; Hurley, D. M.

2018-01-01

Recently, the near-infrared observations of the OH veneer on the lunar surface by the Moon Mineralogy Mapper (M3) have been refined to constrain the OH content to 500-750 parts per million (ppm). The observations indicate diurnal variations in OH up to 200 ppm possibly linked to warmer surface temperatures at low latitude. We examine the M3 observations using a statistical mechanics approach to model the diffusion of implanted H in the lunar regolith. We present results from Monte Carlo simulations of the diffusion of implanted solar wind H atoms and the subsequently derived H and H2 exospheres.

Observations at Venus encounter by the plasma science experiment on Mariner 10

NASA Technical Reports Server (NTRS)

Bridge, H. S.; Lazarus, A. J.; Scudder, J. D.; Ogilvie, K. W.; Hartle, R. E.; Asbridge, J. R.; Bame, S. J.; Feldman, W. C.; Siscoe, G. L.

1974-01-01

Preliminary results from the rearward-looking electrostatic analyzer of the plasma science experiment during the Mariner 10 encounter with Venus are described. They show that the solar-wind interaction with the planet probably involves a bow shock rather than an extended exosphere, but that this is not a thin boundary at the point where it was crossed by Mariner 10. An observed reduction in the flux of electrons with energies greater than 100 electron volts is interpreted as evidence for some direct interaction with the exosphere. Unusual intermittent features observed downstream of the planet indicate the presence of a comet-like tail hundreds of scale lengths in length.

On the semiannual change in exospheric temperature.

NASA Technical Reports Server (NTRS)

Titheridge, J. E.

1972-01-01

Discussion of some uncertainties about the semiannual density variations of the neutral atmosphere at heights above 100 km ascribed by Jacchia (1965), on the basis of long observations of the decay of satellite orbits, to changes in exosphere temperature, but later, because of some difficulties, attributed by Jacchia (1971) to semiannual density variations that may not be produced primarily by changes in temperature. Temperature values derived from ionosphere electron content data recorded since 1965 at several sites in New Zealand using the Faraday rotation of geostationary satellite signals and from their comparison with ionosonde measurements are shown to suggest that the semiannual variations represent primarily changes in temperature and only secondarily in density.

Reconciling the Dawn-Dusk Asymmetry in Mercury's Exosphere with the Micrometeoroid Impact Directionality

NASA Technical Reports Server (NTRS)

Pokorny, Petr; Sarantos, Menelaos; Janches, Diego

2017-01-01

Combining dynamical models of dust from Jupiter-family comets and Halley-type comets, we demonstrate that the seasonal variation of the dust/meteoroid environment at Mercury is responsible for producing the dawn-dusk asymmetry in Mercury's exosphere observed by the MESSENGER spacecraft. Our latest models, calibrated recently from ground-based and space-borne measurements, provide unprecedented statistics that enable us to study the longitudinal and latitudinal distribution of meteoroids impacting Mercury's surface. We predict that the micrometeoroid impact vaporization source is expected to undergo significant motion on Mercury's surface toward the nightside during Mercury's approach to aphelion and toward the dayside when the planet is approaching the Sun.

ARTEMIS Science Objectives

NASA Technical Reports Server (NTRS)

Sibeck, D. G.; Angelopoulos, V.; Brain, D. A.; Delory, G. T.; Eastwood, J. P.; Farrell, W. M.; Grimm, R. E.; Halekas, J. S.; Hasegawa, H.; Hellinger, P.;

High-Resolution Spectroscopy of the Lunar Sodium Exosphere

NASA Technical Reports Server (NTRS)

Mierkiewicz, E. J.; Oliversen, R. J.; Roesler, F. L.; Lupie, O. L.

2014-01-01

We have applied high-resolution Fabry-Perot spectroscopy to the study of the lunar sodium exosphere for the study of exospheric effective temperature and velocity variations. Observing from the National Solar Observatory McMath-Pierce Telescope, we used a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,000 to measure line widths and Doppler shifts of the sodium D2 (5889.95 Å) emission line. Our field of view was 360 km, and measurements were made in equatorial and polar regions from 500 km to 3500 km off the limb. Data were obtained from full moon to 3 days following full moon (waning phase) in March 2009. Measured Doppler line widths within 1100 km of the sunlit east and south lunar limbs for observations between 5 and 40 deg lunar phase imply effective temperatures ranging between 3260 +/- 190 and 1000 +/- 135 K. Preliminary line center analysis indicates velocity displacements between different locations off the lunar limb ranging between 100 and 600 m/s from the lunar rest velocity with a precision of +/-20 to +/-50 m/s depending on brightness. Based on the success of these exploratory observations, an extensive program has been initiated that is expected to constrain lunar atmospheric and surface-process modeling and help quantify source and escape mechanisms.

Modeling the near-Earth interaction between ring current ions and exospheric neutrals: escape through energetic neutral atoms (ENAs)

NASA Astrophysics Data System (ADS)

LLera, K.; Goldstein, J.; McComas, D. J.; Valek, P. W.

2016-12-01

The two major loss processes for ring current decay are precipitation and energetic neutral atoms (ENAs). Since the exospheric neutral density increases with decreasing altitudes, precipitating ring current ions (reaching down to 200 - 800 km in altitude) also produce low-altitude ENA signatures that can be stronger than the ring current emission at equatorial distances ( 2 - 9 Re). The higher density results in multiple collisions between the ring current ions and exospheric oxygen. The affect on hydrogen ions is the focus of this study. Since the H particle sustains energy loss ( 36 eV) at each neutralizing or re-ionizing interaction, the escaped ENAs do not directly reflect the ring current properties. We model the energy loss due to multiple charge exchange and electron stripping interactions of 1 - 100 keV precipitating ring current ions undergo before emerging as low-altitude ENAs. The H particle is either an ion or an ENA throughout the simulation. Their lifetime is analytically determined by the length of one mean free path. We track the ion state with Lorentz motion while the ENA travels ballistically across the geomagnetic field. Our simulations show the energy loss is greater than 20% for hydrogen ring current ions below 30 keV (60 keV for the simulations that wander equatorward). This is the first quantification of the energy loss associated with the creation of low-altitude ENAs. Our model (currently constrained in the meridional plane) has revealed characteristics on how precipitation is affected by the near-Earth neutral exosphere. This ion-neutral interaction removes particles from the loss cone but promotes loss through ENA generation. These findings should be implemented in models predicting the ring current decay and used as an analysis tool to reconstruct the ring current population from observed low-altitude ENAs.

By Permission of the Mantle: Modern and Ancient Deep Earth Volatile Cycles

NASA Astrophysics Data System (ADS)

Hirschmann, M. M.

2011-12-01

The principle volatile elements, H and C, are of surpassing importance to processes and conditions in the interiors and the surfaces of terrestrial planets, affecting everything from mantle dynamics and large scale geochemical differentiation to climate and habitability. The storage of these volatiles in planetary interiors, their inventory in the near-surface environment and exchange between the interiors and the exosphere are governed by petrologic processes. Were it not for the effective incompatibility of these components in mantle lithologies, there might be no oceans, no habitable climate, and no biosphere on the surface. Consequently, deep Earth volatile cycles represent one of the best examples of how petrology influences nearly all other aspects of Earth science. The exosphere of the modern Earth has a high H/C ratio compared to that of the interior sampled by oceanic basalts. A potential explanation for this is that C is subducted to the deep mantle more efficiently than H, such that the exosphere C reservoir shrinks through geologic time. Unfortunately this hypothesis conflicts with the sedimentary record, which suggests that carbonate storage on the continents has increased rather than decreased with time. It also may not be applicable to the first 3 Ga of Earth history, when hotter typical subduction geotherms greatly reduced the efficiency of C subduction. An important question regarding deep Earth volatile cycles is the inventory of H and C in the interior and the exosphere that descend from Earth's earliest differentiation processes. Originally, much of Earth's volatile inventory was presumably present as a thick atmosphere, in part because volatiles were probably delivered late in the accretion history and owing to both the efficiency of impact degassing and of volatile release from early magma ocean(s). Early mantle H2O may descend from the magma ocean, in which portions of a steam atmosphere are dissolved in the magma and then precipitated with nominally anhydrous minerals. In contrast, low magmatic solubility of C-bearing species would suggest that the early mantle was depleted in carbon. Thus, the earliest Earth could have been characterized by an exosphere with low H/C and a mantle with high H/C - the reverse of the modern case. An alternative hypothesis is that significant C was sequestered in the early mantle as a reduced phase- diamond, carbide, or alloy - precipitated during magma ocean solidification. Despite low solubility in magmas, early atmospheric carbon may have been incorporated into solidifying mantle if C solubility diminished with increasing magma ocean depth. Volatile solubilities in magmas typically increase with increasing pressure, but the opposite could be true for C if conditions were more reducing at depth and more oxidizing near the surface. Such conditions would allow operation of a carbon pump, transporting early atmospheric carbon to the solidifying mantle. If such a process operated, then the modern mantle/exosphere H/C fractionation is likely a remnant of this early process. If not, some other explanation for Earth's distribution of H and C must be sought.

The Diffuse X-ray Background, from Earth's Exosphere to the Edge of the Universe: Or, One Astronomer's Signal is Another Astronomer's Contamination

NASA Technical Reports Server (NTRS)

Snowden, Steve

2007-01-01

The "X-ray background" means various things to various people. It's origin is comprised of emission from objects as close as Earth's exosphere to as far away as the most distant clusters of galaxies. It is comprised of the emission of truly diffusely distributed plasmas and the superposition of the emission from unresolved point-like objects. To add to the confusion, in general there is no redshift information so there is very little information on where an individual X-ray may originate. This talk will address the evolution of our understanding of origin of the X-ray background and the current best-guess about what is really going on.

The ancient oxygen exosphere of Mars - Implications for atmosphere evolution

NASA Technical Reports Server (NTRS)

Zhang, M. H. G.; Luhmann, J. G.; Bougher, S. W.; Nagy, A. F.

1993-01-01

The paper considers absorption of oxygen (atoms and ions) by the surface as a mechanism for the early Martian atmosphere escape, due to the effect of high EUV flux of the ancient sun. Hot oxygen exosphere densities in ancient atmosphere and ionosphere are calculated for different EUV fluxes and the escape fluxes associated with these exposures. Using these densities, the ion production rate above the ionopause is calculated for different epochs including photoionization, charge exchange, and solar wind electron impact. It is found that, when the inferred high solar EUV fluxes of the past are taken into account, oxygen equivalent to that in several tens of meters of water, planet-wide, should have escaped Martian atmosphere to space over the last 3 Gyr.

The ancient oxygen exosphere of Mars - Implications for atmosphere evolution

NASA Astrophysics Data System (ADS)

Zhang, M. H. G.; Luhmann, J. G.; Bougher, S. W.; Nagy, A. F.

1993-06-01

The paper considers absorption of oxygen (atoms and ions) by the surface as a mechanism for the early Martian atmosphere escape, due to the effect of high EUV flux of the ancient sun. Hot oxygen exosphere densities in ancient atmosphere and ionosphere are calculated for different EUV fluxes and the escape fluxes associated with these exposures. Using these densities, the ion production rate above the ionopause is calculated for different epochs including photoionization, charge exchange, and solar wind electron impact. It is found that, when the inferred high solar EUV fluxes of the past are taken into account, oxygen equivalent to that in several tens of meters of water, planet-wide, should have escaped Martian atmosphere to space over the last 3 Gyr.

Energetic neutral atom emissions from Titan interaction with Saturn's magnetosphere.

PubMed

Mitchell, D G; Brandt, P C; Roelof, E C; Dandouras, J; Krimigis, S M; Mauk, B H

2005-05-13

The Cassini Magnetospheric Imaging Instrument (MIMI) observed the interaction of Saturn's largest moon, Titan, with Saturn's magnetosphere during two close flybys of Titan on 26 October and 13 December 2004. The MIMI Ion and Neutral Camera (INCA) continuously imaged the energetic neutral atoms (ENAs) generated by charge exchange reactions between the energetic, singly ionized trapped magnetospheric ions and the outer atmosphere, or exosphere, of Titan. The images reveal a halo of variable ENA emission about Titan's nearly collisionless outer atmosphere that fades at larger distances as the exospheric density decays exponentially. The altitude of the emissions varies, and they are not symmetrical about the moon, reflecting the complexity of the interactions between Titan's upper atmosphere and Saturn's space environment.

Neutral Solar Wind Generated by Lunar Exospheric Dust at the Terminator

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Stubbs, Timothy J.

2007-01-01

We calculate the flux of neutral solar wind observed on the lunar surface at the terminator due to solar wind protons penetrating exospheric dust with: (1) grains larger that 0.1 microns and (2) grains larger than 0.01 microns. For grains larger than 0.1 microns, the ratio of the neutral solar wind to solar wind flux is estimated to be approx.10(exp -4)-10(exp -3) at solar wind speeds in excess of 800 km/s, but much lower (less than 10(exp -5) at average to low solar wind speeds. However, when the smaller grain sizes are considered, the ratio of the neutral solar wind flux to solar wind flux is estimated to be greater than or equal to 10(exp -5) at all speeds and at speeds in excess of 700 km/s reaches 10(exp -3)-10(exp -2). These neutral solar wind fluxes are easily measurable with current low energy neutral atom instrumentation. Observations of neutral solar wind from the surface of the Moon could provide a very sensitive determination of the distribution of very small dust grains in the lunar exosphere and would provide data complementary to optical measurements at ultraviolet and visible wavelengths. Furthermore, neutral solar wind, unlike its ionized counterpart, is .not held-off by magnetic anomalies, and may contribute to greater space weathering than expected in certain lunar locations.

Pathways for Energization of Ca in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.

2015-01-01

We investigate the possible pathways to produce the extreme energy observed in the calcium exosphere of Mercury. Any mechanism must explain the facts that Ca in Mercury's exosphere is extremely hot, that it is seen almost exclusively on the dawnside of the planet, and that its content varies seasonally, not sporadically. Simple diatomic molecules or their clusters are considered, focusing on calcium oxides while acknowledging that Ca sulfides may also be the precursor molecules. We first discuss impact vaporization to justify the assumption that CaO and Ca-oxide clusters are expected from impacts on Mercury. Then we discuss processes by which the atomic Ca is energized to a 70,000 K gas. The processes considered are (1) electron-impact dissociation of CaO molecules, (2) spontaneous dissociation of Ca-bearing molecules following impact vaporization, (3) shock-induced dissociative ionization, (4) photodissociation and (5) sputtering. We conclude that electron-impact dissociation cannot produce the required abundance of Ca, and sputtering cannot reproduce the observed spatial and temporal variation that is measured. Spontaneous dissociation is unlikely to result in the high energy that is seen. Of the two remaining processes, shock induced dissociative ionization produces the required energy and comes close to producing the required abundance, but rates are highly dependent on the incoming velocity distribution of the impactors. Photodissociation probably can produce the required abundance of Ca, but simulations show that photodissociation cannot reproduce the observed spatial distribution.

Monte Carlo Modeling of Sodium in Mercury's Exosphere During the First Two MESSENGER Flybys

NASA Technical Reports Server (NTRS)

Burger, Matthew H.; Killen, Rosemary M.; Vervack, Ronald J., Jr.; Bradley, E. Todd; McClintock, William E.; Sarantos, Menelaos; Benna, Mehdi; Mouawad, Nelly

2010-01-01

We present a Monte Carlo model of the distribution of neutral sodium in Mercury's exosphere and tail using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during the first two flybys of the planet in January and September 2008. We show that the dominant source mechanism for ejecting sodium from the surface is photon-stimulated desorption (PSD) and that the desorption rate is limited by the diffusion rate of sodium from the interior of grains in the regolith to the topmost few monolayers where PSD is effective. In the absence of ion precipitation, we find that the sodium source rate is limited to approximately 10(exp 6) - 10(exp 7) per square centimeter per second, depending on the sticking efficiency of exospheric sodium that returns to the surface. The diffusion rate must be at least a factor of 5 higher in regions of ion precipitation to explain the MASCS observations during the second MESSENGER f1yby. We estimate that impact vaporization of micrometeoroids may provide up to 15% of the total sodium source rate in the regions observed. Although sputtering by precipitating ions was found not to be a significant source of sodium during the MESSENGER flybys, ion precipitation is responsible for increasing the source rate at high latitudes through ion-enhanced diffusion.

Simulations of Water Migration in the Lunar Exosphere

NASA Astrophysics Data System (ADS)

Hurley, D.; Benna, M.; Mahaffy, P. R.; Elphic, R. C.; Goldstein, D. B.

2014-12-01

We perform modeling and analysis of water in the lunar exosphere. There were two controlled experiments of water interactions with the surface of the Moon observed by the Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS). The Chang'e 3 landing on the Moon on 14 Dec 2013 putatively sprayed ~120 kg of water on the surface on the Moon at a mid-morning local time. Observations by LADEE near the noon meridian on six of the orbits in the 24 hours following the landing constrain the propagation of water vapor. Further, on 4 Apr 2014, LADEE's Orbital Maintenance Manuever (OMM) #21 sprayed the surface of the Moon with an estimated 0.73 kg of water in the pre-dawn sector. Observations of this maneuver and later in the day constrain the adsorption and release at dawn of adsorbed materials. Using the Chang'e 3 exhaust plume and LADEE's OMM-21 as control experiments, we set limits to the adsorption and thermalization of water with lunar regolith. This enables us to predict the efficiency of the migration of water as a delivery mechanism to the lunar poles. Then we simulate the migration of water through the lunar exosphere using the rate of sporadic inputs from meteoritic sources (Benna et al., this session). Simulations predict the amount of water adsorbed to the surface of the Moon and the effective delivery rate to the lunar polar cold traps.

Modeling Solar-Wind Heavy-Ions' Potential Sputtering of Lunar KREEP Surface

NASA Technical Reports Server (NTRS)

Barghouty, A. F.; Meyer, F. W.; Harris, R. P.; Adams, J. H., Jr.

2012-01-01

Recent laboratory data suggest that potential sputtering may be an important weathering mechanism that can affect the composition of both the lunar surface and its tenuous exosphere; its role and implications, however, remain unclear. Using a relatively simple kinetic model, we will demonstrate that solar-wind heavy ions induced sputtering of KREEP surfaces is critical in establishing the timescale of the overall solar-wind sputtering process of the lunar surface. We will also also show that potential sputtering leads to a more pronounced and significant differentiation between depleted and enriched surface elements. We briefly discuss the impacts of enhanced sputtering on the composition of the regolith and the exosphere, as well as of solar-wind sputtering as a source of hydrogen and water on the moon.

Observation of Solar Wind Charge Exchange Emission from Exospheric Material in and Outside Earth's Magnetosheath

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

2008-01-01

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth s magnetosheath. The light curve of the O VII (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.36). The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Geocoronal Imaging from the Deep Space Gateway

NASA Astrophysics Data System (ADS)

Waldrop, L.; Immel, T.; Clarke, J.; Fillingim, M.; Rider, K.; Qin, J.; Bhattacharyya, D.; Doe, R.

2018-02-01

UV imaging of geocoronal emission at high spatial and temporal resolution from deep space would provide crucial new constraints on global exospheric structure and dynamics, significantly advancing models of space weather and atmospheric escape.

Methane in the lunar exosphere: Implications for solar wind carbon escape

NASA Astrophysics Data System (ADS)

Hodges, R. Richard

2016-07-01

A positive identification of methane in the lunar exosphere has been made in data from the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. Like argon-40, methane is adsorbed on the lunar surface during nighttime. However, higher activation energies for methane delay its desorption at sunrise by about an hour local time, creating a postsunrise bulge with peak concentration of approximately 400-450 molecules cm-3 at a reference altitude of 12 km, which is just above the highest topographic feature on the Moon. The rate of escape of carbon as methane derived from the LADEE data is estimated to be in the range 1.5-4.5 × 1021 s-1. A lower bound for solar carbon escape derived separately from Apollo sample analyses is 3.4 × 1021 s-1.

Two-dimensional description of surface-bounded exospheres with application to the migration of water molecules on the Moon

NASA Astrophysics Data System (ADS)

Schorghofer, Norbert

2015-05-01

On the Moon, water molecules and other volatiles are thought to migrate along ballistic trajectories. Here, this migration process is described in terms of a two-dimensional partial differential equation for the surface concentration, based on the probability distribution of thermal ballistic hops. A random-walk model, a corresponding diffusion coefficient, and a continuum description are provided. In other words, a surface-bounded exosphere is described purely in terms of quantities on the surface, which can provide computational and conceptual advantages. The derived continuum equation can be used to calculate the steady-state distribution of the surface concentration of volatile water molecules. An analytic steady-state solution is obtained for an equatorial ring; it reveals the width and mass of the pileup of molecules at the morning terminator.

Impact Vaporization as a Possible Source of Mercury's Calcium Exosphere

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; Hahn, Joseph M.

2015-01-01

Mercury's calcium exosphere varies in a periodic way with that planet's true anomaly. We show that this pattern can be explained by impact vaporization from interplanetary dust with variations being due to Mercury's radial and vertical excursions through an interplanetary dust disk having an inclination within 5 degrees of the plane of Mercury's orbit. Both a highly inclined dust disk and a two-disk model (where the two disks have a mutual inclination) fail to reproduce the observed variation in calcium exospheric abundance with Mercury true anomaly angle. However, an additional source of impacting dust beyond the nominal dust disk is required near Mercury's true anomaly (?) 25deg +/-5deg. This is close to but not coincident with Mercury's true anomaly (?=45deg) when it crosses comet 2P/Encke's present day orbital plane. Interestingly, the Taurid meteor storms at Earth, which are also due to Comet Encke, are observed to occur when Earth's true anomaly is +/-20 or so degrees before and after the position where Earth and Encke orbital planes cross. The lack of exact correspondence with the present day orbit of Encke may indicate the width of the potential stream along Mercury's orbit or a previous cometary orbit. The extreme energy of the escaping calcium, estimated to have a temperature greater than 50000 K if the source is thermal, cannot be due to the impact process itself but must be imparted by an additional mechanism such as dissociation of a calcium-bearing molecule or ionization followed by recombination.

Searching for helium in the exosphere of HD 209458b

NASA Astrophysics Data System (ADS)

Moutou, C.; Coustenis, A.; Schneider, J.; Queloz, D.; Mayor, M.

2003-07-01

Atmospheric models of the extrasolar, close-in giant planet HD 209458b predict strong absorption features from alkali metals (Seager & Sasselov \\cite{Seager00}; Brown 2001). This was confirmed by the discovery of NaI by HST observations (Charbonneau et al. \\cite{Charbonneau02}). In this study we focus on the search for the helium absorption feature at 10 830 Å, also predicted to be among the strongest ones. Helium is a major component of the planet's exosphere, for which models are yet not as robust as atmosphere models. One full transit was observed with the VLT/ISAAC instrument. We do not report the detection of the HeI feature. The data set is strongly affected by instrumental fringing, at a level up to 5% in the extracted spectra. After filtering, a residual noise of the order of 0.2% remains. An upper limit of the HeI line was derived, which further constrains future models of the HD 209458b planet exosphere. This upper limit, in terms of the feature depth, is 0.5% at 3sigma for a 3 Å bandwidth. Prospects are proposed to lower the detectability limit; the ultimate detectability limit with ISAAC in the absence of electronic fringing and in ideal atmospheric conditions could be as low as a line depth of 0.1% (3 Å width, 3sigma ). Based on data acquired on the Very Large Telescope at Paranal Observatory, ESO Chile.

Line Profile Measurements of the Lunar Exospheric Sodium

NASA Technical Reports Server (NTRS)

Oliversen, Ronald J.; Mierkiewicz, Edwin J.; Line, Michael R.; Roesler, Fred L.; Lupie, Olivia L.

2012-01-01

We report ongoing results of a program to measure the lunar sodium exospheric line profile from near the lunar limb out to two lunar radii (approx 3500 km). These observations are conducted from the National Solar Observatory McMath-Pierce telescope using a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,600 (1.7 km/s) to measure line widths and velocity shifts of the Na D2 (5889 950 A) emission line in equatorial and polar regions at different lunar phases. The typical field of view (FOV) is 3 arcmin (approx 360 km) with an occasional smaller 1 arcmin FOV used right at the limb edge. The first data were obtained from full Moon to 3 days following full Moon (waning phase) in March 2009 as part of a demonstration run aimed at establishing techniques for a thorough study of temperatures and velocity variations in the lunar sodium exosphere. These data indicate velocity displacements from different locations off the lunar limb range between 150 and 600 m/s from the lunar rest velocity with a precision of +/- 20 to +/- 50 m/s depending on brightness. The measured Doppler line widths for observations within 10.5 arcmin of the east and south lunar limbs for observations between 5 deg and 40 deg lunar phase imply temperatures ranging decreasing from 3250 +/- 260K to 1175 +/- 150K. Additional data is now being collected on a quarterly basis since March 2011 and preliminary results will be reported.

Na emission in the Hermean Exosphere as a tracer for particle precipitation dynamics

NASA Astrophysics Data System (ADS)

Orsini, Stefano; Mangano, Valeria; Plainaki, Christina; Mura, Alessandro; Milillo, Anna; Massetti, Stefano; De Angelis, Elisabetta; Rispoli, Rosanna; Lazzarotto, Francesco; Aronica, Alessandro

2017-04-01

In this presentation, we speculate on the Hermean exosphere Na hourly average distributions, as observed by the ground-based Themis solar telescope, and published by Mangano et al. ,2015 (*). From 2009 to 2013, we have selected 26 different days, when the Na signal was observed for 3 or more hours within each selected observation day, in good seeing conditions (sigma <2). We notice the occurrence of basically opposite configurations, i.e. i) when the sodium signal is localized above the poles, or ii) when it is diffused above the sub-solar region. Some time periods show also the existence of a transition phase between the two configurations. In order to identify these Na observations as possible tracers of particle precipitation patterns at Mercury, we compare these different Na emission configurations with the time profiles of particle and magnetic field data, as measured in-situ by MESSENGER, when such data were available. Within the analyzed time sequences, localized Na signals are more frequent ( 67% of cases), mostly linked to quiet IMF conditions. When the signal is more diffused, IMF data seem to indicate the occurrence of significant solar perturbations. The possible relationship between these events and the hermean magnetosphere general configuration is briefly discussed. (*) Mangano, V., Massetti, S., Milillo, A., Plainaki, C., Orsini, S., Rispoli, S. and Leblanc, F.: THEMIS Na exosphere observations of Mercury and their correlation with in-situ magnetic field measurements by MESSENGER. PSS, 115, 102-109, doy: 10.1016/j.pss.2015.04.001, 2015.

Observation of Solar Wind Charge Exchange Emission From Exospheric Material in and Outside Earth's Magnetosheath 2008 September 25

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

2009-01-01

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth's magnetosheath. The light curve of the O vii (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.5). In addition, an average value of the SWCX O vii emission from the magnetosheath over the observation of 2.6 +/- 0.5 LU is derived. The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

SERENA: a Novel Instrument Package on board BepiColombo-MPO to study Neutral and Ionized Particles in the Hermean Environment

NASA Astrophysics Data System (ADS)

Orsini, S.; Livi, S.; Torkar, K.; Barabash, S.; Milillo, A.; Wurz, P.; di Lellis, A. M.; Kallio, E.

2009-06-01

SERENA (`Search for Exospheric Refilling and Emitted Natural Abundances') is an instrument package that will fly on board the BepiColombo Mercury Planetary Orbiter (MPO) it will investigate the Mercury's complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge-exchange processes, and by ionized particles originated through photo-ionization and again by surface release processes. In order to accomplish the scientific goals, in-situ analysis of the environmental elements is necessary, and for such a purpose the SERENA instrument shall include four units: two Neutral Particle Analyzers (ELENA and STROFIO) and two Ion Spectrometers (MIPA and PICAM). The scientific merit of SERENA is presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects.

SERENA: a suite of four instruments (ELENA, STROFIO, PICAM and MIPA) on board BepiColombo-MPO for particle detection in the Hermean Environment

NASA Astrophysics Data System (ADS)

Milillo, Anna; Livi, Stefano; Orsini, Stefano; Torkar, Klaus; Barabash, Stas; Milillo, Anna; Wurz, Peter; di Lellis, Andrea Maria; Kallio, Esa

SERENA (‘Search for Exospheric Refilling and Emitted Natural Abundances') is an instrument package that will fly on board the BepiColombo/Mercury Planetary Orbiter (MPO); it will investigate the Mercury's complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge-exchange processes, and by ionized particles originated through photo-ionization and again by surface release processes. In order to accomplish the scientific goals, in-situ analysis of the environmental elements is necessary, and for such a purpose the SERENA instrument shall include four units: two Neutral Particle Analyzers (ELENA and STROFIO) and two Ion Spectrometers (MIPA and PICAM). The scientific merit of SERENA is presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects.

Observations of Titanium, Aluminum and Magnesium in the Lunar Exosphere by LADEE UVS

NASA Technical Reports Server (NTRS)

Colaprete, A.; Wooden, D.; Cook, A.; Shirley, M.; Sarantos, M.

2016-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) was an orbital lunar science mission designed to address the goals of the 2003 National Research Council decadal survey, the Lunar Exploration Analysis Group Roadmap, and the "Scientific Context for Exploration of the Moon" (SCEM) report, and has been recommended for execution by the 2011 Planetary Missions Decadal Survey. The LADEE mission goal was to determine the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. It will monitor variations in known gasses, such as sodium, potassium, argon and helium, and will search for other, as-yet-undetected gasses of both lunar and extra-lunar origin. Another goal of LADEE was to determine whether dust is present in the lunar exosphere, and reveal the processes that contribute to its sources and variability.

Solar wind pickup of ionized Venus exosphere atoms

NASA Technical Reports Server (NTRS)

Curtis, S. A.

1981-01-01

Previous calculations of electrostatic and electromagnetic growth rates for plasma instabilities have neglected the thermal spread of the distribution function of the planetary ions. We consider the effects of finite temperatures for exospheric ions borne in the solar wind. Specifically, growth rates are calculated for electromagnetic instabilities in the low-frequency case for Alfven waves and the intermediate frequency case for whistlers. Also, electrostatic growth rates are calculated for the intermediate frequency regime. From these growth rates, estimates are derived for the pickup times of the planetary ions. The electromagnetic instabilities are shown to produce the most rapid pickup. In the situation where the angle between the local Venus magnetic field and the plasma flow direction is small, the pickup times for both electromagnetic and electrostatic instabilities become very long. A possible consequence of this effect is to produce regions of enhanced planetary ion density in favorable Venus magnetic field-solar wind flow geometries.

Geocoronal hydrogen studies using Fabry Perot interferometers, part 2: Long-term observations

NASA Astrophysics Data System (ADS)

Nossal, S. M.; Mierkiewicz, E. J.; Roesler, F. L.; Reynolds, R. J.; Haffner, L. M.

2006-09-01

Long-term data sets are required to investigate sources of natural variability in the upper atmosphere. Understanding the influence of sources of natural variability such as the solar cycle is needed to characterize the thermosphere + exosphere, to understand coupling processes between atmospheric regions, and to isolate signatures of natural variability from those due to human-caused change. Multi-year comparisons of thermospheric + exospheric Balmer α emissions require cross-calibrated and well-understood instrumentation, a stable calibration source, reproducible observing conditions, separation of the terrestrial from the Galactic emission line, and consistent data analysis accounting for differences in viewing geometry. We discuss how we address these criteria in the acquisition and analysis of a mid-latitude geocoronal Balmer α column emission data set now spanning two solar cycles and taken mainly from Wisconsin and Kitt Peak, Arizona. We also discuss results and outstanding challenges for increasing the accuracy and use of these observations.

Short-term variations of Mercury's cusps Na emission

NASA Astrophysics Data System (ADS)

Massetti, S.; Mangano, V.; Milillo, A.; Mura, A.; Orsini, S.; Plainaki, C.

2017-09-01

We illustrate the analysis of short-term ground-based observations of the exospheric Na emission (D1 and D2 lines) from Mercury, which was characterized by two high-latitude peaks confined near the magnetospheric cusp footprints. During a series of scheduled observations from THEMIS solar telescope, achieved by scanning the whole planet, we implemented a series of extra measurements by recording the Na emission from a narrow north-south strip only, centered above the two emission peaks. Our aim was to inspect the existence of short-term variations, which were never analyzed before from ground-based observations, and their possible correlation with interplanetary magnetic field variations. Though Mercury possesses a miniature magnetosphere, characterized by fast reconnection events that develop on a timescale of few minutes, ground-based observations show that the exospheric Na emission pattern can be globally stable for a prolonged period (some days) and can exhibits fluctuations in the time range of tens of minutes.

Exospheric perturbations by radiation pressure. II - Solution for orbits in the ecliptic plane

NASA Technical Reports Server (NTRS)

Chamberlain, J. W.

1980-01-01

A previous study (Chamberlain, 1979) gave solutions for the mean time rates of change of orbital elements of satellite atoms in an exosphere influenced by solar radiation pressure; each element was assumed to behave independently. In the present paper, the instantaneous rates of changes for three elements (e, Omega, and phi = omega + Omega) are integrated simultaneously for the case of the inclination i = 0. The results confirm the validity of using mean rates when the orbits are tighly bound to the planet, and serve as examples to be reproduced by the complicated numerical solutions required for arbitrary inclination. Strongly bound hydrogen atoms perturbed in earth orbit by radiation pressure do not seem a likely cause of the geotail extending in the anti-sun direction. Instead, radiation pressure will cause those particles' orbits to form a broad fan-shaped tail and to deteriorate into the earth's atmosphere.

Scattering Properties of Lunar Dust Analogs

NASA Technical Reports Server (NTRS)

Davis, S.; Marshall, J.; Richard, D.; Adler, D.; Adler, B.

2013-01-01

A number of space missions are planned to explore the lunar exosphere which may contain a small population of dust particles. The objective of this paper is to present preliminary results from scattering experiments on a suspension of lunar simulants to support one such mission. The intensity of the light scattered from a lunar simulant is measured with a commercial version of the spectrometer used in the forthcoming LADEE mission. Physical properties of the lunar simulant are described along with two similarly-sized reference microspheres. We confirm that micron-sized particles tend to form agglomerates rather than remaining isolated entities and that certain general characteristic of the target particles can be predicted from intensity measurements alone. These results can be used directly to assess general features of the lunar exosphere from LADEE instrument data. Further analysis of particle properties from such remote sensing data will require measurements of polarization signatures.

Narrow-field imaging of the lunar sodium exosphere

NASA Technical Reports Server (NTRS)

Stern, S. Alan; Flynn, Brian C.

1995-01-01

We present the first results of a new technique for imaging the lunar Na atmosphere. The technique employs high resolution, a narrow bandpass, and specific observing geometry to suppress scattered light and image lunar atmospheric Na I emission down to approximately 50 km altitude. Analysis of four latitudinally dispersed images shows that the lunar Na atmosphere exhibits intersting latitudinal and radial dependencies. Application of a simple Maxwellian collisionless exosphere model indicates that: (1) at least two thermal populations are required to adequately fit the soldium's radial intensity behavior, and (2) the fractional abundances and temperatures of the two components vary systematically with latitude. We conclude that both cold (barometric) and hot (suprathermal) Na may coexist in the lunar atmosphere, either as distinct components or as elements of a continuum of populations ranging in temperature from the local surface temperature up to or exceeding escape energies.

LADEE/LDEX observations of lunar pickup ion distribution and variability

NASA Astrophysics Data System (ADS)

Poppe, A. R.; Halekas, J. S.; Szalay, J. R.; Horányi, M.; Levin, Z.; Kempf, S.

2016-04-01

We report fortuitous observations of low-energy lunar pickup ion fluxes near the Moon while in the solar wind by the Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE). We describe the method of observation and the empirical calibration of the instrument for ion observations. LDEX observes several trends in the exospheric ion production rate, including a scale height of approximately 100 km, a positive, linear correlation with solar wind flux, and evidence of a slight enhancement near 7-8 h local time. We compare the LDEX observations to both LADEE Neutral Mass Spectrometer ion mode observations and theoretical models. The LDEX data are best fit by total exospheric ion production rates of ≈6 × 103 m-3 s-1 with dominant contributions from Al+, CO+, and Ar+, although the LDEX data suggest that the aluminum neutral density and corresponding ion production rate are lower than predicted by recent models.

Mercury's Na Exosphere from MESSENGER Data

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.; Burger, M. H.; Cassidy, T. A.; Sarantos, M.; Vervack, R. J.; McClintock, W. El; Merkel, A. W.; Sprague, A. L.; Solomon, S. C.

2012-01-01

MESSENGER entered orbit about Mercury on March 18, 2011. Since then, the Ultraviolet and Visible Spectrometer (UWS) channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer (MASCS) has been observing Mercury's exosphere nearly continuously. Daily measurements of Na brightness were fitted with non-uniform exospheric models. With Monte Carlo sampling we traced the trajectories of a representative number of test particles, generally one million per run per source process, until photoionization, escape from the gravitational well, or permanent sticking at the surface removed the atom from the simulation. Atoms were assumed to partially thermally accommodate on each encounter with the surface with accommodation coefficient 0.25. Runs for different assumed source processes are run separately, scaled and co-added. Once these model results were saved onto a 3D grid, we ran lines of sight from the MESSENGER spacecraft :0 infinity using the SPICE kernels and we computed brightness integrals. Note that only particles that contribute to the measurement can be constrained with our method. Atoms and molecules produced on the nightside must escape the shadow in order to scatter light if the excitation process is resonant-light scattering, as assumed here. The aggregate distribution of Na atoms fits a 1200 K gas, with a PSD distribution, along with a hotter component. Our models constrain the hot component, assumed to be impact vaporization, to be emitted with a 2500 K Maxwellian. Most orbits show a dawnside enhancement in the hot component broadly spread over the leading hemisphere. However, on some dates there is no dawn/dusk asymmetry. The portion of the hot/cold source appears to be highly variable.

Coronagraphic Observations of the Lunar Sodium Exosphere

NASA Astrophysics Data System (ADS)

Killen, R. M.; Johnson, J. D.; Morgan, T. H.; Potter, A. E.

2017-12-01

We have designed, built and installed a small robotic coronagraph at the Winer Observatory in Sonoita, Arizona, in order to observe the sodium exosphere out to one-half degree around the Moon. Observations are obtained remotely every available clear night from our home base at Goddard Space Flight Center. Our data encompass lunations in 2015, 2016, and 2017, thus we have a long baseline of sodium exospheric calibrated images. We employ an Andover temperature-controlled 1.5 Å wide narrow-band filter centered on the sodium D2 line, and a similar 1.5 Å filter centered blueward of the D2 line by 5 Å. Exposures of 10 minutes are required to image the sodium corona at good signal to noise. Autoguiding is performed locking onto a small bright crater each night. Following each onband-offband exposure pair, on- and off-band images of the lunar surface are collected by taking a 0.1- 0.5 second exposures with the open filter. The sodium is calibrated using the counts in the open Moon images and the Hapke function. We use both dark and bright Hapke parameters for comparison check using Mare and highlands, respectively. In order to obtain the sodium profile around the entire limb, the images are transformed using a polar transform and the profiles are extracted automatically. We have derived zenith column abundances and surface abundances around the lunar limb for each observation and we fit these observations with a 3-dimensional model. We compare our lunar model derived from these observations with the data from the spectrograph onboard the LADEE spacecraft.

Sources of Sodium in the Lunar Exosphere: Modeling Using Ground-Based Observations of Sodium Emission and Spacecraft Data of the Plasma

NASA Technical Reports Server (NTRS)

Sarantos, Menelaos; Killen, Rosemary M.; Sharma, A. Surjalal; Slavin, James A.

2009-01-01

Observations of the equatorial lunar sodium emission are examined to quantify the effect of precipitating ions on source rates for the Moon's exospheric volatile species. Using a model of exospheric sodium transport under lunar gravity forces, the measured emission intensity is normalized to a constant lunar phase angle to minimize the effect of different viewing geometries. Daily averages of the solar Lyman alpha flux and ion flux are used as the input variables for photon-stimulated desorption (PSD) and ion sputtering, respectively, while impact vaporization due to the micrometeoritic influx is assumed constant. Additionally, a proxy term proportional to both the Lyman alpha and to the ion flux is introduced to assess the importance of ion-enhanced diffusion and/or chemical sputtering. The combination of particle transport and constrained regression models demonstrates that, assuming sputtering yields that are typical of protons incident on lunar soils, the primary effect of ion impact on the surface of the Moon is not direct sputtering but rather an enhancement of the PSD efficiency. It is inferred that the ion-induced effects must double the PSD efficiency for flux typical of the solar wind at 1 AU. The enhancement in relative efficiency of PSD due to the bombardment of the lunar surface by the plasma sheet ions during passages through the Earth's magnetotail is shown to be approximately two times higher than when it is due to solar wind ions. This leads to the conclusion that the priming of the surface is more efficiently carried out by the energetic plasma sheet ions.

A Neutral Particle Analyser Proposed On Board Bepicolombo Planetary Orbiter: Serena (searching For Exospheric Refilling and Emitted Neutral Abundances)

NASA Astrophysics Data System (ADS)

Orsini, S.; Npa-Serena Team

The Neutral Particle Analyser SERENA, proposed on board the BepiColombo Mer- cury Planetary Orbiter (MPO), has the purpose of investigating the Hermean exo- spheric and energetic neutral populations. Local and detailed analysis of the exo- spheric composition will be performed by a ram-pointing sensor (MAIA), while en- ergetic neutrals produced through sputtering and charge-exchange processes will be collected by two nadir-pointing sensors (L-ENA, MH-ENA). A central problem in the understanding of the evolution of solar system bodies is the role played by the so- lar wind, solar radiation and micro-meteorite bombardment in controlling mass losses. The direct in situ detection of the Hermean exosphere, the gas evolving from the planet as a product of the different physical processes acting onto the surface, is of crucial importance to understand the past and present evolution of the crust. Current knowl- edge of the origin and evolution of the solar system is based on detailed measurement of chemical, elemental, and isotopic composition of matter. The proposed instrument suite is unique in its capability to perform quantitative analysis and resolve exospheric gas composition under all these three aspects. The value of neutral particles mea- surements for getting a comprehensive picture of the solar wind-planets interaction has been appreciated since the late eighties. Comparison of the measurements in the Mercury environment with those achieved by neutral particle imagers already flying around Earth (IMAGE), Mars (Mars Express), Jupiter and Saturn (Cassini) will allow comparative investigations of evolution and dynamics of planetary magnetospheres.

A Reexamination of Deuterium Fractionation on Mars

NASA Astrophysics Data System (ADS)

Pathare, A.; Paige, D. A.

1997-07-01

The ratio of deuterium to hydrogen in the Martian atmosphere is enhanced by a factor of 5 with respect to the terrestrial value, probably due to fractionation associated with thermal Jeans escape from the top of the atmosphere. Theoretical analyses of the relative efficiency of H and D escape have suggested that the deuterium enrichment implies Mars has outgassed the vast majority of its H2O and that the Martian atmosphere is presently not exchanging water with a juvenile reservoir. However, measurements of high and variable D/H values within hydrous minerals in SNC meteorites strongly suggest that mixing between the atmosphere and juvenile water has taken place. Furthermore, the lack of any observed enrichment of atmospheric (18) O with respect to (16) O, in spite of fractionating nonthermal escape mechanisms, indicates buffering by some juvenile source of oxygen, most probably in the form of a surface or subsurface reservoir of water. We propose that this apparent paradox in the interpretation of isotopic hydrogen and oxygen fractionation --or lack thereof-- can be resolved by re-examining the standard model of deuterium fractionation efficiency on Mars. Specifically, we demonstrate the importance of using upper atmospheric temperatures more representative of the range experienced by the Martian exosphere over the course of the solar cycle. Preliminary calculations involving changes in effusion velocity and diffusive separation as a function of exospheric temperature indicate that incorporating these more representative lower exospheric temperatures will reduce the relative efficiency of D escape, in which case the observed enrichment of deuterium can indeed result from exchange with a juvenile source of water. We are in the process of confirming these computations with a one-dimensional upper atmospheric photochemical model that considers the effects of changing solar activity and exospheric temperature on ionospheric composition. If our initial calculations are correct, and the relative efficiency of D escape is low enough to produce the observed D enrichment by exchange with a juvenile reservoir, then attempts to use the present value of atmospheric D/H to infer the total water outgassed by Mars over billions of years would be in error, since the atmospheric D/H would approach its present value in less than a million years of continual exposure to juvenile water.

Sodium Pick-Up Ion Observations in the Solar Wind Upstream of Mercury

NASA Astrophysics Data System (ADS)

Jasinski, J. M.; Raines, J. M.; Slavin, J. A.; Regoli, L. R.; Murphy, N.

2018-05-01

We present the first observations of sodium pick-up ions upstream of Mercury’s magnetosphere. From these observations we infer properties of Mercury’s sodium exosphere and implications for the solar wind interaction with Mercury’s magnetosphere.

Modeling the Impact Ejected Dust Contribution to the Lunar Exosphere: Results from Experiments and Ground Truth from LADEE

NASA Astrophysics Data System (ADS)

Hermalyn, B.; Colaprete, A.

2013-12-01

A considerable body of evidence indicates the presence of lofted regolith dust above the lunar surface. These observations range from multiple in-situ and orbital horizon glow detections to direct measurement of dust motion on the surface, as by the Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment. Despite this evidence, the specific mechanisms responsible for the lofting of regolith are still actively debated. These include impact ejection, electrostatic lofting, effects of high energy radiation, UV/X- rays, and interplay with solar wind plasma. These processes are highly relevant to one of the two main scientific objectives of the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission (due to launch September, 2013): to directly measure the lunar exospheric dust environment and its spatial and temporal variability towards the goal of better understanding the dust flux. Of all the proposed mechanisms taking place on the lunar surface, the only unequivocal ongoing process is impact cratering. Hypervelocity impact events, which mobilize and redistribute regolith across planetary surfaces, are arguably the most pervasive geologic process on rocky bodies. While many studies of dust lofting state that the impact flux rate is orders of magnitude too low to account for the lunar horizon glow phenomenon and discount its contribution, it is imperative to re-examine these assumptions in light of new data on impact ejecta, particularly from the contributions from mesoscale (impactor size on the order of grain size) and macroscale (impactor > grain size) cratering. This is in large part due to a previous lack of data, for while past studies have established a canonical ejecta model for main-stage ejection of sand targets from vertical impacts, only recent studies have been able to begin quantitatively probing the intricacies of the ejection process outside this main-stage, vertical regime. In particular, it is the high-speed early-time ejecta that will reach significant altitude above the surface and remain aloft ballistically for hours. In addition, ejecta dynamics in the transition regime between microcratering and macro scale events is not yet well understood. As such, there is no currently accepted encompassing model of impact ejecta delivery to the lunar exosphere. It is important to note that the work described here is not to duplicate or exclude other lofting mechanisms -- in reality, the lofting of dust is almost definitely a complex combination of processes -- but instead to provide essential constraints on the impact contribution. This study attempts to constrain the expected contributions from cratering to the lunar exosphere by assessing the ejecta 'background' signal lofted above the surface and the effects of transient focused events (meteor showers) which can produce significant increases in ejecta. In particular, this work couples scaling of previous ejecta studies with Monte-Carlo and ballistics models and will present LADEE data analysis (particularly from the UVS and LDEX instruments) and interpretation in context of constraining the ejected mass distribution. These results are relevant to both our understanding of exospheric dust and for constraint of hazards for future human habitation.

Collecting the Puzzle Pieces: Completing HST's UV+NIR Survey of the TRAPPIST-1 System ahead of JWST

NASA Astrophysics Data System (ADS)

de Wit, Julien

2017-08-01

Using the Spitzer Space Telescope, our team has discovered 7 Earth-sized planets around the nearby Ultra-cool dwarf star TRAPPIST-1. These planets are the first to be simultaneously Earth-sized, temperate, and amenable for in-depth atmospheric studies with space-based observatories (notably, JWST). TRAPPIST-1's system thus provides us with the first opportunity to probe the atmospheres of Earth-sized exoplanets and search for signs of habitability beyond our solar system, which will require spectral information from the UV to the IR to complete their atmospheric puzzles.We request 114 HST orbits to complete the UV+NIR survey of the 7 planets in preparation for their in-depth followup with JWST. The suggested low-density of the planets combined with their complex orbital resonance chain indicate that they migrated inward to their current positions and may harbor large water rich reservoir or leftover primordial H2 atmospheres. We have already ruled out the presence of clear H2 atmospheres for the 5 innermost planets using WFC3 and are requesting 16 WFC3 orbits to complete the TRAPPIST-1 NIR reconnaissance survey. Our primary request consists in 98 STIS orbits to complete the survey for extended H-exospheres around each of the planets. H-exospheres are the most accessible observables for volatile reservoirs, which have not been ruled out by our WFC3 observations. Exosphere detection is only amenable using HST unique capabilities in the UV and are pivotal to guide JWST's in-depth followup. The combined information from HST's UV and NIR observations will allow us put the first critical pieces of the atmospheric puzzle in place for these temperate earth-sized worlds.

Remote Observations of the Lunar Sodium Exosphere

NASA Astrophysics Data System (ADS)

Morgan, T. H.; Killen, R. M.; Potter, A. E.

2015-12-01

We have designed, built and installed a small robotic coronagraph at the Winer Observatory in Sonoita, Arizona, in order to observe the sodium exosphere out to one-half degree around the Moon. We have observed every available clear night from our home base at Goddard Space Flight Center for several lunations in 2015, and thus have a long baseline of sodium exospheric calibrated images. We employ an Andover temperature-controlled 1.5 Å wide narrow-band filter centered on the sodium D2 line, and a similar 1.5 Å filter centered blueward of the D2 line by 5 Å. This filter would yield a sodium signal at least 24% of the scattered lunar light at first quarter. Exposures of 10 minutes are required to image the sodium corona at good signal to noise. Following each exposure pair, taking a 0.1 sec exposure with the open filter collects on- and off-band images of the lunar surface. An example of our resulting image of the sodium corona is shown in Figure 1, with the image of the moon's disk (taken subsequently to the occulted coronal image) superimposed on the occulting disk, thus showing the position and phase of the moon under the disk. We will compare our lunar model derived from these observations with the data from the UV spectrograph onboard the LADEE spacecraft. Figure 1. An image of the lunar sodium corona obtained on March 26, 2015 is shown with the lunar surface superimposed on the coronagraphic image. Using various sized occulting disks, depending on lunar phase, we observe the corona very close to the lunar surface with no scattered light.

On the origin of alkali metals in Europa exosphere

NASA Astrophysics Data System (ADS)

Ozgurel, Ozge; Pauzat, Françoise; Ellinger, Yves; Markovits, Alexis; Mousis, Olivier; LCT, LAM

2016-10-01

At a time when Europa is considered as a plausible habitat for the development of an early form of life, of particular concern is the origin of neutral sodium and potassium atoms already detected in its exosphere (together with magnesium though in smaller abundance), since these atoms are known to be crucial for building the necessary bricks of prebiotic species. However their origin and history are still poorly understood. The most likely sources could be exogenous and result from the contamination produced by Io's intense volcanism and/or by meteoritic bombardment. These sources could also be endogenous if these volatile elements originate directly from Europa's icy mantle. Here we explore the possibility that neutral sodium and potassium atoms were delivered to the satellite's surface via the upwelling of ices formed in contact with the hidden ocean. These metallic elements would have been transferred as ions to the ocean at early epochs after Europa's formation, by direct contact of water with the rocky core. During Europa's subsequent cooling, the icy layers formed at the top of the ocean would have kept trapped the sodium and potassium, allowing their future progression to the surface and final identification in the exosphere of the satellite. To support this scenario, we have used chemistry numerical models based on first principle periodic density functional theory (DFT). These models are shown to be well adapted to the description of compact ice and are capable to describe the trapping and neutralization of the initial ions in the ice matrix. The process is found relevant for all the elements considered, alkali metals like Na and K, as well as for Mg and probably for Ca, their respective abundances depending essentially of their solubility and chemical capabilities to blend with water ices.

Wide-Field Ultraviolet Spectrometer for Planetary Exospheres and Thermospheres

NASA Astrophysics Data System (ADS)

Fillingim, M. O.; Wishnow, E. H.; Miller, T.; Edelstein, J.; Lillis, R. J.; Korpela, E.; England, S.; Shourt, W. V.; Siegmund, O.; McPhate, J.; Courtade, S.; Curtis, D. W.; Deighan, J.; Chaffin, M.; Harmoul, A.; Almatroushi, H. R.

2016-12-01

Understanding the composition, structure, and variability of a planet's upper atmosphere - the exosphere and thermosphere - is essential for understanding how the upper atmosphere is coupled to the lower atmosphere, magnetosphere and near-space environment, and the Sun. Ultraviolet spectroscopy can directly observe emissions from constituents in the exosphere and thermosphere. From such observations, the structure, composition, and variability can be determined.We will present the preliminary design for a wide field ultraviolet imaging spectrometer for remote sensing of planetary atmospheres. The imaging spectrometer achieves an extremely large instantaneous 110 degree field of view with no moving scanning mirror. The imaging resolution is very appropriate for extended atmospheric emission studies, with a resolution of better than 0.3 degrees at the center to 0.4 degrees at the edges of the field. The spectral range covers 120 - 170 nm, encompassing emissions from H, O, C, N, CO, and N2, with an average spectral resolution of 1.5 nm. The instrument is composed of a 2-element wide-field telescope, a 3-element Offner spectrometer, and a sealed MCP detector system contained within a compact volume of about 40 x 25 x 20 cm. We will present the optical and mechanical design as well as the predicted optical performance.The wide instantaneous FOV simplifies instrument and spacecraft operations by removing the need for multiple scans (either from a scan mirror or spacecraft slews) to cover the regions of interest. This instrumentation can allow for two-dimensional spectral information to be built up with simple spacecraft operation or just using spacecraft motion. Applications to the terrestrial geocorona and thermosphere will be addressed as well as applications to the upper atmospheres of other planetary objects.

The search for active Europa plumes in Galileo plasma particle detector data: the E12 flyby

NASA Astrophysics Data System (ADS)

Huybrighs, H.; Roussos, E.; Krupp, N.; Fraenz, M.; Futaana, Y.; Barabash, S. V.; Glassmeier, K. H.

2017-12-01

Hubble Space Telescope observations of Europa's auroral emissions and transits in front of Jupiter suggest that recurring water vapour plumes originating from Europa's surface might exist. If conclusively proven, the discovery of these plumes would be significant, because Europa's potentially habitable ocean could be studied remotely by taking in-situ samples of these plumes from a flyby mission. The first opportunity to collect in-situ evidence of the plumes will not arise before the early 2030's when ESA's JUICE mission or NASA's Europa Clipper are set to arrive. However, it may be possible that NASA's Galileo mission has already encountered the plumes when it was active in the Jupiter system from 1995 to 2003. It has been suggested that the high plasma densities and anomalous magnetic fields measured during one of the Galileo flybys of Europa (flyby E12) could be connected to plume activity. In the context of the search for Europa plume signatures in Galileo particle data we present an overview of the in-situ plasma particle data obtained by the Galileo spacecraft during the E12 flyby. Focus is in particular on the data obtained with the plasma particle instruments PLS (low energy ions and electrons) and EPD (high energy ions and electrons). We search for signs of an extended exosphere/ionosphere that could be consistent with ongoing plume activity. The PLS data obtained during the E12 flyby show an extended interaction region between Europa and the plasma from Jupiter's magnetosphere, hinting at the existence of an extended ionosphere and exosphere. Furthermore we show how the EPD data are analyzed and modelled in order to evaluate whether a series of energetic ion depletions can be attributed to losses on the moon's surface or its neutral exosphere.

