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1

Ultraviolet Radiation Constraints around the Circumstellar Habitable Zones  

E-print Network

Ultraviolet radiation is known to inhibit photosynthesis, induce DNA destruction and cause damage to a wide variety of proteins and lipids. In particular, UV radiation between 200-300 nm becomes energetically very damaging to most of the terrestrial biological systems. On the other hand, UV radiation is usually considered one of the most important energy source on the primitive Earth for the synthesis of many biochemical compounds and, therefore, essential for several biogenesis processes. In this work, we use these properties of the UV radiation to define the bounderies of an ultraviolet habitable zone. We also analyze the evolution of the UV habitable zone during the main sequence stage of the star. We apply these criteria to study the UV habitable zone for those extrasolar planetary systems that were observed by the International Ultraviolet Explorer (IUE). We analyze the possibility that extrasolar planets and moons could be suitable for life, according to the UV constrains presented in this work and other accepted criteria of habitability (liquid water, orbital stability, etc.).

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2006-04-18

2

DETECTABILITY OF EARTH-LIKE PLANETS IN CIRCUMSTELLAR HABITABLE ZONES OF BINARY STAR SYSTEMS WITH SUN-LIKE COMPONENTS  

SciTech Connect

Given the considerable percentage of stars that are members of binaries or stellar multiples in the solar neighborhood, it is expected that many of these binaries host planets, possibly even habitable ones. The discovery of a terrestrial planet in the {alpha} Centauri system supports this notion. Due to the potentially strong gravitational interaction that an Earth-like planet may experience in such systems, classical approaches to determining habitable zones (HZ), especially in close S-type binary systems, can be rather inaccurate. Recent progress in this field, however, allows us to identify regions around the star permitting permanent habitability. While the discovery of {alpha} Cen Bb has shown that terrestrial planets can be detected in solar-type binary stars using current observational facilities, it remains to be shown whether this is also the case for Earth analogs in HZs. We provide analytical expressions for the maximum and rms values of radial velocity and astrometric signals, as well as transit probabilities of terrestrial planets in such systems, showing that the dynamical interaction of the second star with the planet may indeed facilitate the planets' detection. As an example, we discuss the detectability of additional Earth-like planets in the averaged, extended, and permanent HZs around both stars of the {alpha} Centauri system.

Eggl, Siegfried; Pilat-Lohinger, Elke [University of Vienna, Institute for Astrophysics, Tuerkenschanzstr. 17, A-1180 Vienna (Austria)] [University of Vienna, Institute for Astrophysics, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Haghighipour, Nader, E-mail: siegfried.eggl@univie.ac.at [Institute for Astronomy and NASA Astrobiology Institute, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)] [Institute for Astronomy and NASA Astrobiology Institute, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2013-02-20

3

The habitable zone and extreme planetary orbits.  

PubMed

The habitable zone for a given star describes the range of circumstellar distances from the star within which a planet could have liquid water on its surface, which depends upon the stellar properties. Here we describe the development of the habitable zone concept, its application to our own solar system, and its subsequent application to exoplanetary systems. We further apply this to planets in extreme eccentric orbits and show how they may still retain life-bearing properties depending upon the percentage of the total orbit which is spent within the habitable zone. Key Words: Extrasolar planets-Habitable zone-Astrobiology. PMID:23035897

Kane, Stephen R; Gelino, Dawn M

2012-10-01

4

The Galactic Habitable Zone: Galactic Chemical Evolution  

Microsoft Academic Search

We propose the concept of a “Galactic Habitable Zone” (GHZ). Analogous to the Circumstellar Habitable Zone (CHZ), the GHZ is that region in the Milky Way where an Earth-like planet can retain liquid water on its surface and provide a long-term habitat for animal-like aerobic life. In this paper we examine the dependence of the GHZ on Galactic chemical evolution.

Guillermo Gonzalez; Donald Brownlee; Peter Ward

2001-01-01

5

The Habitable Zone  

NSDL National Science Digital Library

This illustration is an approximate representation of the planets in our solar system and their relation to what scientists call The Habitable Zone. The planet distances from the sun are measured in Astronomical Units (AU) and are not to scale.

2008-03-26

6

Research Articles Exomoon Habitability Constrained by Illumination  

E-print Network

, specifically designed to detect Earth-sized planets in the circumstellar irradiation habitable zones (IHZs become feasible. Once they are discovered in the circumstellar habitable zone, questions about a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define

Barnes, Rory

7

Habitable zone lifetimes of exoplanets around main sequence stars.  

PubMed

The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10? years (Gyr). The 7 exoplanets fall in a range between ?1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns. PMID:24047111

Rushby, Andrew J; Claire, Mark W; Osborn, Hugh; Watson, Andrew J

2013-09-01

8

Habitable Zones around Main Sequence Stars  

Microsoft Academic Search

A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2\\/H2O\\/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in

James F. Kasting; Daniel P. Whitmire; Ray T. Reynolds

1993-01-01

9

Potential photosynthetic systems in extraterrestrial habitable zones  

Microsoft Academic Search

A number of photosynthetic systems have evolved on Earth to harvest various portions of the available spectrum from its G2 star. Currently, the number of confirmed extrasolar planets approaches 300, although many are in orbits well outside their habitable zone. This largely results from an observational bias that tends to more easily spot these \\

Gregory Konesky

2008-01-01

10

Habitable zone limits for dry planets.  

PubMed

Most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an "aqua planet" like Earth, the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that "land planets" (desert worlds with limited surface water) have wider habitable zones than aqua planets. For planets at the inner edge of the habitable zone, a land planet has two advantages over an aqua planet: (i) the tropics can emit longwave radiation at rates above the traditional runaway limit because the air is unsaturated and (ii) the dry air creates a dry stratosphere that limits hydrogen escape. At the outer limits of the habitable zone, the land planet better resists global freezing because there is less water for clouds, snow, and ice. Here we describe a series of numerical experiments using a simple three-dimensional global climate model for Earth-sized planets. Other things (CO(2), rotation rate, surface pressure) unchanged, we found that liquid water remains stable at the poles of a low-obliquity land planet until net insolation exceeds 415 W/m(2) (170% that of modern Earth), compared to 330 W/m(2) (135%) for the aqua planet. At the outer limits, we found that a low-obliquity land planet freezes at 77%, while the aqua planet freezes at 90%. High-obliquity land and aqua planets freeze at 58% and 72%, respectively, with the poles offering the last refuge. We show that it is possible that, as the Sun brightens, an aqua planet like Earth can lose most of its hydrogen and become a land planet without first passing through a sterilizing runaway greenhouse. It is possible that Venus was a habitable land planet as recently as 1 billion years ago. PMID:21707386

Abe, Yutaka; Abe-Ouchi, Ayako; Sleep, Norman H; Zahnle, Kevin J

2011-06-01

11

Habitable zones around main sequence stars  

NASA Technical Reports Server (NTRS)

A mechanism for stabilizing climate on the earth and other earthlike planets is described, and the physical processes that define the inner and outer boundaries of the habitable zone (HZ) around the sun and main sequence stars are discussed. Physical constraints on the HZ obtained from Venus and Mars are taken into account. A 1D climate model is used to estimate the width of the HZ and the continuously habitable zone around the sun, and the analysis is extended to other main sequence stars. Whether other stars have planets and where such planets might be located with respect to the HZ is addressed. The implications of the findings for NASA's SETI project are considered.

Kasting, James F.; Whitmire, Daniel P.; Reynolds, Ray T.

1993-01-01

12

UV habitable zones around M stars  

Microsoft Academic Search

During the last decade there was a change in paradigm, which led to consider that terrestrial-type planets within liquid-water habitable zones (LW-HZ) around M stars can also be suitable places for the emergence and evolution of life. Since many dMe stars emit large amount of UV radiation during flares, in this work we analyze the UV constrains for living systems

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2007-01-01

13

Radiative Habitable Zones in Martian Polar Environments  

E-print Network

The biologically damaging solar ultraviolet (UV) radiation (quantified by the DNA-weighted dose) reaches the Martian surface in extremely high levels. Searching for potentially habitable UV-protected environments on Mars, we considered the polar ice caps that consist of a seasonally varying CO2 ice cover and a permanent H2O ice layer. It was found that, though the CO2 ice is insufficient by itself to screen the UV radiation, at 1 m depth within the perennial H2O ice the DNA-weighted dose is reduced to terrestrial levels. This depth depends strongly on the optical properties ofthe H2O ice layers (for instance snow-lile layes). The Earth-like DNA-weighted dose and Photosynthetically Active Radiation (PAR) requirements were used to define the upper and lower limits of the nortern and southern polar radiative habitable zone (RHZ) for which a temporal and spatial mapping was performed. Based on these studies we conclude that phtosynthetic life might be possible within the ice layers of the polar regions. The thickness varies along each Martian polar spring and summer between 1.5 m and 2.4 m for H2= ice-like layers, and a few centimeters for snow-like covers. These Martian Earth-like radiative habitable environments may be primary targets for future Martian astrobiological missions. Special attention should be paid to planetary protection, since the polar RHZ may also be subject to terrestrial contamination by probes.