The Big Picture: Imaging of the Global Geospace Environment by the TWINS Mission

NASA Astrophysics Data System (ADS)

Goldstein, J.; McComas, D. J.

2018-03-01

Encircling our planet at distances of 2.5 to 8 Earth radii is a dynamic plasma population known as the ring current (RC). During geomagnetic storms, the solar wind's interaction with Earth's magnetic field pumps petaJoules of energy into the RC, energizing and transporting particles. To measure the global geospace response, RC imaging is performed by capturing energetic neutral atoms (ENAs) created by charge exchange between geospace ions and the neutral exosphere. The H exosphere is itself imaged via its geocoronal Lyman-α glow. Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a stereoscopic ENA and Lyman-α imaging mission that has recorded the deep minimum of solar cycle (SC) 23 and the moderate maximum of SC 24, observing geospace conditions ranging from utterly quiet to major storms. This review covers TWINS studies of the geospace response published during 2013 to 2017. Stereo ENA imaging has revealed new dimensionality and structure of RC ions. Continuous coverage by two imagers has allowed monitoring storms from start to finish. Deconvolution of the low-altitude signal has extended ENA analysis and revealed causal connections between the trapped and precipitating ion populations. ENA-based temperature and composition analyses have been refined, validated, and applied to an unprecedented sequence of solar activity changes in SC 23 and SC 24. Geocoronal imaging has revealed a surprising amount of time variability and structure in the neutral H exosphere, driven by both Sun and solar wind. Global models have been measurably improved. Routine availability of simultaneous in situ measurements has fostered huge leaps forward in the areas of ENA validation and cross-scale studies.

Ground-Based Observation of Mercury's Sodium at Haleakala Observatory in 2013–2017

NASA Astrophysics Data System (ADS)

Kameda, S.; Kagitani, M.

2018-05-01

In this study, daily variation in Mercury's sodium exosphere was observed at the Haleakala Observatory in Hawaii. We confirmed the seasonal variation of the column density of sodium atoms over the dawn side differs from that over the dusk side.

The Lunar Atmosphere: History, Status, Current Problems, and Context

NASA Technical Reports Server (NTRS)

Stern, S. Alan .

1997-01-01

After decades of speculation and fruitless searches, the lunar atmosphere was first observed by Apollo surface and orbital instruments between 1970 and 1972. With the demise of Apollo in 1972, and the termination of funding for Apollo lunar ground station studies in 1977, the field withered for many years, but has recently enjoyed a renaissance. This reflowering has been driven by the discovery and exploration of sodium and potassium in the lunar exosphere by groundbased observers, the detection of metal ions derived from the Moon in interplanetary space, the possible discoveries of H2O ice at the poles of the Moon and Mercury, and the detections of tenuous atmospheres around more remote sites in the solar system, including Mercury and the Galilean satellites. In this review we summarize the present state of knowledge about the lunar atmosphere, describe the important physical processes taking place within it, and then discuss related topics including a comparison of the lunar atmosphere to other surface boundary exospheres in the solar system.

Centrifugally Stimulated Exospheric Ion Escape at Mercury

NASA Technical Reports Server (NTRS)

Delcourt, Dominique; Seki, K.; Terada, N.; Moore, Thomas E.

2012-01-01

We investigate the transport of ions in the low-altitude magnetosphere magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury.

The ionosphere of Uranus - A myriad of possibilities

NASA Astrophysics Data System (ADS)

Chandler, M. O.; Waite, J. H.

1986-01-01

A one-dimensional model has been used to study the effects of exospheric temperature, methane and water influx, ionospheric outflow, and electron precipitation on the composition and structure of the ionosphere of Uranus. Peak ion concentrations range from 1000 to 1 million per cu cm with a wide variation in peak altitude, which depends strongly on the exospheric temperature. In all the cases considered, H(+) is the major ion in the topside ionosphere. At altitudes near or below the peak, H3(+) and CH5(+) can dominate, depending on the magnitude of CH4 and H2O influx. Atomic hydrogen column depths above the methane absorbing layer exceed 10 to the 17th per sq cm and can produce large (400 R) emissions of resonantly scattered Lyman-alpha. In the sunlit polar cap, electron precipitation with energy fluxes of 0.6 to 1.0 erg/sq cm s results in direct production of Lyman-alpha emissions that exceed 1 kR.

High altitude atmospheric modeling

NASA Technical Reports Server (NTRS)

Hedin, Alan E.

1988-01-01

Five empirical models were compared with 13 data sets, including both atmospheric drag-based data and mass spectrometer data. The most recently published model, MSIS-86, was found to be the best model overall with an accuracy around 15 percent. The excellent overall agreement of the mass spectrometer-based MSIS models with the drag data, including both the older data from orbital decay and the newer accelerometer data, suggests that the absolute calibration of the (ensemble of) mass spectrometers and the assumed drag coefficient in the atomic oxygen regime are consistent to 5 percent. This study illustrates a number of reasons for the current accuracy limit such as calibration accuracy and unmodeled trends. Nevertheless, the largest variations in total density in the thermosphere are accounted for, to a very high degree, by existing models. The greatest potential for improvements is in areas where we still have insufficient data (like the lower thermosphere or exosphere), where there are disagreements in technique (such as the exosphere) which can be resolved, or wherever generally more accurate measurements become available.

The plasmasphere electron content paradox

NASA Astrophysics Data System (ADS)

Krall, J.; Huba, J. D.

2016-09-01

Measurements show that plasmasphere refilling rates decrease with increasing solar activity, while paradoxically, the vertical integration of the plasmasphere electron density (pTEC) increases with increasing solar activity. Using the Naval Research Laboratory SAMI2 (Sami2 is Another Model of the Ionosphere) and SAMI3 (Sami3 is Also a Model of the Ionosphere) codes, we simulate plasmasphere refilling following a model storm, reproducing this observed phenomenon. In doing so, we find that the refilling rate and resulting pTEC values are sensitive to the oxygen profile in the thermosphere and exosphere: the supply of H+ in the topside ionosphere is limited by the local O+ density, through H+O+→H++O charge exchange. At solar minimum, the O+ supply simply increases with the O density in the exosphere. At solar maximum, we find that O-O+ collisions limit the O+ density in the topside ionosphere such that it decreases with increasing O density. The paradox occurs because the pTEC metric gives electrons in the topside ionosphere more weight than electrons in the plasmasphere.

Daily variation of diurnal thermal tides from CHAMP and GOCE accelerometer measurements

NASA Astrophysics Data System (ADS)

Gasperini, Federico; Doornbos, Eelco; Forbes, Jeffrey M.; Bruinsma, Sean; Haeusler, Kathrin; Hagan, Maura

Daily migrating and non-migrating diurnal tides in exospheric temperature derived from simultaneous accelerometer measurements on CHAMP (near 300 km) and GOCE (near 260 km) are studied for the intervals November-December 2009 and March-April 2010. Neutral densities are converted to exospheric temperatures using the NRLMSISe00 empirical model and by iterating on a convenient parameter (e.g. F10.7 solar flux). This methodology is validated using NCAR TIME-GCM simulations for this period as a mock data set, and results are compared to an approach where differences between ascending and descending orbital measurements are used to estimate diurnal tides for CHAMP and GOCE separately. The tidal components analyzed are the westward-propagating components with zonal wave numbers s=1 and s=2 (DW1 and DW2) and the eastward-propagating components with s=-2 and s=-3 (DE2 and DE3). Spectral analyses are used to reveal potential planetary wave modulations of the daily tidal amplitudes.

Seasonal variation of Martian pick-up ions: Evidence of breathing exosphere

NASA Astrophysics Data System (ADS)

Yamauchi, M.; Hara, T.; Lundin, R.; Dubinin, E.; Fedorov, A.; Sauvaud, J.-A.; Frahm, R. A.; Ramstad, R.; Futaana, Y.; Holmstrom, M.; Barabash, S.

2015-12-01

The Mars Express (MEX) Ion Mass Analyser (IMA) found that the detection rate of the ring-like distribution of protons in the solar wind outside of the bow shock to be quite different between Mars orbital summer (around perihelion) and orbital winter (around aphelion) for four Martian years, while the north-south asymmetry is much smaller than the perihelion-aphelion difference. Further analyses using eight years of MEX/IMA solar wind data between 2005 and 2012 has revealed that the detection frequency of the pick-up ions originating from newly ionized exospheric hydrogen with certain flux strongly correlates with the Sun-Mars distance, which changes approximately every two years. Variation due to the solar cycle phase is not distinguishable partly because this effect is masked by the seasonal variation under the MEX capability of plasma measurements. This finding indicates that the variation in solar UV has a major effect on the formation of the pick-up ions, but this is not the only controlling factor.

Observing the Magnetosphere in Soft X-Rays: The Lunar X-Ray Observatory (LXO)

NASA Astrophysics Data System (ADS)

Sibeck, D. G.; Collier, M. R.; Porter, F. S.

2018-02-01

Wide field-of-view soft X-ray imagers in lunar orbit or on the lunar surface can be used to address many heliophysics objectives, including the nature of the solar wind magnetosphere-interaction, the lunar exosphere, and the helium focusing cone.

Lunar exospheric helium observations of LRO/LAMP coordinated with ARTEMIS

NASA Astrophysics Data System (ADS)

Grava, C.; Retherford, K. D.; Hurley, D. M.; Feldman, P. D.; Gladstone, G. R.; Greathouse, T. K.; Cook, J. C.; Stern, S. A.; Pryor, W. R.; Halekas, J. S.; Kaufmann, D. E.

2016-07-01

We present results from Lunar Reconnaissance Orbiter's (LRO) UV spectrograph LAMP (Lyman-Alpha Mapping Project) campaign to study the lunar atmosphere. Several off-nadir maneuvers (lateral rolls) were performed to search for resonantly scattering species, increasing the illuminated line-of-sight (and hence the signal from atoms resonantly scattering the solar photons) compared to previously reported LAMP's "twilight observations" (Cook, J.C., Stern, S.A. [2014]. Icarus 236, 48-55). Helium was the only element distinguishable on a daily basis, and we present latitudinal profiles of its line-of-sight column density in December 2013. We compared the helium line-of-sight column densities with solar wind alpha particle fluxes measured from the ARTEMIS (Acceleration, Reconnection, Turbulence, & Electrodynamics of Moon's Interaction with the Sun) twin spacecraft. Our data show a correlation with the solar wind alpha particle flux, confirming that the solar wind is the main source of the lunar helium. We also support the finding by Benna et al. (Benna, M. et al. [2015]. Geophys. Res. Lett. 42, 3723-3729) and Hurley et al. (Hurley, D.M. et al. [2015]. Icarus, this issue), that a non-zero contribution from endogenic helium, coming from radioactive decay of 232Th and 238U, is present. Moreover, our results suggest that not all of the incident alpha particles are converted to thermalized helium, allowing for a non-negligible fraction to escape as suprathermal helium or simply backscattered from the lunar surface. We compare LAMP-derived helium surface density with the one recorded by the mass spectrometer LACE (Lunar Atmospheric Composition Experiment) deployed on the lunar surface during the Apollo 17 mission, finding good agreement between the two measurements. The LRO/LAMP roll observations presented here are in agreement with the most recent lunar exospheric helium model (Hurley, D.M. et al. [2015]. Icarus, this issue) around mid- to high-latitudes (50-70°) regardless of the local solar time, while there is an underestimation of the model around the low- to mid-latitudes (10-30°), especially around the dawn terminator. The LRO/LAMP roll observations presented here provide unique coverage of local solar time and latitude of the lunar exospheric helium, filling a gap in the knowledge of the structure of the lunar exosphere as a whole. These observations will inform future models of transport of volatiles, since at the terminator the analytic expressions for the surface temperature, essential to determine the energy distribution, the residence time, and the hop length of the particles, is least accurate.

Observational Conditions for the Detection of X-Ray Fluorescence from Sodium by the MIXS Instrument on BepiColombo

NASA Astrophysics Data System (ADS)

Cooper, R.; Grande, M.; Martindale, A.; Bunce, E.

2018-05-01

We model the expected fluorescence from the exosphere and surface of Mercury, as observed by the Mercury Imaging X-ray Spectrometer (MIXS) on the upcoming BepiColombo mission, using code modified from that used for the SMART-1 D-CIXS instrument.

SERENA: A suite of four instruments (ELENA, STROFIO, PICAM and MIPA) on board BepiColombo-MPO for particle detection in the Hermean environment

NASA Astrophysics Data System (ADS)

Orsini, S.; Livi, S.; Torkar, K.; Barabash, S.; Milillo, A.; Wurz, P.; di Lellis, A. M.; Kallio, E.; The Serena Team

2010-01-01

'Search for Exospheric Refilling and Emitted Natural Abundances' (SERENA) is an instrument package that will fly on board the BepiColombo/Mercury Planetary Orbiter (MPO). It will investigate Mercury's complex particle environment that is composed of thermal and directional neutral atoms (exosphere) caused by surface release and charge-exchange processes, and of ionized particles caused by photo-ionization of neutrals as well by charge exchange and surface release processes. In order to investigate the structure and dynamics of the environment, an in-situ analysis of the key neutral and charged components is necessary, and for this purpose the SERENA instrument shall include four units: two neutral particle analyzers (Emitted Low Energy Neutral Atoms (ELENA) sensor and Start from a Rotating FIeld mass spectrometer (STROFIO)) and two ion spectrometers (Miniature Ion Precipitation Analyzer (MIPA) and Planetary Ion Camera (PICAM)). The scientific merits of SERENA are presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects.

Detection of Mercury's Potassium Tail

NASA Astrophysics Data System (ADS)

Schmidt, Carl; Leblanc, Francois; Moore, Luke; Bida, Thomas A.

2017-10-01

Ground-based observations of Mercury's exosphere bridge the gap between the MESSENGER and BepiColombo missions and provide a broad counterpart to their in situ measurements. Here we report the first detection of Mercury's potassium tail in both emission lines of the D doublet. The sodium to potassium abundance ratio at 5 planetary radii down-tail is approximately 95, near the mid-point of a wide range of values that have been quoted over the planet's disk. This is several times the Na/K present in atmospheres of the Galilean satellites and more than an order of magnitude above Mercury's usual analogue, the Moon. The observations confirm that Mercury's anomalously high Na/K ratios cannot be explained by differences in neutral loss rates. The width and structure of the Na and K tails is comparable and both exhibit a persistent enhancement in their northern lobe. We interpret this as a signature of Mercury's offset magnetosphere; the exosphere's source rates are locally enhanced at the southern surface, and sloshing from radiation pressure and gravity guides this population into the northern region of the tail.

The Solar Wind as a Magnetofluid Turbulence Laboratory

NASA Technical Reports Server (NTRS)

Goldstein, Melvyn L.

2011-01-01

The solar wind is the Sun's exosphere. As the solar atmosphere expands into interplanetary space, it is accelerated and heated. Data from spacecraft located throughout the heliosphere have revealed that this exosphere has velocities of several hundred kilometers/sec, densities at Earth orbit of about 5 particles/cu cm, and an entrained magnetic field that at Earth orbit that is about 5 10-5 Gauss. A fascinating feature of the solar wind is that the magnetic field fluctuates in a way that is highly reminiscent of "Alfven waves, i.e., the fluctuating magnetic fields are more-or-less aligned with fluctuations in the velocity of the plasma and, with proper normalization, have approximately equal magnitudes. The imperfect (observed) alignment leads to a variety of complex interactions. In many respects, the flow patterns appear to be an example of fully developed magneto fluid turbulence. Recently, the dissipation range of this turbulence has been studied using search coil magnetometer data from the STAFF instrument on the four Cluster spacecraft. I will attempt to give an overview of selected properties of this large-scale and small-scale turbulence.

Development of a miniature microwave electron cyclotron resonance plasma ion thruster for exospheric micro-propulsion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Indranuj, E-mail: indranuj@aees.kyushu-u.ac.jp; Toyoda, Yuji; Yamamoto, Naoji

A miniature microwave electron cyclotron resonance plasma source [(discharge diameter)/(microwave cutoff diameter) < 0.3] has been developed at Kyushu University to be used as an ion thruster in micro-propulsion applications in the exosphere. The discharge source uses both radial and axial magnetostatic field confinement to facilitate electron cyclotron resonance and increase the electron dwell time in the volume, thereby enhancing plasma production efficiency. Performance of the ion thruster is studied at 3 microwave frequencies (1.2 GHz, 1.6 GHz, and 2.45 GHz), for low input powers (<15 W) and small xenon mass flow rates (<40 μg/s), by experimentally measuring the extractedmore » ion beam current through a potential difference of ≅1200 V. The discharge geometry is found to operate most efficiently at an input microwave frequency of 1.6 GHz. At this frequency, for an input power of 8 W, and propellant (xenon) mass flow rate of 21 μg/s, 13.7 mA of ion beam current is obtained, equivalent to an calculated thrust of 0.74 mN.« less

Neural networks to predict exosphere temperature corrections

NASA Astrophysics Data System (ADS)

Choury, Anna; Bruinsma, Sean; Schaeffer, Philippe

2013-10-01

Precise orbit prediction requires a forecast of the atmospheric drag force with a high degree of accuracy. Artificial neural networks are universal approximators derived from artificial intelligence and are widely used for prediction. This paper presents a method of artificial neural networking for prediction of the thermosphere density by forecasting exospheric temperature, which will be used by the semiempirical thermosphere Drag Temperature Model (DTM) currently developed. Artificial neural network has shown to be an effective and robust forecasting model for temperature prediction. The proposed model can be used for any mission from which temperature can be deduced accurately, i.e., it does not require specific training. Although the primary goal of the study was to create a model for 1 day ahead forecast, the proposed architecture has been generalized to 2 and 3 days prediction as well. The impact of artificial neural network predictions has been quantified for the low-orbiting satellite Gravity Field and Steady-State Ocean Circulation Explorer in 2011, and an order of magnitude smaller orbit errors were found when compared with orbits propagated using the thermosphere model DTM2009.

LCROSS: Volatiles and Exosphere Associated with a Permanently Shadowed Region in Cabeus

NASA Technical Reports Server (NTRS)

Wooden, Diane; Colaprete, Anthony; Heldmann, Jennifer; Ennico, Kimberly; Shirley, Mark; Marshall, William

2010-01-01

We discuss the volatile species in the LCROSS data set in addition to water that were observed by the LCROSS Shepherding Spacecraft before its own demise in the four minutes following the first impact by the Centaur. The stochastic nature of the temporal variations observed by the nadir-viewing near-infrared spectrometer combined with the diversity of the volatile species suggests that these species were in situ in the permanently shadowed crater and were released by a combination of the centaur impact and the resulting warming of the regolith by the impact and ejecta debris blanket. Adding to this intrigue are the pre-impact observations by the UVVisual spectrometer that reveal that the field-of-view into the permanently shadowed crater contains UV emission lines, The UV lines are clearly revealed once the descent of the shepherding spacecraft narrows the field-of-view of the UV-Vis spectrometer so as to exclude any surrounding bright terrain. Our suggestion is that this emission comes from tenuous gases, i.e., there appears to be a potential association between the cold, permanently shadowed region and an exosphere.

Light Scattering by Lunar Exospheric Dust: What could be Learned from LRO LAMP and LADEE UVS?

NASA Astrophysics Data System (ADS)

Glenar, D. A.; Stubbs, T. J.; Richard, D. T.; Stern, S. A.; Retherford, K. D.; Gladstone, R.; Feldman, P. D.; Colaprete, A.; Delory, G. T.

2011-12-01

Two complementary spectrometers, namely the Lunar Reconnaissance Orbiter, Lyman Alpha Mapping Project (LAMP) and the planned Lunar Atmosphere and Dust Environment Explorer (LADEE) Ultraviolet Explorer (UVS) will carry out sensitive searches for high altitude exospheric dust, via detection of scattered sunlight. The combined spectral coverage of these instruments extends from far-UV to near-IR wavelengths. Over this wavelength range, grain size parameter (X=2πr/λ, with r the grain radius and λ the wavelength) changes dramatically, which makes broad wavelength coverage a good diagnostic of grain size. Utilizing different pointing geometries, both LAMP and UVS are able to observe dust over a range of scattering angles, as well as measure the dust vertical profile via limb measurements at multiple tangent heights. We summarize several categories of information that can be inferred from the data sets, using broadband simulations of horizon glow as observed at the limb. Grain scattering properties used in these simulations were computed for multiple grain shapes using Discrete-Dipole theory. Some cautionary remarks are included regarding the use of Mie theory to interpret scattering measurements.

A Saturnian gas ring and the recycling of Titan's atmosphere

NASA Technical Reports Server (NTRS)

Mcdonough, T. R.; Brice, N. M.

1973-01-01

Atoms which escape Titan's atmosphere are unlikely to possess escape velocity from Saturn and can orbit the planet until lost by ionization or collision with Titan. It is predicted that a toroidal ring of between 1 and 1,000 atoms or molecules per cubic centimeter exists around Saturn at a distance of about 10 times the radius of the visible rings. This torus may be detectable from earth orbit and detection or nondetection of it may provide some information about the presence or absence of a Saturnian magnetic field, and the exospheric temperature and atmospheric escape rate of Titan. It is estimated that, if Titan has a large exosphere, 97% or more of the escaping atoms can be recaptured by Titan, thereby decreasing the effective net atmospheric loss rate by up to two orders of magnitude. It is shown that, if Saturn has a magnetic field comparable to Jupiter's the magnetospheric plasma can supply Titan with hydrogen at a rate comparable to the loss rates in some of the models of Trafton (1972) and Sagan (1973).

The effects of spacecraft charging and outgassing on the LADEE ion measurements

NASA Astrophysics Data System (ADS)

Xie, Lianghai; Zhang, Xiaoping; Zheng, Yongchun; Guo, Dawei

2017-05-01

Abnormal ion signals can be usually seen in the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, including a suddenly enhanced current observed by the Lunar Dust Experiment (LDEX) near the sunlight-shadow boundary and an unexpected water ion measured by the neutral mass spectrometer (NMS), with their magnitudes insensitive to the convection electric field of solar wind but dependent on the SW density and the elapsed time of LADEE mission. By analyzing both the LDEX measurements and the NMS measurements, we find that the current enhancement can be caused by a negatively charged spacecraft in the shadow region while the significant water ions should be some artificial ions from spacecraft outgassing. The artificial water ions show a peak near 8:00 LT that may be related to a sunlight-controlled surface outgassing. In addition, the H2O flux can be enhanced near the end of the mission when the spacecraft has a lower altitude. It is found that the H2O enhancement is actually caused by an exosphere-contributed return flux, rather than a real water exosphere.

Field-Aligned Current Systems at Mercury

NASA Astrophysics Data System (ADS)

Heyner, Daniel; Exner, Willi

2017-04-01

Mercury exhibits a very dynamic magnetosphere, which is partially due to strong dayside reconnection and fast magnetospheric convection. It has been shown that dayside reconnection occurs even on low magnetic shear angles across the magnetopause. This drives quasi-steady region 1 field-aligned currents (FAC) that are observable in in-situ MESSENGER data. Here, the structure of the Hermean FAC-system is discussed and compared to the terrestrial counterpart. Due to the lack of a significant ionosphere at Mercury, it has to be examined how much of the poloidal FAC is reflected back to the magnetosphere, closed via toroidal currents in the planetary interior or via Pedersen currents in the tenuous exosphere. This investigation gives insights into the planetary conductivity structure as well as the exospheric plasma densities. Furthermore, it will be examined how much the only partially developed ring current at Mercury produces possible region 2 FAC signatures. We conclude with requirements to simulations that are needed to forecast the FAC structure on the southern hemisphere that will be closely studied with the upcoming BepiColombo mission.

MAJIS (Moons and Jupiter Imaging Spectrometer): the VIS-NIR imaging spectrometer of the JUICE mission

NASA Astrophysics Data System (ADS)

Langevin, Yves; Piccioni, Giuseppe; Dumesnil, Cydalise; Filacchione, Gianrico; Poulet, Francois; MAJIS Team

2016-10-01

MAJIS is the VIS-NIR imaging spectrometer of JUICE. This ambitious mission of ESA's « cosmic vision » program will investigate Jupiter and its system with a specific focus on Ganymede. After a tour of more than 3 years including 2 fly-bys of Europa and up to 20 flybys of Ganymede and Callisto, the end of the nominal mission will be dedicated to an orbital phase around Ganymede with 120 days in a near-circular, near-polar orbit at an altitude of 5000 km and 130 days in a circular near-polar orbit at an altitude of 500 km. MAJIS will adress 17 of the 19 primary science objectives of JUICE, investigating the surface and exosphere of the Galilean satellites (Ganymede during the orbital phase, Europa and Callisto during close flybys, Io from a minimum distance of 570,000 km), the atmosphere / exosphere of Jupiter, small satellites and rings, and their role as sources and sinks of particles in the Jupiter magnetosphere.The main technical characteristics are the following:Spectral range : 0.5 - 5.7 µm with two overlapping channels (VIS-NIR : 0.5 - 2.35 µm ; IR : 2.25 - 5.7 µm)Spatial resolution : 0.125 to 0.15 mradSpectral sampling (VIS-NIR channel) : 2.9 to 3.45 nmSpectral sampling (IR channel) : 5.4 to 6.45 nmThe spectral and spatial resolution will be finalized in october 2016 after the selection of the MAJIS detectors.Passive cooling will provide operating temperatures < 130 K (VIS-NIR) and < 90 K (IR) so as to limit the impact of dark current on performances.The SNR as determined from the photometric model and the noise model will be larger than 100 over most of the spectral range except for high resolution observations of icy moons at low altitude due to limitations on the integration time even with motion compensation provided by a scanner and for exospheric observations due to intrinsic low signal levels.

Simulation of Energetic Neutral Atom Images at Venus

NASA Astrophysics Data System (ADS)

Gunell, H.; Holmström, M.; Biernat, H. K.; Erkaev, N. V.; Lammer, H.; Lichtenegger, H.; Penz, T.

2003-12-01

We present simulated images of energetic neutral atoms (ENAs) produced in charge exchange collisions between solar wind protons and neutral atoms in the exosphere of Venus. The plasma flow around Venus is modelled by a semi-analytical MHD simulation that includes mass-loading (Biernat et al., J. Geophys. Res., vol. 104, 12617--12626, 1999; Biernat,et al., Adv. Space Res., 28, 2001). These results are compared with the results that are obtained when the Spreiter-Stahara flow model (Spreiter and Stahara, Adv Space Res., 14, 5--19, 1994) is used. The ENA images are calculated by combining the proton bulk flow and temperature results of the MHD model with a model of the neutral atmosphere using the energy dependent cross sections for the charge exchange collisions. The ENA production rate is integrated along lines of sight to a virtual instrument, thus simulating what could be measured by a space-craft-carried ENA instrument. The images are found to be dominated by two local maxima. One produced by charge exchange collisions in the solar wind, upstream of the bow shock, and the other close to the dayside ionopause. The main contribution to the ENA flux observed in the ENA images stems from a region of space between the ionopause and the bow shock on the dayside of the planet. The simulated ENA fluxes at Venus are lower than those obtained in similar simulations of ENA images at Mars (Holmström et al., J. Geophys. Res., 107, 1277, doi: 10.1029/2001JA000325, 2002). The reason for the lower ENA flux at Venus is thought to be the smaller extent of Venus' exosphere. The steeper falloff of the neutral gas density with altitude in the exosphere of Venus is caused by Venus' mass, which is 7.5 times greater than the mass of Mars. The dependence of the ENA flux on the altitude of the ionopause is studied numerically, and it is found that the ENA flux decreases as the ionopause altitude is increased.

Refilling the plasmasphere through the exospheric sieve

NASA Astrophysics Data System (ADS)

Krall, J.; Huba, J.; Emmert, J. T.

2016-12-01

The ability to compute plasmasphere densities is critical to many space weather concerns. The sensitivity of refilling to the solar cycle is compelling because, paradoxically, refilling rates are generally lowest when the ionosphere is strongest. In the past, this has been attributed to a dearth of exosphere H at solar maximum. While H is needed to supply H + O+ -> H+ + O charge exchange, recent work demonstrates a significant sensitivity to O [1]. Results will be based on preliminary model-data comparisons using in situ Van Allen Probe EMFISIS data and the SAMI3 ionosphere/plasmasphere code. We will assess the impact of atmospheric composition (i.e., O and H) and solar activity (e.g., F10.7) on plasmasphere refilling rates and density following magnetic storms. SAMI3 (Sami3 is Also a Model of the Ionosphere) is a first-principles ionosphere/plasmasphere model. SAMI3 includes 7 ion species (H+, He+, O+, N+, O2+, N2+, NO+), each treated as a separate fluid, with temperature equations being solved for H+, He+, O+ and e- [2]. SAMI3 uses the empirical MSIS thermosphere/exosphere model to specify O and H densities. SAMI3 includes scaling factors that can be used to tune MSIS densities to bring them in line with measurements of satellite drag. Key inputs for this data-driven modeling are the thermosphere oxygen (O) and hydrogen (H) densities, and the F10.7 proxy for solar ultraviolet irradiance. [1 ]Krall, J., J. T. Emmert, F. Sassi, S. E. McDonald, and J. D. Huba (2016), Day-to-day variability in the thermosphere and its impact on plasmasphere refilling, J. Geophys. Res. Space Physics, 121, doi:10.1002/2015JA022328. [2] Huba, J. and J. Krall (2013), Modeling the plasmasphere with SAMI3, Geophys. Res. Lett., 40, 6-10, doi:10.1029/2012GL054300 Research supported by NRL base funds.

Upstream proton cyclotron waves at Venus near solar maximum

NASA Astrophysics Data System (ADS)

Delva, M.; Bertucci, C.; Volwerk, M.; Lundin, R.; Mazelle, C.; Romanelli, N.

2015-01-01

magnetometer data of Venus Express are analyzed for the occurrence of waves at the proton cyclotron frequency in the spacecraft frame in the upstream region of Venus, for conditions of rising solar activity. The data of two Venus years up to the time of highest sunspot number so far (1 Mar 2011 to 31 May 2012) are studied to reveal the properties of the waves and the interplanetary magnetic field (IMF) conditions under which they are observed. In general, waves generated by newborn protons from exospheric hydrogen are observed under quasi- (anti)parallel conditions of the IMF and the solar wind velocity, as is expected from theoretical models. The present study near solar maximum finds significantly more waves than a previous study for solar minimum, with an asymmetry in the wave occurrence, i.e., mainly under antiparallel conditions. The plasma data from the Analyzer of Space Plasmas and Energetic Atoms instrument aboard Venus Express enable analysis of the background solar wind conditions. The prevalence of waves for IMF in direction toward the Sun is related to the stronger southward tilt of the heliospheric current sheet for the rising phase of Solar Cycle 24, i.e., the "bashful ballerina" is responsible for asymmetric background solar wind conditions. The increase of the number of wave occurrences may be explained by a significant increase in the relative density of planetary protons with respect to the solar wind background. An exceptionally low solar wind proton density is observed during the rising phase of Solar Cycle 24. At the same time, higher EUV increases the ionization in the Venus exosphere, resulting in higher supply of energy from a higher number of newborn protons to the wave. We conclude that in addition to quasi- (anti)parallel conditions of the IMF and the solar wind velocity direction, the higher relative density of Venus exospheric protons with respect to the background solar wind proton density is the key parameter for the higher number of observable proton cyclotron waves near solar maximum.

Numerical simulation of Ganymede's ionosphere

NASA Astrophysics Data System (ADS)

Carnielli, Gianluca; Galand, Marina; Leblanc, François; Leclercq, Ludivine; Modolo, Ronan

2017-04-01

Ganymede is one of the four Galilean moons that orbit around Jupiter and the key moon targeted by the JUpiter and ICy moons Explorer (JUICE) mission. Other than being the largest moon in the solar system, it is also the only one known to generate internally a magnetic field which is strong enough to overcome the background jovian field; thus, the moon carves out its own magnetosphere inside that of Jupiter. In addition, at Ganymede's orbit the jovian plasma is sub-Alfvénic and subsonic. The interaction of Ganymede's magnetosphere with its surroundings therefore differs from that of planetary magnetospheres resulting from the interaction with the super-Alfvénic and supersonic solar wind. All this makes Ganymede a peculiar celestial body to study. One of the main goals of the JUICE mission is to characterize Ganymede's exosphere, ionosphere, and magnetosphere as well as its interaction with the jovian surrounding in great details. Ahead of the arrival of JUICE at Jupiter, models have been developed to predict Ganymede's environment. Observational constraints are primarily given from Galileo and from Earth-based telescopes. They remain limited, especially in terms of the ionospheric number density and temperature. To address the currently poorly constrained ionospheric environment, we have developed a test particle model of Ganymede's plasma environment. The model is driven by the densities of neutral species from the exospheric model of Leblanc et al. (Icarus, 2016) and the electromagnetic field taken from the hybrid model of Leclercq et al. (PSS, 2016). The simulation follows the motion of millions of test particles in the environment of the moon and allows to generate maps of ion densities, bulk velocities, and temperatures. We will present simulation outcomes for different ions, including H+, O+, and O2+. We will also discuss how the results from the simulations are relevant to MHD and exospheric models and in interpreting plasma and particle data obtained by Galileo during its close flybys of Ganymede.

Simulation Study of Solar Wind Interaction with Mercury's Magnetosphere

NASA Astrophysics Data System (ADS)

Richer, E.; Modolo, R.; Chanteur, G. M.; Hess, S.; Mancini, M.; Leblanc, F.

2011-12-01

The three flybys of Mariner 10, the numerous terrestrial observations of Mercury's exosphere and the recent flybys of MESSENGER [1] have brought important information about the Hermean environment. Mercury's intrinsic magnetic field is principally dipolar and its interaction with the Solar Wind (SW) creates a small and very dynamic magnetosphere. Mercury's exosphere is a highly variable [2] and complex neutral environment made of several species : H, He, O, Na, K, Ca, and Mg have already been detected [3,4]. The small number of in situ observations and the fact that the Hermean magnetospheric activity is not observable from Earth make simulation studies of the Hermean environment a useful tool to understand the global interaction of the SW with Mercury. This study presents simulation results from a 3-dimensional parallel multi-species hybrid model of Mercury's magnetosphere interaction with the SW. The SW in this model is representative of conditions at Mercury's aphelion (0.47AU) and is composed of 95% protons and 5% alpha particles. The simulated IMF is oriented accordingly observations during the first flyby of MESSENGER on January 2008 with a cone angle of ~45°. A neutral corona of atomic hydrogen is included in this model and is partly ionized by solar photons, electron impacts and charge exchange between SW ions and neutral H. Two electron fluids with different temperature are implemented to mimic the SW and ionospheric plasma. This model is an adapted version of the 3D parallel model for the Martian environment. Planetary and SW plasmas are treated separately and the dynamic of each ion species can be investigated separately. Simulations have been performed on a grid of 190×350×350 cells with a spatial resolution of Δx~120km. Acknowledgements The authors are indebted to CNES (French space agency) for the funding of their modeling activity through its program Sun - Heliosphere - Magnetosphere and to ANR (French national agency for research) for supporting the HELIOSARES project. References [1] Anderson, B. J., Acuna, M. H., Korth, H., Purucker, M. E., Johnson, C. L., Slavin, J. A., Solomon, S. C. and McNutt, R. L.: The Structure of Mercury's Magnetic Field from MESSENGER's First Flyby, Science, Vol. 321, pp. 82-, 2008 [2] Leblanc, F., Doressoundiram, A., Schneider, N., Mangano, V., López Ariste, A., Lemen, C., Gelly, B., Barbieri, C., remonese, G. : High latitude peaks in Mercury's sodium exosphere: Spectral signature using THEMIS solar telescope, Geophysical Research Letters, Vol. 35, L18204, 2008 [3] Leblanc, F. and Doressoundiram, A. : Mercury exosphere. II. The sodium/potassium ratio, Icarus, Vol. 211, pp. 10-20, 2011 [4] Potter, A. and Morgan, T. : Discovery of sodium in the atmosphere of Mercury, Science, Vol. 229, pp. 651-653, 1985

EXTREME INTENSITY INCREASES OF HIGH-ENERGY PARTICLE RADIATION IN THE EXOSPHERE AS OBSERVED BY SPUTNIK III

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knuth, R.

1962-09-01

Two channels in the telemetered data from Sputnik III investigated the intensity of high-energy photons over 35 kilo-electron-volt. The data from the period between May 15 and Aug. 16, 1958 (corresponding to flight altitudes between 220 and 950 kilometers) were analyzed. The extreme intensity increases observed were illustrated and are discussed. (OTS)

Evidence for Neutrals-Foreshock Electrons Impact at Mars

NASA Astrophysics Data System (ADS)

Mazelle, C. X.; Meziane, K.; Mitchell, D. L.; Garnier, P.; Espley, J. R.; Hamza, A. M.; Halekas, J.; Jakosky, B. M.

2018-05-01

Backstreaming electrons emanating from the bow shock of Mars reported from the Mars Atmosphere and Volatile EvolutioN/Solar Wind Electron Analyzer observations show a flux fall off with the distance from the shock. This feature is not observed at the terrestrial foreshock. The flux decay is observed only for electron energy E ≥ 29 eV. A reported recent study indicates that Mars foreshock electrons are produced at the shock in a mirror reflection of a portion of the solar wind electrons. In this context, and given that the electrons are sufficiently energetic to not be affected by the interplanetary magnetic field fluctuations, the observed flux decrease appears problematic. We investigate the possibility that the flux fall off with distance results from the impact of backstreaming electrons with Mars exospheric neutral hydrogen. We demonstrate that the flux fall off is consistent with the electron-atomic hydrogen impact cross section for a large range of energy. A better agreement is obtained for energy where the impact cross section is the highest. One important consequence is that foreshock electrons can play an important role in the production of pickup ions at Mars far exosphere.

Variation of Lunar Sodium During Passage of the Moon through the Earth's Magnetotail

NASA Technical Reports Server (NTRS)

Potter, Andrew E.; Killen, Rosemary M.; Morgan, Thomas H.

2000-01-01

We measured sodium emission above the lunar equator over a range of lunar altitudes from 100 to 4000 km. The measurements were repeated approximately every 24 hours from June 7 to 16, 1998, covering the period during which the Moon passed through the Earth's magnetotail. Sodium temperatures derived from the altitude dependence of emission intensity ranged from 1200 to 2900 K. This result supports the view that photodesorption is a primary source of sodium in the exosphere since the most probable temperature of sodium form this source is in this range. Passage of the Moon through the Earth's magnetotail (where solar wind is essentially absent) affected the sodium density, such that it was higher before the Moon entered the Earth's magnetotail than after the Moon left it. This suggests that the solar wind plays a role in production of lunar sodium. We propose that its function is to mobilize sodium and bring it to the surface, where photodesorption can eject it into the exosphere. A two-step process such as this could help to explain the latitude dependence of sodium density, which varies as the second or higher power of cosine latitude.

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE)

NASA Technical Reports Server (NTRS)

Elphic, Richard; Delory, Gregory; Colaprete, Anthony; Horanyi, Mihaly; Mahaffy, Paul; Hine, Butler; McClard, Steven; Grayzeck, Edwin; Boroson, Don

2011-01-01

Nearly 40 years have passed since the last Apollo missions investigated the mysteries of the lunar atmosphere and the question of levitated lunar dust. The most important questions remain: what is the composition, structure and variability of the tenuous lunar exosphere? What are its origins, transport mechanisms, and loss processes? Is lofted lunar dust the cause of the horizon glow observed by the Surveyor missions and Apollo astronauts? How does such levitated dust arise and move, what is its density, and what is its ultimate fate? The US National Academy of Sciences/National Research Council decadal surveys and the recent "Scientific Context for Exploration of the Moon" (SCEM) reports have identified studies of the pristine state of the lunar atmosphere and dust environment as among the leading priorities for future lunar science missions. These measurements have become particularly important since recent observations by the Lunar Crater Observation and Sensing Satellite (LCROSS) mission point to significant amounts of water and other volatiles sequestered within polar lunar cold traps. Moreover Chandrayaan/M3, EPOXI and Cassini/VIMS have identified molecular water and hydroxyl on lunar surface regolith grains. Variability in concentration suggests these species are likely to be present in the exosphere, and thus constitute a source for the cold traps. NASA s Lunar Atmosphere and Dust Environment Explorer (LADEE) is currently under development to address these goals. LADEE will determine the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. LADEE will also determine whether dust is present in the lunar exosphere, and reveal its sources and variability. LADEE s results are relevant to surface boundary exospheres and dust processes throughout the solar system, will address questions regarding the origin and evolution of lunar volatiles, and will have implications for future exploration activities. LADEE will be the first mission based on the Ames Common Bus design. LADEE employs a high heritage instrument payload: a Neutral Mass Spectrometer (NMS), an Ultraviolet/Visible Spectrometer (UVS), and the Lunar Dust Experiment (LDEX). It will also carry a space terminal as part of the Lunar Laser Communication Demonstration (LLCD), which is a technology demonstration. LLCD will also supply a ground terminal. LLCD is funded by the Space Operations Mission Directorate (SOMD), managed by GSFC, and built by MIT Lincoln Lab. NMS was directed to the Goddard Space Flight Center (GSFC) and UVS to Ames Research Center (ARC). LDEX was selected through the Stand Alone Missions of Opportunity Notice (SALMON) Acquisition Process, and is provided by the University of Colorado at Boulder. The LADEE NMS covers a m/z range of 2-150 and draws its design from mass spectrometers developed at GSFC for the MSL/SAM, Cassini Orbiter, CONTOUR, and MAVEN missions. The UVS instrument is a next-generation, high-reliability version of the LCROSS UV-Vis spectrometer, spanning 250-800 nm wavelength, with high (<1 nm) spectral resolution. UVS will also perform dust occultation measurements via a solar viewer optic. LDEX senses dust impacts in situ, at LADEE orbital altitudes of 50 km and below, with a particle size range of between 100 nm and 5 micron. Dust particle impacts on a large hemispherical target create electron and ion pairs. The latter are focused and accelerated in an electric field and detected at a microchannel plate. LADEE is an important part of NASA s portfolio of near-term lunar missions; launch is planned for May, 2013. The lunar atmosphere is the most accessible example of a surface boundary exosphere, and may reveal the sources and cycling of volatiles. Dynamic dust activity must be accounted for in the design and operation of lunar surface operations.

How Tiny Collisions Shape Mercury

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

If space rocks are unpleasant to encounter, space dust isnt much better. Mercurys cratered surface tells of billions of years of meteoroid impacts but its thin atmosphere is what reveals its collisional history with smaller impactors. Now new research is providing a better understanding of what were seeing.Micrometeoroids Ho!The inner solar system is bombarded by micrometeoroids, tiny particles of dust (on the scale of a tenth of a millimeter) emitted by asteroids and comets as they make their closest approach to the Sun. This dust doesnt penetrateEarths layers of atmosphere, but the innermost planet of our solar system, Mercury, doesnt have this convenient cushioning.Just as Mercury is affected by the impacts of large meteoroids, its also shaped by the many smaller-scale impacts it experiences. These tiny collisions are thought to vaporize atoms and molecules from the planets surface, which quickly dissociate. This process adds metals to Mercurys exosphere, the planets extremely tenuous atmosphere.Modeling PopulationsDistribution of the directions from which meteoroids originate before impacting Mercurys surface, as averaged over its entire orbit. Local time of 12 hr corresponds to the Sun-facing side. A significant asymmetry is seen between the dawn (6 hrs) and dusk (18 hrs) rates. [Pokorn et al. 2017]The metal distribution in the exosphere provides a way for us to measure the effect of micrometeoroid impacts on Mercury but this only works if we have accurate models of the process. A team of scientists led by Petr Pokorn (The Catholic University of America and NASA Goddard SFC) has now worked to improve our picture of micrometeoroid impact vaporization on Mercury.Pokorn and collaborators argue that two meteoroid populations Jupiter-family comets (short-period) and Halley-type comets (long-period) contribute the dust for the majority of micrometeoroid impacts on Mercury. The authors model the dynamics and evolution of these two populations, reproducing the distribution of directions from which micrometeoroids strike Mercury during its yearly orbit.Schematic of Mercury in its orbit around the Sun. The dawn side leads the orbital motion, while the dusk side trails it.Geometry of an OrbitMercurys orbit is unique in our solar system: it circles the Sun twice for every three rotations on its own axis so if you were on Mercury, youd see a single day pass over the span of two years. As with all prograde planets, the edge leading the Mercurys orbit marks the dawn terminator, while the edge trailing the planets orbital motion marks the dusk terminator.Pokorn and collaborators find a significant asymmetry in the impact vaporization that occurs on Mercurys dawn side versus its dusk side. This is due to impact geometry (since the dusk side is shielded from impacts in the direction of motion) and seasonal variation of the dust/meteoroid environment around the planet. The authors show that the source of impact vaporization shifts toward the nightside as Mercury approaches aphelion, and toward the dayside when the planet approaches the Sun.Importance of Long-Period CometsSeasonal variations of the relative vaporization rate from the authors model (black line) compared to measurements of Mercurys exospheric abundance of Ca. The contribution of long-period comets is shown by the blue line. [Pokorn et al. 2017]The dawn/dusk asymmetry and the seasonal variations predicted by the model are all nicely consistent NASAs MESSENGER spacecraft observations of the metal distribution in Mercurys exosphere.What makes Pokorn and collaborators model work so well? Their inclusion of the long-period, Halley-type comets is key: the high impact velocity of the micrometeoroids produced by this family play a significant role in shaping the impact vaporization rate of Mercurys surface.This work successfully demonstrates that we can use measurements of Mercurys exosphere as a unique tool to constrain the dust population in the inner solar system.CitationPetr Pokorn et al 2017 ApJL 842 L17. doi:10.3847/2041-8213/aa775d

LADEE Mission Update 2 (Beginning of Science Operations) Reporter Package

NASA Image and Video Library

2013-11-19

NASA's Lunar Atmosphere and Dust Environment Explorer, or LADEE, spacecraft has completed the check-out phase of its mission and has begun science operations around the moon. All the science instruments on-board have been examined by the LADEE team and have been cleared to begin collecting and analyzing the dust in the exosphere, or very thin atmosphere, that surrounds the moon.

LRO-LAMP Observations of Lunar Exospheric Helium

NASA Astrophysics Data System (ADS)

Grava, Cesare; Retherford, Kurt D.; Hurley, Dana M.; Feldman, Paul D.; Gladstone, Randy; Greathouse, Thomas K.; Cook, Jason C.; Stern, Alan; Pryor, Wayne R.; Halekas, Jasper S.; Kaufmann, David E.

2015-11-01

We present results from Lunar Reconnaissance Orbiter’s (LRO) UV spectrograph LAMP (Lyman-Alpha Mapping Project) campaign to study the lunar atmosphere. Two kinds of off-nadir maneuvers (lateral rolls and pitches towards and opposite the direction of motion of LRO) were performed to search for resonantly scattering species, increasing the illuminated line-of-sight (and hence the signal from atoms resonantly scattering the solar photons) compared to previously reported LAMP “twilight observations” [Cook & Stern, 2014]. Helium was the only element distinguishable on a daily basis, and we present latitudinal profiles of its line-of-sight column density in December 2013. We compared the helium line-of-sight column densities with solar wind alpha particle fluxes measured from the ARTEMIS (Acceleration, Reconnection, Turbulence, & Electrodynamics of Moon’s Interaction with the Sun) twin spacecraft. Our data show a correlation with the solar wind alpha particle flux, confirming that the solar wind is the main source of the lunar helium, but not with a 1:1 relationship. Assuming that the lunar soil is saturated with helium atoms, our results suggest that not all of the incident alpha particles are converted to thermalized helium, allowing for a non-negligible fraction (~50 %) to escape as suprathermal helium or simply backscattered from the lunar surface. We also support the finding by Benna et al. [2015] and Hurley et al. [2015], that a non-zero contribution from endogenic helium, coming from radioactive decay of 232Th and 238U within the mantle, is present, and is estimated to be (4.5±1.2) x 106 He atoms cm-2 s-1. Finally, we compare LAMP-derived helium surface density with the one recorded by the mass spectrometer LACE (Lunar Atmospheric Composition Experiment) deployed on the lunar surface during the Apollo 17 mission, finding good agreement between the two measurements. These LRO off-nadir maneuvers allow LAMP to provide unique coverage of local solar time and latitude of the lunar exospheric helium, allowing for a better understanding of the temporal and spatial structure of the lunar exosphere.

A seasonal feature in Mercury’s exosphere caused by meteoroids from comet Encke

NASA Astrophysics Data System (ADS)

Christou, Apostolos; Killen, Rosemary M.; Burger, Matthew H.

2015-11-01

The planet Mercury is enveloped in a tenuous atmosphere, the result of a delicate balance between poorly understood sources and sinks (Killen et al, 2007). Meteoroid impacts are a contributing source process (eg Wurz et al, 2010), but their importance compared to other production mechanisms is uncertain.Killen and Hahn (2015) found that seasonal variations in Mercury's calcium exosphere as observed by Mercury Atmospheric, and Surface Composition Spectrometer (MASCS) onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft (Burger et al, 2014) may be attributed to impact vaporization of surface material by the infall of interplanetary dust. However, an additional dust source was required to explain a Ca excess at a True Anomaly Angle (TAA) of 25±5 deg. Killen and Hahn suggested that dust from comet 2P/Encke, crossing Mercury's orbital plane at TAA=45 deg, may be the culprit.We have simulated numerically the stream of meteoroids ejected from Encke in order to identify those particles that impact Mercury at the present epoch and test the Killen and Hahn conjecture. We find that Encke particles evolving solely under the gravity of the major planets and the Sun encounter Mercury at TAA=50-60 deg, well after the peak of the Ca excess emission. This result is independent of the time of ejection. However, the addition of Poynting-Robertson (P-R) drag in our model couples the age and size of the meteoroids to the TAA at encounter, causing smaller, older particles to encounter Mercury progressively earlier in the Hermean year. In particular, mm-sized grains ejected between 10 and 20 kyr ago impact on the nightside hemisphere of Mercury at TAA = 350-30 deg, near the observed peak time of the exospheric feature.During this presentation, we will describe our model results and discuss their implications for the physical mechanism that injects impact-liberated Ca into sunlight as well as the origin and evolution of the Encke stream of meteoroids.Astronomical Research at Armagh Observatory is funded by the Northern Ireland Department of Culture, Arts and Leisure (DCAL).

Hybrid multi-grids simulations of Ganymede's magnetosphere : comparison with Galileo observations.

NASA Astrophysics Data System (ADS)

Leclercq, L.; Modolo, R.; Leblanc, F.

2015-12-01

The Jovian satellite Ganymede is the biggest moon of our solar system. One of the main motivation of our interest for this moon is its own intrinsic magnetic field, which has been discovered during the Galileo mission (Kivelson et al. 1996). The magnetic field of Ganymede directly interacts with the corotating jovian plasma, leading to the formation of a mini-magnetosphere which is embedded in the giant magnetosphere of Jupiter. This is the only known case of interaction between two planetary magnetospheres.In the frame of the European space mission JUICE (Jupiter Icy moon Exploration), we investigate this unique interaction with a 3D parallel multi-species hybrid model. This model is based on the CAM-CL algorithm (Matthews 1994) and has been used to study the ionized environments of Titan, Mars and Mercury. In the hybrid formalism, ions are kinetically treated whereas electrons are considered as a zero-inertial fluid to ensure the quasi-neutrality of the plasma. The temporal evolution of the electromagnetic fields is calculated solving Maxwell's equations. The jovian magnetospheric plasma is described as being composed of oxygen and proton ions. The magnetic field of Ganymede, which includes dipolar and induced components (Kivelson et al, 2002), is distorted by its interaction with the Jovian plasma and formed the Alfvén wings. The planetary plasma is described as being composed of O+, with a scale height equal to 125 km. The description of the exosphere is provided by the 3D multi-species collisional exospheric/atmospheric model of Leblanc et al, (2015) and Turc et al. (2014). The ionization of this neutral exosphere by charge exchanges, by electronic impacts, and by reaction with solar photons contributes to the production of planetary plasma. In this model, calculations are performed on a cartesian simulation grid which is refined (down to ~120 km of spatial resolution) at Ganymede, using a multi-grids approach (Leclercq et al., submitted, 2015). Results are compared with Galileo observations obtained during the G1, G2 and G8 flybys.

High-Resolution, Ground-Based Observations of the Lunar Exosphere during the month of May from 2013 to 2016.

NASA Astrophysics Data System (ADS)

Kuruppuaratchi, D. C. P.; Oliversen, R. J.; Mierkiewicz, E. J.; Robertson, S. D.; Gallant, M.; Rosborough, S.; Sarantos, M.; Derr, N. J.

2017-12-01

We apply high resolution spectroscopy to investigate the lunar exosphere by measuring sodium and potassium spectral line profiles to determine the variations in exospheric effective temperatures and velocities. Observations were made at the National Solar Observatory McMath-Pierce Telescope. We used a dual-etalon Fabry-Perot spectrometer with a resolving power of 180,000 (1.7 km/s) to measure the line widths and radial velocities of Doppler shifted sodium D2 (5889.9509 Å) and potassium D1 (7698.9646 Å) emission lines. The instrument's, 2 arcmin ( 224 km) and 3 arcmin ( 336km), Field of View (FOV) is positioned off the limb in equatorial and high latitude regions. Therefore, observations taken at 1st and 3rd quarter are taken at local noon while observations taken at full moon are at 6 am (dawn) and 6 pm (dusk) locally. We discuss data taken during the month of May/June from 2013 to 2016 for sodium and 2014 to 2016 for potassium. The deconvolved line widths indicate sodium temperatures at large phase angles (phase > 40o) are on the order of 1600 K while temperatures near full Moon are on the order of 4500 K. Line widths and temperatures are largest during full Moon; a trend that is not due to geometrical effects of looking `down' the tail. A slight asymmetry between waxing phase data and waning phase data is seen in all years. At limb relative intensity data for sodium, corrected for the Sun-Moon motion, show intensities that are higher after full Moon; a result that is consistent with enhanced PSD efficiency after the Moon resides in the plasma sheet. The potassium relative intensity decreases significantly as the waxing moon approaches full moon but like sodium its intensity increases after exiting the magnetotail. November results for each year will be compared with May results to establish any orbital trends. This work was partially supported by the NASA Planetary Astronomy programs, NNX11AE38G and NNX13AL30G.

Sputtering analysis of silicates by XY-TOF-SIMS: Astrophysical applications

NASA Astrophysics Data System (ADS)

Martinez, Rafael; Langlinay, Thomas; Ponciano, Cassia; da Silveira, Enio F.; Palumbo, Maria Elisabetta; Strazzulla, Giovanni; Brucato, John R.; Hijazi, Hussein; Boduch, Philippe; Cassimi, Amine; Domaracka, Alicja; Ropars, Frédéric; Rothard, Hermann

2015-08-01

Silicates are the dominant material of many objects in the Solar System, e.g. asteroids, the Moon, the planet Mercury and meteorites. Ion bombardment by cosmic rays and solar wind may alter the reflectance spectra of irradiated silicates by inducing physico-chemical changes known as “space weathering”. Furthermore, sputtered particles contribute to the composition of the exosphere of planets or moons. Mercury’s complex particle environment surrounding the planet is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge-exchange processes, and by ionized particles originated through photo-ionization and again by surface release processes such as ion induced sputtering.As a laboratory approach to understand the evolution of the silicate surfaces and the Na vapor (as well as, in lower concentration, K and Ca) discovered on the solar facing side of Mercury, we measured sputtering yields, velocity spectra and angular distributions of secondary ions from terrestrial silicate analogs. Experiments were performed using highly charged MeV/u and keV/u ions at GANIL in a new UHV set-up (under well controlled surface conditions) [1]. Other experiments were conducted at the Pontifical Catholic University of Rio de Janeiro (PUC-Rio) by using Cf fission fragments (~ 1 MeV/u). Nepheline, an aluminosilicate containing Na and K, evaporated on Si substrates (wafers) was used as model for silicates present in Solar System objects. Production yields, measured as a function of the projectile fluence, allow to study the possible surface stoichiometry changes during irradiation. In addition, from the energy distributions N(E) of sputtered particles it is possible to estimate the fraction of particles that can escape from the gravitational field of Mercury, and those that fall back to the surface and contribute to populate the atmosphere (exosphere) of the planet.The CAPES-COFECUB French-Brazilian exchange program, a CNPq postdoctoral grant, and the EU Cost Action “The Chemical Cosmos” supported this work.References[1] H.Hijazi, H. Rothard, et al. Nucl. Instrum. Meth. B269 (2011) 1003-1006

Lunar exospheric argon modeling

NASA Astrophysics Data System (ADS)

Grava, Cesare; Chaufray, J.-Y.; Retherford, K. D.; Gladstone, G. R.; Greathouse, T. K.; Hurley, D. M.; Hodges, R. R.; Bayless, A. J.; Cook, J. C.; Stern, S. A.

2015-07-01

Argon is one of the few known constituents of the lunar exosphere. The surface-based mass spectrometer Lunar Atmosphere Composition Experiment (LACE) deployed during the Apollo 17 mission first detected argon, and its study is among the subjects of the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) and Lunar Atmospheric and Dust Environment Explorer (LADEE) mission investigations. We performed a detailed Monte Carlo simulation of neutral atomic argon that we use to better understand its transport and storage across the lunar surface. We took into account several loss processes: ionization by solar photons, charge-exchange with solar protons, and cold trapping as computed by recent LRO/Lunar Orbiter Laser Altimeter (LOLA) mapping of Permanently Shaded Regions (PSRs). Recycling of photo-ions and solar radiation acceleration are also considered. We report that (i) contrary to previous assumptions, charge exchange is a loss process as efficient as photo-ionization, (ii) the PSR cold-trapping flux is comparable to the ionization flux (photo-ionization and charge-exchange), and (iii) solar radiation pressure has negligible effect on the argon density, as expected. We determine that the release of 2.6 × 1028 atoms on top of a pre-existing argon exosphere is required to explain the maximum amount of argon measured by LACE. The total number of atoms (1.0 × 1029) corresponds to ∼6700 kg of argon, 30% of which (∼1900 kg) may be stored in the cold traps after 120 days in the absence of space weathering processes. The required population is consistent with the amount of argon that can be released during a High Frequency Teleseismic (HFT) Event, i.e. a big, rare and localized moonquake, although we show that LACE could not distinguish between a localized and a global event. The density of argon measured at the time of LACE appears to have originated from no less than four such episodic events. Finally, we show that the extent of the PSRs that trap argon, 0.007% of the total lunar surface, is consistent with the presence of adsorbed water in such PSRs.

Non-thermal Processes in the Formation of Mercury's Tenuous Exosphere

NASA Astrophysics Data System (ADS)

Schaible, M. J.; Bennett, C.; Jones, B. M.; Orlando, T. M.

2017-12-01

Recent observations from the MESSENGER spacecraft orbiting Mercury have established that a quasi-trapped population of ions and electrons with 1-10 keV energy exists at a distance of about 1.5 RM (RM is Mercury's radius) around much of the planet. Recent observations from the Fast Imaging Plasma Spectrometer (FIPS), taken < 400 km from the surface, have shown a plasma cusp with energetic heavy ions (i.e. Na+ and O+ groups). The sources of these ions are not clear. A newly developed global kinetic transport model suggests that electron-stimulated desorption (ESD), and possibly light ion stimulated desorption (ISD), can directly yield ions that can be transported and dynamically accelerated to the plasma cusp regions observed by FIPS. Neutrals desorbed from the surface by ESD, ISD, photon-stimulated desorption (PSD) and meteorite impact may also be photoionized and transported/injected into the cusp region. Though the relative importance of these mechanisms in the formation of Mercury's tenuous atmosphere and the subsequent effects on the exosphere/magnetosphere dynamics are not known, it is likely that all of these contribute significantly. The goals of this work are to measure desorption cross-sections and ejection velocities for Na+, O+, and water group ions under relevant electron and ion bombardment energies. This program utilizes state-of-the art surface science capabilities to probe the role of ESD and ISD as a source of ions and neutrals present in the exosphere of Mercury. The experimental chamber is equipped with a dosing system, a cryogenic cooled temperature controlled sample holder, as well as pulsed ion and electron sources. The ESD and ISD ion yields and velocity measurements are obtained directly by sampling with a time-of-flight mass spectrometer. The measured ESD ion yields from adsorbate covered Mercury surface analogs such as the sulfur bearing minerals MgS, Na2S and K2S are low. Additionally, ISD experiments using incident protons also yielded low ion signals. These results implicate PSD and neutral desorption as dominant processes. The information obtained from these experiments can be directly incorporated into model simulations for comparison with data recently obtained by the FIPS instrument.

Observation of Signatures of Meteoroidal Water in the Lunar Exosphere by the LADEE NMS Instrument

NASA Astrophysics Data System (ADS)

Benna, M.; Elphic, R. C.; Hurley, D.; Stubbs, T. J.; Mahaffy, P. R.

2017-12-01

During its seven months in orbit, the Neutral Mass Spectrometer (NMS) of the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission measured the composition and variability of the tenuous lunar atmosphere. These measurements led to the detection of signatures of water group neutrals (H2O and/or OH) in the exosphere of the Moon. The signature of water has been measured as sporadic, short-lived signal increases above instrument background levels. The NMS data show that the occurrence rate of the high signal water "spikes" is correlated with periods of major annual meteoroid streams. Moreover, the daily water detection rate is in agreement with the expected evolution of the incoming meteoroidal impact flux at the Moon. Monte Carlo modeling of the evolution of vaporized water indicates that the signatures detected by the NMS instrument are commensurate in size and distribution of the energetic fraction of the vapors released by impacts that occurred near the location of the spacecraft. These measurements provide the first direct constraints on the contribution of meteoroid-delivered water to the sequestered ice in the permanently shadow regions of the lunar poles. They also provide a new technique for real-time observations of meteoroid impacts on airless bodies of the solar system through the detection of their associated volatile signatures.

Thermospheric wind effects on the global distribution of helium in the earth's upper atmosphere. Ph.D. Thesis - Michigan Univ., Ann Arbor

NASA Technical Reports Server (NTRS)

Reber, C. A.

1973-01-01

The momentum and continuity equations for a minor gas are combined with the momentum equation for the major constituents to obtain the time dependent continuity equation for the minor species reflecting a wind field in the background gas. This equation is used to study the distributions of helium and argon at times of low, medium, and high solar activity for a variety of latitudinal-seasonal wind cells. For helium, the exospheric return flow at the higher thermospheric temperatures dominates the distribution to the extent that much larger latitudinal gradients can be maintained during periods of low solar activity than during periods of high activity. By comparison to the exospheric flow, the smoothing effect of horizontal diffusion is almost negligible. The latitudinal variation of helium observed by satellite mass spectrometers can be reproduced by the effect of a wind system of air rising in the summer hemisphere, flowing across the equator with speeds on the order of 100 to 200 m/sec, and descending in the winter hemisphere. Argon, being heavier than the mean mass in the lower thermosphere, reacts oppositely to helium in that it is enhanced in the summer hemisphere and depleted in the winter.

A Systematic Search for Solar Wind Charge Exchange Emission from the Earth's Exosphere with Suzaku

NASA Astrophysics Data System (ADS)

Ishi, D.; Ishikawa, K.; Ezoe, Y.; Ohashi, T.; Miyoshi, Y.; Terada, N.

2017-10-01

We report on a systematic search of all the Suzaku archival data covering from 2005 August to 2015 May for geocoronal Solar Wind Charge eXchange (SWCX). In the vicinity of Earth, solar wind ions strip an electron from Earth's exospheric neutrals, emitting X-ray photons (e.g., Snowden et al. 1997). The X-ray flux of this geocoronal SWCX can change depending on solar wind condition and line of sight direction. Although it is an immediate background for all the X-ray astronomy observations, the X-ray flux prediction and the dependence on the observational conditions are not clear. Using the X-ray Imaging Spectrometer onboard Suzaku which has one of the highest sensitivities to the geocoronal SWCX, we searched the data for time variation of soft X-ray background. We then checked the solar wind proton flux taken with the WIND satellite and compared it with X-ray light curve. We also analyzed X-ray spectra and fitted them with a charge exchange emission line model constructed by Bodewits et al. (2007). Among 3055 data sets, 90 data showed SWCX features. The event rate seems to correlate with solar activity, while the distribution of SWCX events plotted in the solar magnetic coordinate system was relatively uniform.

Venus climate stability and volcanic resurfacing rates

NASA Technical Reports Server (NTRS)

Bullock, M. A.; Grinspoon, D. H.; Pollack, J. B.

1994-01-01

The climate of Venus is to a large degree controlled by the radiative properties of its massive atmosphere. In addition, outgassing due to volcanic activity, exospheric escape processes, and surface/atmosphere interactions may all be important in moderating the abundances of atmospheric CO2 and other volatiles. We have developed an evolutionary climate model for Venus using a systems approach that emphasizes feedbacks between elements in the climate system. Modules for atmospheric radiative transfer, surface/atmosphere interactions, tropospheric chemistry, and exospheric escape processes have so far been developed. Climate feedback loops result from interconnections between modules, in the form of the environmental parameters pressure, temperature, and atmospheric mixing ratios. The radiative transfer module has been implemented by using Rosseland mean opacities in a one dimensional grey radiative-convective model. The model has been solved for the static (time independent) case to determine climate equilibrium points. The dynamics of the model have also been explored by employing reaction/diffusion kinetics for possible surface atmosphere heterogeneous reactions over geologic timescales. It was found that under current conditions, the model predicts that the climate of Venus is at or near an unstable equilibrium point. The effects of constant rate volcanism and corresponding exsolution of volatiles on the stability of the climate model were also explored.

"Hot" Sodium on Mercury

NASA Astrophysics Data System (ADS)

Potter, A. E.; Morgan, T. H.

1997-07-01

In the course of mapping the sodium emission from Mercury, we found that the sodium exosphere appears to extend to considerable altitudes above the planet (Potter and Morgan, 1997). This suggests that some of the sodium is at a high temperature, but blurring of the data by atmospheric seeing makes it difficult to estimate a temperature from the altitude dependence of the emission. Another way to estimate temperature is to measure the broadening of the emission line caused by thermal motions. We attempted this approach earlier (Potter and Morgan, 1987), but the signal-to-noise in the spectrum was low, and the result was somewhat questionable. We have repeated the measurement,using a modern CCD detector, and obtained a spectrum with excellent signal-to- noise at a spectral resolution of about 600,000. The resulting line profile clearly shows a temperature in excess of a thousand degrees. We are initiating detailed analysis of the line profile, and expect that it will provide new insights into the processes that produce sodium in the exosphere of Mercury. Potter, A.E. and T.H. Morgan, 1987, Variation of sodium on Mercury with solar radiation pressure. Icarus 71, 472-477 Potter, A.E. and T.H. Morgan, 1997, Evidence for suprathermal sodium on Mercury. Presented 31st COSPAR meeting, July 14-21, 1996. To be published, Advances in Space Research.

A new model of the lunar ejecta cloud

NASA Astrophysics Data System (ADS)

Christou, A. A.

2014-04-01

Every airless body in the solar system is surrounded by a cloud of ejecta produced by the impact of interplanetary meteoroids on its surface [1]. Such "dust exospheres" have been observed around the Galilean satellites of Jupiter [2, 3]. The prospect of long-term robotic and human operations on the Moon by the US and other countries has rekindled interest on the subject [4]. This interest has culminated with the recent investigation of the Moon's dust exosphere by the LADEE spacecraft [5]. Here a model is presented of a ballistic, collisionless, steady state population of ejecta launched vertically at randomly distributed times and velocities. Assuming a uniform distribution of launch times I derive closed form solutions for the probability density functions (pdfs) of the height distribution of particles and the distribution of their speeds in a rest frame both at the surface and at altitude. The treatment is then extended to particle motion with respect to a moving platform such as an orbiting spacecraft. These expressions are compared with numerical simulations under lunar surface gravity where the underlying ejection speed distribution is (a) uniform (b) a power law. I discuss the predictions of the model, its limitations, and how it can be validated against near-surface and orbital measurements.

A new setup for experimental investigations of solar wind sputtering

NASA Astrophysics Data System (ADS)

Szabo, Paul S.; Berger, Bernhard M.; Chiba, Rimpei; Stadlmayr, Reinhard; Aumayr, Friedrich

2017-04-01

The surfaces of Mercury and Moon are not shielded by a thick atmosphere and therefore they are exposed to bombardment by charged particles, ultraviolet photons and micrometeorites. These influences lead to an alteration and erosion of the surface, and the emitted atoms and molecules form a thin atmosphere, an exosphere, around these celestial bodies [1]. The composition of these exospheres is connected to the surface composition and has been subject to flyby measurements by satellites. Model calculations which include the erosion mechanisms can be used as a method of comparison for such exosphere measurements and allow conclusions about the surface composition. Surface sputtering induced by solar wind ions hereby represents a major contribution to the erosion of the surfaces of Mercury and Moon [1]. However, the experimental database for sputtering of respective analogue materials by solar wind ions, which would be necessary for exact modelling of the space weathering process, is still in its early stages. Sputtering experiments have been performed at TU Wien during the past years using a quartz crystal microbalance (QCM) technique [2]. Target material is deposited on the quartz surface as a thin layer and the quartz's resonance frequency is measured under ion bombardment. The sputter yield can then be calculated from the frequency change and the ion current [2]. In order to remove the restrictions of a thin layer QCM target and simplify experiments with composite targets, a new QCM catcher setup was developed. In the new design, the QCM is placed beside the target holder and acts as a catcher for material that is sputtered from the target surface. By comparing the catcher signal to reference measurements and SDTrimSP simulations [3], the target sputter yield can be determined. In order to test the setup, we have performed experiments with a Au-coated QCM target under 2 keV Ar+ bombardment so that both the mass changes at the target and at the catcher could be obtained simultaneously. The results coincide very well with SDTrimSP predictions showing the feasibility of the new design [4]. Furthermore, Fe-coated QCM targets with different surface roughness were investigated in the new setup. The surface roughness represents a key factor for the solar wind induced erosion of planetary or lunar rocks. It has a strong influence on the absolute sputtering yield as well as on the spatial distribution of sputtered particles and was therefore investigated. As a next step, sputtering experiments with Mercury or Moon analogues will be conducted. Knowledge gained in the course of this research will enhance the understanding of surface sputtering by solar wind ions and used to improve theoretical models of the Mercury's and Moon's exosphere formation. References: [1] E. Kallio, et al., Planetary and Space Science, 56, 1506 (2008). [2] G. Hayderer, et al., Review of Scientific Instruments, 70, 3696 (1999). [3] A. Mutzke, R. Schneider, W. Eckstein, R. Dohmen, SDTrimSP: Version 5.00, IPP Report, 12/8, (2011). [4] B. M. Berger, P. S. Szabo, R. Stadlmayr, F. Aumayr, Nucl. Instrum. Meth. Phys. Res. B, doi: 10.1016/j.nimb.2016.11.039

SELMA: a mission to study lunar environment and surface interaction

NASA Astrophysics Data System (ADS)

Barabash, Stas; Futaana, Yoshifumi

2017-04-01

SELMA (Surface, Environment, and Lunar Magnetic Anomalies) proposed for the ESA M5 mission opportunity is a mission to study how the Moon environment and surface interact. SELMA addresses four overarching science questions: (1) What is the origin of water on the Moon? (2) How do the "volatile cycles" on the Moon work? (3) How do the lunar mini-magnetospheres work? (4) What is the influence of dust on the lunar environment and surface? SELMA uses a unique combination of remote sensing via UV, IR, and energetic neutral atoms and local measurements of plasma, fields, waves, exospheric gasses, and dust. It will also conduct an impact experiment to investigate volatile content in the soil of the permanently shadowed area of the Shakleton crater. SELMA carries an impact probe to sound the Reiner-Gamma mini-magnetosphere and its interaction with the lunar regolith from the SELMA orbit down to the surface. The SELMA science objectives include: - Establish the role of the solar wind and exosphere in the formation of the water bearing materials; - Determine the water content in the regolith of the permanently shadowed region and its isotope composition; - Establish variability, sources and sinks of the lunar exosphere and its relations to impact events; - Investigate a mini-magnetosphere interaction with the solar wind; - Investigate the long-term effects of mini-magnetospheres on the local surface; - Investigate how the impact events affect the lunar dust environments; - Investigate how the plasma effects result in lofting the lunar dust; SELMA is a flexible and short (15 months) mission including the following elements SELMA orbiter, SELMA Impact Probe for Magnetic Anomalies (SIP-MA), passive Impactor, and Relaying CubeSat (RCS). SELMA is placed on quasi-frozen polar orbit 30 km x 200 km with the pericenter over the South Pole. Approximately 9 months after the launch SELMA releases SIP-MA to sound the Reiner-Gamma magnetic anomaly with very high time resolution <0.5 s to investigate small-scale structure of the respective mini-magnetosphere. At the end of the mission the passive impactor impacts the permanently shadowed region of the Shakleton crater >10 sec before SELMA and SELMA orbiter flies through the resulted plume to perform high resolution mass spectroscopy of the released volatiles. The data are downlinked to ground and RCS. RCS stays on orbit for 2 more hours to downlink the complete data set. SELMA orbiter payload include: Remote sensing instruments - Infrared and visible spectrometer with spectral range 400 - 3600 nm; - Wide angle and transient phenomena camera to detect meteoroid impact (>100 g) - Moon UV imaging spectrometer with spectral range 115 - 315 nm - ENA telescope with an angular resolution < 10 ̊ In-situ instruments - Lunar ion spectrometer M/ΔM > 80 - Lunar scattered proton and negative ion experiment: - Lunar electron spectrometer - Moon magnetometer - Plasma wave instrument - Lunar dust detector: M>10-15 kg - Lunar exospheric mass spectrometer: M/ΔM > 1000 SIP-MA payload includes: - Waves and electric field instrument - Impact probe ions and electrons spectrometer - Impact probe magnetometer - Context camera Passive 10 kg copper spherical impactor

Maintaining the NA atmosphere of Mercury

NASA Astrophysics Data System (ADS)

Killen, R. M.; Morgan, T. H.

1993-02-01

The possible sources of the Na atmosphere of Mercury are calculatively studied. The likely structure, composition, and temperature of the planet's upper crust is examined along with the probable flux of Na from depth by grain boundary diffusion and by Knudsen flow. The creation of fresh regolith is considered along with mechanisms for supplying Na from the surface to the exosphere. The implications of the calculations for the probable abundances in the regolith are discussed.

Comparing the Atmospheres of Mercury and the Earth's Moon

NASA Technical Reports Server (NTRS)

Morgan, Thomas H.; Killen, Rosemary M.; Hurley, Dana M.

2012-01-01

The exospheres of Mercury and the Earth's Moon are fundamentally similar, but the differences that do exist between them can help us to develop a better understanding of the processes at work on the two bodies that produce and remove volatiles. The major differences are derived from (1) the different compositions of the two surfaces, (2) the different particle and field em'ironments above the surface of each body (particularly the presence of intrinsic magnetic field of Mercury), and (3) the larger flux of interplanetary dust incident at the orbit of Mercury. The first difference, surface composition, is the most intractable problem, but the most challenging part of that problem, the composition of the Hermean regolith, may be at least partially addressed as the MESSENGER mission completes work over the next year. Much progress has been made with respect to exploring the second difference above--spacecraft such as Helios, Ulysses, WIND, and ACE have measured the solar wind and its composition both in Earth orbit and at distances encompassing the orbit of Mercury. While our knowledge of the solar wind is incomplete, again it is far more detailed than a simple 1/R(sup 2) law would predict. Another problem is that of the flux of charged particles to the surfaces. While Mercury's magnetosphere is the subject of current study with MESSENGER, the influx of charged particles on the Moon has gone beyond a cos (psi) picture, where psi is the solar zenith angle. We know that the influx of ions at the Moon is affected by magnetic anomalies, by craters, and by surface charging. The third external difference is the differing flux of interplanetary dust incident on the two surfaces. In this talk we will consider: (1) the species that one can compare now for these two exospheres (Na, K, and He); (2) the species that you might be able to compare with future measurements (Ca and Mg); arid (3) how intensive ground-based observations of the easiest lunar species to observe from the ground, Na and K, might help us address source processes at work on both surfaces. We will discuss current and planned modeling efforts for both the lunar and Hermean exospheres, and some current and planned observations, both ground-based and space-based.

A Seasonal Feature in Mercury's Exosphere Caused by Meteoroids from Comet Encke

NASA Astrophysics Data System (ADS)

Burger, M. H.; Christou, A.; Killen, R. M.

2015-12-01

The planet Mercury is enveloped in a tenuous atmosphere, the result of a delicate balance between poorly understood sources and sinks (Killen et al, 2007). Meteoroid impacts are a contributing source process (eg Wurz et al, 2010), but their importance compared to other production mechanisms is uncertain. Killen and Hahn (2015) found that seasonal variations in Mercury's calcium exosphere as observed by the MASCS spectrometer onboard the MESSENGER spacecraft (Burger et al, 2014) may be due to impact vaporization of surface material by the infall of interplanetary dust. However, an additional dust source was required to explain a Ca excess at a True Anomaly Angle (TAA) of 25±5 deg. Killen and Hahn suggested that dust from comet 2P/Encke, crossing Mercury's orbital plane at TAA=45 deg, may be the culprit. We have simulated numerically the stream of meteoroids ejected from Encke to test the Killen and Hahn conjecture. We find that Encke particles evolving solely under the gravity of the major planets and the Sun encounter Mercury at TAA=50-60 deg, well after the peak of the Ca excess emission. However, the addition of Poynting-Robertson (P-R) drag in our model couples the age and size of the meteoroids to the TAA at encounter, causing smaller, older particles to encounter Mercury progressively earlier in the Hermean year. In particular, mm-sized grains ejected between 10 and 20 kyr ago impact on the nightside hemisphere of Mercury at TAA = 350-30 deg, near the observed peak time of the exospheric feature. During this presentation, we will describe our model results and discuss their implications for the physical mechanism that injects impact-liberated Ca into sunlight as well as the origin and evolution of the Encke stream of meteoroids. Astronomical research at the Armagh Observatory is funded by the Northern Ireland Department of Culture, Arts and Leisure (DCAL). RMK was supported by NASA Grant NNX07AR78G-S01 as a Participating Scientist on the NASA MESSENGER mission to Mercury and by STROFIO, a NASA Mission of Opportunity on the BepiColombo mission. AAC acknowledge the SFI/HEA Irish Centre for High-End Computing (ICHEC) as well as the Dublin Institute for Advanced Studies (DIAS) for the provision of computational facilities and support.

Solar Wind Interaction with the Martian Upper Atmosphere at Early Mars/Extreme Solar Conditions

NASA Astrophysics Data System (ADS)

Dong, C.; Bougher, S. W.; Ma, Y.; Toth, G.; Lee, Y.; Nagy, A. F.; Tenishev, V.; Pawlowski, D. J.; Combi, M. R.

2014-12-01

The investigation of ion escape fluxes from Mars, resulting from the solar wind interaction with its upper atmosphere/ionosphere, is important due to its potential impact on the long-term evolution of Mars atmosphere (e.g., loss of water) over its history. In the present work, we adopt the 3-D Mars cold neutral atmosphere profiles (0 ~ 300 km) from the newly developed and validated Mars Global Ionosphere Thermosphere Model (M-GITM) and the 3-D hot oxygen profiles (100 km ~ 5 RM) from the exosphere Monte Carlo model Adaptive Mesh Particle Simulator (AMPS). We apply these 3-D model output fields into the 3-D BATS-R-US Mars multi-fluid MHD (MF-MHD) model (100 km ~ 20 RM) that can simulate the interplay between Mars upper atmosphere and solar wind by considering the dynamics of individual ion species. The multi-fluid MHD model solves separate continuity, momentum and energy equations for each ion species (H+, O+, O2+, CO2+). The M-GITM model together with the AMPS exosphere model take into account the effects of solar cycle and seasonal variations on both cold and hot neutral atmospheres. This feature allows us to investigate the corresponding effects on the Mars upper atmosphere ion escape by using a one-way coupling approach, i.e., both the M-GITM and AMPS model output fields are used as the input for the multi-fluid MHD model and the M-GITM is used as input into the AMPS exosphere model. In this study, we present M-GITM, AMPS, and MF-MHD calculations (1-way coupled) for 2.5 GYA conditions and/or extreme solar conditions for present day Mars (high solar wind velocities, high solar wind dynamic pressure, and high solar irradiance conditions, etc.). Present day extreme conditions may result in MF-MHD outputs that are similar to 2.5 GYA cases. The crustal field orientations are also considered in this study. By comparing estimates of past ion escape rates with the current ion loss rates to be returned by the MAVEN spacecraft (2013-2016), we can better constrain the total ion loss to space over Mars history, and thus enhance the science returned from the MAVEN mission.

Volatile Loss from the Proto-Lunar Disk

NASA Astrophysics Data System (ADS)

Albarede, F.

2016-12-01

Exchange of volatile elements between the Moon and Earth depends on the intrinsic volatility of each element in a H-free tenuous gas, gravitational escape, and the mean free path of elements. The H2 pressure in the gas formed by the giant impact is far too low to allow hydrodynamic entrainment of other species. A condition for gravitational escape is, therefore, that thermal velocity exceeds escape velocity at the base of the exosphere where collisions between atoms cease. Away from the Earth, the vertical pull of the disk is only a small fraction of the radial pull of the Earth, which is strong enough to keep all the elements but H and He in terrestrial orbits, and the disk exosphere is thick. The proportion of gas orbiting above the exosphere is small, its temperature has been strongly reduced by adiabatic expansion, and therefore escape of lunar volatiles to Earth should be very limited. Whether elements have been lost by escape from the Moon to Earth nevertheless can be tested by comparing the relative abundances of elements with very similar chemistry and intrinsic volatility, but with very different atomic masses. Standard sequences of mineral condensation from the Solar Nebula and T50 are irrelevant to the proto-lunar disk. Condensation temperatures in the Solar Nebula are known to vary wildly with PH2, and the PH2 of the Solar Nebula is largely insensitive to the condensation of solid mineral phases, such as those forming the mantle and core of planets. Lunar accretion follows an opposite scenario, with an early and dramatic pressure drop due to metal and silicate condensation, which is the rationale behind the intrinsic volatility scale of Albarede et al. (2015). It is observed that, despite a broad mass range, the degree of depletion in the Moon relative to the Earth or CIs is similar for chemical kins, such as the groups of alkali elements (Li, Na, K, Rb, Cs), halogens (F, Cl, Br, I), or Zn and Cd. This observation argues against massive escape of volatile elements from the Moon to Earth and against massive lunar devolatilization. It is therefore suggested that, in agreement with the mineralogy of most lunar samples, volatile depletion of the Moon is inherited from the impactor rather than a result of the impact itself. Albarède, F., E. Albalat, and C.-T. A. Lee (2015), MAPS 50(4), 568-577.

Observations of the Minor Species Al, Fe and Ca(+) in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Bida, Thomas A.; Killen, Rosemary M.

2011-01-01

We report the first detections of Al and Fe, and strict upper limits for Ca(+) in the exosphere of Mercury, using the HIRES spectrometer at the Keck I telescope. We report observed 4-sigma tangent columns of 1.5x10(exp 7) Al atoms per square centimeter at an altitude of 1220 km (1.5 Mercury radii (R(sub M)) from planet center), and that for Fe of 1.6 x 10 per square centimeter at an altitude of 950 km (1.4 R(sub M)). The observed 3-sigma Ca(+) column was 3.9x10(exp 6) ions per square centimeter at an altitude of 1630 km (1.67 R(sub M). A simple model for zenith column abundances of the neutral species were 9.5 x 10(exp 7) Al per square centimeter, and 3.0 x 10(exp 8) Fe per square centimeter. The observations appear to be consistent with production of these species by impact vaporization with a large fraction of the ejecta in molecular form. The scale height of the Al gas is consistent with a kinetic temperature of 3000 - 9000 K while that of Fe is 10500 K. The apparent high temperature of the Fe gas would suggest that it may be produced by dissociation of molecules. A large traction of both Al and Fe appear to condense in a vapor cloud at low altitudes.

Positive and negative ion outflow at Rhea as observed by Cassini

NASA Astrophysics Data System (ADS)

Desai, Ravindra; Jones, Geraint; Regoli, Leonardo; Cowee, Misa; Coates, Andrew; Kataria, Dhiren

2017-04-01

Rhea is Saturn's largest icy moon and hosts an ethereal oxygen and carbon-dioxide atmosphere as was detected when Cassini observed positive and negative pickup ions outflowing from the moon and an extended neutral exosphere. These pickup ions can form current systems which, with the resulting jxB force, act to slow-down the incident magneto-plasma and cause field-line draping. As well as impacting the plasma interaction, the composition and density of picked up ions provide key diagnostics of the moon's sputter-induced atmosphere and surface. During the first Cassini-Rhea encounter (R1), the Cassini Plasma Spectrometer (CAPS) observed positively and negatively charged pickup ions before and after passing through the moon's plasma wake respectively, in agreement with their anticipated cycloidal trajectories. On the subsequent more distant wake encounter (R1.5) however, only positively charged pickup ions were observed, indicating high loss rates of the negative ions in Saturn's magnetosphere. Here, using an updated model of Cassini's Electron Spectrometer response function, we are able to estimate the outward flux of negatively charged pickup ions, the first time such a plasma population has been constrained. Using test-particle simulations we trace both the positive and negative particles back to Rhea's exobase to better understand their production and loss processes and the implications for Rhea's sputter-induced exosphere. We also look to examine whether the calculated ion densities could generate ion cyclotron wave activity.

Solar-Wind Protons and Heavy Ions Sputtering of Lunar Surface Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barghouty, N.; Meyer, Fred W; Harris, Peter R

2011-01-01

Lunar surface materials are exposed to {approx}1 keV/amu solar-wind protons and heavy ions on almost continuous basis. As the lunar surface consists of mostly oxides, these materials suffer, in principle, both kinetic and potential sputtering due to the actions of the solar-wind ions. Sputtering is an important mechanism affecting the composition of both the lunar surface and its tenuous exosphere. While the contribution of kinetic sputtering to the changes in the composition of the surface layer of these oxides is well understood and modeled, the role and implications of potential sputtering remain unclear. As new potential-sputtering data from multi-charged ionsmore » impacting lunar regolith simulants are becoming available from Oak Ridge National Laboratory's MIRF, we examine the role and possible implications of potential sputtering of Lunar KREEP soil. Using a non-equilibrium model we demonstrate that solar-wind heavy ions induced sputtering is critical in establishing the timescale of the overall solar-wind sputtering process of the lunar surface. We also show that potential sputtering leads to a more pronounced and significant differentiation between depleted and enriched surface elements. We briefly discuss the impacts of enhanced sputtering on the composition of the regolith and the exosphere, as well as of solar-wind sputtering as a source of hydrogen and water on the moon.« less

Solar Activity Forecasting for use in Orbit Prediction

NASA Technical Reports Server (NTRS)

Schatten, Kenneth

2001-01-01

Orbital prediction for satellites in low Earth orbit (LEO) or low planetary orbit depends strongly on exospheric densities. Solar activity forecasting is important in orbital prediction, as the solar UV and EUV inflate the upper atmospheric layers of the Earth and planets, forming the exosphere in which satellites orbit. Geomagnetic effects also relate to solar activity. Because of the complex and ephemeral nature of solar activity, with different cycles varying in strength by more than 100%, many different forecasting techniques have been utilized. The methods range from purely numerical techniques (essentially curve fitting) to numerous oddball schemes, as well as a small subset, called 'Precursor techniques.' The situation can be puzzling, owing to the numerous methodologies involved, somewhat akin to the numerous ether theories near the turn of the last century. Nevertheless, the Precursor techniques alone have a physical basis, namely dynamo theory, which provides a physical explanation for why this subset seems to work. I discuss this solar cycle's predictions, as well as the Sun's observed activity. I also discuss the SODA (Solar Dynamo Amplitude) index, which provides the user with the ability to track the Sun's hidden, interior dynamo magnetic fields. As a result, one may then update solar activity predictions continuously, by monitoring the solar magnetic fields as they change throughout the solar cycle. This paper ends by providing a glimpse into what the next solar cycle (#24) portends.

On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman- α monitoring. Detectability constraints for nearby M stars

NASA Astrophysics Data System (ADS)

Castro, Ana I. Gómez de; Beitia-Antero, Leire; Ustamujic, Sabina

2018-04-01

Observations of the Earth's exosphere have unveiled an extended envelope of hydrogen reaching further than 10 Earth radii composed of atoms orbiting around the Earth. This large envelope increases significantly the opacity of the Earth to Lyman α (Ly α) photons coming from the Sun, to the point of making feasible the detection of the Earth's transit signature from 1.35 pc if pointing with an 8 meter primary mirror space telescope through a clean line of sight ( N H < 1017 cm- 2), as we show. In this work, we evaluate the potential detectability of Earth analogs orbiting around nearby M-type stars by monitoring the variability of the Ly α flux variability. We show that, in spite of the interstellar, heliospheric and astrospheric absorption, the transit signature in M5 V type stars would be detectable with a dedicated Ly α flux monitor implemented in a 4-8 m class space telescope. Such monitoring programs would enable measuring the robustness of planetary atmospheres under heavy space weather conditions like those produced by M-type stars. A 2-m class telescope, such as the World Space Observatory, would suffice to detect an Earth-like planet orbiting around Proxima Centauri, if there was such a planet or nearby M5 type stars.

Properties of the mesosphere and thermosphere and comparison with CIRA 72

NASA Astrophysics Data System (ADS)

Champion, K. S. W.

Exospheric temperatures of several reference atmosphere are reviewed and a recommendation is made for the exospheric temperature of a proposed mean CIRA. One of the deficiencies of CIRA 72 and other present thermospheric models is the representation of density changes with geomagnetic activity. This deficiency is illustrated with samples of data. The data show the effects of geomagnetic activity, particle precipitation, a solar proton event, and gravity waves. An empirical model developed from the unique AFGL satellite density data bank using multiple linear regression is reviewed. The present model is for low to moderate solar flux and quiet geomagnetic conditions, but it is planned to extend the model to active conditions. Good progress has been made since CIRA 72 was specified in our knowledge and understanding of the properties of the lower thermosphere, although there are still some unresolved problems. The biggest progress has been made in the theory of tidal effects and of particulate energy deposition and of electrojet heating. On the other hand, it is still not possible to define adequately the systematic variations of the lower boundary conditions of thermospheric models. This is due to lack of knowledge of the systematic variations of the structure properties in the 100 to 120 km altitude region and inadequate information on the mesospheric turbulence profile and variations in the turbopause altitude.

Solar-Storm/Lunar Atmosphere Model (SSLAM): An Overview of the Effort and Description of the Driving Storm Environment

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Halekas, J. S.; Killen, R. M.; Delroy, G. T.; Gross, N.; Bleacher, V; Krauss-Varben, D.; Hurley, D; Zimmerman, M. I.

2012-01-01

On 29 April 1998, a coronal mass ejection (CME) was emitted from the Sun that had a significant impact on bodies located at 1 AU. The terrestrial magnetosphere did indeed become more electrically active during the storm passage but an obvious question is the effect of such a storm on an exposed rocky body like our Moon. The solar-storm/lunar atmosphere modeling effort (SSLAM) brings together surface interactions, exosphere, plasma, and surface charging models all run with a common driver - the solar storm and CME passage occurring from 1-4 May 1998. We present herein an expanded discussion on the solar driver during the 1-4 May 1998 period that included the passage of an intense coronal mass ejection (CME) that had> 10 times the solar wind density and had a compositional component of He++ that exceeded 20%. We also provide a very brief overview oflhe SSLAM system layout and overarching results. One primary result is that the CME driver plasma can greatly increase the exospheric content via sputtering, with total mass loss rates that approach 1 kg/s during the 2-day CME passage. By analogy, we suggest that CME-related sputtering increases might also be expected during a CME passage by a near-earth asteroid or at the Mars exobase, resulting in an enhanced loss of material.

Emission of hydrogen energetic neutral atoms from the Martian subsolar magnetosheath

NASA Astrophysics Data System (ADS)

Wang, X.-D.; Alho, M.; Jarvinen, R.; Kallio, E.; Barabash, S.; Futaana, Y.

2016-01-01

We have simulated the hydrogen energetic neutral atom (ENA) emissions from the subsolar magnetosheath of Mars using a hybrid model of the proton plasma charge exchanging with the Martian exosphere to study statistical features revealed from the observations of the Neutral Particle Detectors on Mars Express. The simulations reproduce well the observed enhancement of the hydrogen ENA emissions from the dayside magnetosheath in directions perpendicular to the Sun-Mars line. Our results show that the neutralized protons from the shocked solar wind are the dominant ENA population rather than those originating from the pickup planetary ions. The simulation also suggests that the observed stronger ENA emissions in the direction opposite to the solar wind convective electric field result from a stronger proton flux in the same direction at the lower magnetosheath; i.e., the proton fluxes in the magnetosheath are not cylindrically symmetric. We also confirm the observed increasing of the ENA fluxes with the solar wind dynamical pressure in the simulations. This feature is associated with a low altitude of the induced magnetic boundary when the dynamic pressure is high and the magnetosheath protons can reach to a denser exosphere, and thus, the charge exchange rate becomes higher. Overall, the analysis suggests that kinetic effects play an important and pronounced role in the morphology of the hydrogen ENA distribution and the plasma environment at Mars, in general.

Global Flux Balance in the Terrestrial H2O Cycle: Reconsidering the Post-Arc Subducted H2O Flux

NASA Astrophysics Data System (ADS)

Parai, R.; Mukhopadhyay, S.

2010-12-01

Quantitative estimates of H2O fluxes between the mantle and the exosphere (i.e., the atmosphere, oceans and crust) are critical to our understanding of the chemistry and dynamics of the solid Earth: the abundance and distribution of water in the mantle has dramatic impacts upon mantle melting, degassing history, structure and style of convection. Water is outgassed from the mantle is association with volcanism at mid-ocean ridges, ocean islands and convergent margins. H2O is removed from the exosphere at subduction zones, and some fraction of the subducted flux may be recycled past the arc into the Earth’s deep interior. Estimates of the post-arc subducted H2O flux are primarily based on the stability of hydrous phases at subduction zone pressures and temperatures (e.g. Schmidt and Poli, 1998; Rüpke et al., 2004; Hacker, 2008). However, the post-arc H2O flux remains poorly quantified, in part due to large uncertainties in the water content of the subducting slab. Here we evaluate estimated post-arc subducted fluxes in the context of mantle-exosphere water cycling, using a Monte Carlo simulation of the global H2O cycle. Literature estimates of primary magmatic H2O abundances and magmatic production rates at different tectonic settings are used with estimates of the total subducted H2O flux to establish the parameter space under consideration. Random sampling of the allowed parameter space affords insight into which input and output fluxes satisfy basic constraints on global flux balance, such as a limit on sea-level change over time. The net flux of H2O between mantle and exosphere is determined by the total mantle output flux (via ridges and ocean islands, with a small contribution from mantle-derived arc output) and the input flux subducted beyond the arc. Arc and back-arc output is derived mainly from the slab, and therefore cancels out a fraction of the trench intake in an H2O subcycle. Limits on sea-level change since the end of the Archaean place constraints on the magnitude of the post-arc subducted H2O flux that can be accommodated by the global water cycle. Estimates of the post-arc subducted flux are up to an order of magnitude larger than the estimated mantle output flux. If the marked imbalance in the estimated global water cycle is accurate, then it must be a recent phenomenon: if propagated back in time, modeled net inward fluxes would consume half a present-day ocean volume of water in as little as 500 Myr (corresponding to ~1200 meters of sea level change given present-day hypsometry). Such changes are inconsistent with the limited sea level changed inferred from the geologic record since the end of the Archaean. The literature post-arc flux estimates reflect water carried to depth via a layer of serpentinized lithospheric mantle within the slab; however, the extent to which oceanic lithosphere may be serpentinized remains poorly constrained. A smaller post-arc subducted H2O flux of 2.3 x108 Tg/Ma would perfectly balance our mean modeled total mantle output. Such a post-arc flux corresponds to ~2% serpentinization of a 10 km thick layer of lithospheric mantle (i.e., a mean water content of ~0.25 wt% H2O).

The investigation of O and N2 densities from the OSO-7 extreme UV data

NASA Technical Reports Server (NTRS)

1975-01-01

The results of solar radiation observations in the extreme ultra-violet spectrum from 200 A to 600 A made by the OSO-7 Satellite were studied. The results of the influence of attenuation by the atmosphere in the 250 to 500 km altitude range are presented. Using published molecular absorption cross-sections at 304 A and 256 A, the Jaccia atmospheric model is validated, and shows that a mean exospheric of 1050 K is appropriate for the sunset data.

The Venus flybys opportunity with BEPICOLOMBO

NASA Astrophysics Data System (ADS)

Mangano, Valeria; de la Fuente, Sara; Montagnon, Elsa; Benkhoff, Johannes; Zender, Joe; Orsini, Stefano

2017-04-01

BepiColombo is a dual spacecraft mission to Mercury to be launched in October 2018 and carried out jointly between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA). The Mercury Planetary Orbiter (MPO) payload comprises eleven experiments and instrument suites. It will focus on a global characterization of Mercury through the investigation of its interior, surface, exosphere and magnetosphere. In addition, it will test Einstein's theory of general relativity. The second spacecraft, the Mercury Magnetosphere Orbiter (MMO), will carry five experiments or instrument suites to study the environment around the planet including the planet's exosphere and magnetosphere, and their interaction processes with the solar wind. The composite spacecraft made of MPO, MMO, a transfer module (MTM) and a sunshield (MOSIF) will be launched on an escape trajectory that will bring it into heliocentric orbit on its way to Mercury. During the cruise of 7.2 years toward the inner part of the Solar System, BepiColombo will make 1 flyby to the Earth, 2 to Venus, and 6 to Mercury. Only part of its payload will be obstructed by the sunshield and the cruise spacecraft configuration, so that the two flybys to Venus will allow operations of many instruments, like: spectrometers at many wavelengths, accelerometer, radiometer, ion and electron detectors. A scientific working group has recently formed from the BepiColombo community to identify potentially interesting scientific cases and to analyse operation timelines. Preliminary outputs will be presented and discussed.

Science Enhancements by the MAVEN Participating Scientists

NASA Technical Reports Server (NTRS)

Grebowsky, J.; Fast, K.; Talaat, E.; Combi, M.; Crary, F.; England, S.; Ma, Y.; Mendillo, M.; Rosenblatt, P.; Seki, K.

2014-01-01

NASA implemented a Participating Scientist Program and released a solicitation for the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) proposals on February 14, 2013. After a NASA peer review panel evaluated the proposals, NASA Headquarters selected nine on June 12, 2013. The program's intent is to enhance the science return from the mission by including new investigations that broaden and/or complement the baseline investigations, while still addressing key science goals. The selections cover a broad range of science investigations. Included are: a patching of a 3D exosphere model to an improved global ionosphere-thermosphere model to study the generation of the exosphere and calculate the escape rates; the addition of a focused study of upper atmosphere variability and waves; improvement of a multi-fluid magnetohydrodynamic model that will be adjusted according to MAVEN observations to enhance the understanding of the solar-wind plasma interaction; a global study of the state of the ionosphere; folding MAVEN measurements into the Mars International Reference Ionosphere under development; quantification of atmospheric loss by pick-up using ion cyclotron wave observations; the reconciliation of remote and in situ observations of the upper atmosphere; the application of precise orbit determination of the spacecraft to measure upper atmospheric density and in conjunction with other Mars missions improve the static gravity field model of Mars; and an integrated ion/neutral study of ionospheric flows and resultant heavy ion escape. Descriptions of each of these investigations are given showing how each adds to and fits seamlessly into MAVEN mission science design.

Lunar Solar Origins Exploration (LunaSOX)

NASA Technical Reports Server (NTRS)

Cooper, John F.; King, Joseph H.; Papitashvili, Natasha; Lipatov, Alexander S.; Sittler, Edward C.; Hartle, Richard E.

2011-01-01

The Moon offers a unique vantage point from which to investigate the Sun and its interaction via the solar wind magnetic fields, plasma, and energetic particles with the geospace system including the Moon itself. The lunar surface and exosphere provide in part a record of solar coronal plasma material input and resultant space weathering over billions of years. The structure and dynamics of solar wind interactions with the Moon provide an accessible near-Earth laboratory environment for study of general solar wind interactions with the vast multitude of airless asteroidal bodies of the inner solar system. Spacecraft in lunar orbit have the often simultaneous opportunity, except when in the Earth's magnetosphere, to make in-situ compositional measurements of the solar wind plasma and to carry out remote observations from the Moon of the solar corona, potentially enabled by lunar limb occultation of the solar disk. The LunaSOX project at NASA Goddard Space Flight Center is addressing these heliophysical science objectives from and of the Moon with support from NASA's Lunar Advanced Science and Exploration Research (LASER) program: (1) specify history of solar wind parameters at and sunward of the Moon through enhanced access (http://lunasox.gsfc.nasa.gov/) to legacy and operational mission data products from the Apollo era to the present, (2) model field and plasma interactions with the lunar surface, exosphere, and wake, as constrained by the available data, through hybrid kinetic code simulations, and (3) advance mission concepts for heliophysics from and of the Moon.

High Resolution Integral Field Spectroscopy of Europa's Sodium Clouds: Evidence for a Component with Origins in Iogenic Plasma.

NASA Astrophysics Data System (ADS)

Schmidt, C.; Johnson, R. E.; Mendillo, M.; Baumgardner, J. L.; Moore, L.; O'Donoghue, J.; Leblanc, F.

2015-12-01

With the object of constraining Iogenic contributions and identifying drivers for variability, we report new observations of neutral sodium in Europa's exosphere. An R~20000 integral field spectrograph at McDonald Observatory is used to generate Doppler maps of sodium cloud structures with a resolution of 2.8 km/s/pixel. In the five nights of observations since 2011, measurements on UT 6.15-6.31 May 2015 uniquely feature fast (10s of km/s) neutral sodium clouds extending nearly 100 Europa radii, more distant than in any previous findings. During these measurements, the satellite geometry was favorable for the transfer of Na from Io to Europa, located at 1:55 to 4:00 and 3:38 to 4:39 Jovian local time, respectively. Eastward emission (away from Jupiter) extends 10-20 Europa radii retaining the moon's rest velocity, while westward emission blue-shifts with distance, and a broad range of velocities are measured, reaching at least 70 km/s at 80 Europa radii. These cloud features are distinct from Io's "banana" and "stream" features, the distant Jupiter-orbiting nebula, and from terrestrial OH and Na contaminant emissions. Io's production was quiescent during this observation, following an extremely active phase in February 2015. These results are consistent with previous findings that Europa's Na exosphere has peak emission between midnight and dawn Jovian local time and support the idea that sodium escape from Io can significantly enhance the emission intensity measured at Europa.

Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki

NASA Astrophysics Data System (ADS)

Koga, Ryoichi; Tsuchiya, Fuminori; Kagitani, Masato; Sakanoi, Takeshi; Yoneda, Mizuki; Yoshioka, Kazuo; Yoshikawa, Ichiro; Kimura, Tomoki; Murakami, Go; Yamazaki, Atsushi; Smith, H. Todd; Bagenal, Fran

2018-05-01

We report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014-2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm-3, which is spread 1.2 RJ in the north-south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

Hst Observations Of The Extended Hydrogen Corona Of Mars

NASA Astrophysics Data System (ADS)

Clarke, John T.; Bertaux, J.; Chaufray, J.; Gladstone, R.; Quemerais, E.; Wilson, J. K.

2009-09-01

HST ACS/SBC UV images of the extended H Ly alpha emission from the Martian hydrogen corona have been obtained over Oct/Nov 2007, with coincident measurements of the altitude profile of the Lyman alpha emission by the SPICAM instrument on Mars Express in orbit about Mars. Careful measurement of the geocoronal emission background permit the measurement of the martian emission to a low level (less than 1 kilo-Rayleigh) out to 4 mars radii from the planet. Similar angular distributions of the emission were seen on 3 days of observations, reflecting the radiative transfer in the optically thick atmosphere, while the overall level of emission was seen to steadily decrease in both data sets over 4 weeks time. The altitude distribution of the emission out to large distances is compared with the results of a radiative transfer model that includes an exospheric population of cold and hot H atoms. In general, the dominant population of H atoms close to the planet is consistent with the measured temperature of the upper atmosphere, while far from the planet one has the highest sensitivity to a superthermal component of the exospheric H. The results will be presented with discussion of the escape rate of H from the martian atmosphere, and how this varied over 4 weeks in Fall 2007. This has implications for the rate of escape of water from the martian atmosphere, and how this can vary with time. These observations were supported by STScI grant GO-11170-01 to Boston University.

A Revised Thermosphere for the Mars Global Reference Atmospheric Model (Mars-GRAM Version 3.4)

NASA Technical Reports Server (NTRS)

Justus, C. G.; Johnson, D. L.; James, B. F.

1996-01-01

This report describes the newly-revised model thermosphere for the Mars Global Reference Atmospheric Model (Mars-GRAM, Version 3.4). It also provides descriptions of other changes made to the program since publication of the programmer's guide for Mars-GRAM Version 3.34. The original Mars-GRAM model thermosphere was based on the global-mean model of Stewart. The revised thermosphere is based largely on parameterizations derived from output data from the three-dimensional Mars Thermospheric Global Circulation Model (MTGCM). The new thermospheric model includes revised dependence on the 10.7 cm solar flux for the global means of exospheric temperature, temperature of the base of the thermosphere, and scale height for the thermospheric temperature variations, as well as revised dependence on orbital position for global mean height of the base of the thermosphere. Other features of the new thermospheric model are: (1) realistic variations of temperature and density with latitude and time of day, (2) more realistic wind magnitudes, based on improved estimates of horizontal pressure gradients, and (3) allowance for user-input adjustments to the model values for mean exospheric temperature and for height and temperature at the base of the thermosphere. Other new features of Mars-GRAM 3.4 include: (1) allowance for user-input values of climatic adjustment factors for temperature profiles from the surface to 75 km, and (2) a revised method for computing the sub-solar longitude position in the 'ORBIT' subroutine.

Remote Sensing the Thermosphere's State Using Emissions From Carbon Dioxide and Nitric Oxide

NASA Astrophysics Data System (ADS)

Weimer, D. R.; Mlynczak, M. G.; Doornbos, E.

2017-12-01

Measurements of emissions from nitric oxide and carbon dioxide in the thermosphere have strong correlations with properties that are very useful to the determination of thermospheric densities. We have compared emissions measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite with neutral density measurements from the Challenging Mini-satellite Payload (CHAMP), the Gravity Recovery and Climate Experiment (GRACE), the Ocean Circulation Explorer (GOCE), and the three Swarm satellites, spanning a time period of over 15 years. It has been found that nitric oxide emissions match changes in the exospheric temperatures that have been derived from the densities through use of the Naval Reasearch Laboratory Mass Spectrometer, Incoherent Scatter Radar Extended Model (NRLMSISE-00) thermosphere model. Similarly, our results indicate that the carbon dioxide emissions have annual and semiannual oscillations that correlate with changes in the amount of oxygen in the thermosphere, also determined by use of the NRLMSISE-00 model. These annual and semi-annual variations are found to have irregular amplitudes and phases, which make them very difficult to accurately predict. Prediction of exospheric temperatures through the use of geomagnetic indices also tends to be inexact. Therefore, it would be possible and very useful to use measurements of the thermosphere's infrared emissions for real-time tracking of the thermosphere's state, so that more accurate calculations of the density may be obtained.

Redistribution of Lunar Polar Water to Mid-latitudes and its Role in Forming an OH veneer - Revisited

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Killen, R. M.; Hurley, D. M.; Hodges, R. R.; Halekas, J. S.; Delory, G. T.

2012-01-01

We suggest that energization processes like ion sputtering and impact vaporization can eject/release polar water molecules residing within lunar cold trapped regions with sufficient velocity to allow their redistribution to mid-latitudes. We consider the possibility that these polar-ejected molecules can be an additional (but not dominant) contribution to the water/OH veneer observed as a 3 micron absorption feature at mid-latitudes by Chandrayaan-I, Cassini, and EPOXI. Taking the conservative case that polar water is ejected only from the floor of polar craters with an 0.1 % icy regolith then overall source rates are near 10(exp 18) H20s/s. This outflow amounts to approx 10(exp -7) kg/s of water to be ejected from each pole and is a water source rate that is 10(exp .5 lower than the overall exospheric source rate for all species. Hence, the out-flowing polar water is a perturbation in the overall exosphere composition & dynamics. This polar water 'fountain' model may not fully account for the relatively high concentrations in the mid-latitude water veneer observed in the IR (approx 10-1000 ppm). However, it may account for some part of the veneer. We note that the polar water fountain source rates scale linearly with ice concentration, and larger mass fractions of polar crater water should provide correspondingly larger fractions of water emission out of the poles which then 'spills' on to mid-latitude surfaces.

Orbital Effects on Mercury's Escaping Sodium Exosphere

NASA Technical Reports Server (NTRS)

Schmidt, Carl A.; Wilson, Jody K.; Baumgardner, Jeffrey; Mendillo, Michael

2009-01-01

We present results from coronagraphic imaging of Mercury's sodium tail over a 7 deg field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R(sub m)) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R(sub m) during the January 2008 MESSENGER Fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury's heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury's escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 x 10(exp 23) atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury's sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury's magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury's sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.

Science Enhancements by the MAVEN Participating Scientists

NASA Astrophysics Data System (ADS)

Grebowsky, J.; Fast, K.; Talaat, E.; Combi, M.; Crary, F.; England, S.; Ma, Y.; Mendillo, M.; Rosenblatt, P.; Seki, K.; Stevens, M.; Withers, P.

2015-12-01

NASA implemented a Participating Scientist Program and released a solicitation for the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) proposals on February 14, 2013. After a NASA peer review panel evaluated the proposals, NASA Headquarters selected nine on June 12, 2013. The program's intent is to enhance the science return from the mission by including new investigations that broaden and/or complement the baseline investigations, while still addressing key science goals. The selections cover a broad range of science investigations. Included are: a patching of a 3D exosphere model to an improved global ionosphere-thermosphere model to study the generation of the exosphere and calculate the escape rates; the addition of a focused study of upper atmosphere variability and waves; improvement of a multi-fluid magnetohydrodynamic model that will be adjusted according to MAVEN observations to enhance the understanding of the solar-wind plasma interaction; a global study of the state of the ionosphere; folding MAVEN measurements into the Mars International Reference Ionosphere under development; quantification of atmospheric loss by pick-up using ion cyclotron wave observations; the reconciliation of remote and in situ observations of the upper atmosphere; the application of precise orbit determination of the spacecraft to measure upper atmospheric density and in conjunction with other Mars missions improve the static gravity field model of Mars; and an integrated ion/neutral study of ionospheric flows and resultant heavy ion escape. Descriptions of each of these investigations are given showing how each adds to and fits seamlessly into MAVEN mission science design.