C. Cordoba-Jabonero; M. -P. Zorzano; F. Selsis; M. R. Patel; C. S. Cockell

2005-07-13

14

Extrasolar Trojan Planets close to Habitable Zones  

E-print Network

We investigate the stability regions of hypothetical terrestrial planets around the Lagrangian equilibrium points L4 and L5 in some specific extrasolar planetary systems. The problem of their stability can be treated in the framework of the restricted three body problem where the host star and a massive Jupiter-like planet are the primary bodies and the terrestrial planet is regarded as being massless. From these theoretical investigations one cannot determine the extension of the stable zones around the equilibrium points. Using numerical experiments we determined their largeness for three test systems chosen from the table of the know extrasolar planets, where a giant planet is moving close to the so-called habitable zone around the host star in low eccentric orbits. The results show the dependence of the size and structure of this region, which shrinks significantly with the eccentricity of the known gas giant.

R. Dvorak; E. Pilat-Lohinger; R. Schwarz; F. Freistetter

2004-08-04

15

Galactic Habitable Zone and Astrobiological Complexity  

NASA Astrophysics Data System (ADS)

This is a short thesis description and for the sake of brevity most things are left out. For more details, those interested are further directed to the thesis related papers in this article reference list. Thesis itself is available at the University of Belgrade library "Svetozar Markovic" (Serbian version only). In this thesis we study the astrobiological history of the Galactic habitable zone through the means of numerical modeling. First group of simulations are unidimensional (time-axis) toy models examine the influence of global regulation mechanisms (gamma-ray bursts and supernovae) on temporal evolution of Galactic astrobiological complexity. It is shown that under the assumption of global regulation classical anti SETI arguments can be undermined. Second group of simulations are more complex bidimensional probabilistic cellular automata models of the Galactic thin disk. They confirm the findings of the toy models and give some insights into the spatial clustering of astrobiological complexity. As a new emerging multidisciplinary science the basic concepts of astrobiology are poorly understood and although all the simulations present here do not include some basic physics (such as Galactic kinematics and dynamics), the input parameters are somewhat arbitrary and could use a future refinement (such as the boundaries of the Galactic habitable zone). This is the cause for low weight and high uncertainty in the output results of the simulations. However, the probabilistic cellular automata has shown as a highly adaptable modeling platform that can simulate various class of astrobiological models with great ease.

Vukotic, B.

2012-12-01

16

Habitable zones around main sequence stars.  

PubMed

A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2/H2O/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in our model by loss of water via photolysis and hydrogen escape. The outer edge of the HZ is determined by the formation of CO2 clouds, which cool a planet's surface by increasing its albedo and by lowering the convective lapse rate. Conservative estimates for these distances in our own Solar System are 0.95 and 1.37 AU, respectively; the actual width of the present HZ could be much greater. Between these two limits, climate stability is ensured by a feedback mechanism in which atmospheric CO2 concentrations vary inversely with planetary surface temperature. The width of the HZ is slightly greater for planets that are larger than Earth and for planets which have higher N2 partial pressures. The HZ evolves outward in time because the Sun increases in luminosity as it ages. A conservative estimate for the width of the 4.6-Gyr continuously habitable zone (CHZ) is 0.95 to 1.15 AU. Stars later than F0 have main sequence lifetimes exceeding 2 Gyr and, so, are also potential candidates for harboring habitable planets. The HZ around an F star is larger and occurs farther out than for our Sun; the HZ around K and M stars is smaller and occurs farther in. Nevertheless, the widths of all of these HZs are approximately the same if distance is expressed on a logarithmic scale. A log distance scale is probably the appropriate scale for this problem because the planets in our own Solar System are spaced logarithmically and because the distance at which another star would be expected to form planets should be related to the star's mass. The width of the CHZ around other stars depends on the time that a planet is required to remain habitable and on whether a planet that is initially frozen can be thawed by modest increases in stellar luminosity. For a specified period of habitability, CHZs around K and M stars are wider (in log distance) than for our Sun because these stars evolve more slowly. Planets orbiting late K stars and M stars may not be habitable, however, b ecause they can become trapped in synchronous rotation as a consequence of tidal damping. F stars have narrower (log distance) CHZ's than our Sun because they evolve more rapidly. Our results suggest that mid-to-early K stars should be considered along with G stars as optimal candidates in the search for extraterrestrial life. PMID:11536936

Kasting, J F; Whitmire, D P; Reynolds, R T

1993-01-01

17

Tides, planetary companions, and habitability: habitability in the habitable zone of low-mass stars  

NASA Astrophysics Data System (ADS)

Earth-scale planets in the classical habitable zone (HZ) are more likely to be habitable if they possess active geophysics. Without a constant internal energy source, planets cool as they age, eventually terminating tectonic activity. Planets orbiting low-mass stars can be very old, due to the longevity of such stars, so they may be rendered sterile to life in this way. However, the presence of an outer companion could generate enough tidal heat in the HZ planet to prevent such cooling. The range of mass and orbital parameters for the companion that give adequate long-term heating of the inner HZ planet, while avoiding very early total desiccation, is probably substantial. We locate the ideal location for the outer of a pair of planets, under the assumption that the inner planet has the same incident flux as Earth, orbiting example stars: a generic late M dwarf (Teff = 2670 K) and the M9V/L0 dwarf DEN1048. Thus discoveries of Earth-scale planets in the HZ zone of old small stars should be followed by searches for outer companion planets that might be essential for current habitability.

Van Laerhoven, C.; Barnes, R.; Greenberg, R.

2014-07-01

18

Sensitivity of Transit Searches to Habitable-Zone Planets  

Microsoft Academic Search

Photon-limited transit surveys in the V band are in principle about 20 times more sensitive to planets of fixed size in the habitable zone around M stars than G stars. In the I band the ratio is about 400. The advantages of a closer habitable zone and smaller stars (together with the numerical superiority of M stars) more than compensate

Andrew Gould; Joshua Pepper; D. L. DePoy

2003-01-01

19

The Habitable Zone of Inhabited Planets  

NASA Astrophysics Data System (ADS)

In this paper we discuss and illustrate the hypothesis that life substantially alters the state of a planetary environment and therefore, modifies the limits of the HZ as estimated for an uninhabited planet. This hypothesis lead to the introduction of the Habitable Zone for Inhabited Planets (hereafter InHZ), defined here as the region where the complex interaction between life and its abiotic environment is able to produce plausible equilibrium states with the necessary physical conditions for the existence and persistence of life itself. We support our hypothesis of an InHZ with three theoretical arguments, multiple evidences coming from observations of the Earth system, several conceptual experiments and illustrative numerical simulations. Conceptually the diference between the InHZ and the Abiotic HZ (AHZ) depends on unique and robust properties of life as an emergent physical phenomenon and not necesarily on the particular life forms bearing in the planet. Our aim here is to provide conceptual basis for the development of InHZ models incorporating consistently life-environment interactions. Although previous authors have explored the effects of life on habitability there is a gap in research developing the reasons why life should be systematically included at determining the HZ limits. We do not provide here definitive limits to the InHZ but we show through simple numerical models (as a parable of an inhabited planet) how the limits of the AHZ could be modified by including plausible interactions between biota and its environment. These examples aim also at posing the question that if limits of the HZ could be modified by the presence of life in those simple dynamical systems how will those limits change if life is included in established models of the AHZ.

Zuluaga, J. I.; Salazar, J. F.; Cuartas-Restrepo, P.; Poveda, G.

2014-06-01

20

Tectonics and the photosynthetic habitable zone (Invited)  

NASA Astrophysics Data System (ADS)

The traditional habitable zone lies between an inner stellar radius where the surface of the planet becomes too hot for liquid water carbon-based life and on outer radius, where the surface freezes. It is effectively the zone where photosynthesis is feasible. The concept extends to putative life on objects with liquid methane at the surface, like Titan. As a practical matter, photosynthesis leaves detectable biosignatures in the geological record; black shale on the Earth indicates that sulfide and probably FeO based photosynthesis existed by 3.8 Ga. The hard crustal rocks and the mantle sequester numerous photosynthetic biosignatures. Photosynthesis can produce detectable free oxygen with ozone in the atmosphere of extrasolar planets. In contrast, there is no outer limit for subsurface life in large silicate objects. Pre-photosynthetic niches are dependable but meager and not very detectable at great antiquity or great distance, with global productivity less than 1e-3 of the photosynthetic ones. Photosynthetic organisms have bountiful energy that modifies their surface environment and even tectonics. For example, metamorphic rocks formed at the expense of thick black shale are highly radioactive and hence self-fluxing. Active tectonics with volcanism and metamorphism prevents volatiles from being sequestered in the subsurface as on Mars. A heat-pipe object, like a larger Io, differs from the Earth in that the volatiles return to the deep interior distributed within massive volcanic deposits rather than concentrated in the shallow oceanic crust. One the Earth, the return of water to the surface by arc volcanoes controls its mantle abundance at the transition between behaving as a trace element and behaving as a major element that affects melting. The ocean accumulates the water that the mantle and crust do not take. The Earth has the “right” amount of water that erosion/deposition and tectonics both tend to maintain near sea level surfaces. The mantle contains carbon (dioxide) that platform carbonates and the deep continental lithosphere do not take. Weathering and formation of carbonates in the oceanic crust dynamically buffers atmospheric CO2 at habitable levels. N2 is an indirect greenhouse gas in that the total pressure increases the effect of CO2. Photosynthetic life affects the nitrogen cycle as NH4+ replaces K+ in subducted black shale. N2 hence correlates with Ar-40 in volcanic gases. The net effect is that atmospheric pressure and hence the greenhouse effect decrease with time. Continents are in part the result of biological weathering. Their presence allows life to directly affect continental albedo as with “Daisy World” and to indirectly affect albedo as high global temperatures lead to reflective deserts.