Observations of the minor species Al and Fe in Mercury's exosphere

NASA Astrophysics Data System (ADS)

Bida, Thomas A.; Killen, Rosemary M.

2017-06-01

We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of resolved emission lines of these metals with Keck-1/HIRES. Al emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 3.1 ± 1.0 and 4.0 ± 1.5 × 107 Al atoms cm-2 at altitudes of 1185 and 1870 km (1.5 and 1.75 RM). The Al radiative intensity was seen to increase where the slit crossed the planetary penumbral shadow, and then decrease monotonically with altitude. Fe emission has been observed once, in 2009, indicating an extended source. We also present observed 3-σ Ca+ upper limits near Mercury's equatorial anti-solar limb, from which an abundance limit of 4.0 × 106 cm-2 at 1650 km altitude is derived for the Ca ion. A simple model for zenith column abundances of the neutral species yields 1.9-5.2 × 107 Al cm-2, and 8.2 × 108 Fe cm-2. The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 6100-8000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules.

Long-term variations of the upper atmosphere parameters on Rome ionosonde observations and their interpretation

NASA Astrophysics Data System (ADS)

Perrone, Loredana; Mikhailov, Andrey; Cesaroni, Claudio; Alfonsi, Lucilla; Santis, Angelo De; Pezzopane, Michael; Scotto, Carlo

2017-09-01

A recently proposed self-consistent approach to the analysis of thermospheric and ionospheric long-term trends has been applied to Rome ionosonde summer noontime observations for the (1957-2015) period. This approach includes: (i) a method to extract ionospheric parameter long-term variations; (ii) a method to retrieve from observed foF1 neutral composition (O, O2, N2), exospheric temperature, Tex and the total solar EUV flux with λ < 1050 Å; and (iii) a combined analysis of the ionospheric and thermospheric parameter long-term variations using the theory of ionospheric F-layer formation. Atomic oxygen, [O] and [O]/[N2] ratio control foF1 and foF2 while neutral temperature, Tex controls hmF2 long-term variations. Noontime foF2 and foF1 long-term variations demonstrate a negative linear trend estimated over the (1962-2010) period which is mainly due to atomic oxygen decrease after ˜1990. A linear trend in (δhmF2)11y estimated over the (1962-2010) period is very small and insignificant reflecting the absence of any significant trend in neutral temperature. The retrieved neutral gas density, ρ atomic oxygen, [O] and exospheric temperature, Tex long-term variations are controlled by solar and geomagnetic activity, i.e. they have a natural origin. The residual trends estimated over the period of ˜5 solar cycles (1957-2015) are very small (<0.5% per decade) and statistically insignificant.

Lunar Sodium and Potassium Exosphere in May 2014

NASA Astrophysics Data System (ADS)

Oliversen, R. J.; Kuruppuaratchi, D. C. P.; Mierkiewicz, E. J.; Derr, N. J.; Rosborough, S.; Gallant, M. A.; Roesler, F. L.

2015-12-01

We apply high resolution spectroscopy to investigate the lunar exosphere by measuring sodium and potassium spectral line profiles to determine the variations in exospheric effective temperatures and velocities. Observations were made at the National Solar Observatory McMath-Pierce Telescope during May 2014. Data were collected over several nights, centered on full moon (May 14) and covering a waxing phase angle of 67° to a waning phase angle of 75°. We used a dual-etalon Fabry-Perot spectrometer with a resolving power of 184,000 (1.63 km s-1) to measure the line widths and radial velocity shifts of the sodium D2 (5889.951 Å) and potassium D1 (7698.965 Å) emission lines. The field of view was 3 arcmin (~330 km) and positioned at several locations, each centered at 1.5 arcmin (~165 km) off the East and West sunlit limbs. The deconvolved line widths indicate significant differences between the sodium and potassium temperatures. The sodium line widths were mostly symmetric as a function of phase for both the waxing and waning phases. At phase angles > 40º (outside of the magnetotail) the full width half maximum (FWHM) line widths are 1.5 - 2.0 km s-1 or ~1500 K for FWHM = 1.75 km s-1. Inside the magnetotail (phase angle < 40º) and near full moon (phase angle ~6°), the FWHM increased to ~4 km s-1. The implied line width temperature is 8000 K, although some of the observed line width may be due to a dispersion in velocities from many contribution along the extended sodium tail. Unlike sodium, the potassium line widths are wider by 50% during the waxing phase compared to the waning phase at phases > 40º. The potassium temperatures pre-magnetotail passage are ~1000 K while the temperatures post-magnetotail passage are ~2000K. At phase angles < 40º, the potassium intensities decreased dramatically; on consecutive days, when the phase angle changed from 44º to 31º to 20º, the relative intensities dropped by 1.0:0.6:0.15. The potassium intensity in the East and West equatorial regions (latitude < 10º) were similar; however, the potassium intensity was brightest off the limb near Aristarchus (latitude ~24º), which was the crater we observed nearest the KREEP region. This work was partially supported by the NASA Planetary Astronomy programs, NNX11AE38G and NNX13AL30G.

Plasma IMS Composition Measurements for Europa, Ganymede, and the Jovian System

NASA Technical Reports Server (NTRS)

Sittler, E. C., Jr.; Cooper, J. F.; Hartle, R. E.; Paterson, W. R.; Christian, E. R.; Lipatov, A. S.; Mahaffy, P R.; Paschalidis, N.; Sarantos, M.; Coplan, M. A.;

Plasma IMS Composition Measurements for Europa, Ganymede, and the Jovian Systems

NASA Technical Reports Server (NTRS)

Sittler, E.; Cooper, J.; Hartle, R.; Paterson ,W.; Christian, E.; Mahaffy, P.; Paschalidis, N.; Lipatov, A.; Sarantos, M.; Coplan, M.;

Saturn Neutron Exosphere as Source for Inner and Innermost Radiation Belts

NASA Technical Reports Server (NTRS)

Cooper, John; Lipatov, Alexander; Sittler, Edward; Sturner, Steven

2011-01-01

Energetic proton and electron measurements by the ongoing Cassini orbiter mission are expanding our knowledge of the highest energy components of the Saturn magnetosphere in the inner radiation belt region after the initial discoveries of these belts by the Pioneer 11 and Voyager 2 missions. Saturn has a neutron exosphere that extends throughout the magnetosphere from the cosmic ray albedo neutron source at the planetary main rings and atmosphere. The neutrons emitted from these sources at energies respectively above 4 and 8 eV escape the Saturn system, while those at lower energies are gravitationally bound. The neutrons undergo beta decay in average times of about 1000 seconds to provide distributed sources of protons and electrons throughout Saturn's magnetosphere with highest injection rates close to the Saturn and ring sources. The competing radiation belt source for energetic electrons is rapid inward diffusion and acceleration of electrons from the middle magnetosphere and beyond. Minimal losses during diffusive transport across the moon orbits, e.g. of Mimas and Enceladus, and local time asymmetries in electron intensity, suggest that drift resonance effects preferentially boost the diffusion rates of electrons from both sources. Energy dependences of longitudinal gradient-curvature drift speeds relative to the icy moons are likely responsible for hemispheric differences (e.g., Mimas, Tethys) in composition and thermal properties as at least partly produced by radiolytic processes. A continuing mystery is the similar radial profiles of lower energy (<10 MeV) protons in the inner belt region. Either the source of these lower energy protons is also neutron decay, but perhaps alternatively from atmospheric albedo, or else all protons from diverse distributed sources are similarly affected by losses at the moon' orbits, e.g. because the proton diffusion rates are extremely low. Enceladus cryovolcanism, and radiolytic processing elsewhere on the icy moon and ring surfaces, are additional sources of protons via ionization and charge exchange from breakup of water molecules. But one must then account somehow for local acceleration to the observed keV-MeV energies, since moon sweeping and E-ring absorption would remove protons diffusing inward from the middle magnetosphere. Although the main rings block further inward diffusion from the inner radiation belts, the exospheric neutron-decay source, combined with much slower diffusion of protons relative to electrons, may produce an innermost radiation belt in the gap between the upper atmosphere and the D-ring. This innermost belt will first be explored in-situ during the final proximal orbits of the Cassini mission.

Monte Carlo simulation of nonadiabatic expansion in cometary atmospheres - Halley

NASA Astrophysics Data System (ADS)

Hodges, R. R.

1990-02-01

Monte Carlo methods developed for the characterization of velocity-dependent collision processes and ballistic transports in planetary exospheres form the basis of the present computer simulation of icy comet atmospheres, which iteratively undertakes the simultaneous determination of velocity distribution for five neutral species (water, together with suprathermal OH, H2, O, and H) in a flow regime varying from the hydrodynamic to the ballistic. Experimental data from the neutral mass spectrometer carried by Giotto for its March, 1986 encounter with Halley are compared with a model atmosphere.

Searching for Lunar Water: The Lunar Volatile Resources Analysis Package

NASA Technical Reports Server (NTRS)

Morse, A. D.; Barber, S. J.; Dewar, K. R.; Pillinger, J. M.; Sheridan, S.; Wright, I, P.; Gibson, E. K.; Merrifield, J. A.; Howe, C. J.; Waugh, L. J.;

Marshall Engineering Thermosphere Model, Version MET-2007

NASA Technical Reports Server (NTRS)

Suggs, R. J.; Suggs, R. M.

2017-01-01

The region of the Earth's atmosphere between about 90 and 500 km altitude is known as the thermosphere, while the region above about 500 km is known as the exosphere. For space vehicle operations, the neutral atmosphere in these regions is significant. Even at its low density, it produces torques and drags on vehicles and affects orbital lifetimes. The thermosphere density above 100 km altitude also modulates the flux of trapped radiation and orbital debris. Atomic oxygen at orbital altitudes is important because it can erode and chemically change exposed vehicle surfaces.

Regarding the Possible Generation of a Lunar Nightside Exo-Ionosphere

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Halekas, J. S.; Stubbs, T. J.; Delory, G. T.; Killen, R. M.; Hartle, R. E.; Collier, M. R.

2011-01-01

The non-condensing neutral helium exosphere is at its most concentrated levels on the cold lunar nightside. We show herein that these He atoms are susceptible to impact ionization from primary and secondary electrons flowing in the vicinity of the negatively-charged nightside lunar surface. The secondary electron beams are a relatively recent discovery and are found to be emitted from the nightside surface at energies consistent with the negative surface potential. The effect is to create an electron impact-created ionosphere in nightside regions. possibly especially potent within polar craters.

Kinetic and Potential Sputtering of Lunar Regolith: The Contribution of the Heavy Highly Charged (Minority) Solar Wind Ions

NASA Technical Reports Server (NTRS)

Meyer, F. W.; Barghouty, A. F.

2012-01-01

Solar wind sputtering of the lunar surface helps determine the composition of the lunar exosphere and contributes to surface weathering. To date, only the effects of the two dominant solar wind constituents, H+ and He+, have been considered. The heavier, less abundant solar wind constituents have much larger sputtering yields because they have greater mass (kinetic sputtering) and they are highly charged (potential sputtering) Their contribution to total sputtering can therefore be orders of magnitude larger than their relative abundances would suggest

Observations of the Minor Species Al and Fe in Mercury's Exosphere

NASA Technical Reports Server (NTRS)

Bida, Thomas A.; Killen, Rosemary M.

2016-01-01

We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of resolved emission lines of these metals with Keck-1/HIRES. Al emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 3.1 +/- 1.0 and 4.0 +/-1.5 x 10(exp 7) Al atoms cm(exp - 2) at altitudes of 1185 and 1870 km (1.5 and 1.75 R(sub M). The Al radiative intensity was seen to increase where the slit crossed the planetary penumbral shadow, and then decrease monotonically with altitude. Fe emission has been observed once, in 2009, indicating an extended source. We also present observed 3- Sigma Ca(+) upper limits near Mercury's equatorial anti-solar limb, from which an abundance limit of 4.0 x 10(exp 6) cm(exp -2) at 1650 km altitude is derived for the Ca ion. A simple model for zenith column abundances of the neutral species yields 1.9 -5.2 x 10(exp 7) Al cm(exp -2) , and 8.2 x 10(exp 8) Fe cm(exp -2) . The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 6100-8000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules.

ExoCube INMS with Neutral Hydrogen Mode

NASA Astrophysics Data System (ADS)

Jones, S.; Paschalidis, N.; Rodriguez, M.; Sittler, E. C., Jr.; Chornay, D. J.; Cameron, T.; Uribe, P.; Nanan, G.; Noto, J.; Waldrop, L.; Mierkiewicz, E. J.; Gardner, D.; Nossal, S. M.; Puig-Suari, J.; Bellardo, J.

2015-12-01

The ExoCube mission launched on Jan 31 2015 into a polar orbit to acquire global knowledge of in situ densities of neutral and ionized H, He, and O in the upper ionosphere and lower exosphere. The CubeSat platform is used in combination with incoherent scatter radar and optical ground stations distributed throughout the Americas. ExoCube seeks to obtain the first in situ measurement of neutral exospheric hydrogen and will measure in situ atomic oxygen for the first time in decades. The compact Ion and Neutral Mass Spectrometer (INMS) developed by GSFC uses the gated Time of Flight technique for in situ measurements of ions and neutrals (H, He, N, O, N2, O2) with M/dM of approximately 10. The compact sensor has a dual symmetric configuration with ion and neutral sensor heads. Neutral particles are ionized by electron impact using a thermionic emitter. In situ measurements of neutral hydrogen are notoriously difficult as historically the signal has been contaminated by hydrogen outgassing which persists even years after commissioning. In order to obtain neutral atmospheric hydrogen fluxes, either the atmospheric peak and outgassing peak must be well resolved, or the outgassing component subtracted off. The ExoCube INMS employs a separate mode, specifically for measuring neutral Hydrogen. The details of this mode and lessons learned will be presented as well as in flight instrument validation data for the neutral channel and preliminary flight ion spectra. At the time of abstract submission, the ExoCube spacecraft is currently undergoing attitude control maneuvers to orient INMS in the ram direction for science operations.

LADEE UVS Observations of Atoms and Dust in the Lunar Tail

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Colaprete, Anthony; Cook, Amanda M.; Shirley, Mark H.; Vargo, Kara E.; Elphic, Richard C.; Stubbs, Timothy J.; Glenar, David A.

2014-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) was a lunar orbiter launched in September 2013 that investigated the composition and temporal variation of the tenuous lunar exosphere and dust environment. A major goal of the mission was to characterize the dust exosphere prior to future lunar exploration activities, which may alter the lunar environment. The Ultraviolet/Visible Spectrometer (UVS) onboard LADEE addresses this goal, utilizing two sets of optics: a limbviewing telescope, and a solar-viewing telescope. We report on spectroscopic (approximately 280 - 820 nm) observations viewing down the lunar wake or along the 'lunar tail' from lunar orbit. Prior groundbased studies have observed the emission from neutral sodium atoms extended along the lunar tail, so often this region is referred to as the lunar sodium tail. UVS measurements were made on the dark side of the moon, with the UVS limb-viewing telescope pointed outward in the direction of the Moon's wake (almost anti-sun), during different lunar phases. These UVS observation activities sample a long column and allow the characterization of scattered light from dust and emission lines from atoms in the lunar tail. Observations in this UVS configuration show the largest excess of scattered blue light in our data set, indicative of the presence of small dust grains in the tail. Once lofted, nanoparticles may become charged and picked up by the solar wind, similar to the phenomena witnessed above Enceladus's northern hemisphere or by the STEREO/WAVES instrument while close to Earth's orbit. The UVS data show that small dust grains as well as atoms become entrained in the lunar tail.

SPICAM on Mars Express: A 10 year in-depth survey of the Martian atmosphere

NASA Astrophysics Data System (ADS)

Montmessin, F.; Korablev, O.; Lefèvre, F.; Bertaux, J.-L.; Fedorova, A.; Trokhimovskiy, A.; Chaufray, J. Y.; Lacombe, G.; Reberac, A.; Maltagliati, L.; Willame, Y.; Guslyakova, S.; Gérard, J.-C.; Stiepen, A.; Fussen, D.; Mateshvili, N.; Määttänen, A.; Forget, F.; Witasse, O.; Leblanc, F.; Vandaele, A. C.; Marcq, E.; Sandel, B.; Gondet, B.; Schneider, N.; Chaffin, M.; Chapron, N.

2017-11-01

The SPICAM experiment onboard Mars Express has accumulated during the last decade a wealth of observations that has permitted a detailed characterization of the atmospheric composition and activity from the near-surface up to above the exosphere. The SPICAM climatology is one of the longest assembled to date by an instrument in orbit around Mars, offering the opportunity to study the fate of major volatile species in the Martian atmosphere over a multi-(Mars)year timeframe. With his dual ultraviolet (UV)-near Infrared channels, SPICAM observes spectral ranges encompassing signatures created by a variety atmospheric gases, from major (CO2) to trace species (H2O, O3). Here, we present a synthesis of the observations collected for water vapor, ozone, clouds and dust, carbon dioxide, exospheric hydrogen and airglows. The assembled climatology covers the MY 27-MY 31 period. However, the monitoring of UV-derived species was interrupted at the end of 2014 (MY30) due to failure of the UV channel. A SO2 detection attempt was undertaken, but proved unsuccessful from regional to global scales (with upper limit greater than already published ones). One particular conclusion that stands out from this overview work concerns the way the Martian atmosphere organizes an efficient mass transfer between the lower and the upper atmospheric reservoirs. This highway to space, as we name it, is best illustrated by water and hydrogen, both species having been monitored by SPICAM in their respective atmospheric reservoir. Coupling between the two appear to occur on seasonal timescales, much shorter than theoretical predictions.

Observations of Mercury's Surface-Bounded Exosphere from Orbit: Results from the Mercury Atmospheric and Surface Composition Spectrometer aboard the MESSENGER Spacecraft

NASA Astrophysics Data System (ADS)

McClintock, W. E.; Burger, M. H.; Cassidy, T. A.; Killen, R. M.; Merkel, A. W.; Sarantos, M.; Solomon, S. C.; Vervack, R. J., Jr.

2015-12-01

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS), on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, conducted orbital observations of Mercury's dayside and nightside exosphere from 29 March 2011 to the end of the mission on 30 April 2015. Over slightly more than four Earth-years, MASCS measured emission profiles versus altitude for calcium (Ca), sodium (Na), and magnesium (Mg) at a daily cadence. These species exhibit different spatial distributions, suggesting distinct source processes. MASCS observed seasonal variations in all three species that are remarkably repeatable from one Mercury year to the next, and did so consistently during the entire 17-Mercury-year duration of the orbital phase of the mission. Whereas MASCS has characterized the seasonal variation, it has provided, at best, only weak evidence for the episodic behavior observed in ground-based studies of Na. Joint analyses of MASCS observations and surface precipitation patterns for energetic particles inferred from observations by the Energetic Particle Spectrometer (EPS) and the Fast Imaging Plasma Spectrometer (FIPS) on MESSENGER have not yielded clear correlations. This lack of correlation may be due in part to the MASCS observational geometries. MASCS has conducted a number of searches for other, weakly emitting species. Hydrogen data from the orbital phase are consistent with profiles observed during MESSENGER's flybys of Mercury. Oxygen detections have proven elusive, and the previously reported observation with a brightness of 4 R may only be an upper limit. Ongoing analysis of weak species data suggests that additional species are present.

Ion Mass Spectroscopy for the Outer Solar System

NASA Astrophysics Data System (ADS)

Reisenfeld, D. B.; Elphic, R. C.; McComas, D. J.; Nordholt, J. E.; Steinberg, J. T.; Wiens, R. C.

2001-01-01

A proven method for determination of the exospheric and surface composition of moons and comets is ion mass spectroscopy. Ions are produced via sputtering of surface constituents by the ambient plasma (solar wind or planetary magnetospheres), and via photo- and electron impact ionization of neutral exospheric/atmospheric constituents. A promising emergent technology in the field of space-based ion mass spectrometry is the low-cost, miniaturized but high-performance ion mass spectrometer (IMS) as exhibited by the Plasma Experiment for Planetary Exploration (PEPE) on Deep Space 1 (DS-1). A technology demonstration instrument, the PEPE IMS realized a mass resolution (M/delta(M)) of approximately 10. Its energy range extends from 5 eV to 9 keV at this mass resolution, and up to 33.5 keV in a lower mass resolution mode. With minimal development, these capabilities can be greatly extended. Already, we have produced a fully functional engineering model having a M/delta(M) = 20 and an energy range extending to 18 keV in the high-mass resolution mode. Further design modifications anticipate extending the mass resolution to 30-40 while still maintaining a miniaturized design. This makes possible many more isotopic and molecular differentiations than achievable with the original PEPE design. A PEPE-class spectrometer can address a significant number of the OPP key strategic objectives. In particular, in situ cometary nucleus analysis, studies of Triton's atmospheric and surface composition, and Europa surface composition analysis, can all be performed through IMS measurements. Additional information is contained in the original extended abstract.

A whole new Mercury: MESSENGER reveals a dynamic planet at the last frontier of the inner solar system

NASA Astrophysics Data System (ADS)

Johnson, Catherine L.; Hauck, , Steven A.

2016-11-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission yielded a wealth of information about the innermost planet. For the first time, visible images of the entire planet, absolute altimetry measurements and a global gravity field, measurements of Mercury's surface composition, magnetic field, exosphere, and magnetosphere taken over more than four Earth years are available. From these data, two overarching themes emerge. First, multiple data sets and modeling efforts point toward a dynamic ancient history. Signatures of graphite in the crust suggest solidification of an early magma ocean, image data show extensive volcanism and tectonic features indicative of subsequent global contraction, and low-altitude measurements of magnetic fields reveal an ancient magnetic field. Second, the present-day Mercury environment is far from quiescent. Convective motions in the outer core support a modern magnetic field whose strength and geometry are unique among planets with global magnetic fields. Furthermore, periodic and aperiodic variations in the magnetosphere and exosphere have been observed, some of which couple to the surface and the planet's deep interior. Finally, signatures of geologically recent volatile activity at the surface have been detected. Mercury's early history and its present-day environment have common elements with the other inner solar system bodies. However, in each case there are also crucial differences and these likely hold the key to further understanding of Mercury and terrestrial planet evolution. MESSENGER's exploration of Mercury has enabled a new view of the innermost planet, and more importantly has set the stage for much-needed future exploration.

Intraannual variability of tides in the thermosphere from model simulations and in situ satellite observations

NASA Astrophysics Data System (ADS)

Häusler, K.; Hagan, M. E.; Forbes, J. M.; Zhang, X.; Doornbos, E.; Bruinsma, S.; Lu, G.

2015-01-01

In this paper, we provide insights into limitations imposed by current satellite-based strategies to delineate tidal variability in the thermosphere, as well as the ability of a state-of-the-art model to replicate thermospheric tidal determinations. Toward this end, we conducted a year-long thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) simulation for 2009, which is characterized by low solar and geomagnetic activity. In order to account for tropospheric waves and tides propagating upward into the ˜30-400 km model domain, we used 3-hourly MERRA (Modern-Era Retrospective Analysis for Research and Application) reanalysis data. We focus on exospheric tidal temperatures, which are also compared with 72 day mean determinations from combined Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellite observations to assess the model's capability to capture the observed tidal signatures and to quantify the uncertainties associated with the satellite exospheric temperature determination technique. We found strong day-to-day tidal variability in TIME-GCM that is smoothed out when averaged over as few as ten days. TIME-GCM notably overestimates the 72 day mean eastward propagating tides observed by CHAMP/GRACE, while capturing many of the salient features of other tidal components. However, the CHAMP/GRACE tidal determination technique only provides a gross climatological representation, underestimates the majority of the tidal components in the climatological spectrum, and moreover fails to characterize the extreme variability that drives the dynamics and electrodynamics of the ionosphere-thermosphere system. A multisatellite mission that samples at least six local times simultaneously is needed to provide this quantification.

Space Weathering of Super-Earths: Model Simulations of Exospheric Sodium Escape from 61 Virgo b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoneda, M.; Berdyugina, S.; Kuhn, J.

Rocky exoplanets are expected to be eroded by space weather in a similar way as in the solar system. In particular, Mercury is one of the dramatically eroded planets whose material continuously escapes into its exosphere and further into space. This escape is well traced by sodium atoms scattering sunlight. Due to solar wind impact, micrometeorite impacts, photo-stimulated desorption and thermal desorption, sodium atoms are released from surface regolith. Some of these released sodium atoms are escaping from Mercury’s gravitational-sphere. They are dragged anti-Sun-ward and form a tail structure. We expect similar phenomena on exoplanets. The hot super-Earth 61 Virmore » b orbiting a G3V star at only 0.05 au may show a similar structure. Because of its small separation from the star, the sodium release mechanisms may be working more efficiently on hot super-Earths than on Mercury, although the strong gravitational force of Earth-sized or even more massive planets may be keeping sodium atoms from escaping from the planet. Here, we performed model simulations for Mercury (to verify our model) and 61 Vir b as a representative super-Earth. We have found that sodium atoms can escape from this exoplanet due to stellar wind sputtering and micrometeorite impacts, to form a sodium tail. However, in contrast to Mercury, the tail on this hot super-Earth is strongly aligned with the anti-starward direction because of higher light pressure. Our model suggests that 61 Vir b seems to have an exo-base atmosphere like that of Mercury.« less

A 2016 Ganymede stellar occultation event

NASA Astrophysics Data System (ADS)

D'Aversa, Emiliano; Oliva, Fabrizio; Sindoni, Giuseppe; Hinse, Tobias Cornelius; Plainaki, Christina; Aoki, Shohei; Person, Michael J.; Carlson, Robert W.; Orton, Glenn S.

2017-04-01

On 2016 April,13th the Jovian satellite Ganymede occulted a 7th magnitude star. The predicted occultation track crossed the Northern Pacific Ocean, Japan, and South Korea. Hence, it was a very favorable event due to the star brightness and to the visibility from the large aperture telescopes at Hawaii. While no other similar event is expected for the next 10 years, only two occultation events are reported in literature in the past, from Earth in 1972 [1] and from Voyager [2], in large disagreement in respect to the atmosphere detection. However, evidence of an exosphere around Ganymede was inferred by [3], through H Lyman alpha emission detected by Galileo UVS, and by [4], through HST/GHRS detection of far-UV atomic O airglow emissions, signature of dissociated molecular oxygen ([5],[6]). Later, the HST/STIS observations by [7] provided further evidence for exospheric neutral hydrogen. Since Ganymede is known to have an intrinsic magnetic field ([8]) reconnecting with the Jovian magnetic field and (partially) shielding the surface equatorial latitudes from the electron impact, the UV emissions have been so far attributed to auroral processes ([6]). Nevertheless, the physical mechanisms governing these processes are not known with certainty (e.g. whether the emissions morphology is determined by the spatial distribution of magnetospheric electrons or by an uneven O2 exosphere or both, see e.g.[9]). We took advantage of this event in order to search for a signature of Ganymede's exosphere in the occultation light curve, by using facilities on Mauna Kea at Hawaii (NASA-IRTF observatory) and at Sobaeksan Optical Astronomy Observatory (SOAO) in South Korea. At IRTF, both MORIS [10] and SpeX [11] instruments have been used, fed by the same optical entrance through a dichroic beam splitter at 0.95 micron. MORIS acquired a high-rate sequence of images about 0.25 sec apart in the visible range, while SpeX acquired a sequence of spectra at a bit lower rate, covering the 0.9-2.5 micron range. Unfortunately, a planned MORIS movie-mode sequence at higher rate failed in starting acquisition. The field of view of the instruments was not large enough to include a reference unocculted body, hence sky fluctuations are the major noise source. At SOAO, a CCD camera in clear filter was used to obtain a shorter sequence of images at a lower rate (about 1 Hz). However, since the larger field of view allowed to observe simultaneously Ganymede and Callisto, we can use the latter as a reference unocculted body in order to cancel out telluric fluctuations. Results from the occultation light curve analysis on the three datasets will be discussed. Acknowledgments - The Infrared Telescope Facility is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration. We express special thanks to Bobby Bus as support astronomer for both MORIS and SpeX observations. SOAO is managed by the Korean Astronomy and Space Science Istitute (KASI). References - [1] Carlson et al.,1973,Science,182,4107. [2] Broadfoot et al.,1981,Journ.of Geophys.Res.,86,8259. [3] Barth et al.,1996,EOS Suppl.77,F430. [4] Hall et al.,1998,ApJ,499,475. [5] McGrath et al.,2004,Cambridge Univ.Press,ISBN 0-521-81808-7,2004,p.457-483. [6] McGrath et al.,2013,Journ.of Geophys.Res.,118,2043. [7] Feldman et al.,2000,ApJ,535,1085. [8] Kivelson et al.,1996,Nature,384,537. [9] Plainaki et al.,2015,Icarus,245,306. [10] Gulbis et al.,2011,PASP,123,461. [11] Rayner et al.2003,PASP,115,362.

On Mars' atmospheric sputtering after MAVEN first two years

NASA Astrophysics Data System (ADS)

Leblanc, F.; Modolo, R.; Curry, S.; Luhmann, J. G.; Lillis, R.; Chaufray, J. Y.; Hara, T.; McFadden, J.; Halekas, J.; Eparvier, F.; Larson, D.; Connerney, J.; Jakosky, B.

2017-09-01

Mars may have lost a significant part of its atmosphere into space along its history, in particular since the end of its internal dynamo, 4.1 Gyr ago. The sputtering of the atmosphere by precipitating planetary picked up ions accelerated by the solar wind is one of the processes that could have significantly contributed to this atmospheric escape. We here present a two years base analysis of MAVEN observation of the precipitating flux, in particular the dependency of the precipitating intensity with solar zenith angle and used this measurement to model the expected escape rate and exosphere induced by this precipitation.

AXIOM: Advanced X-Ray Imaging Of the Magnetosheath

NASA Technical Reports Server (NTRS)

Sembay, S.; Branduardi-Rayrnont, G.; Eastwood, J. P.; Sibeck, D. G.; Abbey, A.; Brown, P.; Carter, J. A.; Carr, C. M.; Forsyth, C; Kataria, D.;

MESSENGER Observations of the Spatial Distribution of Planetary Ions Near Mercury

NASA Technical Reports Server (NTRS)

Zurbuchen, Thomas H.; Raines, Jim M.; Slavin, James A.; Gershman, Daniel J.; Gilbert, Jason A.; Gloeckler, George; Anderson, Brian J.; Baker, Daniel N.; Korth, Haje; Krimigis, Stamatios M.;

Plasma observations near Saturn - Initial results from Voyager 1

NASA Technical Reports Server (NTRS)

Bridge, H. S.; Belcher, J. W.; Lazarus, A. J.; Olbert, S.; Sullivan, J. D.; Bagenal, F.; Gazis, P. R.; Hartle, R. E.; Ogilvie, K. W.; Scudder, J. D.

1981-01-01

The Voyager 1 encounter with Saturn and its satellites yielded extensive measurements of magnetospheric low-energy plasma electrons and positive ions, both heavy and light, probably of hydrogen and nitrogen or oxygen. At radial distances between 15 and 7 Saturn radii on the inbound trajectory, the plasma appears to corotate with a velocity within 20% of that theoretically expected for rigid corotation. The Titan data, taken while the moon was inside the Saturn magnetosphere, shows a clear signature characteristic of the interaction between a subsonic corotating magnetospheric plasma and the atmospheric or ionospheric exosphere of Titan.

Exploration of Mercury: The MESSENGER Mission

NASA Astrophysics Data System (ADS)

McNutt, Ralph

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA’s Discovery Program, has been collecting orbital observations of Mercury since March 2011. Elemental remote sensing of Mercury’s surface indicates that the moderately volatile elements Na, K, and S are not depleted relative to other terrestrial planets. Orbital images document widespread evidence for ancient volcanic activity ranging from effusive to explosive eruptions. High-resolution images have revealed the presence of irregular rimless depressions or “hollows” likely produced by the loss to diurnal heating or sputtering of some volatile-rich material. Polar deposits in permanently shadowed high-latitude regions are dominated by water ice on the basis of neutron spectrometry, surface reflectance, and thermal modeling with measured topography; in most locations the ice is covered by 10-30 cm of anomalously dark volatile material postulated to consist of complex organic compounds. The tectonic history of Mercury is dominated by greater planetary contraction than previously recognized; long-wavelength changes in topography postdated the emplacement of large expanses of volcanic plains. Gravity and topography measurements indicate that mascons and crustal thinning are associated with some impact basins. Mercury’s internal magnetic field is that of a dipole offset from the planet’s center by ~0.2 Mercury radii, a geometry difficult to reconcile with existing dynamo models. Magnetospheric measurements have revealed a highly time-variable and spatially structured particle environment. Despite complex feedbacks among the exosphere, magnetosphere, and surface, the large-scale structure of the exosphere - dominated by Na, Ca, and Mg - shows seasonal variations in general agreement with those expected from variations in solar flux with Mercury true anomaly but little variation with changing solar conditions. Energetic electron events are regular features of Mercury’s magnetosphere, but the causative acceleration mechanism remains a topic of study. MESSENGER is now in a second extended mission. Solar gravitational forces reduce the periapsis altitude between successive orbits. Orbit-correction maneuvers will yield four extended intervals when the periapsis altitude will be 15 to 25 km, and once the remaining propellant is consumed the spacecraft will impact the surface in late March 2015. During this low-altitude campaign, the unprecedented high-resolution views of the surface will help elucidate many of the processes that have shaped Mercury’s surface. MESSENGER’s low-altitude observations will also illuminate the consequences of precipitating ions and energetic electrons at Mercury, the response of the exosphere and magnetosphere to solar wind conditions during the declining phase of the solar cycle, and short-wavelength components of the internal magnetic and gravity fields and their implications for crustal magmatism and the mechanical evolution of Mercury’s lithosphere.

Comparative Study on Hot Atom Coronae of Solar and Extrasolar Planets

NASA Astrophysics Data System (ADS)

Shematovich, Valery

Solar/stellar forcing on the upper atmospheres of the solar and extrasolar planets via both absorption of the XUV (soft X-rays and extreme ultraviolet) radiation and atmospheric sputtering results in the formation of an extended neutral corona populated by the suprathermal (hot) H, C, N, and O atoms (see, e.g., Johnson et al., 2008). The hot corona, in turn, is altered by an inflow of the solar wind/magnetospheric plasma and local pick-up ions onto the planetary exosphere. Such inflow results in the formation of the superthermal atoms (energetic neutral atoms - ENAs) due to the charge exchange with the high-energy precipitating ions and can affect the long-term evolution of the atmosphere due to the atmospheric escape. The origin, kinetics and transport of the suprathermal H, C, N, and O atoms in the transition regions (from thermosphere to exosphere) of the planetary atmospheres are discussed. Reactions of dissociative recombination of the ionospheric ions CO _{2} (+) , CO (+) , O _{2} (+) , and N _{2} (+) with thermal electrons are the main photochemical sources of hot atoms. The dissociation of atmospheric molecules by the solar/stellar XUV radiation and accompanying photoelectron fluxes and the induced exothermic photochemistry are also the important sources of the suprathermal atoms. Such kinetic systems with the non-thermal processes are usually investigated with the different (test particles, DSMC, and hybrid) versions of the kinetic Monte Carlo method. In our studies the kinetic energy distribution functions of suprathermal and superthermal atoms were calculated using the stochastic model of the hot planetary corona (Shematovich, 2004, 2010; Groeller et al., 2014), and the Monte Carlo model (Shematovich et al., 2011, 2013) of the high-energy proton and hydrogen atom precipitation into the atmosphere respectively. These functions allowed us to estimate the space distribution of suprathermals in the planetary transition regions. An application of these numerical models to study the atmospheric gas flow in the transition region from the collision-dominated thermosphere to collisionless exosphere, and the non-thermal escape will be discussed and illustrated with the simple 1D-models of the hot coronae of the solar and extrasolar planets. This work is supported by the RFBR project No. 14-02-00838a and by the Basic Research Program of the Presidium of the Russian Academy of Sciences (Program 22). begin{itemize} Johnson et al., Sp. Sci.Rev., 2008, v. 139, 355. Shematovich, Solar System Res., 2004, v.38, 28. Shematovich, Solar System Res., 2010, v.44, 96. Shematovich et al., J. Geophys. Res., 2011, v.116, A11320; 2013, v. 118, 1231. Groeller et al., Planet. Space Sci., 2014.

Search for an evaporating ocean on the super-Earth HIP 116454b

NASA Astrophysics Data System (ADS)

Bourrier, Vincent

2017-08-01

The super-Earth HIP116454b was the first exoplanet detected by the K2 mission, in transit across a bright and nearby K1 dwarf (V=10.2, d=55 pc). The low density of the planet suggests it must have at least 30% water or a 0.5% H-He envelope. Given the strong XUV irradiation from the young (2 Gyr) host star, this H-He envelope should have been lost through evaporation in a few hundred millions year, suggesting that HIP 116454b likely contains a large mass fraction of water. The shallow transit depth makes difficult the search for water vapor in the lower atmosphere with HST/WFC3. The moderate orbital distance of this warm ( 700 K) planet favors the formation of a super-critical steam envelope, which should be promptly dissociated at high altitude by the XUV irradiation and become observable as hydrogen flowing within and beyond the Roche lobe. The host star is similar to HD 189733, host to an evaporating hot Jupiter, and numerical simulations of HIP116454b show that the hydrogen exosphere resulting from the dissociation of water is observable with HST/STIS at Ly-alpha. The detection of this exosphere would be the first signature of an evolved evaporating ocean on an extrasolar planet, as well as the first validation of internal structure models of exoplanets in this mass regime. It would also determine how to best search for water in the lower atmosphere of HIP116454b with the JWST. A non-detection of escaping hydrogen, as with 55 Cnc e and HD 97658b, would bring useful constraints on the nature of the planetary atmosphere, the evolutionary path of close-in super-Earths, and the progenitors of the rocky evaporation remnants detected by Kepler.

Remote Observations of the Lunar Sodium Corona

NASA Astrophysics Data System (ADS)

Killen, Rosemary M.; Morgan, Thomas H.; Potter, Andrew; SSERVI DREAM2

2017-10-01

We have designed, built and installed a small robotic coronagraph at the Winer Observatory in Sonoita, Arizona, in order to observe the sodium exosphere out to one-half degree around the Moon. Observations are obtained remotely every available clear night from our home base at Goddard Space Flight Center. Our data encompass lunations in 2015, 2016, and 2017, thus we have a long baseline of sodium exospheric calibrated images. We employ an Andover temperature-controlled 1.5 Å wide narrow-band filter centered on the sodium D2 line, and a similar 1.5 Å filter centered blueward of the D2 line by 5 Å. Exposures of 10 minutes are required to image the sodium corona at good signal to noise. Autoguiding is performed locking onto a small bright crater each night. Following each onband-offband exposure pair, on- and off-band images of the lunar surface are collected by taking a 0.1- 0.5 second exposures with the open filter. The sodium is calibrated using the counts in the open Moon images and the Hapke function. We use both dark and bright Hapke parameters for comparison check using Mare and highlands, respectively. In order to obtain the sodium profile around the entire limb, the images are transformed using a polar transform and the profiles are extracted automatically. Example of our resulting images of the sodium corona will be shown, with the image of the moon's disk (taken subsequently to the occulted coronal image) superimposed on the occulting disk, thus showing the position and phase of the moon under the disk. We compare our lunar model derived from these observations with the data from the UV spectrograph onboard the LADEE spacecraft.

The Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission

NASA Technical Reports Server (NTRS)

Spremo, Stevan; Turner, Mark; Caffrey, Robert T.; Hine, Butler Preston

2010-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) is a Lunar science orbiter mission currently under development to address the goals of the National Research Council decadal surveys and the recent "Scientific Context for Exploration of the Moon" (SCEM) [1] report to study the pristine state of the lunar atmosphere and dust environment prior to significant human activities. LADEE will determine the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. LADEE will also determine whether dust is present in the lunar exosphere, and reveal the processes that contribute to its sources and variability. These investigations are relevant to our understanding of surface boundary exospheres and dust processes throughout the solar system, address questions regarding the origin and evolution of lunar volatiles, and have potential implications for future exploration activities. LADEE employs a high heritage science instrument payload including a neutral mass spectrometer, ultraviolet spectrometer, and dust sensor. In addition to the science payloads, LADEE will fly a laser communications system technology demonstration that could provide a building block for future space communications architectures. LADEE is an important component in NASA's portfolio of near-term lunar missions, addressing objectives that are currently not covered by other U.S. or international efforts, and whose observations must be conducted before large-scale human or robotic activities irrevocably perturb the tenuous and fragile lunar atmosphere. LADEE will also demonstrate the effectiveness of a low-cost, rapid-development program utilizing a modular bus design launched on the new Minotaur V launch vehicle. Once proven, this capability could enable future lunar missions in a highly cost constrained environment. This paper describes the LADEE objectives, mission design, and technical approach.

Effects of multiscale phase-mixing and interior conductance in the lunar-like pickup ion plasma wake. First results from 3-D hybrid kinetic modeling

NASA Astrophysics Data System (ADS)

Lipatov, A. S.; Sarantos, M.; Farrell, W. M.; Cooper, J. F.

2018-07-01

The study of multiscale pickup ion phase-mixing in the lunar plasma wake with a hybrid model is the main subject of our investigation in this paper. Photoionization and charge exchange of protons with the lunar exosphere are the ionization processes included in our model. The computational model includes the self-consistent dynamics of the light (H+ or H2+ and He+), and heavy (Na+) pickup ions. The electrons are considered as a fluid. The lunar interior is considered as a weakly conducting body. In this paper we considered for the first time the cumulative effect of heavy neutrals in the lunar exosphere (e.g., Al, Ar), an effect which was simulated with one species of Na+ but with a tenfold increase in total production rates. We find that various species produce various types of plasma tail in the lunar plasma wake. Specifically, Na+ and He+ pickup ions form a cycloid-like tail, whereas the H+ or H2+ pickup ions form a tail with a high density core and saw-like periodic structures in the flank region. The length of these structures varies from 1.5RM to 3.3RM depending on the value of gyroradius for H+ or H2+ pickup ions. The light pickup ions produce more symmetrical jump in the density and magnetic field at the Mach cone which is mainly controlled by the conductivity of the interior, an effect previously unappreciated. Although other pickup ion species had little effect on the nature of the interaction of the Moon with the solar wind, the global structure of the lunar tail in these simulations appeared quite different when the H2+ production rate was high.

A new estimate of micrometeoritic flux at Mercury

NASA Astrophysics Data System (ADS)

Borin, P.; Cremonese, G.; Marzari, F.; Bruno, M.; Marchi, S.

2009-04-01

Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. Recent papers attribute to impacting particles smaller than 1 cm the major contribution to exospheric gases. However, fluxes and impact velocities for different sizes are based on old extrapolations of similar quantities at the Earth. In this work, in order to determine the meteoritic flux at the heliocentric distance of Mercury we utilize the dynamical evolution model of dust particles of Marzari and Vanzani (1994) that numerically solves a (N+1)+M body problem (Sun + N planets + M body with zero mass) with the high-precision integrator RA15 (Everhart 1985). The solar radiation pressure and Poynting-Robertson drag, together with the gravitational interactions of the planets, are taken as major perturbing forces affecting the orbital evolution of the dust particles. From our numerical simulations we extrapolate the flux of particles hitting Mercury's surface and the corresponding distribution of impact velocities. A precise calibration of the particle flux on Mercury has been performed by comparing the predictions of our model concerning the dust infall on the Earth with experimental data. The model provide the flux of different size particles impacting Mercury and their collisional velocity distribution. We compare our results with previous estimates, in particular we take into account the work of Cintala (1992), and we find lower velocities but significantly higher fluxes. Our results show that the number of impacts given by Cintala, measured in N/years, is 80.2 times higher, but the flux measured in g• cm2s, is 409.4 times lower. We can conclude that our model predicts a number of impacts smaller than Cintala, but a much higher mass contribution.

Emirates Mars Ultraviolet Spectrometer (EMUS) Overview from the Emirates Mars Mission

NASA Astrophysics Data System (ADS)

Lootah, F. H.; Almatroushi, H. R.; AlMheiri, S.; Holsclaw, G.; Deighan, J.; Chaffin, M.; Reed, H.; Lillis, R. J.; Fillingim, M. O.; England, S.

2017-12-01

The Emirates Mars Ultraviolet Spectrometer (EMUS) instrument is one of three science instruments on board the "Hope Probe" of the Emirates Mars Mission (EMM). EMM is a United Arab Emirates' (UAE) mission to Mars, launching in 2020, to explore the global dynamics of the Martian atmosphere, while sampling on both diurnal and seasonal timescales. The EMUS instrument is a far-ultraviolet imaging spectrograph that measures emissions in the spectral range 100-170 nm. Using a combination of its one-dimensional imaging and spacecraft motion, it will build up two-dimensional far-ultraviolet images of the Martian disk and near-space environment at several important wavelengths: the Lyman beta atomic hydrogen emission (102.6 nm), the Lyman alpha atomic hydrogen emission (121.6 nm), two atomic oxygen emissions (130.4 nm and 135.6 nm), and the carbon monoxide fourth positive group band emission (140 nm-170 nm). Radiances at these wavelengths will be used to derive the column abundance of atomic oxygen, and carbon monoxide in the Martian thermosphere, and the density of atomic oxygen and atomic hydrogen in the Martian exosphere both with spatial and sub-seasonal variability. The EMUS instrument consists of a single telescope mirror feeding a Rowland circle imaging spectrograph with selectable spectral resolution (1.3 nm, 1.8 nm, or 5 nm), and a photon-counting and locating detector (provided by the Space Sciences Laboratory at the University of California, Berkeley). The EMUS spatial resolution of less than 300 km on the disk is sufficient to characterize spatial variability in the Martian thermosphere (100-200 km altitude) and exosphere (>200 km altitude). The instrument is jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder and Mohammed Bin Rashid Space Centre (MBRSC) in Dubai, UAE.

Emirates Mars Ultraviolet Spectrometer (EMUS) Overview from the Emirates Mars Mission

NASA Astrophysics Data System (ADS)

Almatroushi, Hessa; Lootah, Fatma; Holsclaw, Greg; Deighan, Justin; Chaffin, Michael; Lillis, Robert; Fillingim, Matthew; England, Scott; AlMheiri, Suhail; Reed, Heather

2017-04-01

The Emirates Mars Ultraviolet Spectrometer (EMUS) instrument is one of three science instruments to be carried on board the Emirate Mars Mission (EMM), the "Hope Probe". EMM is a United Arab Emirates' (UAE) mission to Mars launching in 2020 to explore the dynamics in the Martian atmosphere globally, while sampling on both diurnal and seasonal timescales. The EMUS instrument is a far-ultraviolet imaging spectrograph that measures emissions in the spectral range 100-170 nm. Using spacecraft motion, it will build up two-dimensional far-ultraviolet images of the Martian disk and near-space environment at several important wavelengths: Lyman beta atomic hydrogen emission (102.6 nm), Lyman alpha atomic hydrogen emission (121.6 nm), atomic oxygen emission (130.4 nm and 135.6 nm), and carbon monoxide fourth positive group band emission (140 nm-170 nm). Radiances at these wavelengths will be used to derive the column abundance of atomic oxygen, and carbon monoxide in the Martian thermosphere, and the density of atomic oxygen and atomic hydrogen in the Martian exosphere both with spatial and sub-seasonal variability. EMUS consists of a single telescope mirror feeding a Rowland circle imaging spectrograph capable of selectable spectral resolution (1.3 nm, 1.8 nm, or 5 nm) with a photon-counting and locating detector (provided by the Space Sciences Laboratory at the University of California, Berkeley). The EMUS spatial resolution of less than 300km on the disk is sufficient to characterize spatial variability in the Martian thermosphere (100-200 km altitude) and exosphere (>200 km altitude). The instrument is jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder and Mohammed Bin Rashid Space Centre (MBRSC) in Dubai, UAE

Electron Stimulated Desorption Yields at the Mercury's Surface Based On Hybrid Simulation Results

NASA Astrophysics Data System (ADS)

Travnicek, P. M.; Schriver, D.; Orlando, T. M.; Hellinger, P.

2016-12-01

In terms of previous research concerning the solar wind sputtering process, most of the focus has been on ion sputtering by precipitating solar wind protons, however, precipitating electrons can also result in the desorption of neutrals and ions from Mercury's surface and represents a potentially significant source of exospheric and heavy ion components. Electron stimulated desorption (ESD) is not bound by optical selection rules and electron impact energies can vary over a much wider range, including core-level excitations that easily lead to multi-electron shake up events that can cascade into localized multiple charged states that Coulomb explode with extreme kinetic energy release (up to 8 eV = 186,000 K). While considered for the lunar exosphere, ESD has not been adequately studied or quantified as a producer of neutrals and ions. ESD is a well known process which involves the excitation (often ionization) of a surface target followed by charge ejection, bond breaking and ion expulsion due to the resultant Coulomb repulsion. Though the role of ESD processes has not been discussed much with respect to Mercury, the impinging energetic electrons that are transported through the magnetosphere and precipitate can induce significant material removal. Given the energetics and the wide band-gap nature of the minerals, the departing material may also be primarily ionic. The possible role of 5 eV - 1 keV electron stimulated desorption and dissociation in "weathering" the regolith can be significant. ESD yields will be calculated based on the ion and electron precipitation profiles for the already carried out hybrid and electron simulations. Neutral and ion cloud profiles around Mercury will be calculated and combined with those profiles expected from PSD and MIV.

Oxygen Pickup Ions Measured by MAVEN Outside the Martian Bow Shock

NASA Astrophysics Data System (ADS)

Rahmati, A.; Cravens, T.; Larson, D. E.; Lillis, R. J.; Dunn, P.; Halekas, J. S.; Connerney, J. E. P.; Eparvier, F. G.; Thiemann, E.; Mitchell, D. L.; Jakosky, B. M.

2015-12-01

The MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft entered orbit around Mars on September 21, 2014 and has since been detecting energetic oxygen pickup ions by its SEP (Solar Energetic Particles) and SWIA (Solar Wind Ion Analyzer) instruments. The oxygen pickup ions detected outside the Martian bowshock and in the upstream solar wind are associated with the extended hot oxygen exosphere of Mars, which is created mainly by the dissociative recombination of molecular oxygen ions with electrons in the ionosphere. We use analytic solutions to the equations of motion of pickup ions moving in the undisturbed upstream solar wind magnetic and motional electric fields and calculate the flux of oxygen pickup ions at the location of MAVEN. Our model calculates the ionization rate of oxygen atoms in the exosphere based on the hot oxygen densities predicted by Rahmati et al. (2014), and the sources of ionization include photo-ionization, charge exchange, and electron impact ionization. The photo-ionization frequency is calculated using the FISM (Flare Irradiance Spectral Model) solar flux model, based on MAVEN EUVM (Extreme Ultra-Violet Monitor) measurements. The frequency of charge exchange between a solar wind proton and an oxygen atom is calculated using MAVEN SWIA solar wind proton flux measurements, and the electron impact ionization frequency is calculated based on MAVEN SWEA (Solar Wind Electron Analyzer) solar wind electron flux measurements. The solar wind magnetic field used in the model is from the measurements taken by MAVEN MAG (magnetometer) in the upstream solar wind. The good agreement between our predicted pickup oxygen fluxes and the MAVEN SEP and SWIA measured ones confirms detection of oxygen pickup ions and these model-data comparisons can be used to constrain models of hot oxygen densities and photochemical escape flux.

On Mars' Atmospheric Sputtering after Maven First two Years

NASA Astrophysics Data System (ADS)

Leblanc, F.; Modolo, R.; Curry, S.; Luhmann, J. G.; Lillis, R. J.; Chaufray, J. Y.; Hara, T.; McFadden, J. P.; Halekas, J. S.; Epavier, F.; Connerney, J. E. P.; Jakosky, B. M.

2017-12-01

Mars likely lost a significant part of its atmosphere to space during its history. The sputtering of the atmosphere by precipitating planetary picked up ions accelerated by the solar wind is one of the processes that could have significantly contributed to this atmospheric escape, in particular since the cessation of its global magnetic field, 4.0-4.1 Gyr ago. We here present a two year baseline analysis of MAVEN observations of the precipitating flux, in particular the dependence of the precipitating flux on solar zenith angle. We use this measurement to model the expected escape rate and exospheric structure induced by this precipitation.

Mercury's helium exosphere after Mariner 10's third encounter

NASA Technical Reports Server (NTRS)

Curtis, S. A.; Hartle, R. E.

1977-01-01

From Mariner 10 third encounter UV data, a value of .00045 was calculated as the fraction of the solar wind He++ flux intercepted and captured by Mercury's magnetosphere if the observed He atmosphere is maintained by the solar wind. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 x 10 to the 22nd power per sec. A surface temperature distribution was used which satisfies the heat equation over Mercury's entire surface using Mariner 10 determined mean surface thermal characteristics. The means stand off distance of Mercury's magnetopause averaged over Mercury's orbit was also used.

The Impact of Meteoroid Streams on the Lunar Atmosphere and Dust Environment During the LADEE Mission

NASA Technical Reports Server (NTRS)

Stubbs, T. J.; Glenar, D. A.; Wang, Y.; Hermalyn, B.; Sarantos, M.; Colaprete, A.; Elphic, R. C.

2015-01-01

The scientific objectives of the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission are: (1) determine the composition of the lunar atmosphere, investigate processes controlling distribution and variability - sources, sinks, and surface interactions; and (2) characterize the lunar exospheric dust environment, measure spatial and temporal variability, and influences on the lunar atmosphere. Impacts on the lunar surface from meteoroid streams encountered by the Earth-Moon system are anticipated to result in enhancements in the both the lunar atmosphere and dust environment. Here we describe the annual meteoroid streams expected to be incident at the Moon during the LADEE mission, and their anticipated effects on the lunar environment.

The Jovian Electron and Ion Spectrometer (JEI) for the JUICE mission

NASA Astrophysics Data System (ADS)

Fränz, M.; Bührke, U.; Ferreira, P.; Fischer, H.; Heumüller, P.; Krupp, N.; Kühne, W.; Roussos, E.

2017-09-01

The magnetosphere of Jupiter is apart from the Sun the strongest source of charged particles in the Solar system. The interaction of these particles with the exospheres of the Jovian moons forms one of the most complex plasma laboratories encountered by human space flight. For this reason the plasma analyzer package forms a crucial experiment of the Jupiter Icy Moon Explorer (JUICE). As part of the Plasma Environment Package (PEP) we here describe a combined electron and ion spectrometer which is able to measure the electron and ion distribution functions in the energy range 1 to 50000 eV with high sensitivity and time resolution. This instrument is called the Jovian Electron and Ion Analyzer, JEI.

The fate of the hydroxyl radical in the earth's primitive atmosphere and implications for the production of molecular oxygen

NASA Technical Reports Server (NTRS)

Vander Wood, T. B.; Thiemens, M. H.

1980-01-01

Behavior of the hydroxyl radical produced by the photolysis of water vapor in the earth's early atmosphere is examined. Because of the substantial OH radical reactivity with trace species (CO, HCl, SO2, H2S, NH3, and CH4) the formation of molecular oxygen may be prevented, even at a trace species mixing ratio. The photolysis rate of H2O, with corrections for hydrogen exospheric escape, is capable of describing the oxidation of the atmosphere and crust but may not be used to determine the rate of molecular oxygen generation without consideration of the various OH-trace species reactions.