Sleep, N. H.

2009-12-01

21

Prospects for Extrasolar "Earths" in Habitable Zones  

E-print Network

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 102 main-sequence exoplanetary systems confirmed by 19 November 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a half of these systems could have had an Earth-mass planet confined to the HZ for at least the most recent 1000 Ma. The HZ migrates outwards during the main-sequence lifetime, and so this proportion varies with stellar age. About two thirds of the systems could have such a planet confined to the HZ for at least 1000 Ma at sometime during the main-sequence lifetime. Clearly, these systems should be high on the target list for exploration for terrestrial planets. We have reached this conclusion by launching putative Earth-mass planets in various orbits and following their fate with mixed-variable symplectic and hybrid integrators. Whether the Earth-mass planets could form in the HZs of the exoplanetary systems is an urgent question that needs further study.

B. W. Jones; D. R. Underwood; P. N. Sleep

2005-03-08

22

Ultraviolet radiation constraints around the circumstellar habitable zones  

Microsoft Academic Search

Ultraviolet radiation is known to inhibit photosynthesis, induce DNA destruction and cause damage to a wide variety of proteins and lipids. In particular, UV radiation between 200 and 300 nm becomes energetically very damaging to most of the terrestrial biological systems. On the other hand, UV radiation is usually considered one of the most important energy source on the primitive

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2006-01-01

23

The Habitability of Our Earth and Other Earths  

E-print Network

zone and the galactic habitable zone. 597 Annu.Rev.EarthPlanet.Sci.2012.40:597-623.DownloadedfromwwwThe Habitability of Our Earth and Other Earths: Astrophysical, Geochemical, Geophysical zones, circumstellar habitable zones, terrestrial planets, life, abiogenesis Abstract For life

Lineweaver, Charles H.

24

Hazes at the Inner Edge of the Habitable Zone  

Microsoft Academic Search

The ``insolation habitable zone'' (IHZ) is the region around a star where the incoming solar radiation, combined with the forcings from the planet's atmosphere, can keep liquid water stable at the surface of the planet. Historically, studies that consider the forcings from the planet have primarily focused on the greenhouse effect of the planet's atmosphere. To remain habitable, planets at

S. D. Domagal-Goldman; T. D. Robinson; J. Haqq-Misra

2009-01-01

25

Europa, tidally heated oceans, and habitable zones around giant planets  

NASA Technical Reports Server (NTRS)

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. Europa could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such a case, sufficient solar energy could reach liquid water that organisms similar to those found under Antarctic ice could grow. In other solar systems, larger satellites with more significant heat flow could represent environments that are stable over an order of eons and in which life could perhaps evolve. A zone around a giant planet is defined in which such satellites could exist as a tidally-heated habitable zone. This zone can be compared to the habitable zone which results from heating due to the radiation of a central star. In this solar system, this radiatively-heated habitable zone contains the earth.

Reynolds, Ray T.; Mckay, Christopher P.; Kasting, James F.

1987-01-01

26

Habitable zones around exoplanets' host stars  

Microsoft Academic Search

The last decade has witnessed the discovery of an amazing range of planetary sized objects around nearby stars. The number of discovered planets exceeds 260 so far, and it is expected to grow exponentially as new planet detection missions are placed into orbit. The search for habitable planets stands as an important goal for the scientific community with far reaching

Shawqi Al Dallal; Walid Azzam; Waleed Azzam

2008-01-01

27

Planet formation in the habitable zone of alpha Centauri B  

Microsoft Academic Search

Recent studies have shown that alpha Centauri B might be, from an observational point of view, an ideal candidate for the detection of an Earth-like planet in or near its habitable zone (0.5-0.9au). We study here if such habitable planets can form, by numerically investigating the planet-formation stage which is probably the most sensitive to binarity effects: the mutual accretion

P. Thébault; Francesco Marzari; Hans Scholl

2009-01-01

28

Radiative habitable zones in martian polar environments  

Microsoft Academic Search

The biologically damaging solar ultraviolet (UV) radiation (quantified by the DNA-weighted dose) reaches the martian surface in extremely high levels. Searching for potentially habitable UV-protected environments on Mars, we considered the polar ice caps that consist of a seasonally varying CO2 ice cover and a permanent H2O ice layer. It was found that, though the CO2 ice is insufficient by

Carmen Córdoba-Jabonero; María-Paz Zorzano; Franck Selsis; Manish R. Patel; Charles S. Cockell

2005-01-01

29

What Can The Habitable Zone Gallery Do for You?  

NASA Astrophysics Data System (ADS)

The Habitable Zone Gallery (www.hzgallery.org) has been online since August 2011 as a service to the exoplanet community to provide Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table, a plot with the period and eccentricity of each of the planets with respect to their time spent in the HZ, a gallery of known systems which plots the orbits and the location of the HZ with respect to those orbits, and orbital movies. Recently, we have added new features including: implementation of both conservative and optimistic HZs, more user-friendly table and movies, movies for circumbinary planets, and a count of planets whose orbits lie entirely within the system’s HZ. Here we discuss various educational and scientific applications of the site such as target selection, exploring planets with eccentric or circumbinary orbits, and investigating habitability.

Gelino, Dawn M.; Kane, Stephen R.

2014-06-01

30

Comparable Habitable Zones of Stars - Duration: 0:25.  

NASA Video Gallery

The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evapo...

31

Habitable Zones Around Stars and the Search for Extraterrestrial Life  

Microsoft Academic Search

The habitable zone, or HZ, is defined as the region around a star in which liquid water can exist on the surface of a planet. Liquid water can exist in subsurface environments on planets or moons outside of the HZ (e.g., Jupiter's moon, Europa), but this possibility is of little significance, as such environments cannot be observed or otherwise investigated.

J. F. Kasting

2001-01-01

32

CANDIDATE PLANETS IN THE HABITABLE ZONES OF KEPLER STARS  

SciTech Connect

A key goal of the Kepler mission is the discovery of Earth-size transiting planets in ''habitable zones'' where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p{sub HZ} that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p{sub HZ}. Sixty-two planets have p{sub HZ} > 0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}{sub Circled-Plus }) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.

Gaidos, Eric, E-mail: gaidos@hawaii.edu [Department of Geology and Geophysics, University of Hawai'i at Manoa, Honolulu, HI 96822 (United States)

2013-06-20

33

STABILIZING CLOUD FEEDBACK DRAMATICALLY EXPANDS THE HABITABLE ZONE OF TIDALLY LOCKED PLANETS  

SciTech Connect

The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.

Yang Jun; Abbot, Dorian S. [Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States); Cowan, Nicolas B., E-mail: abbot@uchicago.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2131 Tech Drive, Evanston, IL 60208 (United States)

2013-07-10

34

Europa, tidally heated oceans, and habitable zones around giant planets.  

PubMed

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. In our own solar system, Europa, one of the Galilean satellites of Jupiter, could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such case, sufficient solar energy could reach liquid water that organisms similar to those found under Antarctic ice could grow. In other solar systems, larger satellites with more significant heat flow could represent environments that are stable over an order of Aeons and in which life could perhaps evolve. We define a zone around a giant planet in which such satellites could exist as a tidally-heated habitable zone. This zone can be compared to the habitable zone which results from heating due to the radiation of a central star. In our solar system, this radiatively-heated habitable zone contains the Earth. PMID:11538217

Reynolds, R T; McKay, C P; Kasting, J F

1987-01-01

35

Habitable zones of host stars during the post-MS phase  

Microsoft Academic Search

A star will become brighter and brighter with stellar evolution, and the distance of its habitable zone will become larger\\u000a and larger. Some planets outside the habitable zone of a host star during the main sequence phase may enter the habitable\\u000a zone of the host star during other evolutionary phases. A terrestrial planet within the habitable zone of its host

Jianpo Guo; Fenghui Zhang; Zhanwen Han

2010-01-01

36

Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?  