Exospheric perturbations by radiation pressure. 2: Solution for orbits in the ecliptic plane

NASA Technical Reports Server (NTRS)

Chamberlain, J. W.

1980-01-01

The instantaneous rates of change for the orbital elements eccentricity, longitude of perigee from the Sun, and longitude from the Sun of the ascending node are integrated simultaneously for the case of the inclination i = 0. The results confirm the validity of using mean rates when the orbits are tightly bound to the planet and serve as examples to be reproduced by the complicated numerical solutions required for arbitrary inclination. Strongly bound hydrogen atoms escaping from Earth due to radiation pressure do not seem a likely cause of the geotail extending in the anti-sun direction. Instead, radiation pressure will cause those particles' orbits to deteriorate into the Earth's atmosphere.

Microchannel plate life testing for UV spectroscopy instruments

NASA Astrophysics Data System (ADS)

Darling, N. T.; Siegmund, O. H. W.; Curtis, T.; McPhate, J.; Tedesco, J.; Courtade, S.; Holsclaw, G.; Hoskins, A.; Al Dhafri, S.

2017-08-01

The Emirates Mars Mission (EMM) UV Spectrograph (EMUS) is a far ultraviolet (102 nm to 170 nm) imaging spectrograph for characterization of the Martian exosphere and thermosphere. Imaging is accomplished by a photon counting open-face microchannel plate (MCP) detector using a cross delay line (XDL) readout. An MCP gain stabilization ("scrub") followed by lifetime spectral line burn-in simulation has been completed on a bare MCP detector at SSL. Gain and sensitivity stability of better than 7% has been demonstrated for total dose of 2.5 × 1012 photons cm-2 (2 C · cm-2 ) at 5.5 kHz mm-2 counting rates, validating the efficacy of an initial low gain full-field scrub.

Mpo - the Bepicolombo Mercury Planetary Orbiter.

NASA Astrophysics Data System (ADS)

Benkhoff, J.

2008-09-01

Introduction: BepiColombo is an interdisciplinary mission to explore the planet Mercury through a partnership between ESA and Japan's Aerospace Exploration Agency (JAXA). From their dedicated orbits two spacecrafts, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO), will be studying the planet and its environment Both orbiter will be launched together on an ARIANE 5. The launch is foreseen for Summer 2014 with arrival in Summer 2020. Solar electric propulsion will be used for the journey to Mercury. In November 2004, the BepiColombo scientific payload has been officially approved. Payload of BepiColombo: The MPO scientific payload comprises eleven instruments/instrument packages; the MMO scientific payload consists of five instruments/instrument packages. Together, the scientific payload of both spacecraft will provide the detailed information necessary to understand Mercury and its magnetospheric environment and to find clues to the origin and evolution of a planet close to its parent star. The MPO will focus on a global characterization of Mercury through the investigation of its interior, surface, exosphere and magnetosphere. In addition, it will be testing Einstein's theory of general relativity. Major effort was put into optimizing the scientific return by defining the payload complement such that individual measurements can be interrelated and complement each other. A detailed overview of the status of BepiColombo will be given with special emphasis on the MPO and its payload complement. BepiColombo factsheet BepiColombo is Europe's first mission to Mercury, the innermost planet of the Solar System, and ESA's first science mission in collaboration with Japan. A satellite 'duo' - consisting of an orbiter for planetary investigation and one for magnetospheric studies - Bepi- Colombo will reach Mercury after a six-year journey towards the inner Solar System, to make the most extensive and detailed study of the planet ever performed so far. BepiColombo will also contribute to the understanding of the history and formation of the inner planets of the Solar System in general, including the Earth. The 'Mercury Planetary Orbiter' (MPO), under ESA's responsibility, will study the surface and the internal composition of the planet at different wavelengths and with different techniques. The Mercury Magnetospheric Orbiter (MMO), under the responsibility of the Japan Aerospace Exploration Agency (ISAS/JAXA), will study the magnetosphere, that is the region of space around the planet that is dominated by its magnetic field. Objectives BepiColombo will study and understand the composition, geophysics, atmosphere, magnetosphere and history of Mercury, the least explored planet in the inner Solar System. In particular, the mission objectives are: • markedly higher than that of all other terrestrial planets, Moon included • to understand if the core of Mercury is liquid or solid, and if the planet is still tectonically active today • to understand why such a small planet possesses an intrinsic magnetic field, while Venus, Mars and the Moon do not have any, and investigate if Mercury's magnetised environment is characterised by features reminiscent of the aurorae, radiation belts and magnetospheric substorms observed at Earth • to understand why spectroscopic observations not reveal the presence of any iron, while this element is supposedly the major constituent of the planet • to investigate if the permanently shadowed craters of the polar regions contain sulphur or water ice • to observe the yet unseen hemisphere of Mercury • to study the production mechanisms of the exosphere and to understand the interaction between planetary magnetic field and the solar wind in the absence of a ionosphere • to obtain new clues about the composition of the primordial solar nebula and about the formation of the solar system • to test general relativity with improved accuracy, taking advantage of the proximity of the Sun Since and considering that the advance Mercury's perihelion was explained in terms of relativistic spacetime curvature. MPO Scientific Instruments BepiColombo Mercury Planetary Orbiter's and Mercury Magnetospheric Orbiter's instruments were selected in November 2004, by ESA and JAXA respectively. The MPO will carry a highly sophisticated suit of eleven scientific instruments, ten of which will be provided by Principal Investigators through national funding by ESA Member States and one from Russia: BepiColombo Laser Altimeter (BELA) will characterise the topography and surface morphology of Mercury. It will also provide a digital terrain model that, compared with the data from the MORE instrument, will allow to obtain information about the internal structure, the geology, the tectonics, and the age of the planet's surface. The objectives of the Italian Spring Accelerometer (ISA) are strongly connected with those of the MORE experiment. Together the experiments can give information on Mercury's interior structure as well as test Einstein's theory of the General Relativity. Mercury Magnetometer (MPO-MAG) will provide measurements that will lead to the detailed description of Mercury's planetary magnetic field and its source, to better understand the origin, evolution and current state of the planetary interior , as well as the interaction between Mercury's magnetosphere with the planet's itself and with the solar wind. Mercury Thermal Infrared Spectrometer (MERTIS) will provide detailed information about the mineralogical composition of Mercury's surface layer with a high spectral resolution, crucial for selecting the valid model for origin and evolution of the planet. Mercury Gamma ray and Neutron Spectrometer (MGNS) will determine the elemental compositions of the surface and subsurface of Mercury, and will determine the regional distribution of volatile depositions on the polar areas which are permanently shadowed from the Sun. Mercury Imaging X-ray Spectrometer (MIXS) will use the `X-ray fluorescence' analysis method to produce a global map of the surface atomic composition at high spatial resolution. This technique has been also used by the D-CIXS instrument on ESA's SMART-1 mission to the Moon. Mercury Orbiter Radio science Experiment (MORE) will help to determine the gravity field of Mercury as well as the size and physical state of its core. It will provide crucial experimental constraints to models of the planet's internal structure and test theories of gravity with unprecedented accuracy. The Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS) spectrometer is devoted to the characterisation of Mercury's exosphere composition and dynamics. It will also search for surface ice layers in permanently shadowed regions of high-latitude craters. Search for Exosphere Refilling and Emitted Neutral Abundances (Neutral and ionised particle analyser) ( SERENA) will study the gaseaous interaction between surface, exosphere, magnetosphere and solar wind. Spectrometers and Imagers for MPO Bepi- Colombo Integrated Observatory System (SYMBIO-SYS) will examine (also in stereo and colour) the surface geology, volcanism, global tectonics, surface age and composition, and geophysics. Solar Intensity X-ray Spectrometer (SIXS will perform measurements of X-rays and particles of solar origin at high time resolution and a very wide field of view.

Cassini's Grand Finale and Recent Science Highlights

NASA Astrophysics Data System (ADS)

Spilker, Linda J.

2017-06-01

After almost 13 years in Saturn orbit, the Cassini-Huygens mission has entered its final year of data collection. Cassini will return its final bits of unique data on 15 September 2017 as it plunges into Saturn’s atmosphere, vaporizing and satisfying planetary protection requirements.Since early 2016 Cassini’s orbital inclination was slowly increased towards its final inclination. In November Cassini transitioned to a series of 20 orbits with periapses just outside Saturn's F ring that included some of the closest flybys of the tiny ring moons and excellent views of the F ring and outer A ring.Cassini's final close flyby of Titan in April 2017 propelled it across Saturn’s main rings and into its final orbits. Cassini's Grand Finale began in April 2017 and is comprised of 22 orbits at an inclination of 63 degrees. Cassini is repeatedly diving between the innermost ring and Saturn's upper atmosphere providing insights into fundamental questions unattainable during the rest of the mission. It is the first spacecraft to explore this region.These close orbits provide the highest resolution observations of both the rings and Saturn, and direct in situ sampling of the ring particles' composition, plasma, Saturn's exosphere and the innermost radiation belts. Saturn's gravitational field will be measured to unprecedented accuracy, providing information on Saturn's interior structure and mass distribution in the rings. Probing the magnetic field will give insight into the nature of the magnetic dynamo and the true rotation rate of Saturn's interior. The ion and neutral mass spectrometer will sniff the exosphere and upper atmosphere and examine water-based molecules originating from the rings. The cosmic dust analyzer will sample particle composition from different parts of the main rings.Recent science highlights and science objectives from Cassini’s final orbits will be discussed.This work was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2017 California Institute of Technology. Government sponsorship is acknowledged.

Statistical analysis of micrometeoroids at the heliocentric distance of Mercury

NASA Astrophysics Data System (ADS)

Borin, P.; Cremonese, G.; Marzari, F.

2007-08-01

This work shows preliminary results of a study of the orbital evolution of dust particles originating from the Main Belt in order to obtain a statistical analysis, then to provide an estimate of the flux of particles hitting the Mercury's surface. We can distinguish two population of meteoroids depending on their dynamical evolution: small particles (r < 1 cm) dominated by the Poynting-Robertson drag, and large particles (r > 1 cm) driven by gravity only. In this work we consider small particles and, in particular, the micrometeoroids produced by collisional fragmentation of cometary or asteroidal bodies. The main effects that determine the distribution of dust in the Solar System are the gravitational attractions of the Sun and planets, Poynting-Robertson drag, solar radiation pressure, solar wind pressure and the effects of different magnetic fields. In order to determine the meteoritic flux at the heliocentric distance of Mercury we utilize the dynamical evolution model of dust particles of Marzari and Vanzani (1994) that numerically solves a (N+1)+M body problem (Sun + N planets + M body with zero mass) with the high-precision integrator RA15 (Everhart 1985). The solar radiation pressure and Poynting-Robertson drag, together with the gravitational interactions of the planets, are taken as major perturbing forces affecting the orbital evolution of the dust particles. We will perform numerical simulations with different initial conditions for the dust particles, depending on the sources, with the aim of estimating to flux of dust on the surface of Mercury. Meteoroid impacts have a very important role in the evolution of Mercury's surface and exosphere. Since the exobase is presently on the surface of the planet, the sources and sinks of the exosphere are tightly linked to the composition and structure of the planet surface. We intend also to evaluate a possible asymmetry between the leading and trailing surface of Mercury in terms of impact frequency.

Overview of Results from the Cassini Magnetospheric Imaging Instrument (MIMI) During the First Year of Operations

NASA Technical Reports Server (NTRS)

Krimigis, S. M.; Mitchell, D. G.; Hamilton, D. C.; Krupp, N.; Livi, S.; Roelof, E. C.; Dandouras, J.; Mauk, B. H.; Brandt, J. P.; Paranicas, C.

2005-01-01

The MIMI investigation comprises three sensors covering the indicated energy ranges: the Ion and Neutral Camera (INCA) -- 7 keV/nuc 3 Mev) and protons (1.6 < E < 160 Mev) from the back end of the dual field-of-view telescope. The Saturn observation sequences began in January, 2004 and culminated in Saturn Orbit Insertion on July 1, 2004. The MIMI sensors observed substantial activity in interplanetary space for several months prior to SOI, including several interplanetary shocks associated with corotating interaction regions, numerous increases most likely originating from particle streams in the vicinity of the Saturnian bow shock and energetic neutral atoms (ENA) emanating from Saturn s magnetosphere. Results following SOI revealed: a dynamical magnetosphere with a day-night asymmetry and an 11-hour periodicity; several water-product ions (O+, OH+, H2O+), but little N+; inferred quantities of neutral gas sufficient to cause major losses in the trapped ions and electrons in the middle and inner magnetosphere; a Titan exosphere that is a copious source of ENA; INCA imaging through ENA has also revealed a previously unknown radiation belt residing inward of the D-ring that is most likely the result of double charge-exchange between the main radiation belt and the upper layers of Saturn s exosphere. Finally, there is ample evidence for the presence of substorm-like injections of plasma that subsequently corotates for a number of days before dissipating on the night-side magnetotail. The observations will be presented and discussed in the context of current theoretical models.

Particle Environment Package (PEP) for the ESA JUICE mission

NASA Astrophysics Data System (ADS)

Barabash, Stas; Brandt, Pontus; Wurz, Peter; PEP Team

2016-10-01

PEP is a suite of six (6) sensors arranged in 4 units to measure charged and neutral particles in the Jupiter magnetospheres and at the moons to answer four overarching science questions:1. How does the corotating magnetosphere of Jupiter interact with the complex and diverse environment of Ganymede?2. How does the rapidly rotating magnetosphere of Jupiter interact with the seemingly inert Callisto?3. What are the governing mechanisms and their global impacts of release of material into the Jovian magnetosphere from seemingly inert Europa and active Io?4. How do internal and solar wind drivers cause such energetic, time variable and multi-scale phenomena in the steadily rotating giant magnetosphere of Jupiter?PEP measures positive and negative ions, electrons, exospheric neutral gas, thermal plasma and energetic neutral atoms present in all domains of the Jupiter system over nine decades of energy from < 0.001 eV to > 1 MeV with full angular coverage.PEP provides instantaneous measurements of 3D flow of the ion plasma and composition to understand the magnetosphere and magnetosphere-moon interactions. It also measures instantaneously 3D electron plasma to investigate auroral processes at the moon and Jupiter. Measurements of the angular distributions of energetic electrons at sub-second resolution probe the acceleration mechanisms and magnetic field topology and boundaries.PEP combines global imaging via remote sensing using energetic neutral atoms (ENA) with in-situ measurements and performs global imaging of Europa/Io tori and magnetosphere combined with energetic ion measurements. Using low energy ENAs originating from the particle - surface interaction PEP investigate space weathering of the icy moons by precipitation particles. PEP will first-ever directly sample of the exospheres of Europa, Ganymede, and Callisto with extremely high mass resolution (M/ΔM > 1100).The PEP sensors are (1) an ion mass analyzer, (2) an electron spectrometer, (3) a low energy ENA imager, (4) a high energy ENA and energetic ions imager, (5) an energetic electron sensor, and (6) a neutral gas and ions mass spectrometer.

A steady-state model of the lunar ejecta cloud

NASA Astrophysics Data System (ADS)

Christou, Apostolos

2014-05-01

Every airless body in the solar system is surrounded by a cloud of ejecta produced by the impact of interplanetary meteoroids on its surface [1]. Such ``dust exospheres'' have been observed around the Galilean satellites of Jupiter [2,3]. The prospect of long-term robotic and human operations on the Moon by the US and other countries has rekindled interest on the subject [4]. This interest has culminated with the - currently ongoing - investigation of the Moon's dust exosphere by the LADEE spacecraft [5]. Here a model is presented of a ballistic, collisionless, steady state population of ejecta launched vertically at randomly distributed times and velocities and moving under constant gravity. Assuming a uniform distribution of launch times I derive closed form solutions for the probability density functions (pdfs) of the height distribution of particles and the distribution of their speeds in a rest frame both at the surface and at altitude. The treatment is then extended to particle motion with respect to a moving platform such as an orbiting spacecraft. These expressions are compared with numerical simulations under lunar surface gravity where the underlying ejection speed distribution is (a) uniform (b) a power law. I discuss the predictions of the model, its limitations, and how it can be validated against near-surface and orbital measurements.[1] Gault, D. Shoemaker, E.M., Moore, H.J., 1963, NASA TN-D 1767. [2] Kruger, H., Krivov, A.V., Hamilton, D. P., Grun, E., 1999, Nature, 399, 558. [3] Kruger, H., Krivov, A.V., Sremcevic, M., Grun, E., 2003, Icarus, 164, 170. [4] Grun, E., Horanyi, M., Sternovsky, Z., 2011, Planetary and Space Science, 59, 1672. [5] Elphic, R.C., Hine, B., Delory, G.T., Salute, J.S., Noble, S., Colaprete, A., Horanyi, M., Mahaffy, P., and the LADEE Science Team, 2014, LPSC XLV, LPI Contr. 1777, 2677.

How large is the subducted water flux? New constraints on mantle regassing rates

NASA Astrophysics Data System (ADS)

Parai, R.; Mukhopadhyay, S.

2012-02-01

Estimates of the subducted water (H2O) flux have been used to discuss the regassing of the mantle over Earth history. However, these estimates vary widely, and some are large enough to have reduced the volume of water in the global ocean by a factor of two over the Phanerozoic. In light of uncertainties in the hydration state of subducting slabs, magma production rates and mantle source water contents, we use a Monte Carlo simulation to set limits on long-term global water cycling and the return flux of water to the deep Earth. Estimates of magma production rates and water contents in primary magmas generated at ocean islands, mid-ocean ridges, arcs and back-arcs are paired with estimates of water entering trenches via subducting oceanic slab in order to construct a model of the deep Earth water cycle. The simulation is constrained by reconstructions of Phanerozoic sea level change, which suggest that ocean volume is near steady-state, though a sea level decrease of up to 360 m may be supported. We provide limits on the return flux of water to the deep Earth over the Phanerozoic corresponding to a near steady-state exosphere (0-100 meter sea level decrease) and a maximum sea level decrease of 360 m. For the near steady-state exosphere, the return flux is 1.4 - 2.0- 0.3+ 0.4 × 1013 mol/yr, corresponding to 2-3% serpentinization in 10 km of lithospheric mantle. The return flux that generates the maximum sea level decrease over the Phanerozoic is 3.5- 0.3+ 0.4 × 1013 mol/yr, corresponding to 5% serpentinization in 10 km of lithospheric mantle. Our estimates of the return flux of water to the mantle are up to 7 times lower than previously suggested. The imbalance between our estimates of the return flux and mantle output flux leads to a low rate of increase in bulk mantle water content of up to 24 ppm/Ga.

Moon-Magnetosphere Interactions at Saturn: Recent Highlights from Cassini Observations and Modelling

NASA Astrophysics Data System (ADS)

Simon, S.; Kriegel, H.; Saur, J.; Neubauer, F. M.; Wennmacher, A.; Motschmann, U.; Dougherty, M. K.

2012-09-01

Since the arrival of the Cassini spacecraft at Saturn in July 2004, newly collected plasma and magnetic field data have greatly expanded our knowledge on the giant planet's magnetosphere and its multifaceted family of moons. More than 160 orbits around the planet have already been accomplished by Cassini, encompassing 85 close flybys of Saturn's largest satellite Titan as well as 20 encounters of Enceladus. This small icy moon had been identified as the major source of magnetospheric plasma and neutral particles during the first year of Cassini's tour in the Saturnian system. In addition, the spacecraft has paid visits to several of the other icy satellites in the inner and middle magnetosphere: Rhea (3 flybys), Dione (3 flybys) and Tethys (1 flyby). The inner icy satellites and Titan are located within Saturn's magnetosphere for average solar wind conditions, revolving around the giant planet on prograde orbits in its equatorial plane. Since their orbital velocities are clearly exceeded by the speed of the at least partially corotating magnetospheric plasma, the moons are continuously "overtaken" by the magnetospheric flow. Thus, their trailing hemispheres are permanently exposed to a bombardment with thermal magnetospheric plasma. The characteristics of the resulting plasma interaction process depend on the properties of the moon itself as well as on the parameters (density, velocity, temperature, magnetic field strength) of the incident magnetospheric flow and the energetic particle population. In this presentation, we shall review some recent advances in our understanding of the interaction between Saturn's moons and their plasma environment: Enceladus: Electron absorption by submicron dust grains within the plume gives rise to a negative sign of the Hall conductance in Enceladus' plume. The resulting twist of the magnetic field, referred to as the Anti-Hall effect, has been observed during all targeted Enceladus flybys accomplished to date. We present an analytical model as well as advanced hybrid plasma simulations of these puzzling processes. Titan: Due to the oscillatory dynamics of Saturn's magnetodisk current sheet, the magnetospheric upstream conditions near Titan's orbit are in continuous fluctuation. In consequence, the moon's ionosphere is permanently "contaminated" by fossil magnetic fields, even when being located inside Saturn's magnetosphere. We present Cassini MAG observations, illustrating the high variability of the ambient flow conditions near Titan's orbit. Dione: An analysis of Cassini MAG data revealed Dione to possess a dilute, time-varying exosphere. Particle densities in this exosphere are controlled by a transient radiation belt, located at Dione's L shell. Based on an analytical model of the magnetic field perturbations, we impose quantitative constraints on the characteristics of Dione's transient exosphere. Rhea: Although Rhea's dilute atmosphere is "magnetically invisible", the moon possesses a weak Alfven wing. In contrast to the situation at Enceladus, Titan or Dione, this structure is generated by the finite extension of Rhea's plasma wake along the corotational flow direction. We present recent Cassini observations and modelling results of this peculiar structure. Finally, we briefly discuss some remaining puzzles on moon-plasma interactions at Saturn.

ENA diagnostic of the solar wind interaction with Mars and Venus

NASA Astrophysics Data System (ADS)

Barabash, Stas

Charge - exchange of the solar wind ions flowing around non-magnetized Mars and Venus on their exospheres results in hydrogen energetic neutral atom (ENA) emissions. Accelerated planetary ions may also experience charge - exchange resulting in planetary ENAs, mainly oxygen. The ENAs carry information on the ion distribution functions integrated over the line-of-sight and are used for remote sensing of the original plasma populations. The ASPERA-3/4 instruments (Analyzer of Space Plasmas and Energetic Atoms) onboard Mars Express and Venus Express missions performed the first-ever measurements of ENAs from these bodies in the energy range 100 eV - 10 keV. ENAs are mostly emitted by the magnetospheath plasma flowing around the induced magnetosphere. Due to lower gravity the Martian exosphere extends further in the magnetosheath than at Venus that makes Mars a “brighter ENA source”. We thus focus mostly on Mars and only briefly discuss ENA observations at Venus. ENA emissions from an elementary emitting volume in the magnetosheath are highly anisotropic and occur along the tangential line to the stream-line in this point. That makes impossible to obtain a global ENA image of the object from a single vantage point contrary to, for example, “classical” ENA imaging of the terrestrial ring current. At Mars the statistically obtained emission pattern shows an increase in the ENA flux perpendicular to the sun direction resembling a thick layer or a wall. The emissions coming mostly from the sub-solar point show an increase in the direction opposite to the convective electric field indicating the induced magnetosphere boundary is not cylindrically symmetric and closer to planet in this direction. Measurements of ENAs turned out to be an effective way to reveal the global dynamics of an induced magnetosphere. Arrival of an interplanetary shock to Mars and the associated compression of the induced magnetosphere are clearly detected as an abrupt termination of the ENA signal because the ENA wall suddenly moved away from the spacecraft. When the spacecraft stays sufficiently long inside the ENA wall, oscillations of the ENA signal with a period of 30 sec - few min (~0.01 Hz) can be observed. The oscillations of the similar frequency are observed in the electron and ion fluxes in the magnetosheath as well as magnetic field. Their physics is not understood. Mars Express/ASPERA-3 detected a slight increase of the ENA emissions above the magnetic anomalies. It may be related to the increase of the neutral densities above these regions. Contrary to the predictions, Mars Express/ASPERA-3 did not detect any oxygen ENAs. That allowed to provide upper limits for the hydrogen exospheric densities which turned out to be much lower at the solar minimum than expected. Finally, we introduce a few “exotic” ideas of using ENAs for studies the near-Venus and near-Mars space. Using ENAs backscattered from the atmosphere one may obtain global precipitating maps. Using the neutral solar wind passing through the upper atmosphere at the terminate region, one may realize neutral solar wind occultation geometry and use the ENA signal variation for the upper atmosphere profiling.

A 3D Multi-fluid MHD Study of the Interaction of the Solar Wind with the Ionosphere/Atmosphere System of Mars.

NASA Astrophysics Data System (ADS)

Najib, Dalal; Nagy, Andrew; Toth, Gabor; Ma, Yingjuan

We use our new four species multi-fluid model to study the interaction of the solar wind with Mars. The lower boundary of our model is at 100 km, below the main ionospheric peak, and the radial resolution is about 10 km in the ionosphere, thus the model does a very good job in reproducing the ionosphere and the associated processes. We carry out calculations for high and low solar activity conditions and establish the importance of mass loading by the extended exosphere of Mars. We also calculate the atmospheric escape of the ionospheric species, including pick up ions. Finally, we compare our model results with the Viking, MGS and Mars Express observations.

The effects of thermospheric winds and chemistry in the diurnal variations of thermospheric species

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.

1977-01-01

The reported investigation considers on the basis of a theoretical model, the diurnal variations of the thermospheric composition (H, He, O, O2, and Ar) in terms of thermal expansion with diffusive equilibrium and transport effects associated with thermospheric winds, chemistry, and exospheric flow. The theoretical results are compared with satellite composition data which indicate that the fundamental diurnal tide can be reasonably well understood. It is found that winds are only important for molecular oxygen below 180 km, while thermal expansion due to the larger mass is relatively more important for O2 than for O. Distinct from O, photodissociation and in particular photoionization of O2 are very significant for molecular oxygen.

Models of Jovian decametric radiation. [astronomical models of decametric waves

NASA Technical Reports Server (NTRS)

Smith, R. A.

1975-01-01

A critical review is presented of theoretical models of Jovian decametric radiation, with particular emphasis on the Io-modulated emission. The problem is divided into three broad aspects: (1) the mechanism coupling Io's orbital motion to the inner exosphere, (2) the consequent instability mechanism by which electromagnetic waves are amplified, and (3) the subsequent propagation of the waves in the source region and the Jovian plasmasphere. At present there exists no comprehensive theory that treats all of these aspects quantitatively within a single framework. Acceleration of particles by plasma sheaths near Io is proposed as an explanation for the coupling mechanism, while most of the properties of the emission may be explained in the context of cyclotron instability of a highly anisotropic distribution of streaming particles.

Twilight and nighttime ionospheric temperatures from oxygen wavelengths 6300 and 5577 spectral line profiles

NASA Technical Reports Server (NTRS)

Feibelman, W. A.; Hake, R. D., Jr.; Sipler, D. P.; Biondi, M. A.

1971-01-01

Fabry-Perot interferometer measurements of atomic oxygen 6300 A and 5577 A line profiles from twilight and nightglow are used to determine the neutral temperatures in F2 and E regions of the earth's ionosphere. The exospheric temperatures T sub n (infinity) determined from the 6300 A profiles are usually somewhat higher than those calculated from Jacchia's model, with differences as large as approximately 300 K noted when T sub n (infinity) = 1500 to 1600 K. The post-sunset and pre-dawn rate of change of T sub n (infinity) is often substantially larger than the Jacchia prediction. The 5577 A (E-region) measured temperatures range from 200 to 220 K on quiet nights to 500 to 600 K during geomagnetic storms.

Effects of the Solar Wind Pressure on Mercury's Exosphere: Hybrid Simulations

NASA Astrophysics Data System (ADS)

Travnicek, P. M.; Schriver, D.; Orlando, T. M.; Hellinger, P.

2017-12-01

We study effects of the changed solar wind pressure on the precipitation of hydrogen on the Mercury's surface and on the formation of Mercury's magnetosphere. We carry out a set of global hybrid simulations of the Mercury's magnetosphere with the interplanetary magnetic field oriented in the equatorial plane. We change the solar wind pressure by changing the velocity of injected solar wind plasma (vsw = 2 vA,sw; vsw = 4 vA,sw; vsw = 6 vA,sw). For each of the cases we examine proton and electron precipitation on Mercury's surface and calculate yields of heavy ions released from Mercury's surface via various processes (namely: Photo-Stimulated Desorption, Solar Wind Sputtering, and Electron Stimulated Desorption). We study circulation of the released ions within the Mercury's magnetosphere for the three cases.

Data analysis and interpretation of lunar dust exosphere

NASA Technical Reports Server (NTRS)

Andrews, George A., Jr.

1992-01-01

The lunar horizon glow observed by Apollo astronauts and captured on film during the Surveyor mission is believed to result from the scattering of sunlight off lunar fines suspended in a dust layer over the lunar surface. For scale heights on the order of tens of kilometers, it is anticipated that the size of the dust particles will be small enough to admit Rayleigh scattering. Such events would result in scattered light which is polarized to a degree which is a function of observation angle and produce spectra containing large high frequency components ('bluing'). Believing these signatures to be observable from ground based telescopes, observational data has been collected from McDonald Observatory and the task of reduction and analysis of this data is the focus of the present report.

Solar wind and extreme ultraviolet modulation of the lunar ionosphere/exosphere

NASA Technical Reports Server (NTRS)

Freeman, J. W.

1976-01-01

The ALSEP/SIDE detectors routinely monitor the dayside lunar ionosphere. Variations in the ionosphere are found to correlate with both the 2800 MHz radio index which can be related to solar EUV and with the solar wind proton flux. For the solar wind, the ionospheric variation is proportionately greater than that of the solar wind. This suggests an amplification effect on the lunar atmosphere due perhaps to sputtering of the surface or, less probably, an inordinate enhancement of noble gases in the solar wind. The surface neutral number density is calculated under the assumption of neon gas. During a quiet solar wind this number agrees with or is slightly above that expected for neon accreted from the solar wind. During an enhanced solar wind the neutral number density is much higher.

Electrical stress and strain in lunar regolith simulants

NASA Astrophysics Data System (ADS)

Marshall, J.; Richard, D.; Davis, S.

2011-11-01

Experiments to entrain dust with electrostatic and fluid-dynamic forces result in particulate clouds of aggregates rather than individual dust grains. This is explained within the framework of Griffith-flaw theory regarding the comminution/breakage of weak solids. Physical and electrical inhomogeneities in powders are equivalent to microcracks in solids insofar as they facilitate failure at stress risers. Electrical charging of powders induces bulk sample stresses similar to mechanical stresses experienced by strong solids, depending on the nature of the charging. A powder mass therefore "breaks" into clumps rather than separating into individual dust particles. This contrasts with the expectation that electrical forces on the Moon will eject a submicron population of dust from the regolith into the exosphere. A lunar regolith will contain physical and electrostatic inhomogeneities similar to those in most charged powders.

Venus: The Atmosphere, Climate, Surface, Interior and Near-Space Environment of an Earth-Like Planet

NASA Astrophysics Data System (ADS)

Taylor, Fredric W.; Svedhem, Håkan; Head, James W.

2018-02-01

This is a review of current knowledge about Earth's nearest planetary neighbour and near twin, Venus. Such knowledge has recently been extended by the European Venus Express and the Japanese Akatsuki spacecraft in orbit around the planet; these missions and their achievements are concisely described in the first part of the review, along with a summary of previous Venus observations. The scientific discussions which follow are divided into three main sections: on the surface and interior; the atmosphere and climate; and the thermosphere, exosphere and magnetosphere. These reports are intended to provide an overview for the general reader, and also an introduction to the more detailed topical surveys in the following articles in this issue, where full references to original material may be found.

A Massively Parallel Particle Code for Rarefied Ionized and Neutral Gas Flows in Earth and Planetary Atmospheres, Ionospheres and Magnetospheres

NASA Technical Reports Server (NTRS)

Combi, Michael R.

2004-01-01

In order to understand the global structure, dynamics, and physical and chemical processes occurring in the upper atmospheres, exospheres, and ionospheres of the Earth, the other planets, comets and planetary satellites and their interactions with their outer particles and fields environs, it is often necessary to address the fundamentally non-equilibrium aspects of the physical environment. These are regions where complex chemistry, energetics, and electromagnetic field influences are important. Traditional approaches are based largely on hydrodynamic or magnetohydrodynamic MHD) formulations and are very important and highly useful. However, these methods often have limitations in rarefied physical regimes where the molecular collision rates and ion gyrofrequencies are small and where interactions with ionospheres and upper neutral atmospheres are important.

Magnetic moment and plasma environment of HD 209458b as determined from Lyα observations.

PubMed

Kislyakova, Kristina G; Holmström, Mats; Lammer, Helmut; Odert, Petra; Khodachenko, Maxim L

2014-11-21

Transit observations of HD 209458b in the stellar Lyman-α(Lyα) line revealed strong absorption in both blue and red wings of the line interpreted as hydrogen atoms escaping from the planet's exosphere at high velocities. The following sources for the absorption were suggested: acceleration by the stellar radiation pressure, natural spectral line broadening, or charge exchange with the stellar wind. We reproduced the observation by means of modeling that includes all aforementioned processes. Our results support a stellar wind with a velocity of ≈400 kilometers per second at the time of the observation and a planetary magnetic moment of ≈1.6 × 10(26) amperes per square meter. Copyright © 2014, American Association for the Advancement of Science.

Investigations of Moon Polar Regions from Luna-Resource and Luna-Glob Landers - Science Instruments and Operational Plan on Surface

NASA Astrophysics Data System (ADS)

Tretyakov, V.; Mitrofanov, I.; Litvak, M.; Malakhov, A.; Mokrousov, M.

2012-04-01

Scientific goals for Landers of Luna-Resource and Luna-Glob missions will be presented. Both project aimed on search for volatiles and water ice in upper layer of regolith, study structure and content of regolith and investigate of moon's surface exosphere in lunar polar regions. Science devices for payload, which were selected in accordance to the main goals of these missions, will be described. Criteria for potential landing sites selection will be considered: from engineering suitability (flatness and roughness of surface, radio visibility, solar irradiation and so on) and from scientific applicability for these missions. The detailed plan of surface operations during fist moon day will be presented and preliminary plans for sunset and for second and others days will be discussed.

Long-Term Periodicity of the Mars Exospheric Density from MRO and Mars Odyssey Radio Tracking Data

NASA Astrophysics Data System (ADS)

Genova, A.; Goossens, S. J.; Lemoine, F. G.; Mazarico, E.; Smith, D. E.; Zuber, M. T.

2014-12-01

The Mars Odyssey and Mars Reconnaissance Orbiter (MRO) missions have collected more than 11 years of continuous tracking data of spacecraft in orbit around Mars. The radio science data are generally used to determine the static and seasonal gravity field of the central body. However, these two spacecraft are in different sun-synchronous orbits that cover a wide range of altitudes (250-410 km) where investigation of the atmosphere and climate of Mars so far have not been supported by in situ and remote sensing measurements. The drag perturbation acting on the probes provides indirect measurements of the Martian atmospheric density. Therefore, we focused our work on the determination of the long-term periodicity of the atmospheric constituents in the Mars exosphere with Mars Odyssey and MRO radio tracking data. We implemented the Drag Temperature Model (DTM) -Mars model into our Precise Orbit Determination (POD) program GEODYN-II to adequately reproduce variations in temperature and (partial) density along ODY and MRO trajectories. The recovery of Mars' atmospheric dynamics using Doppler tracking data requires the accurate modeling of all forces acting on the spacecraft. The main non-conservative force, apart from drag, is solar radiation pressure. Spacecraft panel reflectivities and the radiation pressure-scaling factor are not estimated, but we adjusted empirical once-per-revolution along-track periodic accelerations (cosine and sine) over each orbital arc to mitigate solar radiation pressure mismodeling. After converging the orbital data arcs, and editing out all the data during superior conjunctions, we combined the MRO and Mars Odyssey arcs in a global solution where we estimated spacecraft initial states, time-correlated drag scale factors, and annual and semi-annual variability of the major constituents in the Mars upper atmosphere. We will show that the updated DTM-Mars model provides a better prediction of the long-term variability of the dominant species, which are CO2, O, and He at the MRO and ODY orbit altitudes. The indirect measurements of atmospheric density profiles at those altitudes provide additional information to improve general circulation models, which already suitably represent lower altitudes in the atmosphere.

PREFACE: 14th Annual International Astrophysics Conference: Linear and Nonlinear Particle Energization throughout the Heliosphere and Beyond

NASA Astrophysics Data System (ADS)

Zank, G. P.

2015-09-01

The 14th Annual International Astrophysics Conference was held at the Sheraton Tampa Riverwalk Hotel, Tampa, Florida, USA, during the week of 19-24 April 2015. The meeting drew some 75 participants from all over the world, representing a wide range of interests and expertise in the energization of particles from the perspectives of theory, modelling and simulations, and observations. The theme of the meeting was "Linear and Nonlinear Particle Energization throughout the Heliosphere and Beyond." Energetic particles are ubiquitous to plasma environments, whether collisionless such as the supersonic solar wind, the magnetospheres of planets, the exospheres of nonmagnetized planets and comets, the heliospheric-local interstellar boundary regions, interstellar space and supernova remnant shocks, and stellar wind boundaries. Energetic particles are found too in more collisional regions such as in the solar corona, dense regions of the interstellar medium, accretion flows around stellar objects, to name a few. Particle acceleration occurs wherever plasma boundaries, magnetic and electric fields, and turbulence are present. The meeting addressed the linear and nonlinear physical processes underlying the variety of particle acceleration mechanisms, the role of particle acceleration in shaping different environments, and acceleration processes common to different regions. Both theory and observations were addressed with a view to encouraging crossdisciplinary fertilization of ideas, concepts, and techniques. The meeting addressed all aspects of particle acceleration in regions ranging from the Sun to the interplanetary medium to magnetospheres, exospheres, and comets, the boundaries of the heliosphere, and beyond to supernova remnant shocks, galactic jets, stellar winds, accretion flows, and more. The format of the meeting included 25-minute presentations punctuated by two 40-minute talks, one by Len Fisk that provided an historical overview of particle acceleration in the heliosphere (see the paper by Fisk, L., 50 Years of Research on Particle Acceleration in the Heliosphere, in this volume), and another by Len Burlaga, who presented a summary of the exciting new interstellar medium magnetic field observations being returned by Voyager 1 (see the paper by Burlaga, L., Voyager Observations of the Magnetic Field in the Heliosheath and the LISM, in this volume).

Long-Range Solar Activity Predictions: A Reprieve from Cycle #24's Activity

NASA Technical Reports Server (NTRS)

Richon, K.; Schatten, K.

2003-01-01

We discuss the field of long-range solar activity predictions and provide an outlook into future solar activity. Orbital predictions for satellites in Low Earth Orbit (LEO) depend strongly on exospheric densities. Solar activity forecasting is important in this regard, as the solar ultra-violet (UV) and extreme ultraviolet (EUV) radiations inflate the upper atmospheric layers of the Earth, forming the exosphere in which satellites orbit. Rather than concentrate on statistical, or numerical methods, we utilize a class of techniques (precursor methods) which is founded in physical theory. The geomagnetic precursor method was originally developed by the Russian geophysicist, Ohl, using geomagnetic observations to predict future solar activity. It was later extended to solar observations, and placed within the context of physical theory, namely the workings of the Sun s Babcock dynamo. We later expanded the prediction methods with a SOlar Dynamo Amplitude (SODA) index. The SODA index is a measure of the buried solar magnetic flux, using toroidal and poloidal field components. It allows one to predict future solar activity during any phase of the solar cycle, whereas previously, one was restricted to making predictions only at solar minimum. We are encouraged that solar cycle #23's behavior fell closely along our predicted curve, peaking near 192, comparable to the Schatten, Myers and Sofia (1996) forecast of 182+/-30. Cycle #23 extends from 1996 through approximately 2006 or 2007, with cycle #24 starting thereafter. We discuss the current forecast of solar cycle #24, (2006-2016), with a predicted smoothed F10.7 radio flux of 142+/-28 (1-sigma errors). This, we believe, represents a reprieve, in terms of reduced fuel costs, etc., for new satellites to be launched or old satellites (requiring reboosting) which have been placed in LEO. By monitoring the Sun s most deeply rooted magnetic fields; long-range solar activity can be predicted. Although a degree of uncertainty in the long-range predictions remains, requiring future monitoring, we do not expect the next cycle's + 2-sigma value will rise significantly above solar cycle #23's activity level.

Kinetic Modeling of the Lunar Dust-Plasma Environment

NASA Astrophysics Data System (ADS)

Kallio, Esa; Alho, Markku; Alvarez, Francisco; Barabash, Stas; Dyadechkin, Sergey; Fernandes, Vera; Futaana, Yoshifumi; Harri, Ari-Matti; Haunia, Touko; Heilimo, Jyri; Holmström, Mats; Jarvinen, Riku; Lue, Charles; Makela, Jakke; Porjo, Niko; Schmidt, Walter; Shahab, Fatemi; Siili, Tero; Wurz, Peter

2014-05-01

Modeling of the lunar dust and plasma environment is a challenging task because a self-consistent model should include ions, electrons and dust particles and numerous other factors. However, most of the parameters are not well established or constrained by measurements in the lunar environment. More precisely, a comprehensive model should contain electrons originating from 1) the solar wind, 2) the lunar material (photoelectrons, secondary electrons) and 3) the lunar dust. Ions originate from the solar wind, the lunar material, the lunar exosphere and the dust. To model the role of the dust in the lunar plasma environment is a highly complex task since the properties of the dust particles in the exosphere are poorly known (e.g. mass, size, shape, conductivity) or not known (e.g. charge and photoelectron emission) and probably are time dependent. Models should also include the effects of interactions between the surface and solar wind and energetic particles, and micrometeorites. Largely different temporal and spatial scales are also a challenge for the numerical models. In addition, the modeling of a region on the Moon - for example on the South Pole - at a given time requires also knowledge of the solar illumination conditions at that time, mineralogical and electric properties of the local lunar surface, lunar magnetic anomalies, solar UV flux and the properties of the solar wind. Harmful effects of lunar dust to technical devices and to human health as well as modeling of the properties of the lunar plasma and dust environment have been topics of two ESA funded projects L-DEPP and DPEM. In the presentation we will summarize some basic results and characteristics of plasma and fields near and around the Moon as studied and discovered in these projects. Especially, we analyse three different space and time scales by kinetic models: [1] the "microscale" region near surface with an electrostatic PIC (ions and electrons are particles) model, [2] the "mesoscale" region including lunar magnetic anomalies and [3] the global scale Moon-solar wind interaction with hybrid (ions as particles in massless electron fluid) models.

Multi-fluid MHD simulations of Europa's interaction with Jupiter's magnetosphere

NASA Astrophysics Data System (ADS)

Harris, C. D. K.; Jia, X.; Slavin, J. A.; Rubin, M.; Toth, G.

2017-12-01

Several distinct physical processes generate the interaction between Europa, the smallest of Jupiter's Galilean moons, and Jupiter's magnetosphere. The 10˚ tilt of Jupiter's dipole causes time varying magnetic fields at Europa's orbit which interact with Europa's subsurface conducting ocean to induce magnetic perturbations around the moon. Jovian plasma interacts with Europa's icy surface to sputter off neutral particles, forming a tenuous exosphere which is then ionized by impact and photo-ionization to form an ionosphere. As jovian plasma flows towards the moon, mass-loading and interaction with the ionosphere slow the flow, producing magnetic perturbations that propagate along the field lines to form an Alfvén wing current system, which connects Europa to its bright footprint in Jupiter's ionosphere. The Galileo mission has shown that the plasma interaction generates significant magnetic perturbations that obscure signatures of the induced field from the subsurface ocean. Modeling the plasma-related perturbations is critical to interpreting the magnetic signatures of Europa's induction field, and therefore to magnetic sounding of its interior, a central goal of the upcoming Europa Clipper mission. Here we model the Europa-Jupiter interaction with multi-fluid magnetohydrodynamic simulations to understand quantitatively how these physical processes affect the plasma and magnetic environment around the moon. Our model separately tracks the bulk motion of three different ion fluids (exospheric O2+, O+, and magnetospheric O+), and includes sources and losses of mass, momentum and energy to each of the ion fluids due to ionization, charge-exchange and recombination. We include calculations of the electron temperature allowing for field-aligned electron heat conduction, and Hall effects due to differential ion-electron motion. Compared to previous simulations, this multi-fluid model allows us to more accurately determine the precipitation flux of jovian plasma to Europa's surface, which has significant implications for space weathering at the moon. Including the Hall effect in our simulations enables us to determine the effects of separate ion-electron bulk motion throughout the interaction, and our simulations reveal noticeable asymmetries and small-scale features in the Alfvén wings.

Emirates Mars Mission (EMM) Overview

NASA Astrophysics Data System (ADS)

Sharaf, Omran; Amiri, Sarah; AlMheiri, Suhail; Alrais, Adnan; Wali, Mohammad; AlShamsi, Zakareyya; AlQasim, Ibrahim; AlHarmoodi, Khuloud; AlTeneiji, Nour; Almatroushi, Hessa; AlShamsi, Maryam; AlAwadhi, Mohsen; McGrath, Michael; Withnell, Pete; Ferrington, Nicolas; Reed, Heather; Landin, Brett; Ryan, Sean; Pramann, Brian

2017-04-01

United Arab Emirates (UAE) has entered the space exploration race with the announcement of Emirates Mars Mission (EMM), the first Arab Islamic mission to another planet, in 2014. Through this mission, UAE is to send an unmanned probe, called Hope probe, to be launched in summer 2020 and reach Mars by 2021 to coincide with UAE's 50th anniversary. Through a sequence of subsequent maneuvers, the spacecraft will enter a large science orbit that has a periapsis altitude of 20,000 km, an apoapsis altitude of 43,000 km, and an inclination of 25 degrees. The mission is designed to (1) characterize the state of the Martian lower atmosphere on global scales and its geographic, diurnal and seasonal variability, (2) correlate rates of thermal and photochemical atmospheric escape with conditions in the collisional Martian atmosphere, and (3) characterize the spatial structure and variability of key constituents in the Martian exosphere. These objectives will be met by four investigations with diurnal variability on sub-seasonal timescales which are (1) determining the three-dimensional thermal state of the lower atmosphere, (2) determining the geographic and diurnal distribution of key constituents in the lower atmosphere, (3) determining the abundance and spatial variability of key neutral species in the thermosphere, and (4) determining the three-dimensional structure and variability of key species in the exosphere. EMM will collect these information about the Mars atmospheric circulation and connections through a combination of three distinct instruments that image Mars in the visible, thermal infrared and ultraviolet wavelengths and they are the Emirates eXploration Imager (EXI), the Emirates Mars InfraRed Spectrometer (EMIRS), and the EMM Mars Ultraviolet Spectrometer (EMUS). EMM has passed its Mission Concept Review (MCR), System Requirements Review (SRR), System Design Review (SDR), and Preliminary Design Review (PDR) phases. The mission is led by Emiratis from Mohammed Bin Rashid Space Centre, Dubai, UAE, and it will expand the nation's human capital through knowledge transfer programs set with international partners from the University of Colorado Laboratory for Atmospheric and Space Physics (LASP), University of California Berkeley Space Sciences Lab (SSL), and Arizona State University (ASU) School of Earth and Space Exploration.

No hydrogen exosphere detected around the super-Earth HD 97658 b

NASA Astrophysics Data System (ADS)

Bourrier, V.; Ehrenreich, D.; King, G.; Lecavelier des Etangs, A.; Wheatley, P. J.; Vidal-Madjar, A.; Pepe, F.; Udry, S.

2017-01-01

The exoplanet HD 97658 b provides a rare opportunity to probe the atmospheric composition and evolution of moderately irradiated super-Earths. It transits a bright K star at a moderate orbital distance of 0.08 au. Its low density is compatible with a massive steam envelope that could photodissociate at high altitudes and become observable as escaping neutral hydrogen. Our analysis of three transits with HST/STIS at Lyman-α reveals no such signature, suggesting that the thermosphere of HD 97658 b is not hydrodynamically expanding and is subjected to a low escape of neutral hydrogen (<108 g s-1 at 3σ). Using HST/STIS Lyman-α observations and Chandra/ACIS-S and XMM-Newton/EPIC X-ray observations at different epochs, we find that HD 97658 is in fact a weak and soft X-ray source with signs of chromospheric variability in the Lyman-α line core. We determine an average reference for the intrinsic Lyman-α line and X-EUV (XUV) spectrum of the star, and show that HD 97658 b is in mild conditions of irradiation compared to other known evaporating exoplanets with an XUV irradiation about three times lower than the evaporating warm Neptune GJ436 b. This could be the reason why the thermosphere of HD 97658 b is not expanding: the low XUV irradiation prevents an efficient photodissociation of any putative steam envelope. Alternatively, it could be linked to a low hydrogen content or inefficient conversion of the stellar energy input. The HD 97658 system provides clues for understanding the stability of low-mass planet atmospheres in terms of composition, planetary density, and irradiation. Our study of HD 97658 b can be seen as a control experiment of our methodology, confirming that it does not bias detections of atmospheric escape and underlining its strength and reliability. Our results show that stellar activity can be efficiently discriminated from absorption signatures by a transiting exospheric cloud. They also highlight the potential of observing the upper atmosphere of small transiting planets to probe their physical and chemical properties.

Observing Planets and Small Bodies in Sputtered High Energy Atom (SHEA) Fluxes

NASA Technical Reports Server (NTRS)

Milillo, A.; Orsini, S.; Hsieh, K. C.; Baragiola, R.; Fama, M.; Johnson, R.; Mura, A.; Plainaki, Ch.; Sarantos, M.; Cassidy, T. A.;

Measurement and modeling of the refilling plasmasphere during 2001

DOE PAGES

Krall, J.; Huba, J. D.; Jordanova, V. K.; ...

2016-03-18

The Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) and the RAM-CPL (Ring current Atmosphere interaction Model-Cold PLasma) codes are used to model observed plasmasphere dynamics during 25 November 2001 to 1 December 2001 and 1–5 February 2001. Model results compare well to plasmasphere observations of electron and mass densities. Comparison of model results to refilling data and to each other shows good agreement, generally within a factor of 2. We find that SAMI3 plasmaspheric refilling rates and ion densities are sensitive to the composition and temperature of the thermosphere and exosphere, and to photoelectron heating.more » Furthermore, results also support our previous finding that the wind-driven dynamo significantly impacts both refilling rates and plasmasphere dynamics during quiet periods.« less

Measurement and modeling of the refilling plasmasphere during 2001

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krall, J.; Huba, J. D.; Jordanova, V. K.

The Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) and the RAM-CPL (Ring current Atmosphere interaction Model-Cold PLasma) codes are used to model observed plasmasphere dynamics during 25 November 2001 to 1 December 2001 and 1–5 February 2001. Model results compare well to plasmasphere observations of electron and mass densities. Comparison of model results to refilling data and to each other shows good agreement, generally within a factor of 2. We find that SAMI3 plasmaspheric refilling rates and ion densities are sensitive to the composition and temperature of the thermosphere and exosphere, and to photoelectron heating.more » Furthermore, results also support our previous finding that the wind-driven dynamo significantly impacts both refilling rates and plasmasphere dynamics during quiet periods.« less

Hydrogen Balmer alpha intensity distributions and line profiles from multiple scattering theory using realistic geocoronal models

NASA Technical Reports Server (NTRS)

Anderson, D. E., Jr.; Meier, R. R.; Hodges, R. R., Jr.; Tinsley, B. A.

1987-01-01

The H Balmer alpha nightglow is investigated by using Monte Carlo models of asymmetric geocoronal atomic hydrogen distributions as input to a radiative transfer model of solar Lyman-beta radiation in the thermosphere and atmosphere. It is shown that it is essential to include multiple scattering of Lyman-beta radiation in the interpretation of Balmer alpha airglow data. Observations of diurnal variation in the Balmer alpha airglow showing slightly greater intensities in the morning relative to evening are consistent with theory. No evidence is found for anything other than a single sinusoidal diurnal variation of exobase density. Dramatic changes in effective temperature derived from the observed Balmer alpha line profiles are expected on the basis of changing illumination conditions in the thermosphere and exosphere as different regions of the sky are scanned.

Upper atmosphere and ionosphere of Mars.

PubMed

Donahue, T M

1966-05-06

It is argued that the single-layer ionosphere at 125 kilometers discovered in the Mariner IV occultation experiment is an Fl region coinciding with the ultraviolet photoionization peak. The CO(2) density there must be of the order of 10(11) molecules per cubic centimeter. Such a density is consistent with the properties of the lower atmosphere by Mariner IV anid the temperature model of Chamberlain and McElroy if the atmosphere is mainly CO(2) below 70 kilometers. The absence of an F2 region can be explained even if the density ratio of O to CO(2) is 100 at 230 kilometers on the basis of the rapid conversion of O(+) to O(2) by CO(2). Thus a model with an exospheric temperature of 400 degrees K, a modest degree of CO(2) dissociation, and diffusive separation above 70 kilometers is possible.

Auroral zone effects on hydrogen geocorona structure and variability

NASA Technical Reports Server (NTRS)

Moore, T. E.; Biddle, A. P.; Waite, J. H., Jr.; Killeen, T. L.

1985-01-01

The effect of diurnal and magnetospheric modulations on the structure of the hydrogen geocorona is analyzed on the basis of recent observations. Particular attention is given to the enhancement of neutral escape by plasma effects, including the recently observed phenomenon of low-altitude ion acceleration. It is found that, while significant fluxes of neutral H should be produced by transverse ion acceleration in the auroral zone, the process is probably insufficient to account for the observed polar depletion of hydrogen atoms. Analysis of recent exospheric temperature measurements from the Dynamics Explorer-2 satellite suggest that neutral heating in and near the high latitude cusp may be the major contributor to depleted atomic hydrogen densities at high latitudes. Altitude profiles of the production rates for escaping neutral hydrogen atoms during periods of maximum, minimum, and typical solar activity are provided.

The Lunar Atmosphere and Dust Environment Explorer (LADEE): Initial Science Results

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Hine, B.; Delory, G. T.; Salute, J. S.; Noble, S.; Colaprete, A.; Horanyi, M.; Mahaffy, P.

2014-01-01

On September 6, 2013, a nearperfect launch of the first Minotaur V rocket successfully carried NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) into a higheccentricity geocentric orbit. The launch, from NASA's Wallops Flight Facility in Virginia, was visible from much of the eastern seaboard. Over the next 30 days, LADEE performed three phasing orbits, with near-perfect maneuvers that placed apogee at ever higher altitudes in preparation for rendezvous with the Moon. LADEE arrived at the Moon on October 6, 2013, during the government shutdown. LADEE's science objectives are twofold: (1) Determine the composition of the lunar atmosphere, investigate processes controlling its distribution and variability, including sources, sinks, and surface interactions; (2) Characterize the lunar exospheric dust environment, measure its spatial and temporal variability, and effects on the lunar atmosphere, if any.

Extreme ultraviolet observations from Voyager 1 encounter with Jupiter

NASA Technical Reports Server (NTRS)

Broadfoot, A. L.; Belton, M. J. S.; Takacs, P. Z.; Sandel, B. R.; Shemansky, D. E.; Holberg, J. B.; Ajello, J. M.; Atreya, S. K.; Donahue, T. M.; Moos, H. W.

1979-01-01

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S(+2), S(+3), O(+2) indicating an electron temperature of 100,000 K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (greater than or equal to 1000 K) with a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Extracting lunar dust parameters from image charge signals produced by the Lunar Dust Experiment

NASA Astrophysics Data System (ADS)

Stanley, J.; Kempf, S.; Horanyi, M.; Szalay, J.