Microsoft Academic Search

We present some new ideas about the possibility of life developing around subgiant and red giant stars. Our study concerns the temporal evolution of the habitable zone. The distance between the star and the habitable zone, as well as its width, increases with time as a consequence of stellar evolution. The habitable zone moves outward after the star leaves the

Bruno Lopez; Jean Schneider; William C. Danchi

2005-01-01

37

THESIS: the terrestrial habitable-zone exoplanet spectroscopy infrared spacecraft  

Microsoft Academic Search

THESIS, the Transiting Habitable-zone Exoplanet Spectroscopy Infrared Spacecraft, is a concept for a medium\\/Probe class exoplanet mission. Building on the recent Spitzer successes in exoplanet characterization, THESIS would extend these types of measurements to super-Earth-like planets. A strength of the THESIS concept is simplicity, low technical risk, and modest cost. The mission concept has the potential to dramatically advance our

Mark R. Swain; Gautam Vasisht; Thomas Henning; Giovanna Tinetti; Jean-Phillippe Beaulieu

2010-01-01

38

THESIS: terrestrial and habitable zone infrared spectroscopy spacecraft  

Microsoft Academic Search

THESIS is a concept for a medium class mission designed for spectroscopic characterization of extrasolar planets between 2-14 microns. The concept leverages off the recent first-steps made by Spitzer and Hubble in characterizing the atmospheres of alien gas giants. Under favourable circumstances, THESIS is capable of identifying biogenic molecules in habitable-zone planets, thereby determining conditions on worlds where life might

G. Vasisht; M. R. Swain; R. L. Akeson; A. Burrows; D. Deming; C. J. Grillmair; T. P. Greene

2008-01-01

39

Terrestrial, Habitable-Zone Exoplanet Frequency from Kepler  

Microsoft Academic Search

Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and host-star spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitable-zone exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude 0.5 Earth radius and periods <42 days. It is also assumed

Wesley A. Traub

2011-01-01

40

Extrasolar `Earths' in Habitable Zones: Targets of Opportunity  

Microsoft Academic Search

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 102 main-sequence exoplanetary systems confirmed by 25 September 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a half of these systems could have had an Earth-mass

B. W. Jones; D. R. Underwood; P. N. Sleep

2004-01-01

41

The generalized runaway greenhouse and the outer limit of habitable zones (Invited)  

Microsoft Academic Search

The inner limit of the habitable zone is determined by atmospheric blowoff and the water vapor runaway greenhouse, but it is not immediately apparent that there should be an outer limit to the habitable zone, as one could simply contemplate pumping greenhouse gases into the atmosphere until the temperature rises into the habitable range. Silicate\\/carbonate rocky planets offer a nearly

R. Pierrehumbert

2009-01-01

42

Determination of Habitable Zones in Extrasolar Planetary Systems: Where are Gaia's Sisters?  

E-print Network

on the identification of the "habitable zone" in main-sequence star planetary systems accommodating Earth1 Determination of Habitable Zones in Extrasolar Planetary Systems: Where are Gaia's Sisters-like components. Our definition of habitability is based on the long-term possibility of photosynthetic biomass

43

THESIS: the terrestrial habitable-zone exoplanet spectroscopy infrared spacecraft  

NASA Astrophysics Data System (ADS)

THESIS, the Transiting Habitable-zone Exoplanet Spectroscopy Infrared Spacecraft, is a concept for a medium/Probe class exoplanet mission. Building on the recent Spitzer successes in exoplanet characterization, THESIS would extend these types of measurements to super-Earth-like planets. A strength of the THESIS concept is simplicity, low technical risk, and modest cost. The mission concept has the potential to dramatically advance our understanding of conditions on extrasolar worlds and could serve as a stepping stone to more ambitious future missions. We envision this mission as a joint US-European effort with science objectives that resonate with both the traditional astronomy and planetary science communities.

Swain, Mark R.; Vasisht, Gautam; Henning, Thomas; Tinetti, Giovanna; Beaulieu, Jean-Phillippe

2010-07-01

44

THESIS: terrestrial and habitable zone infrared spectroscopy spacecraft  

NASA Astrophysics Data System (ADS)

THESIS is a concept for a medium class mission designed for spectroscopic characterization of extrasolar planets between 2-14 microns. The concept leverages off the recent first-steps made by Spitzer and Hubble in characterizing the atmospheres of alien gas giants. Under favourable circumstances, THESIS is capable of identifying biogenic molecules in habitable-zone planets, thereby determining conditions on worlds where life might exist. By systematically characterizing many worlds, from rocky planets to gas-giants, THESIS would deliver transformational science of profound interest to astronomers and the general public.

Vasisht, G.; Swain, M. R.; Akeson, R. L.; Burrows, A.; Deming, D.; Grillmair, C. J.; Greene, T. P.

2008-07-01

45

Relative stellar occurrence of exoplanets in habitable zones of the main sequence F, G, K stars  

NASA Astrophysics Data System (ADS)

We have determined the stellar occurrence of exoplanets in the habitable zones of the main sequence F, G, K stars using the statistical analysis of confirmed exoplanets and that of the Kepler candidates. We predict the greatest occurrence of exoplanets in the habitable zones of the main sequence G stars. An optimistic definition of habitable zone gives 0.114 Earth-size exoplanets per star in habitable zones of the main sequence G stars for the confirmed exoplanets and 0.336-0.041-0.032 Earth-size exoplanets per star in habitable zones of the main sequence G stars for the Kepler candidates. The possibility of detecting habitable exoplanets is much higher for the star from the main sequence G stars, the exoplanet detection missions can be focused in the region around the stars of this spectral class.