2015-12-01

The Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) is an impact ionization dust detector used to characterize the lunar dust exosphere generated by the impacts of large interplanetary particles and meteor streams (Horanyi et al., 2015). In addition to the mass and speed of these lofted particles, LDEX is sensitive to their charge. The resulting signatures of impact events therefore provide valuable information about not only the ambient plasma environment, but also the speed vectors of these dust grains. Here, impact events produced from LDEX's calibration at the Dust Accelerator Laboratory are analyzed using an image charge model derived from the electrostatic simulation program, Coulomb. We show that parameters such as dust grain speed, size, charge, and position of entry into LDEX can be recovered and applied to data collected during LADEE's seven-month mission.

Return to Mercury: a global perspective on MESSENGER's first Mercury flyby.

PubMed

Solomon, Sean C; McNutt, Ralph L; Watters, Thomas R; Lawrence, David J; Feldman, William C; Head, James W; Krimigis, Stamatios M; Murchie, Scott L; Phillips, Roger J; Slavin, James A; Zuber, Maria T

2008-07-04

In January 2008, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft became the first probe to fly past the planet Mercury in 33 years. The encounter revealed that Mercury is a dynamic system; its liquid iron-rich outer core is coupled through a dominantly dipolar magnetic field to the surface, exosphere, and magnetosphere, all of which interact with the solar wind. MESSENGER images confirm that lobate scarps are the dominant tectonic landform and record global contraction associated with cooling of the planet. The history of contraction can be related to the history of volcanism and cratering, and the total contractional strain is at least one-third greater than inferred from Mariner 10 images. On the basis of measurements of thermal neutrons made during the flyby, the average abundance of iron in Mercury's surface material is less than 6% by weight.

New Understanding of Mercury's Magnetosphere from MESSENGER'S First Flyby

NASA Technical Reports Server (NTRS)

Slavin, James A.; Acuna, Mario H.; Anderson, Brian J.; Baker, Daniel N.; Benna, Mehdi; Gloeckler, George; Gold, Robert E.; Ho, George C.; Killen, M.; Korth, Haje;

The first laboratory measurements of sulfur ions sputtering water ice

NASA Astrophysics Data System (ADS)

Galli, André; Pommerol, Antoine; Vorburger, Audrey; Wurz, Peter; Tulej, Marek; Scheer, Jürgen; Thomas, Nicolas; Wieser, Martin; Barabash, Stas

2015-04-01

The upcoming JUpiter ICy moons Explorer mission to Europa, Ganymede, and Callisto has renewed the interest in the interaction of plasma with an icy surface. In particular, the surface release processes on which exosphere models of icy moons rely should be tested with realistic laboratory experiments. We therefore use an existing laboratory facility for space hardware calibration in vacuum to measure the sputtering of water ice due to hydrogen, oxygen, and sulfur ions at energies from 1 keV to 100 keV. Pressure and temperature are comparable to surface conditions encountered on Jupiter's icy moons. The sputter target is a 1cm deep layer of porous, salty water ice. Our results confirm theoretical predictions that the sputter yield from oxygen and sulfur ions should be similar. Thanks to the modular set-up of our experiment we can add further surface processes relevant for icy moons, such as electron sputtering, sublimation, and photodesorption due to UV light.

Mars atmospheric losses induced by the solar wind: current knowledge and perspective

NASA Astrophysics Data System (ADS)

Ermakov, Vladimir; Zelenyi, Lev; Vaisberg, Oleg; Sementsov, Egor; Dubinin, Eduard

2017-04-01

Solar wind induced atmospheric losses have been studied since earlier 1970th. Several loss channels have been identified including pick-up of exospheric photo-ions and ionospheric ions escape. Measurements performed during several solar cycles showed variation of these losses by about factor of 10, being largest at maximum solar activity. MAVEN spacecraft equipped with comprehensive set of instruments with high temporal and mass resolution operating at Mars since fall 2014 ensures much better investigation of solar wind enforcing Martian environment, Mars atmospheric losses processes and mass loss rate. These issues are very important for understanding of Martian atmospheric evolution including water loss during cosmogonic time. Simultaneous observations by MAVEN and MEX spacecraft open the new perspective in study of Martian environment. In this report we discuss results of past and current missions and preliminary analysis of heavy ions escape using simultaneous measurements of MEX and MAVEN spacecraft.

Venus Interior Probe Using In-Situ Power and Propulsion (VIP-INSPR)

NASA Technical Reports Server (NTRS)

Bugga, Ratnakumar V.

2016-01-01

Venus, despite being our closest neighboring planet, is under-explored due to its hostile and extreme environment, with a 92 bar pressure and 467 C temperature at the surface. The temperature decreases at higher altitudes, almost at the rate of 7.9 C/km, reaching the Earth surface conditions at 65 km. Due to the less extreme conditions, balloon missions could survive as long as 46 h at an altitude of 54 km. However, because of the opacity of the Venus atmosphere filled with clouds of sulfuric acid and CO2, orbiter or balloon missions are not as revealing and informative in characterizing the surface, as similar missions on Moon and Mars. To understand the evolutionary paths of Venus in relation to Earth, it is imperative to gather basic information on the crust, mantle, core, atmosphere/exosphere and bulk composition of Venus, through in-situ investigations using landers, probes and variable altitude areal platforms.

A 3D Multi-fluid MHD Study of the Interaction of the Solar Wind with the Ionosphere/Atmosphere System of Venus.

NASA Astrophysics Data System (ADS)

Najib, D.; Nagy, A.; Toth, G.; Ma, Y.-J.

2011-10-01

We use the latest version of our four species multifluid model to study the interaction of the solar wind with Venus. The model solves simultaneously the continuity, momentum and energy equations of the different ions. The lower boundary of our model is at 100 km, below the main ionospheric peak, and the radial resolution is about 10 km in the ionosphere, thus the model does a very good job in reproducing the ionosphere and the associated processes. We carry out calculations for high and low solar activity conditions and establish the importance of mass loading by the extended exosphere of Venus. We demonstrate the importance of using the multi-fluid rather than a single fluid model. We also calculate the atmospheric escape of the ionospheric species and compare our model results with the observed parameters from Pioneer Venus and Venus Express.

Neutral atmospheric models compatible with satellite orbital decay and incoherent scatter measurements

NASA Technical Reports Server (NTRS)

Rohrbaugh, J. L.

1972-01-01

A correlation study was made of the variations of the exospheric temperature extrema with various combinations of the monthly mean and daily values of the 2800 MHz and Ca:2 solar indices. The phase and amplitude of the semi-annual component and the term dependent on Kp were found to remain almost the same for the maximum and minimum temperature. The term dependent on the 27 day component of the solar activity was found to be about four times as large for the diurnal maximum as for the minimum. Measurements at Arecibo have shown that temperature gradient changes at 125 km are consistent with the phase difference between the neutral temperature and density maxima. This is used to develop an empirical model which is compatible with both the satellite measurements and the available incoherent scatter measurements. A main feature of this model is that day length is included as a major model parameter.

Sputtering of Lunar Regolith Simulant by Protons and Multicharged Heavy Ions at Solar Wind Energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, Fred W; Harris, Peter R; Taylor, C. N.

2011-01-01

We report preliminary results on sputtering of a lunar regolith simulant at room temperature by singly and multiply charged solar wind ions using quadrupole and time-of-flight (TOF) mass spectrometry approaches. Sputtering of the lunar regolith by solar-wind heavy ions may be an important particle source that contributes to the composition of the lunar exosphere, and is a possible mechanism for lunar surface ageing and compositional modification. The measurements were performed in order to assess the relative sputtering efficiency of protons, which are the dominant constituent of the solar wind, and less abundant heavier multicharged solar wind constituents, which have highermore » physical sputtering yields than same-velocity protons, and whose sputtering yields may be further enhanced due to potential sputtering. Two different target preparation approaches using JSC-1A AGGL lunar regolith simulant are described and compared using SEM and XPS surface analysis.« less

Surface charging of a crater near lunar terminator

NASA Astrophysics Data System (ADS)

Anuar, A. K.

2017-05-01

Past lunar missions have shown the presence of dust particles in the lunar exosphere. These particles originate from lunar surface and are due to the charging of lunar surface by the solar wind and solar UV flux. Near the lunar terminator region, the low conductivity of the surface and small scale variations in surface topology could cause the surface to charge to different surface potentials. This paper simulates the variation of surface potential for a crater located in the lunar terminator regions using Spacecraft Plasma Interaction Software (SPIS). SPIS employs particle in cell method to simulate the motion of solar wind particles and photoelectrons. Lunar crater has been found to create mini-wake which affects both electron and ion density and causes small scale potential differences. Simulation results show potential difference of 300 V between sunlit area and shadowed area which creates suitable condition for dust levitation to occur.

A New Instrument Design for Imaging Low Energy Neutral Atoms

NASA Technical Reports Server (NTRS)

Keller, John W.; Collier, Michael R.; Chornay, Dennis; Rozmarynowski, Paul; Getty, Stephanie; Cooper, John F.; Smith, Billy

2007-01-01

The MidSTAR-2 satellite, to be built at the US Naval Academy as a follow-on to the successful MidSTAR-1 satellite (http://web.ew.usna.edu/midstar/), will launch in 2011 and carry three Goddard Space Flight Center (GSFC) experiments developed under Goddard's Internal Research and Development (IRAD) program. One of these GSFC instruments, the Miniature Imager for Neutral Ionospheric atoms and Magnetospheric Electrons (MINI-ME) builds on the heritage of the Goddard-developed Low-Energy Neutral Atom (LENA) imager launched on the IMAGE spacecraft in 2000. MINI-ME features a Venetian-blind conversion surface assembly that improves both light rejection and conversion efficiency in a smaller and lighter package than LENA making this an highly effective instrument for viewing solar wind charge exchange with terrestrial and planetary exospheres. We will describe the MINI-ME prototyping effort and its science targets.

Science Objectives for a Soft X-ray Mission

NASA Astrophysics Data System (ADS)

Sibeck, D. G.; Connor, H. K.; Collier, M. R.; Collado-Vega, Y. M.; Walsh, B.

2016-12-01

When high charge state solar wind ions exchange electrons with exospheric neutrals, soft X-rays are emitted. In conjunction with flight- proven wide field-of-view soft X-ray imagers employing lobster-eye optics, recent simulations demonstrate the feasibility of imaging magnetospheric density structures such as the bow shock, magnetopause, and cusps. This presentation examines the Heliospheric scientific objectives that such imagers can address. Principal amongst these is the nature of reconnection at the dayside magnetopause: steady or transient, widespread or localized, component or antiparallel as a function of solar wind conditions. However, amongst many other objectives, soft X-ray imagers can provide crucial information concerning the structure of the bow shock as a function of solar wind Mach number and IMF orientation, the presence or absence of a depletion layer, the occurrence of Kelvin-Helmholtz or pressure-pulse driven magnetopause boundary waves, and the effects of radial IMF orientations and the foreshock upon bow shock and magnetopause location.

The Radio & Plasma Wave Investigation (RPWI) for JUICE

NASA Astrophysics Data System (ADS)

Wahlund, J.-E.

2013-09-01

We present the Radio & Plasma Waves Investigation (RPWI) selected for implementation on the JUICE mission. RPWI consists of a highly integrated instrument package that provides a whole set of plasma and fields measurements. The RPWI instrument has outstanding new capabilities not previously available to outer planet missions, and that would address many fundamental planetary science objectives. Specifically, RPWI would be able to study the electro-dynamic influence of the Jovian magnetosphere on the exospheres, surfaces and conducting oceans of Ganymede, Europa and Callisto. RPWI would also be able to monitor the sources of radio emissions from auroral regions of Ganymede and Jupiter, and possibly also from lightning activity in Jupiter's clouds. Moreover, RPWI will search for exhaust plumes from cracks on the icy moons, as well as μm-sized dust and related dust-plasmasurface interaction processes occurring near the icy moons of Jupiter.

Stair-Step Particle Flux Spectra on the Lunar Surface: Evidence for Nonmonotonic Potentials?

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Newheart, Anastasia; Poppe, Andrew R.; Hills, H. Kent; Farrell, William M.

2016-01-01

We present examples of unusual "stair-step" differential flux spectra observed by the Apollo 14 Suprathermal Ion Detector Experiment on the lunar dayside surface in Earth's magnetotail. These spectra exhibit a relatively constant differential flux below some cutoff energy and then drop off precipitously, by about an order of magnitude or more, at higher energies. We propose that these spectra result from photoions accelerated on the lunar dayside by nonmonotonic potentials (i.e.,potentials that do not decay to zero monotonically) and present a model for the expected differential flux. The energy of the cutoff and the magnitude of the differential flux are related to the properties of the local space environment and are consistent with the observed flux spectra. If this interpretation is correct, these surface-based ion observations provide a unique perspective that both complements and enhances the conclusions obtained by remote-sensing orbiter observations on the Moon's exospheric and electrostatic properties.

The Sheath Transport Observer for the Redistribution of Mass (STORM) Image

NASA Technical Reports Server (NTRS)

Kuntz, Kip; Collier, Michael; Sibeck, David G.; Porter, F. Scott; Carter, J. A.; Cravens, Thomas; Omidi, N.; Robertson, Ina; Sembay, S.; Snowden, Steven L.

2008-01-01

All of the solar wind energy that powers magnetospheric processes passes through the magnetosheath and magnetopause. Global images of the magnetosheath and magnetopause boundary layers will resolve longstanding controversy surrounding fundamental phenomena that occur at the magnetopause and provide information needed to improve operational space weather models. Recent developments showing that soft X-rays (0.15-1 keV) result from high charge state solar wind ions undergoing charge exchange recombination through collisions with exospheric neutral atoms has led to the realization that soft X-ray imaging can provide global maps of the high-density shocked solar wind within the magnetosheath and cusps, regions lying between the lower density solar wind and magnetosphere. We discuss an instrument concept called the Sheath Transport Observer for the Redistribution of Mass (STORM), an X-ray imager suitable for simultaneously imaging the dayside magnetosheath, the magnetopause boundary layers, and the cusps.

The Sheath Transport Observer for the Redistribution of Mass (STORM) Imager

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Sibeck, David G.; Porter, F. Scott; Burch, J.; Carter, J. A.; Cravens, Thomas; Kuntz, Kip; Omidi, N.; Read, A.; Robertson, Ina;

Laboratory Impact Experiments

NASA Astrophysics Data System (ADS)

Horanyi, M.; Munsat, T.

2017-12-01

The experimental and theoretical programs at the SSERVI Institute for Modeling Plasmas, Atmospheres, and Cosmic Dust (IMPACT) address the effects of hypervelocity dust impacts and the nature of the space environment of granular surfaces interacting with solar wind plasma and ultraviolet radiation. These are recognized as fundamental planetary processes due their role in shaping the surfaces of airless planetary objects, their plasma environments, maintaining dust haloes, and sustaining surface bound exospheres. Dust impacts are critically important for all airless bodies considered for possible human missions in the next decade: the Moon, Near Earth Asteroids (NEAs), Phobos, and Deimos, with direct relevance to crew and mission safety and our ability to explore these objects. This talk will describe our newly developed laboratory capabilities to assess the effects of hypervelocity dust impacts on: 1) the gardening and redistribution of dust particles; and 2) the generation of ionized and neutral gasses on the surfaces of airless planetary bodies.

The Dynamics of Helium and its Impact on the Upper Thermosphere

NASA Astrophysics Data System (ADS)

Sutton, E. K.; Thayer, J. P.; Wang, W.; Solomon, S. C.; Schmidt, F.

2015-12-01

The TIE-GCM was recently augmented to include helium and argon, two approximately inert species that can be used as tracers of dynamics in the thermosphere. The former species is treated as a major species due to its large abundance near the upper boundary. The effects of exospheric transport are also included in order to simulate realistic seasonal and latitudinal helium distributions. The latter species is treated as a classical minor species, imparting absolutely no forces on the background atmosphere. In this study, we examine the interplay of the various dynamical terms - i.e. background circulation, molecular and Eddy diffusion - as they drive departures from the distributions that would be expected under assumptions of diffusive equilibrium. As this has implications on the formulation of all semi-empirical thermospheric models, we use this understanding to identify the conditions under which helium can significantly affect nowcasts and forecasts of neutral density.

ROSAT Observations of Solar Wind Charge Exchange with the Lunar Exosphere

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Snowden, S. L.; Benna, M.; Carter, J. A.; Cravens, T. E.; Hills, H. Kent; Hodges, R. R.; Kuntz, K. D.; Porter, F. Scott; Read, A.;

Wide Field-of-View Soft X-Ray Imaging for Solar Wind-Magnetosphere Interactions

NASA Technical Reports Server (NTRS)

Walsh, B. M.; Collier, M. R.; Kuntz, K. D.; Porter, F. S.; Sibeck, D. G.; Snowden, S. L.; Carter, J. A.; Collado-Vega, Y.; Connor, H. K.; Cravens, T. E.;

Superthermal electron processes in the upper atmosphere of Uranus: Aurora and electroglow

NASA Technical Reports Server (NTRS)

Waite, J. H., Jr.; Chandler, M. O.; Yelle, R. V.; Sandel, B. R.

1987-01-01

Strong ultraviolet emissions from the upper atmosphere of Uranus suggest that both auroral and electroglow phenomena are of significant aeronomical consequences in the structure of the upper atmosphere. Combined modeling and data analysis were performed to determine the effect of electroglow and auroral phenomena on the global heat and atomic hydrogen budgets in the Uranus upper atmosphere. The results indicate that the auroral and electroglow heat sources are not adequate to explain the high exospheric temperature observed at Uranus, but that the atomic hydrogen supplied by these processes is more than sufficient to explain the observations. The various superthermal electron distributions modeled have significantly different efficiencies for the various processes such as UV emission, heating, ionization, and atomic hydrogen production, and produce quite different H2 band spectra. However, additional information on the UV spectra and global parameters is needed before modeling can be used to distinguish between the possible mechanisms for electroglow.

Imaging the Sources and Full Extent of the Sodium Tail of the Planet Mercury

NASA Technical Reports Server (NTRS)

Baumgardner, Jeffrey; Wilson, Jody; Mendillo, Michael

2008-01-01

Observations of sodium emission from Mercury can be used to describe the spatial and temporal patterns of sources and sinks in the planet s surface-boundary-exosphere. We report on new data sets that provide the highest spatial resolution of source regions at polar latitudes, as well as the extraordinary length of a tail of escaping Na atoms. The tail s extent of approx.1.5 degrees (nearly 1400 Mercury radii) is driven by radiation pressure effects upon Na atoms sputtered from the surface in the previous approx.5 hours. Wide-angle filtered-imaging instruments are thus capable of studying the time history of sputtering processes of sodium and other species at Mercury from ground-based observatories in concert with upcoming satellite missions to the planet. Plasma tails produced by photo-ionization of Na and other gases in Mercury s neutral tails may be observable by in-situ instruments.

Chemistry and evolution of Titan's atmosphere

NASA Technical Reports Server (NTRS)

Strobel, D. F.

1982-01-01

The chemistry and evolution of Titan's atmosphere are reviewed, in light of the scientific findings from the Voyager mission. It is argued that the present N2 atmosphere may be Titan's initial atmosphere, rather than one photochemically derived from an original NH3 atmosphere. The escape rate of hydrogen from Titan is controlled by photochemical production from hydrocarbons. CH4 is irreversibly converted to less hydrogen-rich hydrocarbons, which over geologic time accumulate on the surface to a layer thickness of about 0.5 km. Magnetospheric electrons interacting with Titan's exosphere may dissociate enough N2 into hot, escaping N atoms to remove about 0.2 of Titan's present atmosphere over geologic time. The energy dissipation of magnetospheric electrons exceeds solar EUV energy deposition in Titan's atmosphere by an order of magnitude, and is the principal driver of nitrogen photochemistry. The environmental conditions in Titan's upper atmosphere are favorable to building up complex molecules, particularly in the north polar cap region.

Geodynamo, solar wind, and magnetopause 3.4 to 3.45 billion years ago.

PubMed

Tarduno, John A; Cottrell, Rory D; Watkeys, Michael K; Hofmann, Axel; Doubrovine, Pavel V; Mamajek, Eric E; Liu, Dunji; Sibeck, David G; Neukirch, Levi P; Usui, Yoichi

2010-03-05

Stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss. Although the early Earth retained its water and atmosphere, and thus evolved as a habitable planet, little is known about Earth's magnetic field strength during that time. We report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3.4 to 3.45 billion years ago. The measured field strength is approximately 50 to 70% that of the present-day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of < or = 5 Earth radii, similar to values observed during recent coronal mass ejection events. The data also suggest lower-latitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition.

The Permanently Shadowed Regions of Dwarf Planet Ceres

NASA Technical Reports Server (NTRS)

Schorghofer, Norbert; Mazarico, Erwan; Platz, Thomas; Preusker, Frank; Schroeder, Stefan E.; Raymond, Carol A.; Russell, Christopher T.

2016-01-01

Ceres has only a small spin axis tilt (4 deg), and craters near its rotational poles can experience permanent shadow and trap volatiles, as is the case on Mercury and on Earth's Moon. Topography derived from stereo imaging by the Dawn spacecraft is used to calculate direct solar irradiance that defines the extent of the permanently shadowed regions (PSRs). In the northern polar region, PSRs cover approximately 1800 sq km or 0.13% of the hemisphere, and most of the PSRs are cold enough to trap water ice over geological time periods. Based on modeling of the water exosphere, water molecules seasonally reside around the winter pole and ultimately an estimated 0.14% of molecules get trapped. Even for the lowest estimates of the amount of available water, this predicts accumulation rates in excess of loss rates, and hence, there should be fresh ice deposits in the cold traps.

A comparison of empirical and experimental O7+, O8+, and O/H values, with applications to terrestrial solar wind charge exchange

NASA Astrophysics Data System (ADS)

Whittaker, Ian C.; Sembay, Steve

2016-07-01

Solar wind charge exchange occurs at Earth between the neutral planetary exosphere and highly charged ions of the solar wind. The main challenge in predicting the resultant photon flux in the X-ray energy bands is due to the interaction efficiency, known as the α value. This study produces experimental α values at the Earth, for oxygen emission in the range of 0.5-0.7 keV. Thirteen years of data from the Advanced Composition Explorer are examined, comparing O7+ and O8+ abundances, as well as O/H to other solar wind parameters allowing all parameters in the αO7,8+ calculation to be estimated based on solar wind velocity. Finally, a table is produced for a range of solar wind speeds giving average O7+ and O8+ abundances, O/H, and αO7,8+ values.

A very high frequency radio interferometer for investigating ionospheric disturbances using geostationary satellites. Determination of changes in exospheric electron content by a comparison of group delay and Faraday rotation

NASA Technical Reports Server (NTRS)

Terry, R.; Flaherty, B. J.; Dubroff, R. E.

1972-01-01

The theory and development of a VHF correlation radio interferometer for investigating ionospheric disturbances are discussed. The system was developed to receive signals from the geostationary Applications Technology Satellites. Amplitude and phase variations of the signal passing through the ionosphere can be detected by this instrument. The system consists of two superheterodyne receivers separated by a distance known as the baseline of the system. Since the system is a phase sensitive instrument, the local oscillators of the two receivers must be phase coherent. This is accomplished by using phase-locked loops for generating the local oscillators. The two signals from the separate receivers are cross-correlated by multiplying the two signals together and then time averaging the result. The sensitivity of the instrument is increased by off-setting one of the local oscillators by a small amount.

A Forecast of Reduced Solar Activity and Its Implications for NASA

NASA Technical Reports Server (NTRS)

Schatten, Kenneth; Franz, Heather

2005-01-01

The "Solar Dynamo" method of solar activity forecasting is reviewed. Known generically as a 'precursor" method, insofar as it uses observations which precede solar activity generation, this method now uses the Solar Dynamo Amplitude (SODA) Index to estimate future long-term solar activity. The peak amplitude of the next solar cycle (#24), is estimated at roughly 124 in terms of smoothed F10.7 Radio Flux and 74 in terms of the older, more traditional smoothed international or Zurich Sunspot number (Ri or Rz). These values are significantly smaller than the amplitudes of recent solar cycles. Levels of activity stay large for about four years near the peak in smoothed activity, which is estimated to occur near the 2012 timeflame. Confidence is added to the prediction of low activity by numerous examinations of the Sun s weakened polar field. Direct measurements are obtained by the Mount Wilson Solar Observatory and the Wilcox Solar Observatory. Further support is obtained by examining the Sun s polar faculae (bright features), the shape of coronal soft X-ray "holes," and the shape of the "source surface" - a calculated coronal feature which maps the large scale structure of the Sun s field. These features do not show the characteristics of well-formed polar coronal holes associated with typical solar minima. They show stunted polar field levels, which are thought to result in stunted levels of solar activity during solar cycle #24. The reduced levels of solar activity would have concomitant effects upon the space environment in which satellites orbit. In particular, the largest influences would affect orbit determination of satellites in LEO (Low Earth Orbit), based upon the altered thermospheric and exospheric densities. A decrease in solar activity would result in smaller satellite decay rates, as well as fewer large solar events that can destroy satellite electronic functions. Other effects of reduced solar activity upon the space environment include enhanced galactic cosmic rays and more space debris at low altitudes (from the decay of old satellite parts, etc.). The reasons are well known: namely, solar activity serves to sweep the inner heliosphere of galactic cosmic rays, and lower exospheric densities result in decreased drag on LEO debris, allowing longer lifetimes.

Ar Atmosphere: Implications for Structure and Composition of Mercury's Crust

NASA Technical Reports Server (NTRS)

Killen, R. M.; Morgan, T. H.

2001-01-01

We examine the possibilities of sustaining an argon atmosphere by diffusion from the upper 10 km of crust, and alternatively by effusion from a molten or previously molten area at great depth . Ar-40 in the atmospheres of the planets is a measure of potassium abundance in the interiors since Ar-40 is a product of radiogenic decay of K-40 by electron capture with the subsequent emission of a 1.46 eV gamma-ray. Although the Ar-40 in the earth's atmosphere is expected to have accumulated since the late bombardment, Ar-40 in surface-bounded exospheres is eroded quickly by photoionization and electron impact ionization. Thus, the argon content in the exospheres of the Moon, Mercury and probably Europa is representative of current effusion rather than accumulation over the lifetime of the body. Argon content will be a function of K content, temperature, grain size distribution, connected pore volume and possible seismic activity. Although Mercury and the Moon differ in many details, we can train the solutions to diffusion equations to predict the average lunar atmosphere. Then these parameters can be varied for Hermean conditions. Assuming a lunar crustal potassium abundance of 300 ppm, the observed argon atmosphere requires equilibrium between the argon production in the upper 9 Km of the moon (1.135 x 10(exp -3) cm(exp -3) s(exp -1)) and its loss. Hodges et al. conclude that this loss rate and the observed time variability requires argon release through seismic activity, tapping a deep argon source. An important observation is that the extreme surface of the Moon is enhanced in argon rather than depleted, as one would expect from outgassing of radiogenic argon. Manka and Michel concluded that ion implantation explains the surface enhancement of Ar-40. About half of the argon ions produced in the lunar atmosphere would return to the surface, where they would become embedded in the rocks. Similarly, at Mercury we expect the surface rocks to be enhanced in Ar-40 wherever the magnetosphere has been open over time. Thus the measurement of surface composition will reveal the long-term effects of solar wind-magnetosphere interaction. Additional information is contained in the original extended abstract.

Mass spectrometry of planetary exospheres at high relative velocity: direct comparison of open- and closed source measurements

NASA Astrophysics Data System (ADS)

Meyer, Stefan; Tulej, Marek; Wurz, Peter

2016-04-01

The exploration of habitable worlds around the gas giants in the Solar System is of major interest in upcoming planetary missions. Exactly this theme is addressed by the Jupiter Icy Moons Explorer (JUICE) mission of ESA, which will characterise Ganymede, Europa and Callisto as planetary objects and potential habitats [1], [2]. We developed a prototype of the Neutral gas and Ion Mass spectrometer (NIM) of the Particle Environment Package (PEP) for the JUICE mission intended for composition measurements of neutral gas and thermal plasma. NIM/PEP will be used to measure the chemical composition of the exospheres of the icy Jovian moons. Besides direct ion measurement, the NIM instrument is able to measure the inflowing neutral gas in two different modes: in neutral mode the gas enters directly the ion source (open source) and in thermal mode, the gas gets thermally accommodated to wall temperature by several collisions inside an equilibrium sphere before entering the ion source (closed source). We performed measurements with the prototype NIM using a neutral gas beam of 1 up to 5 km/s velocity in the neutral and thermal mode. The current trajectory of JUICE foresees a flyby velocity of 4 km/s at Europa, other flybys are in the range of 1 up to 7 km/s and velocity in Ganymede orbits is around 2 km/s. Different species are used for gas beam, such as noble gases Ne, Ar, Kr as well as molecules like H2, Methane, Ethane, Propane and more complex ones. We will present the results of these measurements with respect to fragmentation and density enhancements in the closed source mode. Furthermore, we will give a direct comparison between open and closed source mode measurements. References: [1] ESA, "JUICE assessment study report (Yellow Book)", ESA/SRE(2011)18, 2012. [2] O. Grasset, M.K. Dougherty, A. Coustenis, E.J. Bunce, C. Erd, D. Titov, M. Blanc, A. Coates, P. Drossart, L.N. Fletcher, H. Hussmann, R. Jaumann, N. Krupp, J.-P. Lebreton, O. Prieto-Ballesteros, P. Tortora, F. Tosi, T. Van Hoolst, "JUpiter Icy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system", Planet. Space Sci., 2013, 78, pp. 1 - 21.

Plasma IMS Composition Measurements for Europa and the Other Galilean Moons

NASA Technical Reports Server (NTRS)

Sittler, Edward; Cooper, John; Hartle, Richard; Lipatov, Alexander; Mahaffy, Paul; Paterson, William; Pachalidis, Nick; Coplan, Mike; Cassidy, Tim

2010-01-01

NASA and ESA are planning the joint Europa Jupiter System Mission (EJSM) to the Jupiter system with specific emphasis to Europa and Ganymede, respectively. The Japanese Space Agency is also planning an orbiter mission to explore Jupiter's magnetosphere and the Galilean satellites. For NASA's Jupiter Europa Orbiter (JEO) we are developing the 3D Ion Mass Spectrometer (IMS) with two main goals which can also be applied to the other Galilean moons, 1) measure the plasma interaction between Europa and Jupiter's magnetosphere and 2) infer the 4 pi surface composition to trace elemental and significant isotopic levels. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second gives information about transfer of material between the Galilean moons, and between the moon surfaces and subsurface layers putatively including oceans. The measurement of the interactions for all the Galilean moons can be used to trace the in situ ion measurements of pickup ions back to either Europa's or Ganymede's surface from the respectively orbiting spacecraft. The IMS instrument, being developed under NASA's Astrobiology Instrument Development Program, would maximally achieve plasma measurement requirements for JEO and EJSM while moving forward our knowledge of Jupiter system composition and source processes to far higher levels than previously envisaged. The composition of the global surfaces of Europa and Ganymede can be inferred from the measurement of ejected neutrals and pick-up ions using at minimum an in situ payload including MAG and IMS also fully capable of meeting Level 1 mission requirements for ocean detection and survey. Elemental and isotopic analysis of potentially extruded oceanic materials at the moon surfaces would further support the ocean objectives. These measurements should be made from a polar orbiting spacecraft about Europa or Ganymede at height 100 km. The ejecta produced by sputtering of the surfaces of Europa and Ganymede has been shown to be representative of the surface composition. Level 2 science on surface geology and composition can then be further enhanced by addition of the following: 3D Ion Neutral Mass Spectrometer (INNS), 3D plasma electron spectrometer (ELS), and hot plasma energetic particle instrument. The measurement approach is to alternate between times measuring pickup ions and times measuring plasma and magnetic field parameters along the spacecraft trajectory. By measuring the pickup ion energy, arrival direction and mass-per-charge, the ion can be traced back along the ejection trajectory to the approximate area of origin if the 3-D electric field and magnetic field are known. In situ observations of plasma flow velocities and vector magnetic fields can be used to determine the local convective electric field (E = -VXB) along the spacecraft trajectory. By combining this information with models of the magnetospheric interaction with Europa, one can generate 3D maps of the electric and magnetic field and compute the trajectories of the pickup ions back to the surface or exospheric points of origin. In the case of Ganymede there is the additional complexity of its own internal dipole magnetic field, while Io's volcanic activity introduces the complexity of a highly structured denser atmosphere. Callisto with its less globally extended exosphere will have a simpler interaction than for Europa (i.e., more like our moon). We will discuss these differences in light of the above proposed technique. Finally, the INNS observations and neutral exosphere models are needed to estimate production rates of pickup ions. The hot plasma measurements are needed to correct for sputtering rates which can be time dependent and electron plasma observations for electron impact ionization rates. Instrument characteristics, field-of-view requirements, modes of operation and effects of radiation on instrument functionality will be discussed.

Loss of Water to Space from Mars: Processes and Implications

NASA Astrophysics Data System (ADS)

Kass, D. M.

2001-12-01

One of the major sinks for water on Mars is the loss to space. This occurs via a complex series of processes that transport the individual atoms to the upper atmosphere, where several escape mechanisms remove them. Hydrogen and deuterium are lost primarily by Jeans escape. Non-thermal processes also remove H and D, but are only important in determining D loss at solar minimum under modern conditions. The present H loss rate is equivalent to the loss of 10-3~pr-\\micron~yr-1 of water. The loss of oxygen is more complicated. The three main processes are indirect (or ionospheric) sputtering, solar wind pickup of O+, and O2+ dissociative recombination. Their relative importance has varied over the history of Mars. The combined effect of the O loss processes is to remove a ~ 50~m global layer of water over the last 3.5 Gyr. Based on photochemical modeling, the loss of oxygen and hydrogen are balanced (over geological timescales) by a feedback process. During the early history of Mars, impact erosion and hydrodynamic blow-off may have removed significant water. But, it is difficult to estimate their quantitative effects. The transport of individual H, D and O atoms to the exosphere where they can escape is not completely understood. It occurs primarily via intermediate species, H2, HD, O2 and CO2. The H2 and HD are formed by photolysis of water and the odd hydrogen photochemistry. One open issue is the mechanism regulating the partitioning of D between HDO and HD (which controls the supply of D available for escape from the exosphere). The various loss processes isotopically enrich Martian water since the exospheric escape source region is depleted. Jeans escape and the transport from the lower atmosphere further fractionate hydrogen, the most useful isotopic system. Based on recent observations, the D/H fractionation factor, F ~ 0.02. Measurements of atmospheric water vapor indicate it is enriched in deuterium, with a D/H ratio ~ 5 times the terrestrial value. Since most of the water on Mars is likely to be in the form of ice, it is presumably further fractionated by ~ 0.8 due to ice/water vapor interactions. This yields an effective D/H enrichment of ~ 7 for reservoirs in equilibrium with the atmosphere. From a loss to space point of view, Martian water can be divided into three reservoirs. The first is the thin, 10 pr-\\micron, atmospheric water. The second is a global exchangeable reservoir in long term isotopic equilibrium with the atmosphere. This probably encompasses the polar caps, ice in polar layered deposits and any other near surface ice or adsorbed water. The third, more speculative, reservoir is a non-exchanging reservoir (a deep sub-surface cryosphere). In addition, due to the small size of the atmospheric reservoir, difficulty in isotopically equilibrating it with the entire exchangeable reservoir, and the relatively rapid H2 loss rate, there is also an intermediate exchangeable reservoir of ~ 4~mm. This is probably either a surface layer on the polar caps or near surface ice deposits. By assuming an initial terrestrial D/H ratio for Martian water (based on condritic meteorites) and a loss to space of ~ 50~m (based on the total O loss), the size of the exchangeable reservoir can be estimated. Two conceptual models are possible, depending on whether or not the non-exchangeable reservoir replenishes the exchangeable one. Quantitatively, the two models yield almost identical reservoir sizes, ~ 9~m (about the size of the northern polar cap). If, due to slow rate of isotopic diffusion in ice, the exchangeable reservoir actually has the same isotopic enrichment as the atmosphere, it would contain ~ 12~m of water.

Ringing After a High-Energy Collision: Ambipolar Oscillations During Impact Plasma Expansion

NASA Technical Reports Server (NTRS)

Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.

2012-01-01

High-velocity impacts on the Moon and other airless bodies deliver energy and material to the lunar surface and exosphere. The target and i mpactor material may become vaporized and ionized to form a collision al plasma that expands outward and eventually becomes collisionless. In the present work, kinetic simulations of the later collision less stage of impact plasma expansion are performed. Attention is paid to characterizing "ambipolar oscillations" in which thermodynamic distur bances propagate outward to generate "ringing" within the expanding e lectron cloud, which could radiate an electromagnetic signature of lo cal plasma conditions. The process is not unlike a beam-plasma intera ction, with the perturbing electron population in the present case ac ting as a highly thermal "beam" that resonates along the expanding de nsity gradient. Understanding the electromagnetic aspects of impact p lasma expansion could provide insight into the lasting effects of nat ural, impact-generated currents on airless surfaces and charging haza rds to human exploration infrastructure and instrumentation.

Preshock region acceleration of implanted cometary H(+) and O(+)

NASA Astrophysics Data System (ADS)

Gombosi, T. I.

1988-01-01

A self-consistent, three-fluid model of plasma transport and implanted ion acceleration in the unshocked solar wind is presented. The solar wind plasma is depleted by charge exchange with the expanding cometary exosphere, while implanted protons and heavy ions are produced by photoionization and charge transfer and lost by charge exchange. A generalized transport equation describing convection, adiabatic and diffusive velocity change, and the appropriate production terms is used to describe the evolution of the two cometary ion components, while the moments of the Boltzmann equation are used to calculate the solar wind density and pressure. The flow velocity is obtained self-consistently by combining the conservation equations of the three ion species. The results imply that second-order Fermi acceleration can explain the implanted spectra observed in the unshocked solar wind. Comparison of measured and calculated distribution indicates that spatial diffusion of implanted ions probably plays an important role in forming the energetic particle environment in the shock vicinity.

Formation of the lunar helium corona and atmosphere

NASA Technical Reports Server (NTRS)

Hodges, R. R., Jr.

1977-01-01

Helium is one of the dominant gases of the lunar atmosphere. Its presence is easily identified in data from the mass spectrometer at the Apollo 17 landing site. The major part of these data was obtained in lunar nighttime, where helium concentration reaches the maximum of its diurnal cyclic variation. The large night to day concentration ratio agrees with the basic theory of exospheric lateral transport reported by Hodges and Johnson (1968). A reasonable fraction of atmospheric helium atoms has a velocity in excess of the gravitational escape velocity. The result is a short average lifetime and a tenuous helium atmosphere. A description is presented of an investigation which shows that the atmosphere of the moon has two distinct components including low energy atoms, which are gravitationally bound in trajectories that intersect the lunar surface, and higher energy atoms, which are trapped in satellite orbits. The total helium abundance in the lunar corona is shown to be about 1.3 times 10 to the 30th power atoms.

Modeling the coma of 2060 Chiron

NASA Technical Reports Server (NTRS)

Boice, D. C.; Konno, I.; Stern, S. Alan; Huebner, W. F.

1991-01-01

Observations of comet-like activity and a resolved coma have established that 2060 Chiron is a comet. Determinations of its radius range from 65 to 200 km. This unusually large size for a comet suggests that the atmosphere of Chiron is intermediate to the tightly bound, thin atmospheres typical of planets and satellite and the greatly extended atmospheres in free expansion typical of cometary comae. Under certain conditions it may gravitationally bind an atmosphere that is thick compared to its size, while a significant amount of gas escapes to an extensive exosphere. These attributes coupled with reports of sporadic outbursts at large heliocentric distances and the identification of CN in the coma make Chiron a challenging object to model. Simple models of gas production and the dusty coma were recently presented but a general concensus on many basic features has not emerged. Development was begun on a more complete coma model of Chiron. The objectives are to report progress on this model and give the preliminary results for understanding Chiron.

Copernicus measurement of the Jovian Lyman-alpha emission and its aeronomical significance

NASA Technical Reports Server (NTRS)

Atreya, S. K.; Kerr, R. B.; Upson, W. L., II; Festou, M. C.; Donahue, T. M.; Barker, E. S.; Cochran, W. D.; Bertaux, J. L.

1982-01-01

It is pointed out that the intensity of the Lyman-alpha emission is a good indicator of the principal aeronomical processes on the major planets. The high-resolution ultraviolet spectrometer aboard the Orbiting Astronomical Observatory Copernicus was used in 1980 April and May to detect the Jovian Lyman-alpha emission by spectroscopically discriminating it from other Doppler shifted Lyman-alpha emissions such as those of the geocorona, and the interplanetary medium. Taking into consideration the reported emission data, it appears that an unusually large energy input due to the particle precipitation in the auroral region must have been responsible for the large observed Lyman-alpha intensity during the Voyager encounter. At most other times, the observed Jovian Lyman-alpha intensity can be explained, within the range of statistical uncertainty, by a model that takes into consideration the solar EUV flux, the solar Lyman-alpha flux, the high exospheric temperature, and the eddy diffusion coefficient without energy input from the auroral sources.

Transport, charge exchange and loss of energetic heavy ions in the earth's radiation belts - Applicability and limitations of theory

NASA Technical Reports Server (NTRS)

Spjeldvik, W. N.

1981-01-01

Computer simulations of processes which control the relative abundances of ions in the trapping regions of geospace are compared with observations from discriminating ion detectors. Energy losses due to Coulomb collisions between ions and exospheric neutrals are considered, along with charge exchange losses and internal charge exchanges. The time evolution of energetic ion fluxes of equatorially mirroring ions under radial diffusion is modelled to include geomagnetic and geoelectric fluctutations. Limits to the validity of diffusion transport theory are discussed, and the simulation is noted to contain provisions for six ionic charge states and the source effect on the radiation belt oxygen ion distributions. Comparisons are made with ion flux data gathered on Explorer 45 and ISEE-1 spacecraft and results indicate that internal charge exchanges cause the radiation belt ion charge state to be independent of source charge rate characteristics, and relative charge state distribution is independent of the radially diffusive transport rate below the charge state redistribution zone.

Energetic Particles Dynamics in Mercury's Magnetosphere

NASA Technical Reports Server (NTRS)

Walsh, Brian M.; Ryou, A.S.; Sibeck, D. G.; Alexeev, I. I.

2013-01-01

We investigate the drift paths of energetic particles in Mercury's magnetosphere by tracing their motion through a model magnetic field. Test particle simulations solving the full Lorentz force show a quasi-trapped energetic particle population that gradient and curvature drift around the planet via "Shabansky" orbits, passing though high latitudes in the compressed dayside by equatorial latitudes on the nightside. Due to their large gyroradii, energetic H+ and Na+ ions will typically collide with the planet or the magnetopause and will not be able to complete a full drift orbit. These simulations provide direct comparison for recent spacecraft measurements from MESSENGER. Mercury's offset dipole results in an asymmetric loss cone and therefore an asymmetry in particle precipitation with more particles precipitating in the southern hemisphere. Since the planet lacks an atmosphere, precipitating particles will collide directly with the surface of the planet. The incident charged particles can kick up neutrals from the surface and have implications for the formation of the exosphere and weathering of the surface

Ceres Obliquity History and Its Implications for the Permanently Shadowed Regions

NASA Technical Reports Server (NTRS)

Ermakov, A. I.; Mazarico, E.; Schroder, S. E.; Carsenty, U.; Schorghofer, N.; Preusker, F.; Raymond, C. A.; Russell, C. T.; Zuber, Maria T.

2017-01-01

Due to the small current obliquity of Ceres ( epsilon approximately equal to 4), permanently shadowed regions (PSRs) exist on the dwarf planets surface. Since the existence and persistence of the PSRs depend on the obliquity, we compute the obliquity history over the last 3 My and find that it undergoes large oscillations with a period of 24.5 ky and a maximum of max 19:5. During periods of large obliquity, most of the present-day PSRs receive direct sunlight. Some craters in Ceres polar regions possess bright crater floor deposits (BCFDs).We find an apparent correlation between BCFDs and the most persistent PSRs. In the north, only two PSRs remain at max and they both contain BCFDs. In the south, one of the two only craters that remain in shadow at max contains a BCFD. The location of BCFDs within persistent PSRs strongly suggests BCFDs consist of volatiles accumulated in PSR cold traps: either water molecules trapped from the exosphere or exposed ground ice.

New Opportunities in Geospace Remote Sensing

NASA Astrophysics Data System (ADS)

Solomon, S. C.

2017-12-01

This paper will discuss scientific objectives that can be addressed with the serendipitous constellation of thermosphere-ionosphere observations provided by the NASA Ionospheric Connection Explorer (ICON) and Global-scale Observations of the Limb and Disk (GOLD) missions, the international Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2), instruments on the International Space Station and the Defense Meteorological Satellite Program, the European SWARM satellites, the NSF-sponsored AMPERE project, and the ongoing TIMED mission. The confluence of these space-based observations provide opportunities to extend the capabilities of ground-based observational networks, and to exploit opportunities for the development of numerical models and data assimilation methods. A particular focus is the global-scale context provided through GOLD mission measurements, and the challenges presented by their analysis and interpretation. GOLD can be considered a pathfinder for opportunistic instrumentation on commercial vehicles at geostationary orbit, so further speculation will be presented on what other future observations of the thermosphere-ionosphere and exosphere-plasmasphere could be made from these platforms.

A theory of local and global processes which affect solar wind electrons. 1: The origin of typical 1 AU velocity distribution functions: Steady state theory

NASA Technical Reports Server (NTRS)

Scudder, J. D.

1978-01-01

A detailed first principle kinetic theory for electrons which is neither a classical fluid treatment nor an exospheric calculation is presented. This theory illustrates the global and local properties of the solar wind expansion that shape the observed features of the electron distribution function, such as its bifurcation, its skewness and the differential temperatures of the thermal and suprathermal subpopulations. Coulomb collisions are substantial mediators of the interplanetary electron velocity distribution function and they place a zone for a bifurcation of the electron distribution function deep in the corona. The local cause and effect precept which permeates the physics of denser media is modified for electrons in the solar wind. The local form of transport laws and equations of state which apply to collision dominated plasmas are replaced with global relations that explicitly depend on the relative position of the observer to the boundaries of the system.

Composition and evolution of the atmosphere of Venus

NASA Technical Reports Server (NTRS)

Donahue, Thomas (Principal Investigator)

1996-01-01

The contract year started by analyzing Jovian atmospheric data acquired by the Galileo Probe Mass Spectrometer (GPMS). Two Venus hydrogen projects got underway as well. The first study strives to understand how to reconcile the standard treatment of the evolution of the H2O and HDO resevoirs on Venus over 4.5 Gyr in the presence of H and D escape and injection by comets. The second study is calculating the charge exchange contribution to hydrogen loss rates, using realistic models for exospheric H, H(+), D, D(+), and ion temperature from PV data. This report includes the following papers as attachments and supporting data: 'The Galileo Probe Mass Spectrometer: Composition of Jupiter's Atmosphere'; 'Chemical Composition Measurements of the Atmosphere of Jupiter with the Galileo Probe Mass Spectrometer'; 'Ion/Neutral Escape of Hydrogen and Deuterium: Evolution of Water'; 'Hydrogen and Deuterium in the Thermosphere of Venus: Solar Cycle Variations and Escape'; and 'Solar Cycle Variations in H(+) and D(+) Densities in the Venus Ionosphere: Implications for Escape'.

The Lunar Atmosphere as a Cosmic-Ray Detector

NASA Technical Reports Server (NTRS)

Wilson, T. L.

2007-01-01

The recent discovery of a tenuous sodium (Na) atmosphere on the Moon and Mercury has renewed interest in studying the lunar atmosphere since the physics involved for the two bodies is thought to be of similar nature. Na came as a surprise because it had been missed by in situ UV measurements made during the Apollo program. The new lunar observations involve the visible D1 (5896 ) and D2 (5890 ) wavelengths which are highly efficient at scattering sunlight. Although its lunar source and morphology is still not completely understood, Na is present as a collisionless exosphere - apparently in the form of a cometary-type coma with a tail that can extend hundreds of lunar radii during Leonid showers. The global shape of the atmosphere, in particular for the shaded antisolar side, has been modelled by Smyth. Since planetary atmospheres can be used as cosmic-ray (CR) spectrometers by means of their fluorescence excited by CR-induced air shower particles, the subject of the Moon s atmosphere as a CR detector will be discussed here.

The upper atmosphere of Uranus

NASA Technical Reports Server (NTRS)

Strobel, Darrell F.; Yelle, Roger V.; Shemansky, Donald E.; Atreya, Sushil K.

1991-01-01

Voyager measurements of the upper atmosphere of Uranus are analyzed and developed. The upper atmosphere of Uranus is predominantly H2, with at most 10 percent He by volume, and the dominant constituent of the exosphere is H. The thermosphere is warm, with an asymptotic isothermal temperature of about 800 K. Atomic hydrogen at this temperature forms an extensive thermal corona and creates gas drag that severely limits the lifetime of small ring particles. The upper atmosphere emits copious amounts of UV radiation from pressures greater than 0.01 microbar. The depth of this emission level imposes a powerful constraint on permissible emission mechanisms. Electron excitation from a thin layer near the exobase appears to violate this constraint. Solar fluorescence is consistent with the observed trend in solar zenith-angle variation of the emissions and is absent from the night side of the planet. On Uranus, it accounts for the observed Lyman beta to H2 bands intensity ratio and an important fraction of the observed intensity (about 55 percent).

Io: IUE observations of its atmosphere and the plasma torus

NASA Technical Reports Server (NTRS)

Ballester, G. E.; Moos, H. W.; Feldman, P. D.; Strobel, D. F.; Skinner, T. E.; Bertaux, J.-L.; Festou, M. C.

1988-01-01

Two of the main components of the atmosphere of Io, neutral oxygen and sulfur, were detected with the IUE. Four observations yield brightnesses that are similar, regardless of whether the upstream or the downstream sides of the torus plasma flow around Io is observed. A simple model requires the emissions to be produced by the interaction of O and S columns in the exospheric range with 2 eV electrons. Cooling of the 5 eV torus electrons is required prior to their interaction with the atmosphere of Io. Inconsistencies in the characteristics of the spectra that cannot be accounted for in this model require further analysis with improved atomic data. The Io plasma torus was monitored with the IUE. The long-term stability of the warm torus is established. The observed brightnesses were analyzed using a model of the torus, and variations of less than 30 percent in the composition are observed, the quantitative results being model dependent.

Energetic oxygen precipitation as a source of vibrationally excited N/sub 2//sup +/ in emissions observed at low latitudes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tinsley, B.A.; Rohrbaugh, R.P.; Sahai, Y.

Observations have been made at Mt. Haleakala, Hawaii (dip lat.approx.22/sup 0/N) and Cachoeira Paulista, Brasil (dip lat.approx.12/sup 0/S) of emissions excited by particle precipitation during periods of magnetic activity. The first negative bands of N/sub 2//sup +/ were found to have a high degree of vibrational excitation at both sites, and withi the absence of emissions attributable to hydrogen and helium, this finding leads to the interpretation that the excitation was due to a flux of precipitating oxygen atoms or ions, more plausibly the former, produced by charge exchange of ring current O/sup +/ ions with exospheric neutral constituents. Moremore » laboratory work is needed to properly interpret the data, but crude estimates of the associated energy deposition and ionization production fall in the range 10/sup -1/ to 10/sup +1/mWm/sup -2/, and 10/sup 0/-10/sup 2/ cm/sup -3/s/sup -1/ respectively.« less

Reconstructing Ion Spectra from Low-Altitude ENAs: Moderate to Large Storms.

NASA Astrophysics Data System (ADS)

LLera, K.; Goldstein, J.; McComas, D. J.; Valek, P. W.

2015-12-01

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) Energetic neutral atom (ENA) imagers regularly observe Low-altitude Emission (LAE) intensifications during geomagnetic storm intervals. Since LAEs are produced by the interaction between ions and the near-Earth exosphere (altitudes ~200-800 km), they are a global signature of how the ring current decays in response to solar wind conditions. In this "optically thick" region, an ENA readily becomes reionized, and an ion is readily neutralized. Therefore, emerging ENAs that contribute to the LAE signal (detectable several RE away) have undergone multiple charge exchange and electron stripping interactions. Accounting for the ~36 eV energy loss per interaction, we developed a model to quantify the total energy lost by emergent LAEs. The analytical tool is applied to an ensemble of moderate to large storms (including the recent 17 March and 23 June storms in 2015) to reconstruct the parent ion spectra from TWINS ENA images. We examine the ion spectra energy characteristics among the various storm events.

Ion Composition in Titan's Exosphere from the Cassini Plasma Spectrometer

NASA Astrophysics Data System (ADS)

Woodson, A.; Smith, H. T.; Johnson, R. E.

2013-12-01

A primary goal of the Cassini mission has been to characterize the complex interaction between Saturn's magnetosphere and Titan's ionosphere. To this end, the Cassini spacecraft carries two instruments-the Ion and Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS)-capable of energy- and mass-analysis. The Ion Mass Spectrometer (IMS), one of three instruments composing CAPS, is designed to characterize diffuse plasmas throughout the magnetosphere while the INMS is optimized for measurements within Titan's upper atmosphere. As such, mass-resolved ion compositions confirming a variety of hydrocarbons and nitriles have been extracted from INMS data for numerous Titan encounters. Similar analysis of IMS data, however, has largely been resolution-limited to the identification of 'light' and 'heavy' ion groups in the wake. Herein we present a technique for extracting Dalton-resolved ion compositions from IMS spectra acquired below ~5 Titan radii. The method is then applied to data from the T40 encounter and the resulting relative abundances compared with those derived from the INMS data for the same encounter.

Ultraviolet Views of Enceladus, Tethys, and Dione

NASA Technical Reports Server (NTRS)

Hansen, C. J.; Hendrix, A. R.

2005-01-01

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has collected ultraviolet observations of many of Saturn's icy moons since Cassini's insertion into orbit around Saturn. We will report on results from Enceladus, Tethys and Dione, orbiting in the Saturn system at distances of 3.95, 4.88 and 6.26 Saturn radii, respectively. Icy satellite science objectives of the UVIS include investigations of surface age and evolution, surface composition and chemistry, and tenuous exospheres. We address these objectives by producing albedo maps, and reflection and emission spectra, and observing stellar occultations. UVIS has four channels: EUV: Extreme Ultraviolet (55 nm to 110 nm), FUV: Far Ultraviolet (110 to 190 nm), HSP: High Speed Photometer, and HDAC: Hydrogen-Deuterium Absorption Cell. The EUV and FUV spectrographs image onto a 2-dimensional detector, with 64 spatial rows by 1024 spectral columns. To-date we have focused primarily on the far ultraviolet data acquired with the low resolution slit width (4.8 angstrom spectral resolution). Additional information is included in the original extended abstract.

Planetary X-ray studies: past, present and future

NASA Astrophysics Data System (ADS)

Branduardi-Raymont, Graziella

2016-07-01

Our solar system is a fascinating physics laboratory and X-ray observations are now firmly established as a powerful diagnostic tool of the multiple processes taking place in it. The science that X-rays reveal encompasses solar, space plasma and planetary physics, and the response of bodies in the solar system to the impact of the Sun's activity. This talk will review what we know from past observations and what we expect to learn in the short, medium and long term. Observations with Chandra and XMM-Newton have demonstrated that the origin of Jupiter's bright soft X-ray aurorae lies in the Charge eXchange (CX) process, likely to involve the interaction with atmospheric neutrals of local magnetospheric ions, as well as those carried in the solar wind. At higher energies electron bremsstrahlung is thought to be the X-ray emitting mechanism, while the whole planetary disk acts as a mirror for the solar X-ray flux via Thomson and fluorescent scattering. This 'X-ray mirror' phenomenon is all that is observed from Saturn's disk, which otherwise lacks X-ray auroral features. The Earth's X-ray aurora is bright and variable and mostly due to electron bremsstrahlung and line emission from atmospheric species. Un-magnetised planets, Venus and Mars, do not show X-ray aurorae but display the interesting combination of mirroring the solar X-ray flux and producing X-rays by Solar Wind Charge eXchange (SWCX) in their exospheres. These processes respond to different solar stimulation (photons and solar wind plasma respectively) hence their relative contributions are seen to vary according to the Sun's output. Present and future of planetary X-ray studies are very bright. We are preparing for the arrival of the Juno mission at Jupiter this summer and for coordinated observations with Chandra and XMM-Newton on the approach and later during Juno's orbital phase. These will allow direct correlation of the local plasma conditions with the X-ray emissions and the establishment of the relative contributions of different processes. SWCX X-ray emission from the Earth's exosphere is turning from unwanted variable background in astrophysical observations to a novel and global diagnostic tool for investigating solar-terrestrial interactions: this underpins the development of the ESA-CAS joint mission SMILE (Solar Wind Magnetosphere Ionosphere Link Explorer) due for launch in 2021. On the longer term ATHENA (Advanced Telescope for High ENergy Astrophysics, launch 2028) will provide planetary targets with vastly improved X-ray sensitivity on that currently afforded by XMM-Newton.

Joint Europa Mission (JEM) : A multi-scale study of Europa to characterize its habitability and search for life.

NASA Astrophysics Data System (ADS)

Blanc, Michel; Prieto Ballesteros, Olga; Andre, Nicolas; Cooper, John F.

2017-04-01

Europa is the closest and probably the most promising target to perform a comprehensive characterization of habitability and search for extant life. We propose that NASA and ESA join forces to design an ambitious planetary mission we call JEM (for Joint Europa Mission) to reach this objective. JEM will be assigned the following overarching goal: Understand Europa as a complex system responding to Jupiter system forcing, characterize the habitability of its potential biosphere, and search for life in its surface, sub-surface and exosphere. Our observation strategy to address these goals will combine three scientific measurement sequences: measurements on a high-latitude, low-latitude Europan orbit providing a continuous and global mapping of planetary fields (magnetic and gravity) and of the neutral and charged environment during a period of three months; in-situ measurements at the surface, using a soft lander operating during 35 days, to search for bio-signatures at the surface and sub-surface and operate a geophysical station; measurements of the chemical composition of the very low exosphere and plumes in search for biomolecules. The implementation of these three observation sequences will rest on the combination of two science platforms equipped with the most advanced instrumentation: a soft lander to perform all scientific measurements at the surface and sub-surface at a selected landing site, and a carrier/relay/orbiter to perform the orbital survey and descent sequences. In this concept, the orbiter will perform science operations during the relay phase on a carefully optimized halo orbit of the Europa-Jupiter system before moving to its final Europan orbit. The design of both orbiter and lander instruments will have to accommodate the very challenging radiation mitigation and Planetary Protection issues. The proposed lander science platform is composed of a geophysical station and of two complementary astrobiology facilities dedicated to bio-signature characterization experiments operating respectively in the solid and in the liquid phases, fed by a common articulated arm. The "Astrobiology Wet Laboratory" will be a specific European contribution. We propose an innovative distribution of roles to make JEM an appealing and affordable joint venture for the two agencies: while NASA would provide an SLS launcher, the lander stack and mission operations, ESA would provide the carrier-orbiter-relay platform. The delivery of the orbiter by ESA could take advantage of a double European heritage: an adaptation of the ORION ESM bus to JEM, complemented by avionics derived from JUICE.

Groundbased Observations of sodium at Mercury during the First MESSENGER Flyby

NASA Astrophysics Data System (ADS)

Potter, A. E.; Killen, R. M.; Mouawad, N.

2008-09-01

Abstract Groundbased observations of the sodium exospheric emission at Mercury taken at the McMathPierce Solar Telescope at Kitt Peak, Arizona, were conducted during the period of January 1018, 2008. During these observations, we mapped the distribution of sodium D2 emission over the planet. The procedure for mapping sodium using an image slicer and tiptilt image stabilization has been described by Potter et al. [1]. The emission maps were used to construct maps of sodium column density. Herein we discuss the temporal and spatial variability of the sodium emission on the observed side of planet. Maps of surface reflectance in the continuum near the sodium D2 line (left ) and column abundance of sodium in the exosphere (right) are shown for January 12, 13 and 14, in Figures 1, 2, and 3, respectively. The maximum column density was in the range 1.15 to 1.40 x 1011 atoms/cm2 during this period. The sodium distribution is uneven, with higher values of column density at high southern and northern E P S C EPSC Abstracts, Vol. 3, EPSC2008-A-00311, 2008 European Planetary Science Congress, Author(s) 2008 latitudes. This may be the effect of solar radiation acceleration [2] which was near its maximum value, ranging from 164 to 171 cm/sec2, or 0.44 to 0.46 of surface gravity. As a consequence of high radiation pressure, sodium atoms are driven to high latitudes. However, the distribution for January 12 shows a considerable excess in high southern latitudes, suggesting a source of sodium at those latitudes. This dataset brackets observations taken with the Ultraviolet and Visible Spectrometer (UVVS) on the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument [3] onboard the MESSENGER spacecraft [4] during the first flyby of the planet, January 14, 2008. An analogy between both data sets will be discussed. References [1] Potter, A.E., Plymate C., Keller C., Killen R.M., and Morgan T.H. (2006) Adv. Space Res. 38, 599603. [2] Potter, A.E., R. M. Killen, M. Sarantos. (2006) Icarus, 181, 112. [3] McClintock, W. E., and Lankton, M.R. (2007) Space Sci. Rev. 131, 481522. [4] Solomon, S. C., et al. (2001) Planet. Space Sci. 49, 14451465. Acknowledgements: The National Solar Observatory is funded by the National Science Foundation. Groundbased observations were funded by the NASA Planetary Astronomy Program. MESSENGER is a NASA Discovery mission.

Dust particles investigation for future Russian lunar missions.

NASA Astrophysics Data System (ADS)

Dolnikov, Gennady; Horanyi, Mihaly; Esposito, Francesca; Zakharov, Alexander; Popel, Sergey; Afonin, Valeri; Borisov, Nikolay; Seran, Elena; Godefroy, Michel; Shashkova, Inna; Kuznetsov, Ilya; Lyash, Andrey; Vorobyova, Elena; Petrov, Oleg; Lisin, Evgeny

One of the complicating factors of the future robotic and human lunar landing missions is the influence of the dust. Meteorites bombardment has accompanied by shock-explosive phenomena, disintegration and mix of the lunar soil in depth and on area simultaneously. As a consequence, the lunar soil has undergone melting, physical and chemical transformations. Recently we have the some reemergence for interest of Moon investigation. The prospects in current century declare USA, China, India, and European Union. In Russia also prepare two missions: Luna-Glob and Luna-Resource. Not last part of investigation of Moon surface is reviewing the dust condition near the ground of landers. Studying the properties of lunar dust is important both for scientific purposes to investigation the lunar exosphere component and for the technical safety of lunar robotic and manned missions. The absence of an atmosphere on the Moon's surface is leading to greater compaction and sintering. Properties of regolith and dust particles (density, temperature, composition, etc.) as well as near-surface lunar exosphere depend on solar activity, lunar local time and position of the Moon relative to the Earth's magneto tail. Upper layers of regolith are an insulator, which is charging as a result of solar UV radiation and the constant bombardment of charged particles, creates a charge distribution on the surface of the moon: positive on the illuminated side and negative on the night side. Charge distribution depends on the local lunar time, latitude and the electrical properties of the regolith (the presence of water in the regolith can influence the local distribution of charge). On light side of Moon near surface layer there exists possibility formation dusty plasma system. Altitude of levitation is depending from size of dust particle and Moon latitude. The distribution dust particle by size and altitude has estimated with taking into account photoelectrons, electrons and ions of solar wind, solar emission. Dust analyzer instrument PmL for future Russian lender missons intends for investigation the dynamics of dusty plasma near lunar surface. PmL consist of three blocks: Impact Sensor and two Electric Field Sensors. Dust Experiment goals are: 1) Impact sensor to investigate the dynamics of dust particles near the lunar surface (speed, charge, mass, vectors of a fluxes) a) high speed micrometeorites b) secondary particles after micrometeorites soil bombardment c) levitating dust particles due to electrostatic fields PmL instrument will measure dust particle impulses. In laboratory tests we used - min impulse so as 7•10-11 N•c, by SiO2 dust particles, 20-40 µm with velocity about 0,5 -2,5 m/c, dispersion 0.3, and - max impulse was 10-6 N•c with possibility increased it by particles Pb-Sn 0,7 mm with velocity 1 m/c, dispersion ±0.3. Also Impact Sensor will measure the charge of dust particle as far as 10-15 C ( 1000 electrons). In case the charge and impulse of a dust particle are measured we can obtain velocity and mass of them. 2) Electric field Sensor will measure the value and dynamics of the electric fields the lunar surface. Two Electric Field Sensors both are measured the concentration and temperature of charged particles (electrons, ions, dust particles). Uncertainty of measurements is 10%. Electric Field Sensors contain of Lengmure probe. Using Lengmure probe to dark and light Moon surface we can obtain the energy spectra photoelectrons in different period of time. PmL instrument is developing, working out and manufacturing in IKI. Simultaneously with the PmL dust instrument to study lunar dust it would be very important to use an onboard TV system adjusted for imaging physical properties of dust on the lunar surface (adhesion, albedo, porosity, etc), and to collect dust particles samples from the lunar surface to return these samples to the Earth for measure a number of physic-chemical properties of the lunar dust, e.g. a quantum yield of photoemission, what is very important for modeling physical processes in the lunar exosphere.

Modeling Broadband X-Ray Absorption of Massive Star Winds

NASA Technical Reports Server (NTRS)

Leutenegger, Maurice A.; Cohen,David H.; Zsargo, Janos; Martell, Erin M.; MacArthur, James P.; Owocki, Stanley P.; Gagne, Marc; Hillier, D. John

2010-01-01

We present a method for computing the net transition of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes all observed X-rays are emitted without attenuation from above the radius of optical depth unity. Our model is implemented in XSPEC as a pre-calculated table that can be coupled to a user-defined table of the wavelength dependent wind opacity. We provide a default wind opacity model that is more representative of real wind opacities than the commonly used neutral ISM tabulation. Preliminary modeling of Chandra grating data indicates that the X-ray hardness trend of OB stars with spectral subtype cars largely be understood as a wind absorption effect.

SWCX Emission from the Helium Focusing Cone - Preliminary Results

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Kuntz, K. D.; Collier, M. R.

2008-01-01

Preliminary results from an XMM-Newton campaign to study solar wind charge exchange (SWCX) emission from the heliospheric focusing cone of interstellar helium are presented. The detections of enhanced O VII and O VIII emission from the cone are at the 2(sigma) and 4(sigma) levels. The solar wind charge exchange (SWCX) emission in the heliosphere not associated with distinct objects (e.g., comets and planets including exospheric material in and near Earth s magnetosheath) is proportional to the flux of the solar wind and the space density of neutral material. The neutral material originates in the interstellar medium (ISM) and passes through the solar system due to the relative motion of the Sun and the ISM. The flow of the neutral material through the solar system is strongly perturbed by the Sun both by gravity and by radiation pressure. Because of the relative radiative scattering cross sections and the effect of solar gravitation the density of interstellar hydrogen near the Sun is reduced while interstellar helium is gravitationally focused. This creates a helium focusing cone downstream of the Sun [e.g., 1, and references therein].

Experimental Investigation of Neutral Species from Micrometeoroid Bombardment

NASA Astrophysics Data System (ADS)

Collette, A.; Sternovsky, Z.; Rocha, J. R.; Munsat, T. L.; Horanyi, M.

2014-12-01

Surface-boundary exospheres exist in a balance between source and loss processes. An important area of uncertainty, highlighted by the MESSENGER observations of Mg and Ca at Mercury, and the recently concluded LADEE observations at the Moon, is the role of micrometeoroid bombardment as a source process for liberating surface species. Unlike sputtering or photon stimulated desorption processes, the physics of micrometeoroid impacts are still poorly understood; in particular, no comprehensive model exists to predict partitioning of impact products between ejecta fragments, charged particles, and neutrals. We present initial experiments at the IMPACT dust accelerator facility (University of Colorado Boulder) aimed at directly measuring the fraction of neutral species liberated in micrometeoroid impacts. Simulated micrometeoroids (micron- and submicron-sized iron spheres) are fired at targets containing refractory elements, including fused silica (SiO2), sapphire (Al2O3), and magnesium fluoride (MgF2). Total quantities of specific impact-generated neutral species are measured using a mass spectrometer, as a function of impactor speed and mass, and compared with well-established scaling laws for charged particle production.

Onboard data processing and compression for a four-sensor suite: the SERENA experiment.

NASA Astrophysics Data System (ADS)

Mura, A.; Orsini, S.; Di Lellis, A.; Lazzarotto, F.; Barabash, S.; Livi, S.; Torkar, K.; Milillo, A.; De Angelis, E.

2013-09-01

SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is an instrument package that will fly on board the BepiColombo/Mercury Planetary Orbiter (MPO). SERENA instrument includes four units: ELENA (Emitted Low Energy Neutral Atoms), a neutral particle analyzer/imager to detect ion sputtering and backscattering from Mercury's surface; STROFIO (Start from a Rotating FIeld mass spectrometer), a mass spectrometer to identify atomic masses released from the surface; MIPA (Miniature Ion Precipitation Analyzer) and PICAM (Planetary Ion Camera), two ion spectrometers to monitor the precipitating solar wind and measure the plasma environment around Mercury. The System Control Unit architecture is such that all four sensors are connected to a high resolution FPGA, which dialogs with a dedicated high-performance data processing unit. The unpredictability of the data rate, due to the peculiarities of these investigations, leads to several possible scenarios for the data compression and handling. In this study we first discuss about the predicted data volume that comes from the optimized operation strategy, and then we report on the instrument data processing and compression.

The Neutral Atoms Detector Technologies Developed for the SERENA Package for BepiColombo

NASA Astrophysics Data System (ADS)

di Lellis, A. M.; Orsini, S.; Livi, S.; Wurz, P.; Milillo, A.

2004-04-01

A comprehensive suite for the particle detection in the Mercury environment, the SERENA instrument, is going to be proposed for the ESA cornerstone BepiColombo mission. The SERENA package consists of the sensors STROFIO and ELENA, which identify the neutral particles and measure their energies in the range from fractions of eV to a few keVs, and the sensors PICAM and MIPA for measuring and analyzing ionized particles from some eV to tens of keV. The proposed neutral sensor STROFIO will observe and analyze the bulk of the thermal / supra-thermal (0-50 eV) exospheric gas along the ram direction, while ELENA will be devoted to detect the sputtering emission (E min < 100eV; E max > 1 keV) within 1-D (2 deg x 60 deg) nadir cross track slices from the planet surface. The paper describes the new design techniques approached for the neutral particles identification and the related miniaturized datahandling unit. Such design technologies could be fruitfully exported to different applications for planetary exploration.

Venus nighttime hydrogen bulge

NASA Technical Reports Server (NTRS)

Brinton, H. C.; Taylor, H. A., Jr.; Niemann, H. B.; Mayr, H. G.; Nagy, A. F.; Cravens, T. E.; Strobel, D. F.

1980-01-01

The concentration of atomic hydrogen in the Venus thermosphere near 165 km altitude and approximately 18 deg north latitude has been derived from Pioneer Venus in situ measurements of H(+), O(+), O and CO2 concentrations, under the assumption of chemical equilibrium. Altitude profiles of derived H concentration suggest that chemical equilibrium prevails to an altitude of at least 200 km on the dayside and to 165 km on the nightside. Measurements below these limits were made by the ion and neutral mass spectrometers on the orbiter spacecraft between December 1978 and July 1979, while periapsis traversed a complete diurnal cycle. The hydrogen concentration is found to rise sharply at both terminators from a dayside value of approximately 50,000/cu cm, and to exhibit an asymmetric nightside distribution with a peak density in the predawn sector approximately 400 times greater than the dayside value. Analysis suggests that wind-induced diffusion, combined with exospheric return flow, can account for the observed hydrogen behavior. The large day-night temperature contrast enhances advective transport, which produces the large H concentration diurnal variation; the shift of the H concentration nighttime maximum toward dawn is caused by atmospheric superrotation.

On solar radiation-driven surface transport of sodium atoms at Mercury

NASA Astrophysics Data System (ADS)

Ip, W.-H.

1990-06-01

The ballistic motion of the exospheric sodium atoms on the surface Mercury is modeled, taking into account the solar radiation pressure acceleration and partial surface thermal accommodation. The Monte Carlo simulations show that there should be a significant degree of limb brightening as well as brightness enhancement over the poles. To maintain the observed sodium optical emission, a surface production rate on the order of 5-9 x 10 to the 24th atoms/s is needed. It is also found that, under the present set of assumptions, a reasonable agreement can be reached between theoretical results and ground-based measurements for the dependence of the disk-averaged abundance of the sodium atoms on the solar radiation pressure acceleration. If the low-altitude portion of the planetary surface is shielded from the magnetospheric convective electric field, the effective loss rate of the sodium atoms via photoionization and magnetospheric pickup may be reduced to about 2 x 10 to the 24th atoms/s, with the polar regions acting as the main area of ion outflows.

Reference Atmosphere for Mercury

NASA Technical Reports Server (NTRS)

Killen, Rosemary M.

2002-01-01

We propose that Ar-40 measured in the lunar atmosphere and that in Mercury's atmosphere is due to current diffusion into connected pore space within the crust. Higher temperatures at Mercury, along with more rapid loss from the atmosphere will lead to a smaller column abundance of argon at Mercury than at the Moon, given the same crustal abundance of potassium. Because the noble gas abundance in the Hermean atmosphere represents current effusion, it is a direct measure of the crustal potassium abundance. Ar-40 in the atmospheres of the planets is a measure of potassium abundance in the interiors, since Ar-40 is a product of radiogenic decay of K-40 by electron capture with the subsequent emission of a 1.46 eV gamma-ray. Although the Ar-40 in the Earth's atmosphere is expected to have accumulated since the late bombardment, Ar-40 in the atmospheres of Mercury and the Moon is eroded quickly by photoionization and electron impact ionization. Thus, the argon content in the exospheres of the Moon and Mercury is representative of current effusion rather than accumulation over the lifetime of the planet.

Global exospheric temperatures and densities under active solar conditions. [measured by OGO-6

NASA Technical Reports Server (NTRS)

Wydra, B. J.

1975-01-01

Temperatures measured by the OGO-6 satellite using the 6300 A airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity indicated a seasonal and local time effect and also a latitude and delay time variation different from previous density derived temperatures. A new magnetic index is proposed that is better correlated with the observed temperatures. The temperature variations at high latitudes were examined for three levels of magnetic activity for both solstices and equinox conditions. A temperature maximum in the pre-midnight sector and a minimum in the noon sector were noted and seasonal and geomagnetic time and latitude effects discussed. Neutral temperature, density, pressure and boundary oxygen variations for the great storm of March 8, 1970 are presented.

MESSENGER, MErcury: Surface, Space ENvironment, GEochemistry, and Ranging; A Mission to Orbit and Explore the Planet Mercury

NASA Technical Reports Server (NTRS)

1999-01-01

MESSENGER is a scientific mission to Mercury. Understanding this extraordinary planet and the forces that have shaped it is fundamental to understanding the processes that have governed the formation, evolution, and dynamics of the terrestrial planets. MESSENGER is a MErcury Surface, Space ENvironment, GEochemistry and Ranging mission to orbit Mercury for one Earth year after completing two flybys of that planet following two flybys of Venus. The necessary flybys return significant new data early in the mission, while the orbital phase, guided by the flyby data, enables a focused scientific investigation of this least-studied terrestrial planet. Answers to key questions about Mercury's high density, crustal composition and structure, volcanic history, core structure, magnetic field generation, polar deposits, exosphere, overall volatile inventory, and magnetosphere are provided by an optimized set of miniaturized space instruments. Our goal is to gain new insight into the formation and evolution of the solar system, including Earth. By traveling to the inner edge of the solar system and exploring a poorly known world, MESSENGER fulfills this quest.

Studies for the Loss of Atomic and Molecular Species from Io

NASA Technical Reports Server (NTRS)

Combi, Michael R.

1997-01-01

The general objective of this project has been to advance our theoretical understanding of Io's atmosphere and how various atomic and molecular species are lost from this atmosphere and are distributed in the circumplanetary environment of Jupiter. The scientific objectives of the larger collaborative program between AER, Inc., and the University of Michigan have been to undertake theoretical modeling studies to simulate the distributions of the exospheric gases in Io's corona and extended clouds, to investigate the importance of the various physical processes that shape their relative abundances, and with these tools to analyze observations of O, S and Na obtained by four observers: M.A. McGrath of the Space Telescope Science Institute and G.E. Ballester of the University of Michigan who each have obtained Hubble Space Telescope observations of O and S near Io, F. Scherb who continues an effort to obtain 6300 A OI observations as part of the University of Wisconsin Fabry-Perot program, and N.M. Schneider of the University of Colorado who obtained an extensive set of spectral and spatial observations of the Na emission near Io in the D-lines.

Sodium Ion Dynamics in the Magnetospheric Flanks of Mercury

NASA Astrophysics Data System (ADS)

Aizawa, Sae; Delcourt, Dominique; Terada, Naoki

2018-01-01

We investigate the transport of planetary ions in the magnetospheric flanks of Mercury. In situ measurements from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft show evidences of Kelvin-Helmholtz instability development in this region of space, due to the velocity shear between the downtail streaming flow of solar wind originating protons in the magnetosheath and the magnetospheric populations. Ions that originate from the planet exosphere and that gain access to this region of space may be transported across the magnetopause along meandering orbits. We examine this transport using single-particle trajectory calculations in model Magnetohydrodynamics simulations of the Kelvin-Helmholtz instability. We show that heavy ions of planetary origin such as Na+ may experience prominent nonadiabatic energization as they E × B drift across large-scale rolled up vortices. This energization is controlled by the characteristics of the electric field burst encountered along the particle path, the net energy change realized corresponding to the maximum E × B drift energy. This nonadiabatic energization also is responsible for prominent scattering of the particles toward the direction perpendicular to the magnetic field.

Unmasking the Secrets of Mercury

NASA Image and Video Library

2015-04-16

The MASCS instrument onboard NASA MESSENGER spacecraft was designed to study both the exosphere and surface of Mercury. To learn more about the minerals and surface processes on Mercury, the Visual and Infrared Spectrometer (VIRS) portion of MASCS has been diligently collecting single tracks of spectral surface measurements since MESSENGER entered orbit. The track coverage is now extensive enough that the spectral properties of both broad terrains and small, distinct features such as pyroclastic vents and fresh craters can be studied. To accentuate the geological context of the spectral measurements, the MASCS data have been overlain on the MDIS monochrome mosaic. Click on the image to explore the colorful diversity of surface materials in more detail! Instrument: Mercury Atmosphere and Surface Composition Spectrometer (MASCS) Map Projection: Orthographic VIRS Color Composite Wavelengths: 575 nm as red, 415 nm/750 nm as green, 310 nm/390 nm as blue Center Latitude (All Globes): 0° Center Longitude (Top Left Globe): 270° E Center Longitude (Top Right Globe): 0° E Center Longitude (Bottom Left Globe): 90° E Center Longitude (Bottom Right Globe): 180° E http://photojournal.jpl.nasa.gov/catalog/PIA19419

New Observations of UV Emissions from Europa

NASA Technical Reports Server (NTRS)

McGrath, Melissa; Sparks, William

2009-01-01

The recent top prioritization of the Europa Jupiter System Mission for the next outer solar system flagship mission is refocusing attention on Europa and the other Galilean satellites and their contextual environments in the Jupiter system. Surface sputtering by magnetospheric plasma generates a tenuous atmosphere for Europa, dominated by 02 gas. This tenuous gas is in turn excited by plasma electrons, producing ultraviolet and visible emissions. Two sets of imaging observations have been published to date, UV images from the Hubble Space Telescope, and visible eclipse images from Cassini. Three additional sets of HST UV observations were acquired in February 2007, April 2007 and June 2009. The signal to noise ratio in these data are not high, however, given the paucity of data and its increasing importance in terms of planning for EJSM, we have attempted to extract as much new information as possible from these data. This talk will summarize our analysis to date, and discuss them in terms of existing models, which attempt to explain the image morphology either in terms of the underlying source production and loss processes, or in terms of the plasma interaction with the exosphere.

Non-LTE models of Titan's upper atmosphere

NASA Technical Reports Server (NTRS)

Yelle, Roger V.

1991-01-01

Models for the thermal structure of Titan's upper atmosphere, between 0.1 mbar and 0.01 nbar are presented. The calculations include non-LTE heating/cooling in the rotation-vibration bands of CH4, C2H2, and C2H6, absorption of solar IR radiation in the near-IR bands of CH4 and subsequent cascading to the nu-4 band of CH4, absorption of solar EUV and UV radiation, thermal conduction and cooling by HCN rotational lines. Unlike earlier models, the calculated exospheric temperature agrees well with observations, because of the importance of HCN cooling. The calculations predict a well-developed mesopause with a temperature of 135-140 K at an altitude of approximately 600 km and pressure of about 0.1 microbar. The mesopause is at a higher pressure than predicted by earlier calculations because non-LTE radiative transfer in the rotation-vibration bands of CH4, C2H2, and C2H6 is treated in an accurate manner. The accuracy of the LTE approximation for source functions and heating rates is discussed.

Geocoronal structure. 3. Optically thin, Doppler-broadened line profiles

NASA Astrophysics Data System (ADS)

Bishop, James; Chamberlain, Joseph W.

1987-11-01

Theoretical line profiles, applicable to the analysis of geocoronal Hα prifile measurements, are presented for illustrative cases. While retaining a number of simplifications (classical exobase and diffusive equilibrium plasmasphere conditions), distinctive spectral signatures of mechanisms governing the geocorona are isolated. Examining the consequences of solar radiation pressure dynamics is the main point here. In the prototype evaporative case, radiation pressure acts to form narrow profiles via the creation of an extensive quasi-satellite component. Comparison with a simple extension of the earlier analytic theory discloses the influence of an exopause in this regard. The main modifications to evaporative spectral shapes in the geocoronal application, for shadow heights greater than 2 RE, are predicted to be (1) a blueward ``shift'' or bias near line center, for look directions parallel to the antisolar axis, generated by loss mechanisms acting over the time of flight of exospheric constituents (for example, solar ionization) and (2) an enhanced redward wing at spectral displacements exceeding that defined by the shadow height escape speed, produced by plasmaspheric charge exchange collisions. Implications of these results for recent observations of geocoronal Hα line profiles are briefly discussed.

Dynamical influences on thermospheric composition: implications for semi-empirical models

NASA Astrophysics Data System (ADS)

Sutton, E. K.; Solomon, S. C.

2014-12-01

The TIE-GCM was recently augmented to include helium and argon, two approximately inert species that can be used as tracers of dynamics in the thermosphere. The former species is treated as a major species due to its large abundance near the upper boundary. The effects of exospheric transport are also included in order to simulate realistic seasonal and latitudinal helium distributions. The latter species is treated as a classical minor species, imparting absolutely no forces on the background atmosphere. In this study, we examine the interplay of the various dynamical terms - i.e. background circulation, molecular and Eddy diffusion - as they drive departures from the distributions that would be expected under the assumption of diffusive equilibrium. As this has implications on the formulation of all empirical thermospheric models, we use this understanding to address the following questions: (1) how do errors caused by the assumption of diffusive equilibrium manifest within empirical models of the thermosphere? and (2) where and when does an empirical model's output disagree with its underlying datasets due to the inherent limitations of said model's formulation?

NASA SSERVI Contributions to Lunar Science and Exploration

NASA Technical Reports Server (NTRS)

Pendleton, Yvonne J.

2015-01-01

NASA's Solar System Exploration Research Virtual Institute (SSERVI) represents a close collaboration between science, technology and exploration that will enable deeper understanding of the Moon and other airless bodies as we move further out of low-Earth orbit. The new Solar System Exploration Research Virtual Institute (SSERVI) will focus on the scientific aspects of exploration as they pertain to the Moon, Near Earth Asteroids (NEAs) and the moons of Mars. The Institute focuses on interdisciplinary, exploration-related science centered around all airless bodies targeted as potential human destinations. Areas of study reported here will represent the broad spectrum of lunar, NEA, and Martian moon sciences encompassing investigations of the surface, interior, exosphere, and near-space environments as well as science uniquely enabled from these bodies. We will provide a detailed look at research being conducted by each of the 9 domestic US teams as well as our 7 international partners. The research profile of the Institute integrates investigations of plasma physics, geology/geochemistry, technology integration, solar system origins/evolution, regolith geotechnical properties, analogues, volatiles, ISRU and exploration potential of the target bodies.

Sputtering by the Solar Wind: Effects of Variable Composition

NASA Technical Reports Server (NTRS)

Killen, R. M.; Arrell, W. M.; Sarantos, M.; Delory, G. T.

2011-01-01

It has long been recognized that solar wind bombardment onto exposed surfaces in the solar system will produce an energetic component to the exospheres about those bodies. Laboratory experiments have shown that there is no increase in the sputtering yield caused by highly charged heavy ions for metallic and for semiconducting surfaces, but the sputter yield can be noticeably increased in the case of a good insulating surface. Recently measurements of the solar wind composition have become available. It is now known that the solar wind composition is highly dependent on the origin of the particular plasma. Using the measured composition of the slow wind, fast wind, solar energetic particle (SEP) population, and coronal mass ejection (CME), broken down into its various components, we have estimated the total sputter yield for each type of solar wind. Whereas many previous calculations of sputtering were limited to the effects of proton bombardment. we show that the heavy ion component. especially the He++ component. can greatly enhance the total sputter yield during times when the heavy ion population is enhanced. We will discuss sputtering of both neutrals and ions.

MIRI: Comparison of Mars Express MARSIS ionospheric data with a global climate model

NASA Astrophysics Data System (ADS)

Gonzalez-Galindo, Francisco; Forget, Francois; Gurnett, Donald; Lopez-Valverde, Miguel; Morgan, David D.; Nemec, Frantisek; Chaufray, Jean-Yves; Diéval, Catherine

2016-07-01

Observations and computational models are the two fundamental stones of our current knowledge of the Martian atmosphere, and both are expected to contribute to the MIRI effort. Data-model comparisons are thus necessary to identify possible bias in the models and to complement the information provided by the observations. Here we present the comparison of the ionosphere determined from Mars Express MARSIS AIS observations with that simulated by a ground-to-exosphere Global Climate Model for Mars, the LMD-MGCM. We focus the comparison on the density and altitude of the main ionospheric peak. In general, the observed latitudinal and solar zenith angle variability of these parameters is well reproduced by the model, although the model tends to slightly underestimate both the electron density and altitude of the peak. The model predicts also a latitudinal variability of the peak electron density that is not observed. We will discuss the different factors affecting the predicted ionosphere, and emphasize the importance of a good knowledge of the electronic temperature in producing a correct representation of the ionosphere by the model.

Exospheric temperature and composition from satellite beacon measurements

NASA Technical Reports Server (NTRS)

Titheridge, J. E.

1974-01-01

Routine measurements of the slab thickness of the ionosphere, from 1965 to 1971, are used to infer the changes in neutral temperature and ion composition at a mean latitude of 40 S. Values of neutral temperature at solar maximum are 5 to 10% above Northern Hemisphere backscatter results. The diurnal and seasonal changes agree closely with satellite drag and backscatter measurements, except that the maximum temperature occurs after sunset in winter. Winter night-time values of the O(+)/H(+) transition height were 500 km in 1965-1966, 800 km in 1968-1969, and 700 km in 1971. Changes in the transition height lag about six months behind the changes in solar flux. Diurnal variations have a minimum just before sunrise and a maximum 1 to 3 hr after noon. On winter nights the transition height descends to the level set by chemical equilibrium. On summer nights the transition height is always above this level, giving a continual production of H(+) which serves as an additional source for maintaining the night-time ionosphere in the winter hemisphere.

Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star

NASA Astrophysics Data System (ADS)

Bourrier, Vincent; Lovis, Christophe; Beust, Hervé; Ehrenreich, David; Henry, Gregory W.; Astudillo-Defru, Nicola; Allart, Romain; Bonfils, Xavier; Ségransan, Damien; Delfosse, Xavier; Cegla, Heather M.; Wyttenbach, Aurélien; Heng, Kevin; Lavie, Baptiste; Pepe, Francesco

2018-01-01

The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope. Spin–orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars. Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet. We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere.

Lunar Atmosphere and Dust Environment Explorer Integration and Test

NASA Technical Reports Server (NTRS)

Wright, Michael R.; McCormick, John L.

2010-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) is a NASA collaborative flight project to explore the lunar exosphere. It is being developed through a unique partnership between NASA's Ames Research Center (ARC) and Goddard Space Flight Center (GSFC). Each center brings its own experience and flight systems heritage to the task of integrating and testing the LADEE subsystems, instruments, and spacecraft. As an "in-house" flight project being implemented at low-cost and moderate risk, LADEE relies on single-string subsystems and protoflight hardware to accomplish its mission. Integration and test (l&T) of the LADEE spacecraft with the instruments will be performed at GSFC, and includes assembly, integration, functional testing, and flight qualification and acceptance testing. Due to the nature of the LADEE mission, l&T requirements include strict contamination control measures and instrument calibration procedures. Environmental testing will include electromagnetic compatibility (EMC), vibro-acoustic testing, and thermal-balance/vacuum. Upon successful completion of spacecraft l&T, LADEE will be launched from NASA's Wallops Flight Facility. Launch of the LADEE spacecraft is currently scheduled for December 2012.

Nature of the Venus thermosphere derived from satellite drag measurements (solicited paper)

NASA Astrophysics Data System (ADS)

Keating, G.; Theriot, M.; Bougher, S.

2008-09-01

From drag measurements obtained by Pioneer Venus and Magellan, the Venus upper atmosphere was discovered to be much colder than Earth's, even though Venus is much closer to the Sun than the Earth. On the dayside, exospheric temperatures are near 300K compared to Earth's of near 1200K [1]. This is thought to result principally from 15 micron excitation of carbon dioxide by atomic oxygen resulting in very strong 15 micron emission to space, cooling off the upper atmosphere [2]. On the nightside the Venus upper atmosphere is near 100K [3], compared to Earth where temperatures are near 900K. The nightside Venus temperatures drop with altitude contrary to a thermosphere where temperatures rise with altitude. As a result, the very cold nightside is called a "cryosphere" rather than a thermosphere. This is the first cryosphere discovered in the solar system [1]. Temperatures sharply drop near the terminator. Apparently, heat is somehow blocked near the terminator from being significantly transported to the nightside [4]. Recently, drag studies were performed on a number of Earth satellites to establish whether the rise of carbon dioxide on Earth was cooling the Earth's thermosphere similar to the dayside of Venus. Keating et al. [5] discovered that a 10 percent drop in density near 350km at solar minimum occurred globally over a period of 20 years with a 10 per cent rise in carbon dioxide. This should result in about a factor of 2 decline in density from 1976 values, by the end of the 21st century brought on by thermospheric cooling. Subsequent studies have confirmed these results. Thus we are beginning to see the cooling of Earth's upper atmosphere apparently from the same process cooling the Venus thermosphere. Fig. 1 VIRA Exospheric Temperatures Atmospheric drag data from the Pioneer Venus Orbiter and Magellan were combined to generate an improved version of the Venus International Reference Atmosphere (VIRA) [6], [7]. A "fountain effect" was discovered where the atmosphere rises on the dayside producing adiabatic cooling and drops on the nightside producing some adiabatic heating. (See figure 1). The thermosphere was discovered from drag measurements to respond to the near 27-day period of the rotating Sun, for which regions of maximum solar activity reappear every 27 days. The increased euv emission from active regions increased temperatures and thermospheric density, (See Figure 2). Fig. 2 Exospheric Temperatures Compared to 10.7cm Solar Index Second diurnal survey (12/5/79 - 3/6/80) Pioneer Venus Orbiter measurements (OAD) 11 day running means [2] Estimates were also made of the response to the 11- year Solar Cycle by combining the Pioneer Venus and Magellan data. Dayside exospheric temperatures changed about 80K over the solar cycle, [8]. Earlier estimates of temperature change gave 70K based on Lyman alpha measurements. The responses to solar variability were much weaker than on Earth due apparently to the much stronger O/CO2 cooling on Venus which tended to act as a thermostat on thermospheric temperatures. Another discovery from drag measurements was the 4 to 5 day oscillation of the Venus thermosphere [3], (See figure 3). These oscillations are interpreted as resulting from the 4-day super-rotation of the atmosphere near the cloud tops. Other indications of the super-rotation of the thermosphere come from displacement of the helium bulge and atomic hydrogen bulge from midnight to near 4AM. Fig. 3 Four to Five Day Oscillations in Thermospheric Densities Magellan 1992. During 2008, the Venus Express periapsis will be dropped from 250km down to approximately 180km to allow drag measurements to be made in the North Polar Region, [9]. Drag measurements above 200km have already been obtained from both Pioneer Venus and Magellan so measurements near 180km should be accurate. In 2009, the periapsis may be decreased to a lower altitude allowing accelerometer measurements to be obtained of drag as a function of altitude, to determine density, scale height, inferred temperature, pressure, and other parameters as a function of altitude. The risk involved in the orbital decay and accelerometer measurements is minimal. We have not lost any spacecraft orbiting Venus or Mars due to unexpected thermospheric drag effects in over 30 years. The Venus Express accelerometer drag experiment is very similar to accelerometer experiments aboard Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter which orbit Mars. The Venus Express drag measurements of the polar region will allow a global empirical model of the thermosphere to emerge. Previous drag measurements have been made principally near the equator. The experiment may help us understand on a global scale, tides, winds, gravity waves, planetary waves, and the damping of waves. Comparisons will be made between low and high latitude results; between the middle and upper atmosphere; and with other instruments that provide information from current and previous measurements. The character of the sharp temperature gradient near the day/night terminator needs to be studied at all latitudes. The cryosphere we discovered on the nightside needs to be studied at high latitudes. The rotating vortex dipole over the North Pole surrounded by a colder "collar" needs to be analyzed to identify how wave activity extends into the polar thermosphere. We have already discovered super-rotation in the equatorial thermosphere, but we need to study 4-day super-rotation at higher latitudes to obtain a global picture of the thermosphere. The super-rotation may affect escape rates and the evolution of the atmosphere. References: [1] Keating, G. M., et al: Venus Thermosphere and Exosphere: First Satellite Drag Measurements of an Extraterrestrial Atmosphere. Science, Vol. 203, No. 4382, 772-774, Feb. 23, 1979. [2] Keating, G. M. and Bougher, S.W.: Isolation of Major Venus Cooling Mechanism and Implications for Earth and Mars, Journal of Geophysical Research, Vol. 97, 4189-4197, 1992. [3] Keating, G.M.; Taylor, F.W.; Nicholson, J. V. II; and Hinson, E.W. : Short-Term Cyclic Variations and Diurnal Variations of the Venus Upper Atmosphere, Science, Vol. 205, No. 4401, 62-64, July 6, 1979. [4] Bougher, S. W.; Dickinson, R. E.; Ridley, E. C.; Roble, R. G.; Nagy, A. F.; and Cravens, T. E.: Venus mesosphere and thermosphere, II, Global circulation, temperature, and density variations, Icarus, Vol. 68, 284-312, 1986. [5] Keating, G. M. et al.: Evidence of Long-Term Global Decline in the Earth's Thermospheric Densities Apparently Related to Anthropogenic Effects, Geophysical Research Letters, Vol. 27, No. 10, 1522-1526, 2000. [6] Keating, G. M. et al.: Models of Venus Neutral Upper Atmosphere Structure and Composition: The Venus International Reference Atmosphere (Edited by A. L. Kliore, V. I. Moros, and G. M. Keating) Advances in Space Research, Vol. 5, No. 11, 117-171,1985. [7] Keating, G. M.; Hsu, N.C., and Lyu, J.: Improved Thermospheric Model for the Venus International Reference Atmosphere, Proceedings of the 31st Scientific Assembly of COSPAR, Birmingham, England, 139, 1996 (Invited) [8] Keating, G. M. and Hsu, N. C.: The Venus Atmospheric Response to Solar Cycle Variations, Geophysical Research Letters, Vol. 20, 2751-2754, 1993. [9] Keating, G.M. et al: Future drag measurements from Venus Express. Adv

Cassini's Ring Grazing and Grand Finale Orbits: Topping Off an Awesome Mission

NASA Astrophysics Data System (ADS)

Edgington, Scott; Spilker, Linda; Coustenis, Athena

2017-04-01

The Cassini-Huygens mission, a joint collaboration between NASA, ESA, and the Italian Space Agency, is in its last year of operations after nearly 13 years in orbit around Saturn. Cassini will send back its final bits of unique data on September 15th, 2017 as it plunges into Saturn's atmosphere, vaporizing and satisfying planetary protection requirements. Before that time Cassini will continue its legacy of exploration and discovery in 2017 and return unique science data provided by orbits taking the spacecraft into unexplored regions near Saturn and its rings. From the new vantage points, Cassini will continue to study seasonal and temporal changes in the system as northern summer solstice approaches. With the exception of one remaining targeted Titan flyby, all of Cassini's close icy satellite flybys, including those of Enceladus, are now completed. In November 2016, Cassini transitioned to a series of orbits with peripases just outside Saturn's F ring. These 20 orbits include close flybys of some tiny ring moons and excellent views of the F ring and Saturn's outer A ring. The 126th and final close flyby of Titan will propel Cassini across Saturn's main rings and into its Grand Finale series of orbits. Cassini's Grand Finale, starting in April 2017, is comprised of 22 orbits at an inclination of 63 degrees. Cassini will repeatedly dive between Saturn's innermost rings and upper atmosphere providing insights into fundamental questions unattainable during the rest of the mission. Cassini will be the first spacecraft to explore this region. These close orbits provide the highest resolution observations of both the rings and Saturn, and direct in-situ sampling of the ring particles, composition, plasma, Saturn's exosphere and the innermost radiation belts. Saturn's gravitational field will be measured to unprecedented accuracy, providing information on the interior structure of the planet, winds in the outer layers of Saturn's atmosphere, and the mass distribution in the rings. Probing the magnetic field will give insight into the nature of the magnetic dynamo, telling us: why the magnetic field is weak; why it exhibits little, if any, axial tilt; and the true rotation rate of the planet. The ion and neutral mass spectrometer will sniff the exosphere and upper atmosphere for molecules that escape the atmosphere itself and water-based molecules originating from the rings. The cosmic dust analyzer will sample the composition of particles from different parts of the main rings. Until the execution of these final orbits, the answers to such new questions will remain mysteries. The science highlights of Cassini's Grand Finale orbits will be discussed. This work was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2017 California Institute of Technology. Government sponsorship is acknowledged.

Investigation of dust particles with future Russian lunar missions: achievements of further development of PmL instrument.

NASA Astrophysics Data System (ADS)

Kuznetsov, Ilya; Zakharov, Alexander; Afonin, Valeri; Seran, Elena; Godefroy, Michel; Shashkova, Inna; Lyash, Andrey; Dolnikov, Gennady; Popel, Sergey; Lisin, Evgeny

2016-07-01

One of the complicating factors of the future robotic and human lunar landing missions is the influence of the dust. Meteorites bombardment has accompanied by shock-explosive phenomena, disintegration and mix of the lunar soil in depth and on area simultaneously. As a consequence, the lunar soil has undergone melting, physical and chemical transformations. Recently we have the some reemergence for interest of Moon investigation. The prospects in current century declare USA, China, India, and European Union. In Russia also prepare two missions: Luna-Glob and Luna-Resource. Not last part of investigation of Moon surface is reviewing the dust condition near the ground of landers. Studying the properties of lunar dust is important both for scientific purposes to investigation the lunar exosphere component and for the technical safety of lunar robotic and manned missions. The absence of an atmosphere on the Moon's surface is leading to greater compaction and sintering. Properties of regolith and dust particles (density, temperature, composition, etc.) as well as near-surface lunar exosphere depend on solar activity, lunar local time and position of the Moon relative to the Earth's magneto tail. Upper layers of regolith are an insulator, which is charging as a result of solar UV radiation and the constant bombardment of charged particles, creates a charge distribution on the surface of the moon: positive on the illuminated side and negative on the night side. Charge distribution depends on the local lunar time, latitude and the electrical properties of the regolith (the presence of water in the regolith can influence the local distribution of charge). On the day side of Moon near surface layer there exists possibility formation dusty plasma system. Altitude of levitation is depending from size of dust particle and Moon latitude. The distribution of dust particles by size and altitude has estimated with taking into account photoelectrons, electrons and ions of solar wind, solar emission. Dust analyzer instrument PmL for future Russian lander missions intends for investigation the dynamics of dusty plasma near lunar surface. PmL consists of three parts in the case of Luna-Glob: Impact Sensor and two Electric Field Sensors (EFC). There are 9 parts of PmL instrument for Luna-Resource mission: two Impact Sensors, 5 EFC (three on the Boom and two on the lander) and 2 Solar Wind and Dust Analyzers. These days the engineering model of PmL for LG-mission is finished. We obtained first practical results from the simulating chambers with dust particles injectors and plasma inside. All the important achievements are presented in this report as well as the roadmap for further development of PmL instruments in both of Russian lunar missions.

First Results from NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE)

NASA Technical Reports Server (NTRS)

Elphic, R.; Colaprete, A.; Horanyi, M; Mahaffy, Paul; Boroson, D.; Delory, G.; Noble, s; Hine, B; Salute, J.

2013-01-01

As of early August, 2013, the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission is scheduled for launch on a Minotaur V rocket from Wallops Flight Facility during a five-day launch period that opens on Sept. 6, 2013 (early Sept. 7 UTC). LADEE will address 40 year-old mysteries of the lunar atmosphere and the question of levitated lunar dust. It will also pioneer the next generation of optical space communications. LADEE will assess the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. LADEE will also determine whether dust is present in the lunar exosphere, and reveal its sources and variability. These investigations are relevant to our understanding of surface boundary exospheres and dust processes occurring at many objects throughout the solar system, address questions regarding the origin and evolution of lunar volatiles, and have potential implications for future exploration activities. Following a successful launch, LADEE will enter a series of phasing orbits, which allows the spacecraft to arrive at the Moon at the proper time and phase. This approach accommodates any dispersion in the Minotaur V launch injection. LADEE's arrival at the moon in early October. The spacecraft will approach the moon from its leading edge, travel behind the Moon out of sight of the Earth, and then re-emerge and execute a three-minute Lunar Orbit Insertion maneuver. This will place LADEE in an elliptical retrograde equatorial orbit with an orbital period of approximately 24 hours. A series of maneuvers is then performed to reduce the orbit to become nearly circular with a 156-mile (250- kilometer) altitude. Spacecraft checkout and science instrument commissioning will commence in early-October and will nominally span 30 days but can be extended for an additional 30 days in the event of contingencies. Following commissioning, the 100-day Science Phase is performed at an orbit with periapsis between 20-60 km. This orbit must be constantly managed due to the Moon's highly inhomogeneous gravity field. During the Science Phase, the moon will rotate more than three times underneath the LADEE orbit. LADEE employs a high heritage instrument payload: a Neutral Mass Spectrometer (NMS) from Goddard Space Flight Center, an Ultraviolet/Visible Spectrometer (UVS) from Ames Research Center, and a dust detection experiment (LDEX) from the University of Colorado/LASP. It will also carry the Lunar Laser Communications Demonstration (LLCD) as a technology demonstration. The LLCD is funded by the Human Exploration Operations Mission Directorate (HEOMD), managed by GSFC, and built by the MIT Lincoln Lab. Contingent upon LADEE's successful lunar orbit insertion and checkout, we will report the early results from the science investigations.

Development of a mass spectrometer for planetary exosphere exploration: from simulations to a flight like design

NASA Astrophysics Data System (ADS)

Meyer, Stefan; Tulej, Marek; Wurz, Peter

2017-04-01

The exploration of habitable environments around the gas giants in the Solar System is of major interest in upcoming planetary missions. Exactly this theme is addressed by the Jupiter Icy Moons Explorer (JUICE) mission of ESA, which will characterise Ganymede, Europa and Callisto as planetary objects and potential habitats [1], [2]. We developed a prototype of the Neutral gas and Ion Mass spectrometer (NIM) of the Particle Environment Package (PEP) for the JUICE mission intended for composition measurements of neutral gas and thermal plasma [3]. NIM/PEP will be used to measure the chemical composition of the exospheres of the icy Jovian moons. Besides direct ion measurement, the NIM instrument is able to measure the inflowing neutral gas in two different modes: in neutral mode the gas enters directly the ion source (open source) and in thermal mode, the gas gets thermally accommodated to wall temperature by several collisions inside an equilibrium sphere before entering the ion source (closed source). We started the development of NIM with detailed ion-optical simulations and optimisations using SIMION software. Based on the ion-optical design we developed a prototype of NIM with several iterations. We tested the prototype NIM under realistic mission conditions and thereby successfully verified its required functionality. We will present the development process from ion-optical simulation up to NIM prototype test results and the concluded flight like design. Furthermore, we will provide an insight into the working principle of NIM and its performance, based on measurement data. References: 1) ESA, "JUICE assessment study report (Yellow Book)", ESA/SRE(2011)18, 2012. 2) O. Grasset, M.K. Dougherty, A. Coustenis, E.J. Bunce, C. Erd, D. Titov, M. Blanc, A. Coates, P. Drossart, L.N. Fletcher, H. Hussmann, R. Jaumann, N. Krupp, J.-P. Lebreton, O. Prieto-Ballesteros, P. Tortora, F. Tosi, T. Van Hoolst, "JUpiter Icy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system", Planet. Space Sci., 2013, 78, pp. 1 - 21. 3) S. Barabash, P. Wurz, P. Brandt, M. Wieser, M. Holmström, Y. Futaana, G. Stenberg, H. Nilsson, A. Eriksson, M. Tulej, A. Vorburger, N. Thomas, C. Paranicas, D.G. Mitchell, G. Ho, B.H. Mauk, D. Haggerty, J.H. Westlake, M. Fränz, N. Krupp, E. Roussos, E. Kallio, W. Schmidt, K. Szego, S. Szalai, K. Khurana, Xianzhe Jia, C. Paty, R.F. Wimmer-Schweingruber, B. Heber, K. Asamura, M. Grande, H. Lammer, T. Zhang, S. McKenna-Lawlor, S.M. Krimigis, T. Sarris, and D. Grodent, "Particle Environment Package (PEP)," proceedings of the European Planetary Science Congress, 8 (2013), EPSC2013-709.

A low energy ion beam facility for mass spectrometer calibration: First results

NASA Astrophysics Data System (ADS)

Meyer, Stefan; Tulej, Marek; Wurz, Peter

2018-01-01

The exploration of habitable environments around the gas giants in the Solar System is of major interest in upcoming planetary missions. Exactly this theme is addressed by the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA), which will characterise Ganymede, Europa, and Callisto as planetary objects and potential habitats. The NIM, Neutral gas and Ion Mass spectrometer, is part of the PEP experiment and will be used to measure the chemical composition of the exospheres of the icy Jovian moons. We designed and developed a calibration facility (SATANS, Supersonic cATion and ANion Source), especially for use with the NIM instrument. In a first step, we established a low energy ion beam for positive ions in the range of 0.01-30 eV. Then we conducted beam velocity calibrations with a velocity uncertainty <5%, which provided exact settings and formulas for the cation beam velocity of different gas mixtures in the range of 1-15 km/s. In addition, first results are obtained by using the NIM prototype for direct ion beam measurements under realistic JUICE mission conditions, i.e., for velocities from 1 up to 7 km/s and even more.

EUV observation from the Earth-orbiting satellite, EXCEED

NASA Astrophysics Data System (ADS)

Yoshioka, K.; Murakami, G.; Yoshikawa, I.; Ueno, M.; Uemizu, K.; Yamazaki, A.

2010-01-01

An Earth-orbiting small satellite “EXtreme ultraviolet spectrosCope for ExosphEric Dynamics” (EXCEED) which will be launched in 2012 is under development. The mission will carry out spectroscopic and imaging observation of EUV (Extreme Ultraviolet: 60-145 nm) emissions from tenuous plasmas around the planets (Venus, Mars, Mercury, and Jupiter). It is essential for EUV observation to put on an observing site outside the Earth’s atmosphere to avoid the absorption. It is also essential that the detection efficiency must be very high in order to catch the faint signals from those targets. In this mission, we employ cesium iodide coated microchannel plate as a 2 dimensional photon counting devise which shows 1.5-50 times higher quantum detection efficiency comparing with the bared one. We coat the surface of the grating and entrance mirror with silicon carbides by the chemical vapor deposition method in order to archive the high diffraction efficiency and reflectivity. The whole spectrometer is shielded by the 2 mm thick stainless steel to prevent the contamination caused by the high energy electrons from the inner radiation belt. In this paper, we will introduce the mission overview, its instrument, and their performance.

Survey of pickup ion signatures in the vicinity of Titan using CAPS/IMS

NASA Astrophysics Data System (ADS)

Regoli, L. H.; Coates, A. J.; Thomsen, M. F.; Jones, G. H.; Roussos, E.; Waite, J. H.; Krupp, N.; Cox, G.

2016-09-01

Pickup ion detection at Titan is challenging because ion cyclotron waves are rarely detected in the vicinity of the moon. In this work, signatures left by freshly produced pickup heavy ions (m/q ˜ 16 to m/q ˜ 28) as detected in the plasma data by the Cassini Plasma Spectrometer/Ion Mass Spectrometer (CAPS/IMS) instrument on board Cassini are analyzed. In order to discern whether these correspond to ions of exospheric origin, one of the flybys during which the reported signatures were observed is investigated in detail. For this purpose, ion composition data from time-of-flight measurements and test particle simulations to constrain the ions' origin are used. After being validated, the detection method is applied to all the flybys for which the CAPS/IMS instrument gathered valid data, constraining the region around the moon where the signatures are observed. The results reveal an escape region located in the anti-Saturn direction as expected from the nominal corotation electric field direction. These findings provide new constraints for the area of freshly produced pickup ion escape, giving an approximate escape rate of 3.3-2+3×1023 ions· s-1.

Global-scale Observations of the Limb and Disk (GOLD): Science Implementation

NASA Astrophysics Data System (ADS)

Solomon, S. C.; McClintock, W. E.; Eastes, R.; Anderson, D. N.; Andersson, L.; Burns, A. G.; Codrescu, M.; Daniell, R. E.; England, S.; Eparvier, F. G.; Evans, J. S.; Krywonos, A.; Lumpe, J. D.; Richmond, A. D.; Rusch, D. W.; Siegmund, O.; Woods, T. N.

2017-12-01

The Global-scale Observations of the Limb and Disk (GOLD) is a NASA mission of opportunity that will image the Earth's thermosphere and ionosphere from geostationary orbit. GOLD will investigate how the thermosphere-ionosphere (T-I) system responds to geomagnetic storms, solar radiation, and upward propagating tides and how the structure of the equatorial ionosphere influences the formation and evolution of equatorial plasma density irregularities. GOLD consists of a pair of identical imaging spectrographs that will measure airglow emissions at far-ultraviolet wavelengths from 132 to 162 nm. On the disk, temperature and composition will be determined during the day using emissions from molecular nitrogen Lyman-Birge-Hopfield (LBH) band and atomic oxygen 135.6 nm, and electron density will be derived at night from 135.6 nm emission. On the limb, exospheric temperature will be derived from LBH emission profiles, and molecular oxygen density will be measured using stellar occultations. This presentation describes the GOLD mission science implementation including the as-built instrument performance and the planned observing scenario. It also describes the results of simulations performed by the GOLD team to validate that the measured instrument performance and observing plan will return adequate data to address the science objectives of the mission.

MAVEN - Mars Atmosphere and Volatile EvolutioN Mission

NASA Technical Reports Server (NTRS)

Grebowsky, Joseph M.; Jakosky, Bruce M.

2011-01-01

NASA's MAVEN mission (to be launched in late 2013) is the first mission to Mars devoted to sampling all of the upper atmosphere neutral and plasma environments, including the well-mixed atmosphere, the exosphere, ionosphere, outer magnetosphere and near-Mars solar wind. It will fill in some measurement gaps remaining from the successful Mars Global Surveyor and the on-going Mars Express missions. The primary science objectives of MAVEN are: 1. Provide a comprehensive picture of the present state of the upper atmosphere and ionosphere of Mars; 2. Understand the processes controlling the present state; and 3. Determine how loss of volatiles to outer space in the present epoch varies with changing solar condition - EUY, solar wind and interplanetary magnetic field measurements will provide the varying solar energy inputs into the system. Knowing how these processes respond to the Sun's energy inputs in the current epoch will provide a framework for projecting atmospheric processes back in time to profile MARS' atmospheric evolution and to explore "where the water went", A description will be given of the science objectives, the instruments, and the current status of the project, emphasizing the value of having collaborations between the MAVEN project and the Mars upper atmosphere science community.

Possible Detection of Water in the Exosphere of (21) Lutetia

NASA Astrophysics Data System (ADS)

Wurz, P.; Altwegg, K.; Balsiger, H. R.; Jäckel, A.; Schläppi, B.; Hässig, M.; Hofer, L.; Mall, U. A.; Fiethe, B.; Gombosi, T. I.; Fuselier, S. A.; Reme, H.; Berthelier, J.; de Keyser, J. M.

2010-12-01

The Rosetta spacecraft performed a flyby at (21) Lutetia on 10 July 2010 with a closest approach of 3160 km. Among the scientific instruments on Rosetta is the ROSINA experiment, a suite of two mass spectrometers (DFMS and RTOF) and the pressure gauge, COPS. ROSINA successfully recorded data during the flyby. Most of the recorded signals were the result of spacecraft outgasing, arising from areas that were in shadow during the time proceeding the flyby and became illuminated (and therefore heated) when the spacecraft’s attitude was changed for the asteroid observations. These outgasing signals are well understood and are almost identical to the signals observed during the rehearsal manoeuvre in deep space performed in preparation for this flyby. In addition to these outgasing signals we identified a small water signal that has its likely origin in the asteroid. Preliminary analysis shows that Lutetia is losing water at the rate of Q = 1.4x10^26 H2O/s, within a factor 2. Finding water released from this asteroid makes it likely that Lutetia is a C-type asteroid, similar to the carbonaceous chondrites, which are know to contain water up to the percent level.

Tables of thermospheric temperature, density and composition derived from satellite and ground based measurements. Volume 1: Ap=4

NASA Technical Reports Server (NTRS)

Hedin, A. E.

1979-01-01

The tables contain the neutral temperature, neutral densities for N2, O2, O, Ar, He and H, mean molecular weight, and total mass density as predicted by the Mass Spectrometer and Incoherent Scatter empirical thermosphere model for selected altitudes, latitudes, local times, days and other geophysical conditions. The model is based on a least squares fit to density data from mass spectrometers on five satellites and temperature data from four incoherent scatter stations, providing coverage for most of solar sunspot cycle 20. Included in the model data base are longitudinally average N3, He, and O densities from the OGO-6 mass spectrometer longitudinally average N2, He, O and Ar densities from the AEROS-A (NATE) mass spectrometer the N2, He, O, and Ar densities from the San Marco 3 mass spectrometer the N2 densities from the AE-B mass spectrometer and the N2, He, O, and Ar densities from the AE-C (OSS, NACE, NATE) mass spectrometers. The O2 and H densities are inferred using ion mass spectrometer data from AE-C (BIMS). Neutral exospheric temperature data are included from Arecibo, St. Santin, Millstone Hill and Jicamarca.

Preliminary report of results from the plasma science experiment on Mariner 10

NASA Technical Reports Server (NTRS)

Bridge, H. S.; Lazarus, A. J.; Ogilvie, K. W.; Scudder, J. D.; Hartle, R. E.; Asbridge, J. R.; Bame, S. J.; Feldman, W. C.; Siscoe, G. L.; Yeates, C. M.

1974-01-01

Preliminary measurements of electron number density and temperature near Venus and Mercury and some results on flow speeds are presented. It is concluded that the interaction of the solar wind with Venus probably results in a bow shock characterized by H/r = 0.01 (ratio of the ionospheric scale height to the planetocentric distance of the nose of the ionopause); an extended exosphere appears unlikely. This direct interaction is indicated by the behavior of electrons with energies of 100-500 eV. Some unusual downstream effects suggest a comet-like tail several hundred scale lengths long. Near Mercury, a fully developed bow shock and magnetosheath were observed. Inside the magnetosheath there is a region analogous to the magnetosphere of the earth and populated by electrons of lower density and temperature than those found in the solar wind. The solar wind ram pressure corresponds to a stagnation pressure equivalent to a 170 gamma magnetic field. The strong solar wind interaction with Mercury is definitely magnetic, but not ionospheric or atmospheric. Spectra and particle flux varied widely while the spaceship was within the magnetosphere itself; temporal events like substorms may be responsible.

Charge Exchange X-Ray Emission due to Highly Charged Ion Collisions with H, He, and H2: Line Ratios for Heliospheric and Interstellar Applications

NASA Astrophysics Data System (ADS)

Cumbee, R. S.; Mullen, P. D.; Lyons, D.; Shelton, R. L.; Fogle, M.; Schultz, D. R.; Stancil, P. C.

2018-01-01

The fundamental collisional process of charge exchange (CX) has been established as a primary source of X-ray emission from the heliosphere, planetary exospheres, and supernova remnants. In this process, X-ray emission results from the capture of an electron by a highly charged ion from a neutral atom or molecule, to form a highly excited, high-charge state ion. As the captured electron cascades down to the lowest energy level, photons are emitted, including X-rays. To provide reliable CX-induced X-ray spectral models to realistically simulate these environments, line ratios and spectra are computed using theoretical CX cross sections obtained with the multi-channel Landau-Zener, atomic-orbital close-coupling, molecular-orbital close-coupling, and classical trajectory Monte Carlo methods for various collisional velocities relevant to astrophysics. X-ray spectra were computed for collisions of bare and H-like C to Al ions with H, He, and H2 with results compared to available experimental data. Using these line ratios, XSPEC models of CX emission in the northeast rim of the Cygnus Loop supernova remnant and the heliosphere are shown as examples with ion velocity dependence.

Subaru HDS transmission spectroscopy of the transiting extrasolar planet HD209458b

NASA Astrophysics Data System (ADS)

Narita, N.; Suto, Y.; Winn, J. N.; Turner, E. L.; Aoki, W.; Leigh, C. J.; Sato, B.; Tamura, M.; Yamada, T.

2006-02-01

We have searched for absorption in several common atomic species due to the atmosphere or exosphere of the transiting extrasolar planet HD 209458b, using high precision optical spectra obtained with the Subaru High Dispersion Spectrograph (HDS). Previously we reported an upper limit on Hα absorption of 0.1% (3σ) within a 5.1Å band. Using the same procedure, we now report upper limits on absorption due to the optical transitions of Na D, Li, Hα, Hβ, Hγ, Fe, and Ca. The 3σ upper limit for each transition is approximately 1% within a 0.3Å band (the core of the line), and a few tenths of a per cent within a 2Å band (the full line width). The wide-band results are close to the expected limit due to photon-counting (Poisson) statistics, although in the narrow-band case we have encountered unexplained systematic errors at a few times the Poisson level. These results are consistent with all previously reported detections (Charbonneau et al. 2002, ApJ, 568, 377) and upper limits (Bundy & Marcy 2000, PASP, 112, 1421; Moutou et al. 2001, A&A, 371, 260), but are significantly more sensitive yet achieved from ground based observations.

The Extreme Ultraviolet spectrometer on bard the Hisaki satellite

NASA Astrophysics Data System (ADS)

Yoshioka, K.; Murakami, G.; Yamazaki, A.; Tsuchiya, F.; Kagitani, M.; Kimura, T.; Yoshikawa, I.

2017-12-01

The extreme ultraviolet spectroscope EXCEED (EXtrem ultraviolet spetrosCope for ExosphEric Dynamics) on board the Hisaki satellite was launched in September 2013 from the Uchinoura space center, Japan. It is orbiting around the Earth with an orbital altitude of around 950-1150 km. This satellite is dedicated to and optimized for observing the atmosphere and magnetosphere of terrestrial planets such as Mercury, Venus, Mars, as well as Jupiter. The instrument consists of an off axis parabolic entrance mirror, switchable slits with multiple filters and shapes, a toroidal grating, and a photon counting detector, together with a field of view guiding camera. The design goal is to achieve a large effective area but with high spatial and spectral resolution. Based on the after-launch calibration, the spectral resolution of EXCEED is found to be 0.3-0.5 nm FWHM (Full Width at Half Maximum) over the entire spectral band, and the spatial resolution is around 17". The evaluated effective area is larger than 1cm2. In this presentation, the basic concept of the instrument design and the observation technique are introduced. The current status of the spacecraft and its future observation plan are also shown.

Sodium Atoms in the Lunar Exotail: Observed Velocity and Spatial Distributions

NASA Technical Reports Server (NTRS)

Line, Michael R.; Mierkiewicz, E. J.; Oliversen, R. J.; Wilson, J. K.; Haffner, L. M.; Roesler, F. L.

2011-01-01

The lunar sodium tail extends long distances due to radiation pressure on sodium atoms in the lunar exosphere. Our earlier observations determined the average radial velocity of sodium atoms moving down the lunar tail beyond Earth along the Sun-Moon-Earth line (i.e., the anti-lunar point) to be 12.4 km/s. Here we use the Wisconsin H-alpha Mapper to obtain the first kinematically resolved maps of the intensity and velocity distribution of this emission over a 15 x times 15 deg region on the sky near the anti-lunar point. We present both spatially and spectrally resolved observations obtained over four nights around new moon in October 2007. The spatial distribution of the sodium atoms is elongated along the ecliptic with the location of the peak intensity drifting 3 degrees east along the ecliptic per night. Preliminary modeling results suggest that the spatial and velocity distributions in the sodium exotail are sensitive to the near surface lunar sodium velocity distribution and that observations of this sort along with detailed modeling offer new opportunities to describe the time history of lunar surface sputtering over several days.

Ion acceleration by multiple reflections at Martian bow shock

NASA Astrophysics Data System (ADS)

Yamauchi, M.; Futaana, Y.; Fedorov, A.; Frahm, R. A.; Dubinin, E.; Lundin, R.; Sauvaud, J.-A.; Winningham, J. D.; Barabash, S.; Holmström, M.

2012-02-01

The ion mass analyzer (IMA) on board Mars Express revealed bundled structures of ions in the energy domain within a distance of a proton gyroradius from the Martian bow shock. Seven prominent traversals during 2005 were examined when the energy-bunched structure was observed together with pick-up ions of exospheric origin, the latter of which is used to determine the local magnetic field orientation from its circular trajectory in velocity space. These seven traversals include different bow shock configurations: (a) quasi-perpendicular shock with its specular direction of the solar wind more perpendicular to the magnetic field (QT), (b) quasi-perpendicular shock with its specular reflection direction of the solar wind more along the magnetic field (FS), and (c) quasi-parallel (QL) shock. In all seven cases, the velocity components of the energy-bunched structure are consistent with multiple specular reflections of the solar wind at the bow shock up to at least two reflections. The accelerated solar wind ions after two specular reflections have large parallel components with respect to the magnetic field for both QL cases whereas the field-aligned speed is much smaller than the perpendicular speed for all QT cases.

The Phobos neutral and ionized torus

NASA Astrophysics Data System (ADS)

Poppe, A. R.; Curry, S. M.; Fatemi, S.

2016-05-01

Charged particle sputtering, micrometeoroid impact vaporization, and photon-stimulated desorption are fundamental processes operating at airless surfaces throughout the solar system. At larger bodies, such as Earth's Moon and several of the outer planet moons, these processes generate tenuous surface-bound exospheres that have been observed by a variety of methods. Phobos and Deimos, in contrast, are too gravitationally weak to keep ejected neutrals bound and, thus, are suspected to generate neutral tori in orbit around Mars. While these tori have not yet been detected, the distribution and density of both the neutral and ionized components are of fundamental interest. We combine a neutral Monte Carlo model and a hybrid plasma model to investigate both the neutral and ionized components of the Phobos torus. We show that the spatial distribution of the neutral torus is highly dependent on each individual species (due to ionization rates that span nearly 4 orders of magnitude) and on the location of Phobos with respect to Mars. Additionally, we present the flux distribution of torus pickup ions throughout the Martian system and estimate typical pickup ion fluxes. We find that the predicted pickup ion fluxes are too low to perturb the ambient plasma, consistent with previous null detections by spacecraft around Mars.

Neutral Mass Spectrometer (NMS) for the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission

NASA Technical Reports Server (NTRS)

Collier, Michael R.; Mahaffy, Paul R.; Benna, Mehdi; King, Todd T.; Hodges, Richard

2011-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission currently scheduled for launch in early 2013 aboard a Minotaur V will orbit the moon at a nominal periselene of 50 km to characterized the lunar atmosphere and dust environment. The science instrument payload includes a neutral mass spectrometer as well as an ultraviolet spectrometer and a dust detector. Although to date only He, Ar-40, K, Na and Rn-222 have been firmly identified in the lunar exosphere and arise from the solar wind (He), the lunar regolith (K and Na) and the lunar interior (Ar-40, Rn-222), upper limits have been set for a large number of other species, LADEE Neutral Mass Spectrometer (NMS) observations will determine the abundance of several species and substantially lower the present upper limits for many others. Additionally, LADEE NMS will observe the spatial distribution and temporal variability of species which condense at nighttime and show peak concentrations at the dawn terminator (e,g, Ar-40), possible episodic release from the lunar interior, and the results of sputtering or desorption processes from the regolith. In this presentation, we describe the LADEE NMS hardware and the anticipated science results.

Miniaturized Ion and Neutral Mass Spectrometer for CubeSat Atmospheric Measurements

NASA Technical Reports Server (NTRS)

Rodriguez, M.; Paschalidis, N.; Jones, S.; Sittler, E.; Chornay, D.; Uribe, P.; Cameron, T.

2016-01-01

To increase the number of single point in-situ measurements of thermosphere and exosphere ion and neutral composition and density, miniaturized instrumentation is in high demand to take advantage of the increasing platform opportunities available in the smallsat/cubesat industry. The INMS (Ion-Neutral Mass Spectrometer) addresses this need by providing simultaneous measurements of both the neutral and ion environment, essentially providing two instruments in one compact model. The 1.3U volume, 570 gram, 1.8W nominal power INMS instrument makes implementation into cubesat designs (3U and above) practical and feasible. With high dynamic range (0.1-500eV), mass dynamic range of 1-40amu, sharp time resolution (0.1s), and mass resolution of MdM16, the INMS instrument addresses the atmospheric science needs that otherwise would have required larger more expensive instrumentation. INMS-v1 (version 1) launched on Exocube (CalPoly 3U cubesat) in 2015 and INMS-v2 (version 2) is scheduled to launch on Dellingr (GSFC 6U cubesat) in 2017. New versions of INMS are currently being developed to increase and add measurement capabilities, while maintaining its smallsat/cubesat form.

Plasma IMS Composition Measurements for Europa and the Other Galilean Moons

NASA Astrophysics Data System (ADS)

Sittler, Edward; Cooper, John; Hartle, Richard; Lipatov, Alexander; Mahaffy, Paul; Paterson, William; Pachalidis, Nick; Coplan, Mike; Cassidy, Tim

2010-05-01

NASA and ESA are planning the joint Europa Jupiter System Mission (EJSM) to the Jupiter system with specific emphasis to Europa and Ganymede, respectively. The Japanese Space Agency is also planning an orbiter mission to explore Jupiter's magnetosphere and the Galilean satellites. For NASA's Jupiter Europa Orbiter (JEO) we are developing the 3D Ion Mass Spectrometer (IMS) with two main goals which can also be applied to the other Galilean moons, 1) measure the plasma interaction between Europa and Jupiter's magnetosphere and 2) infer the 4? surface composition to trace elemental [1] and significant isotopic levels. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second gives information about transfer of material between the Galilean moons, and between the moon surfaces and subsurface layers putatively including oceans. The measurement of the interactions for all the Galilean moons can be used to trace the in situ ion measurements of pickup ions back to either Europa's or Ganymede's surface from the respectively orbiting spacecraft. The IMS instrument, being developed under NASA's Astrobiology Instrument Development Program, would maximally achieve plasma measurement requirements for JEO and EJSM while moving forward our knowledge of Jupiter system composition and source processes to far higher levels than previously envisaged. The composition of the global surfaces of Europa and Ganymede can be inferred from the measurement of ejected neutrals and pick-up ions using at minimum an in situ payload including MAG and IMS also fully capable of meeting Level 1 mission requirements for ocean detection and survey. Elemental and isotopic analysis of potentially extruded oceanic materials at the moon surfaces would further support the ocean objectives. These measurements should be made from a polar orbiting spacecraft about Europa or Ganymede at height ~ 100 km. The ejecta produced by sputtering of the surfaces of Europa and Ganymede has been shown to be representative of the surface composition [2,3]. Level 2 science on surface geology and composition can then be further enhanced by addition of the following: 3D Ion Neutral Mass Spectrometer (INMS), 3D plasma electron spectrometer (ELS), and hot plasma energetic particle instrument. The measurement approach is to alternate between times measuring pickup ions and times measuring plasma and magnetic field parameters along the spacecraft trajectory. By measuring the pickup ion energy, arrival direction and mass-per-charge, the ion can be traced back along the ejection trajectory to the approximate area of origin if the 3-D electric field and magnetic field are known. In situ observations of plasma flow velocities and vector magnetic fields can be used to determine the local convective electric field (E = -VXB) along the spacecraft trajectory. By combining this information with models of the magnetospheric interaction with Europa [3,4], one can generate 3D maps of the electric and magnetic field and compute the trajectories of the pickup ions back to the surface or exospheric points of origin. In the case of Ganymede there is the additional complexity of its own internal dipole magnetic field, while Io's volcanic activity introduces the complexity of a highly structured denser atmosphere. Callisto with its less globally extended exosphere will have a simpler interaction than for Europa (i.e., more like our moon). We will discuss these differences in light of the above proposed technique. Finally, the INMS observations and neutral exosphere models are needed to estimate production rates of pickup ions. The hot plasma measurements are needed to correct for sputtering rates which can be time dependent and electron plasma observations for electron impact ionization rates. Instrument characteristics, field-of-view requirements, modes of operation and effects of radiation on instrument functionality will be discussed. 1. Cassidy, T. A., Johnson, R. E., Tucker, O. J., 2009. Trace constituents of Europa's atmosphere. Icarus 201, 182-190. 2. Johnson, R. E., et al., Europa (ed R. Pappalardo et al.), Univ of Arizona Press, in press, 2009. 3. Schilling, N., Neubauer, F. M., Saur, J., 2008. Influence of the internally induced magnetic field on the plasma interaction of Europa. Journal of Geophysical Research (Space Physics) 113, 3203. 4. Lipatov, A. S., Cooper, J. F., Paterson, W. R., Sittler, E. C., and Hartle, R. E., Jovian's plasma torus interaction with Europa: 3D Hybrid kinetic simulation. First results, submitted to Plan. Sp. Sci., 2009.

First Results from NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE)

NASA Astrophysics Data System (ADS)

Elphic, R. C.; Colaprete, A.; Horanyi, M.; Mahaffy, P. R.; Delory, G. T.; Noble, S. K.; Boroson, D.; Hine, B.; Salute, J.

2013-12-01

As of early August, 2013, the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission is scheduled for launch on a Minotaur V rocket from Wallops Flight Facility during a five-day launch period that opens on Sept. 6, 2013 (early Sept. 7 UTC). LADEE will address 40 year-old mysteries of the lunar atmosphere and the question of levitated lunar dust. It will also pioneer the next generation of optical space communications. LADEE will assess the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. LADEE will also determine whether dust is present in the lunar exosphere, and reveal its sources and variability. These investigations are relevant to our understanding of surface boundary exospheres and dust processes occurring at many objects throughout the solar system, address questions regarding the origin and evolution of lunar volatiles, and have potential implications for future exploration activities. Following a successful launch, LADEE will enter a series of phasing orbits, which allows the spacecraft to arrive at the Moon at the proper time and phase. This approach accommodates any dispersion in the Minotaur V launch injection. LADEE's arrival at the moon depends on the launch date, but with the Sept. 6 launch date it should arrive at the Moon in early October. The spacecraft will approach the moon from its leading edge, travel behind the Moon out of sight of the Earth, and then re-emerge and execute a three-minute Lunar Orbit Insertion maneuver. This will place LADEE in an elliptical retrograde equatorial orbit with an orbital period of approximately 24 hours. A series of maneuvers is then performed to reduce the orbit to become nearly circular with a 156-mile (250-kilometer) altitude. Spacecraft checkout and science instrument commissioning will commence in early-October and will nominally span 30 days but can be extended for an additional 30 days in the event of contingencies. Following commissioning, the 100-day Science Phase is performed at an orbit with periapsis between 20-60 km. This orbit must be constantly managed due to the Moon's highly inhomogeneous gravity field. During the Science Phase, the moon will rotate more than three times underneath the LADEE orbit. LADEE employs a high heritage instrument payload: a Neutral Mass Spectrometer (NMS) from Goddard Space Flight Center, an Ultraviolet/Visible Spectrometer (UVS) from Ames Research Center, and a dust detection experiment (LDEX) from the University of Colorado/LASP. It will also carry the Lunar Laser Communications Demonstration (LLCD) as a technology demonstration. The LLCD is funded by the Human Exploration Operations Mission Directorate (HEOMD), managed by GSFC, and built by the MIT Lincoln Lab. Contingent upon LADEE's successful lunar orbit insertion and checkout, we will report the early results from the science investigations.

Lunar Atmosphere and Dust Environment Explorer Integration and Test

NASA Technical Reports Server (NTRS)

Wright, Michael R.; McCormick, John L.; Hoffman, Richard G.

2010-01-01

Integration and test (I&T) of the Lunar Atmosphere and Dust Environment Explorer (LADEE) is presented. A collaborative NASA project between Goddard Space Flight Center and Ames Research Center, LADEE's mission is to explore the low lunar orbit environment and exosphere for constituents. Its instruments include two spectrometers, a dust detector, and a laser communication technology demonstration. Although a relatively low-cost spacecraft, LADEE has I&T requirements typical of most planetary probes, such as prelaunch contamination control, sterilization, and instrument calibration. To lead to a successful mission, I&T at the spacecraft, instrument, and observatory level must include step-by-step and end-to-end functional, environmental, and performance testing. Due to its compressed development schedule, LADEE I&T planning requires adjusting test flows and sequences to account for long-lead critical-path items and limited spares. A protoflight test-level strategy is also baselined. However, the program benefits from having two independent but collaborative teams of engineers, managers, and technicians that have a wealth of flight project experience. This paper summarizes the LADEE I&T planning, flow, facilities, and probe-unique processes. Coordination of requirements and approaches to I&T when multiple organizations are involved is discussed. Also presented are cost-effective approaches to I&T that are transferable to most any spaceflight project I&T program.

Cosmic Ray Flux in the Presence of a Neutral Background

NASA Technical Reports Server (NTRS)

Wilson, Thomas L.; Lodhi, Arfin; Diaz, Abel

2007-01-01

The study of cosmic rays (CRs) is a very mature subject developed around the concept of radiative particle flux phi as a mono-variant function of energy E, that is phi = phi(E). This is based on the notion of the cosmos as being filled with cosmic radiation in the form of a collisionless exosphere of plasma. Neutrals, however, are likewise ubiquitous in space and planetary trapped-radiation belts. It will be shown that in the presence of a neutral background of density rho, flux phi is actually bivariant in energy E and rho, creating a surface phi(E,rho). This is an intrinsic property of charged-particle flux, that flux is not merely a function of E but is dependent upon density rho when a background of neutrals is present. The effect is produced by multiple scattering of charged particles off neutral and ionized atoms along with ionization loss where charged and neutral populations interact. For the harder portion of CR spectra, flux is mono-variant but at nonrelativistic energies (below approx, 350 MeV) it becomes sensitive to the presence of neutral backgrounds. The dependence of phi(E,rho) upon background neutrals is helpful in discussing the anomalous CR (ACR) flux made up of ionized components of the heliospheric neutral atmosphere.

Metals from deep atmosphere to exosphere in hot-Jupiters

NASA Astrophysics Data System (ADS)

Lecavelier des Etangs, Alain

2017-08-01

With STIS/UV observations we detected magnesium atoms at high altitude in the atmosphere of the hot-Jupiter HD209458b, probing lower regions in the atmosphere than previously done with Lyman-alpha observations (Vidal-Madjar et al. 2013). With the present program, we will search for magnesium and other heavy species in escaping atmospheres of 2 giant planets orbiting hot A and F-type stars: WASP-94Ab and WASP-33b.The observations will provide unprecedented information on the physical conditions (velocity, temperature, and density) in the upper atmosphere of these two hot-Jupiters. Targets have been selected for the expected high significance level of the atmospheric detections (>10 sigma). These exoplanets present favorable configuration for upper atmosphere observations because of the combination of high escape rates and large spatial extensions of the magnesium clouds surrounding them. The atmospheric signatures of the magnesium and other metals are therefore expected to be easily detectable. Moreover, the two selected exoplanets have highly different equilibrium temperatures, below and above the MgSiO3 condensation temperature. Consequently, because the metals observed in the escaping flow originate from deeper in the atmosphere where haze can condensate, the observations will constrain the physical processes taking place in the clouds that cannot be observed directly.

ULF waves in the Martian foreshock: MAVEN observations

NASA Astrophysics Data System (ADS)

Shan, Lican; Mazelle, Christian; Meziane, Karim; Ruhunusiri, Suranga; Espley, Jared; Halekas, Jasper; Connerney, Jack; McFadden, Jim; Mitchell, Dave; Larson, Davin; Brain, Dave; Jakosky, Bruce; Ge, Yasong; Du, Aimin

2016-04-01

Foreshock ULF waves constitute a significant physical phenomenon of the plasma environment for terrestrial planets. The occurrence of these ULF waves, associated with backstreaming ions reflected and accelerated at the bow shock, implies specific conditions and properties of the shock and its foreshock. Using measurements from MAVEN, we report clear observations of this type of ULF waves in the Martian foreshock. We show from different case studies that the peak frequency of the wave case in spacecraft frame is too far from the local ion cyclotron frequency to be associated with local pickup ions taking into account the Doppler shifted frequency from a cyclotron resonance, the obliquity of the mode, resonance broadening and experimental uncertainties. On the opposite their properties fit very well with foreshock waves driven unstable by backtreaming field-aligned ion beams. The propagation angle is usually less than 30 degrees from ambient magnetic field. The waves also display elliptical and left-hand polarizations with respect to interplanetary magnetic field in the spacecraft frame. It is clear for these cases that foreshock ions are simultaneous present for the ULF wave interval. Such observation is important in order to discriminate with the already well-reported pickup ion (protons) waves associated with exospheric hydrogen in order to quantitatively use the later to study seasonal variations of the hydrogen corona.

Mars Global Reference Atmospheric Model 2000 Version (Mars-GRAM 2000): Users Guide

NASA Technical Reports Server (NTRS)

Justus, C. G.; James, B. F.

2000-01-01

This report presents Mars Global Reference Atmospheric Model 2000 Version (Mars-GRAM 2000) and its new features. All parameterizations for temperature, pressure, density, and winds versus height, latitude, longitude, time of day, and L(sub s) have been replaced by input data tables from NASA Ames Mars General Circulation Model (MGCM) for the surface through 80-km altitude and the University of Arizona Mars Thermospheric General Circulation Model (MTGCM) for 80 to 170 km. A modified Stewart thermospheric model is still used for higher altitudes and for dependence on solar activity. "Climate factors" to tune for agreement with GCM data are no longer needed. Adjustment of exospheric temperature is still an option. Consistent with observations from Mars Global Surveyor, a new longitude-dependent wave model is included with user input to specify waves having 1 to 3 wavelengths around the planet. A simplified perturbation model has been substituted for the earlier one. An input switch allows users to select either East or West longitude positive. This memorandum includes instructions on obtaining Mars-GRAM source code and data files and for running the program. It also provides sample input and output and an example for incorporating Mars-GRAM as an atmospheric subroutine in a trajectory code.

Nitrogen isotopic components in the early solar system

NASA Technical Reports Server (NTRS)

Kerridge, J. F.

1994-01-01

It is quite common to take the terrestrial atmospheric value of (15)N/(14)N (0.00366) as typical of nitrogen in the early solar system, but in fact there is little reason to suppose that this value had a nebula-wide significance. Indeed, it is not clear that there was a unique solar-system-wide (15)N/(14)N ratio, of whatever value. Here we review what is known about the distribution of the nitrogen isotopes among those solar-system objects that have been sampled so far and conclude that those isotopes reveal widespread inhomogeneity in the early solar system. Whether the isotopically distinct primordial components implied by this analysis were solid or gaseous or a mixture of both is not known. The isotopic composition of N in the Earth's mantle is controversial: estimates range from a 1.1 percent depletion in (15)N to a 1.4 percent enrichment. (Isotopic compositions will be expressed throughout as percent deviations from the terrestrial atmospheric value.) The present-day Martian atmosphere is characterized by a value of plus 62 percent but this enrichment in (15)N is attributed to selective loss of (14)N from the Martian exosphere. Modelling of this fractionation leads to an estimated primordial composition similar to the terrestrial atmospheric value, through the precision of this model-dependent result is unclear.

Satellite accelerometer measurements of neutral density and winds during geomagnetic storms

NASA Technical Reports Server (NTRS)

Marcos, F. A.; Forbes, J. M.

1986-01-01

A new thermospheric wind measurement technique is reported which is based on a Satellite Electrostatic Triaxial Accelerometer (SETA) system capable of accurately measuring accelerations in the satellite's in-track, cross-track and radial directions. Data obtained during two time periods are presented. The first data set describes cross-track winds measured between 170 and 210 km during a 5-day period (25 to 29 March 1979) of mostly high geomagnetic activity. In the second data set, cross-track winds and neutral densities from SETA and exospheric temperatures from the Millstone Hill incoherent scatter radar are examined during an isolated magnetic substorm occurring on 21 March 1979. A polar thermospheric wind circulation consisting of a two cell horizontal convection pattern is reflected in both sets of cross-track acceleration measurements. The density response is highly asymmetric with respect to its day/night behavior. Latitude structures of the density response at successive times following the substorm peak suggest the equatorward propagation of a disturbance with a phase speed between 300 and 600 m/s. A deep depression in the density at high latitudes (less than 70 deg) is evident in conjunction with this phenomenon. The more efficient propagation of the disturbance to lower latitudes during the night is probably due to the midnight surge effect.

How Well Does the Present Surface Inventory of Water on Mars Constrain the Past?

NASA Technical Reports Server (NTRS)

Clifford, S. M.; McCubbin, F. M.

2016-01-01

Over the past 40 years, estimates of the total outgassed inventory of water on Mars have ranged from a global equivalent layer (GEL) approximately 7-1000 m deep. However, Carr and Head have recently argued that it is not the total inventory of outgassed water that is important, but the amount that exists in climatically exchangeable surface and near surface reservoirs - suggesting that any exchange with water in the deep subsurface is precluded by the existence of a thick cryosphere, at least during the Amazonian and Hesperian. Based on this assumption and their estimate of the present day near-surface inventory of H2O (approximately 34 m GEL, stored as ice in the polar layered deposits (PLD), lobate debris aprons, ice-rich latitude dependent mantles, and as shallow ground ice), they extrapolate the evolution of this inventory backward in time, taking into account the introduction of new water by volcanism, outflow channel activity, and the loss of water by exospheric escape. They conclude that, at the end of the Noachian, Mars had a near-surface water inventory of approximately 24 m and approximately 62 m by the end of the Hesperian - inventories that Carr and Head argue were incompatible with the existence of a former ocean.

An extremely high altitude plume seen at Mars morning terminator

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, Agustin; Garcia-Muñoz, Antonio; Garcia-Melendo, Enrique; Perez-Hoyos, Santiago; Gomez-Forrellad, Josep M.; Pellier, Christophe; Delcroix, Marc; Lopez-Valverde, Miguel Angel; Gonzalez-Galindo, Francisco; Jaeschke, Wayne; Parker, Donald C.; Phillips, James H.; Peach, Damian

2014-11-01

We report the occurrence in March and April 2012 of two bright very high altitude plumes at the Martian terminator at 250 km or more above the surface, thus well into the ionosphere and bordering on the exosphere. They were located at about 195 deg West longitude and -45 deg latitude (at Terra Cimmeria) and lasted for about 10 days. The features showed day-to-day variability, and were seen at the morning terminator but not at the evening limb, which indicates rapid evolution in less than 10 hours and a cyclic behavior. Photometric measurements are used to explore two possible scenarios to explain their nature. If the phenomenon is due to suspended particles (dust, CO2 or H2O ice clouds) reflecting solar radiation, the mean size is about 0.1 microns with a nadir optical depth > 0.06. Alternatively, the plume could be auroral emission above a region with a strong magnetic anomaly and where aurora has previously been detected. Importantly, both explanations defy our current understanding of the Mars upper atmosphere.AcknowledgementsThis work was supported by the Spanish MINECO projects AYA2012-36666 with FEDER support, CONSOLIDER program ASTROMOL CSD2009-00038 and AYA2011-30613-CO2-1. Grupos Gobierno Vasco IT765-13 and UPV/EHU UFI11/55.

Pluto and Charon's Visible Spectrum (3500-9000 Å)

NASA Astrophysics Data System (ADS)

Cook, J. C.; Wyckoff, S.

2003-05-01

Uncertainty in the chemical composition of Pluto's atmosphere severely limits our understanding of its physical properties. The only atmospheric gas identified spectroscopically to date has been CH4 (Young et al., 1997), while an upper limit has been set for CO gas (Young et al., 2001). Infrared detection of surface N2 ice (Owen et al., 1993) together with models based on occultation data (Elliot and Young, 1992) indicate that Pluto's atmosphere is probably dominated by CO and/or N2 (Yelle and Lunine, 1989; Hubbard et al., 1990; Stansberry et al., 1994). If the atmosphere is in vapor pressure equilibrium with the surface ice, then N2 gas would dominate the atmosphere with abundances ≳ 90% (Owen et al., 1993). Here we report on a search to identify atmospheric spectral features using data collected with the Steward Observatory 90'' Bok Telescope and the B & C Spectrograph. Pluto-Charon spectra were obtained on five nights in May and June 2003 using 300 l/mm grating blazed in the blue and red spectral regions. We present spectra covering the visible range from 3500 to 9000 Å : (λ /Δ λ ˜ 750 at 6000 Å), and discuss limits set on gases in the atmosphere and extended exosphere of the Pluto-Charon system. J. C. Cook would like to acknowledge support from NASA Space Grant Fellowship.

Titan Ion Composition at Magnetosphere-Ionosphere Transition Region

NASA Technical Reports Server (NTRS)

Sittler, Edward C.; Hartle, R. E.; Shappirio, M.; Simpson, D. J.; COoper, J. F.; Burger, M. H.; Johnson, R. E.; Bertucci, C.; Luhman, J. G.; Ledvina, S. A.;

Dusk/dawn atmospheric asymmetries on tidally-locked satellites: O2 at Europa

NASA Astrophysics Data System (ADS)

Oza, Apurva V.; Johnson, Robert E.; Leblanc, François

2018-05-01

We use a simple analytic model to examine the effect of the atmospheric source properties on the spatial distribution of a volatile in a surface-bounded atmosphere on a satellite that is tidally-locked to its planet. Spatial asymmetries in the O2 exosphere of Europa observed using the Hubble Space Telescope appear to reveal on average a dusk enhancement in the near-surface ultraviolet auroral emissions. Since the hop distances in these ballistic atmospheres are small, we use a 1-D mass conservation equation to estimate the latitudinally-averaged column densities produced by suggested O2 sources. Although spatial asymmetries in the plasma flow and in the surface properties certainly affect the spatial distribution of the near-surface aurora, the dusk enhancements at Europa can be understood using a relatively simple thermally-dependent source. Such a source is consistent with the fact that radiolytically produced O2 permeates their porous regoliths and is not so sensitive to the local production rate from ice. The size of the shift towards dusk is determined by the ratio of the rotation rate and atmospheric loss rate. A thermally-dependent source emanating from a large reservoir of O2 permeating Europa's icy regolith is consistent with the suggestion that its subsurface ocean might be oxidized by subduction of such radiolytic products.

Ion Acceleration by Multiple Reflections at Martian Bow Shock

NASA Astrophysics Data System (ADS)

Yamauchi, M.; Futaana, Y.; Fedorov, A.; Frahm, R. A.; Dubinin, E.; Lundin, R.; Sauvaud, J.-A.; Winningham, J. D.; Barabash, S.; Holmström, H.

2012-04-01

The ion mass analyzer (IMA) on board Mars Express revealed bundled structures of ions in the energy domain within a distance of a proton gyroradius from the Martian bow shock. Seven prominent traversals during 2005 were examined when the energy-bunched structure was observed together with pick-up ions of exospheric origin, the latter of which is used to determine the local magnetic field orientation from its circular trajectory in velocity space. These seven traversals include different bow shock configurations: (a) quasi-perpendicular shock with its specular direction of the solar wind more perpendicular to the magnetic field (QT), (b) quasi-perpendicular shock with its specular reflection direction of the solar wind more along the magnetic field (FS), and (c) quasi-parallel (QL) shock. In all seven cases, the velocity components of the energy-bunched structure are consistent with multiple specular reflections of the solar wind at the bow shock up to at least two reflections. The accelerated solar wind ions after two specular reflections have large parallel components with respect to the magnetic field for the QL shock whereas the field-aligned speed is much smaller than the perpendicular speed for the QT shock. The reflected ions escape into the solar wind when and only when the reflection is in the field-aligned direction.

MESSENGER's first Mercury flyby: A summary of scientific observations

NASA Astrophysics Data System (ADS)

Solomon, Sean C.; McNutt, Ralph L.; Boynton, William V.; Evans, Larry G.; Head, James W.; Krimigis, Stamatios M.; Murchie, Scott; Phillips, Roger J.; Slavin, James A.; Zuber, Maria T.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, developed under NASA's Discovery Program, will be the first probe to orbit the planet Mercury in March 2011. Launched in August 2004, MESSENGER successfully completed the first of three flybys of Mercury in January 2008. The Mercury Dual Imaging System acquired an 11-color mosaic of part of the hemisphere not seen by Mariner 10, including the entire Caloris basin; several large monochrome mosaics at a range of resolutions; a series of color frames designed for photometric analysis; and inbound and outbound movies. The Mercury Atmospheric and Surface Composition Spectrometer obtained the first high-resolution spectral reflectance measurements (at ultraviolet to near-infrared wavelengths) of surface composition, conducted limb scans of exospheric species, and mapped the composition and structure of the tail region. The Magnetometer measured Mercury's internal field at low latitudes and documented the major plasma boundaries of Mercury's magnetosphere. The Energetic Particle and Plasma Spectrometer made the first measurements of low-energy ions in Mercury's magnetosphere. The Mercury Laser Altimeter carried out the first space altimetric profile of the planet. Other instruments in the payload provided baseline measurements that will aid in the interpretation of data from the mission orbital phase. Together, the MESSENGER flyby observations have begun to advance our understanding of the innermost planet.

Gone with the Wind: Three Years of MAVEN Measurements of Atmospheric Loss at Mars

NASA Astrophysics Data System (ADS)

Brain, David; MAVEN Team

2017-10-01

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission is making measurements of the Martian upper atmosphere and near space environment, and their interactions with energy inputs from the Sun. A major goal of the mission is to evaluate the loss of atmospheric gases to space in the present epoch, and over Martian history. MAVEN is equipped with instruments that measure both the neutral and charged upper atmospheric system (thermosphere, ionosphere, exosphere, and magnetosphere), inputs from the Sun (extreme ultraviolet flux, solar wind and solar energetic particles, and interplanetary magnetic field), and escaping atmospheric particles. The MAVEN instruments, coupled with models, allow us to more completely understand the physical processes that control atmospheric loss and the particle reservoirs for loss.Here, we provide an overview of the significant results from MAVEN over approximately 1.5 Mars years (nearly three Earth years) of observation, from November 2014 to present. We argue that the MAVEN measurements tell us that the loss of atmospheric gases to space was significant over Martian history, and present the seasonal behavior of the upper atmosphere and magnetosphere. We also discuss the influence of extreme events such as solar storms, and a variety of new discoveries and observations of the Martian system made by MAVEN.

Calibration of the Neutral Mass Spectrometer for the Lunar Atmosphere and Dust Environment Explorer

NASA Technical Reports Server (NTRS)

Mahaffy, P. R.; Hodges, R. R.; Harpold, D. N.; King, T. T.; Jaeger, F.; Raaen, E.; Lyness, E.; Collier, M.; Benna, M.

2012-01-01

Science objectives of the LADEE Mission are to (1) determine the composition, and time variability of the tenuous lunar atmosphere and (2) to characterize the dust environment and its variability. These studies will extend the in-situ characterization of the environment that were carried out decades ago with the Apollo missions and a variety of ground based studies. The focused LADEE measurements will enable a more complete understanding of dust and gas sources and sinks. Sources of gas include UV photo-stimulated desorption, sputtering by plasma and micrometeorites, as well as thermal release of species such as argon from the cold service or venting from the lunar interior. Sinks include recondensation on the surface and escape through a variety of mechanisms. The LADEE science payload consists of an Ultraviolet Spectrometer, a Neutral Mass Spectrometer, and a Dust Detector. The LADEE orbit will include multiple passes at or below 50 km altitude and will target repeated sampling at the sunrise terminator where exospheric density will be highest for some thermally released species. The science mission will be implemented in approximately three months to allow measurements to be made over a period of one or more lunations In addition to the science mission NASA will use this mission to demonstrate optical communication technology away from low Earth orbit.

Variability of the composition of Io's exosphere deduced from the spectrum of ion cyclotron waves

NASA Astrophysics Data System (ADS)

Wang, Y. L.; Russell, C. T.; Raeder, J.; Kivelson, M. G.

2000-10-01

The spectrum of ion cyclotron waves seen during the Io flybys, I0, I24, I25 and I27 is quite varied. On I0 the cyclotron waves had a single strong peak near the gyrofrequency of SO2+. On I24 there were two peaks, one at the SO+ gyrofrequency and one at the SO2+ gyrofrequency, with the former stronger. On I25, the spectrum was similar but the relative strength of the peaks reversed. On I27 the spectrum was similar to I24 with the addition of a broad band centered on the H2S+ gyrofrequency. These varying strength emissions centered at the gyrofrequency of discrete ion gyrofrequencies imply that the chemical composition of the upper atmosphere is quite variable. The strength of the waves also appears to vary from one pass to the next, with the weakest signals occurring furthest from noon solar phase angle. This latter effect may be a geometrical in origin, associated with the varying dayside atmosphere relative to the corotating plasma. A simple model of the ion pickup process and transport of fast neutrals across field lines can explain the observed local time effect, and some of the radial variation of the torus properties.

Soft X-ray study of solar wind charge exchange from the Earth's magnetosphere : Suzaku observations and a future X-ray imaging mission concept

NASA Astrophysics Data System (ADS)

Ezoe, Y.; Ishisaki, Y.; Ohashi, T.; Ishikawa, K.; Miyoshi, Y.; Fujimoto, R.; Terada, N.; Kasahara, S.; Fujimoto, M.; Mitsuda, K.; Nishijo, K.; Noda, A.

2013-12-01

Soft X-ray observations of solar wind charge exchange (SWCX) emission from the Earth's magnetosphere using the Japanese X-ray astronomy satellite Suzaku are shown, together with our X-ray imaging mission concept to characterize the solar wind interaction with the magnetosphere. In recent years, the SWCX emission from the Earth's magnetosphere, originally discovered as unexplained noise during the soft X-ray all sky survey (Snowden et al. 1994), is receiving increased attention on studying geospace. The SWCX is a reaction between neutrals in exosphere and highly charged ions in the magnetosphere originated from solar wind. Robertson et al. (2005) modeled the SWCX emission as seen from an observation point 50 Re from Earth. In the resulting X-ray intensities, the magnetopause, bow shock and cusp were clearly visible. High sensitivity soft X-ray observation with CCDs onboard recent X-ray astronomy satellites enables us to resolve SWCX emission lines and investigate time correlation with solar wind as observed with ACE and WIND more accurately. Suzaku is the 5th Japanese X-ray astronomy satellite launched in 2005. The line of sight direction through cusp is observable, while constraints on Earth limb avoidance angle of other satellites often limits observable regions. Suzaku firstly detected the SWCX emission while pointing in the direction of the north ecliptic pole (Fujimoto et al. 2007). Using the Tsyganenko 1996 magnetic field model, the distance to the nearest SWCX region was estimated as 2-8 Re, implying that the line of sight direction can be through magnetospheric cusp. Ezoe et al. (2010) reported SWCX events toward the sub-solar side of the magnetosheath. These cusp and sub-solar side magnetosheath regions are predicted to show high SWCX fluxes by Robertson et al. (2005). On the other hand, Ishikawa et al. (2013) discovered a similarly strong SWCX event when the line of sight direction did not transverse these two regions. Motivated by these detections, Ishikawa et al. have conducted the systematic search of the Suzaku's 6 years archival data for the SWCX events. From ~2000 data sets, ~40 showed correlations between the X-ray light curve and solar wind flux. The SWCX emissivity is calculated in each observation by normalizing the observed X-ray flux by the solar wind flux observed as ACE and WIND, and is discussed in the context of the exospheric neutral distribution and magnetospheric structure. These soft X-ray studies with Earth-orbiting satellites are now leading X-ray astronomers and space plasma physicists to propose an X-ray imaging mission of the Earth's magnetosphere. Soft X-ray imaging from high altitude (e.g., the Moon orbit) offers the capability of mapping plasma structures at <0.1 Re scale and time cadence at

Planetary Data Archiving Activities of ISRO

NASA Astrophysics Data System (ADS)

Gopala Krishna, Barla; D, Rao J.; Thakkar, Navita; Prashar, Ajay; Manthira Moorthi, S.

ISRO has launched its first planetary mission to moon viz., Chandrayaan-1 on October 22, 2008. This mission carried eleven instruments; a wealth of science data has been collected during its mission life (November 2008 to August 2009), which is archived at Indian Space Science Data Centre (ISSDC). The data centre ISSDC is responsible for the Ingest, storage, processing, Archive, and dissemination of the payload and related ancillary data in addition to real-time spacecraft operations support. ISSDC is designed to provide high computation power, large storage and hosting a variety of applications necessary to support all the planetary and space science missions of ISRO. State-of-the-art architecture of ISSDC provides the facility to ingest the raw payload data of all the science payloads of the science satellites in automatic manner, processes raw data and generates payload specific processed outputs, generate higher level products and disseminates the data sets to principal investigators, guest observers, payload operations centres (POC) and to general public. The data archive makes use of the well-proven archive standards of the Planetary Data System (PDS). The long term Archive for five payloads of Chandrayaan-1 data viz., TMC, HySI, SARA, M3 and MiniSAR is released from ISSDC on19th April 2013 (http://www.issdc.gov.in) to the users. Additionally DEMs generated from possible passes of Chandrayaan-1 TMC stereo data and sample map sheets of Lunar Atlas are also archived and released from ISSDC along with the LTA. Mars Orbiter Mission (MOM) is the recent planetary mission launched on October 22, 2013; currently enroute to MARS, carrying five instruments (http://www.isro.org) viz., Mars Color Camera (MCC) to map various morphological features on Mars with varying resolution and scales using the unique elliptical orbit, Methane Sensor for Mars (MSM) to measure total column of methane in the Martian atmosphere, Thermal Infrared Imaging Spectrometer (TIS) to map surface composition & mineralogy of mars, Mars Exospheric Neutral Composition Analyser (MENCA) to study the composition and density of the Martian neutral atmosphere and Lyman Alpha Photometer (LAP) to investigate the loss process of water in Martian atmosphere, towards fulfilling the mission objectives. Active archive created in PDS for some of the instrument data during the earth phase of the mission is being analysed by the PIs. The Mars science data from the onboard instruments is expected during September 2014. The next planetary mission planned to moon is Chandrayaan-2 which consists of an orbiter having five instruments (http://www.isro.org) viz, (i) Imaging IR Spectrometer (IIRS) for mineral mapping, (ii) TMC-2 for topographic mapping, (iii) MiniSAR to detect water ice in the permanently shadowed regions on the Lunar poles, up to a depth of a few meters, (iv) Large Area Soft X-ray spectrometer (CLASS) & Solar X-ray Monitor (XSM) for mapping the major elements present on the lunar surface and (v)Neutral Mass Spectrometer (ChACE2) to carry out a detailed study of the lunar exosphere towards moon exploration; a rover for some specific experiments and a Lander for technology experiment and demonstration. The data is planned to be archived in PDS standards.

Observation of Neutral Sodium Above Mercury During the Transit of November 8, 2006

NASA Technical Reports Server (NTRS)

Potter, A. E.; Killen, R. M.; Reardon, Kevin P.; Bida, T. A.

2013-01-01

We mapped the absorption of sunlight by sodium vapor in the exosphere of Mercury during the transit of Mercury on November 8, 2006, using the IBIS Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope operated by the National Solar Observatory at Sunspot, New Mexico. The measurements were reduced to line-of-sight equivalent widths for absorption at the sodium D2 line around the shadow of Mercury. The sodium absorption fell off exponentially with altitude up to about 600 km. However there were regions around north and south polar-regions where relatively uniform sodium absorptions extended above 1000 km. We corrected the 0-600 km altitude profiles for seeing blur using the measured point spread function. Analysis of the corrected altitude distributions yielded surface densities, zenith column densities, temperatures and scale heights for sodium all around the planet. Sodium absorption on the dawn side equatorial terminator was less than on the dusk side, different from previous observations of the relative absorption levels. We also determined Earthward velocities for sodium atoms, and line widths for the absorptions. Earthward velocities resulting from radiation pressure on sodium averaged 0.8 km/s, smaller than a prediction of 1.5 km/s. Most line widths were in the range of 20 mA after correction for instrumental broadening, corresponding to temperatures in the range of 1000 K.

Statistical Similarities Between WSA-ENLIL+Cone Model and MAVEN in Situ Observations From November 2014 to March 2016

NASA Astrophysics Data System (ADS)

Lentz, C. L.; Baker, D. N.; Jaynes, A. N.; Dewey, R. M.; Lee, C. O.; Halekas, J. S.; Brain, D. A.

2018-02-01

Normal solar wind flows and intense solar transient events interact directly with the upper Martian atmosphere due to the absence of an intrinsic global planetary magnetic field. Since the launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, there are now new means to directly observe solar wind parameters at the planet's orbital location for limited time spans. Due to MAVEN's highly elliptical orbit, in situ measurements cannot be taken while MAVEN is inside Mars' magnetosheath. To model solar wind conditions during these atmospheric and magnetospheric passages, this research project utilized the solar wind forecasting capabilities of the WSA-ENLIL+Cone model. The model was used to simulate solar wind parameters that included magnetic field magnitude, plasma particle density, dynamic pressure, proton temperature, and velocity during a four Carrington rotation-long segment. An additional simulation that lasted 18 Carrington rotations was then conducted. The precision of each simulation was examined for intervals when MAVEN was in the upstream solar wind, that is, with no exospheric or magnetospheric phenomena altering in situ measurements. It was determined that generalized, extensive simulations have comparable prediction capabilities as shorter, more comprehensive simulations. Generally, this study aimed to quantify the loss of detail in long-term simulations and to determine if extended simulations can provide accurate, continuous upstream solar wind conditions when there is a lack of in situ measurements.

Overview of the LADEE Ultraviolet-visible Spectrometer: Design, Performance and Planned Operations

NASA Technical Reports Server (NTRS)

Colaprete, A.; Elphic, R. C.; Landis, D.; Karcz, J.; Osetinsky, L.; Shirley, M.; Vargo, K.; Wooden, D.

2013-01-01

The Lunar Atmosphere and Dust Environment Explorer (LADEE) is an orbital lunar science mission currently under development to address the goals of the 2003 National Research Council decadal survey, the Lunar Exploration Analysis Group Roadmap, and the "Scientific Context for Exploration of the Moon" (SCEM) report, and has been recommended for execution by the 2011 Planetary Missions Decadal Survey. The mission s focus is to study the pristine state of the lunar atmosphere and dust environment prior to possible lunar exploration activities by countries, including the United States, China, India, and Japan, among others. Activity on the lunar surface has the potential of altering the tenuous lunar atmosphere, but changing the type and concentration of gases in the atmosphere. Before these activities occur it is important to make measurements of the current lunar atmosphere in its unmodified state. LADEE will determine the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. It will monitor variations in known gases, such as sodium, potassium, argon and helium, and will search for other, as-yet-undetected gases of both lunar and extra-lunar origin. LADEE will also determine whether dust is present in the lunar exosphere, and reveal the processes that contribute to its sources and variability. Launch is planned for August, 2013.

Using Dawn to Observe SEP Events Past 2 AU

NASA Astrophysics Data System (ADS)

Villarreal, M. N.; Russell, C. T.; Prettyman, T. H.

2017-12-01

The launch of the STEREO spacecraft provided much insight into the longitudinal and radial distribution of solar energetic particles (SEPs) relative to their origin site. However, almost all of the observations of SEP events have been made exclusively near 1 AU. The Dawn mission, which orbited around Vesta before arriving at Ceres, provides an opportunity to analyze these events at much further distances. Although Dawn's Gamma Ray and Neutron Detector (GRaND) is not optimized for SEP characterization, it is sensitive to protons greater than 4 MeV, making it capable of detecting a solar energetic particle event in its vicinity. Solar energetic particles in this area of the solar system are important as they are believed to cause sputtering at bodies such as Ceres and comets (Villarreal et al., 2017; Wurz et al., 2015). In this study, we use Dawn's GRaND data from 2011-2015 when Dawn was at distances between 2-3 AU. We compare the SEP events seen by Dawn with particle measurements at 1 AU using STEREO, Wind, and ACE to understand how the SEP events evolved past 1 AU.References: Villarreal, M. N., et al. (2017), The dependence of the Cerean exosphere on solar energetic particle events, Astrophys. J. Lett., 838, L8.Wurz, P. et al. (2015), Solar wind sputtering of dust on the surface of 67P/Churyumov-Gerasimenko, A&A, 583, A22.