Pintr, Pavel; Pe?inová, Vlasta; Lukš, Antonín; Pathak, Anirban

2014-09-01

46

Accounting planetary habitability using non standard conditions. Impact on the definition of Habitable Zone  

NASA Astrophysics Data System (ADS)

Although during the 1960s, atmospheric disequilibrium has been proposed as a sign of habitability of Earth and, in general, of a planet [1, 2], no calculation has been done until now. In order to provide a first evaluation of Earth's atmospheric disequilibrium, we have developed a new formulation to account for the thermodynamic conditions of a wide range of planetary atmospheres, from terrestrial planets to icy satellites, to hot exoplanets. Using this new formulation, we estimate the departure of different planetary atmospheres from their equilibrium conditions, computing the dissipation of free energy due to all chemical processes [3]. In particular, we focus on the effect of our proposed changes on O2/CO2 chemistry (comparing Io satellite atmosphere and Earth Mesosphere), N2 (Venus, Earth and Titan) and H2O stability on terrestrial planets and exoplanets. Our results have an impact in the definition of Habitable Zone by considering appropriate physical-chemical conditions of planetary atmospheres. References [1] J. E. Lovelock, A physical basis for life detection experiments. Nature, 207, 568-570 (1965). [2] J. E. Lovelock, Thermodynamics and the recognition of alien biospheres. Proc. R. Soc. Lond., B. 189, 167 - 181 (1975). [3] Simoncini E., Delgado-Bonal A., Martin-Torres F.J., Accounting thermodynamic conditions in chemical models of planetary atmospheres. Submitted to Astrophysical Journal.

Simoncini, E.; Delgado-Bonal, A.; Martin-Torres, F. J.

2012-12-01

47

Abiotic Oxygen-dominated Atmospheres on Terrestrial Habitable Zone Planets  

NASA Astrophysics Data System (ADS)

Detection of life on other planets requires identification of biosignatures, i.e., observable planetary properties that robustly indicate the presence of a biosphere. One of the most widely accepted biosignatures for an Earth-like planet is an atmosphere where oxygen is a major constituent. Here we show that lifeless habitable zone terrestrial planets around any star type may develop oxygen-dominated atmospheres as a result of water photolysis, because the cold trap mechanism that protects H2O on Earth is ineffective when the atmospheric inventory of non-condensing gases (e.g., N2, Ar) is low. Hence the spectral features of O2 and O3 alone cannot be regarded as robust signs of extraterrestrial life.

Wordsworth, Robin; Pierrehumbert, Raymond

2014-04-01

48

Planetary Atmosphere Stability in the Habitable Zones of M-stars  

Microsoft Academic Search

The traditional habitable zone depends on conditions suitable for long term stability of liquid water on the surface of planets. It is suggested that the frequent intense stellar CME events could have led to so rapid erosion of planetary atmospheres that generally speaking there is essentially no habitable zones around Earth-mass planets around M-stars. However, fast atmosperic mass loss should

Feng Tian

2010-01-01

49

The Orbits of Terrestrial Planets in the Habitable Zones of Known Extrasolar Planetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

B. W. Jones; P. N. Sleep

2003-01-01

50

Considerations for the habitable zone of super-Earth planets in Gliese 581  

Microsoft Academic Search

We assess the possibility that planets Gliese 581 c and d are within the habitable zone. In analogy with our solar system, we use an empirical definition of the habitable zone. We include assumptions such as planetary climates, and atmospheric circulation on gravitationally locked synchronous rotation. Based on the different scenarios, we argue that both planets in Gliese 581 could

P. Chylek; M. R. Perez

2007-01-01

51

The Orbits of Terrestrial Planets in the Habitable Zones of Known Extrasolar Planetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, ? Eridani, and ? Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and ? Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

Barrie W Jones; P. Nick Sleep

52

Assessing circumbinary habitable zones using latitudinal energy balance modelling  

NASA Astrophysics Data System (ADS)

Previous attempts to describe circumbinary habitable zones (HZs) have been concerned with the spatial extent of the zone, calculated analytically according to the combined radiation field of both stars. By contrast to these `spatial HZs', we present a numerical analysis of the `orbital HZ', an HZ defined as a function of planet orbital elements. This orbital HZ is better equipped to handle (for example) eccentric planet orbits, and is more directly connected to the data returned by exoplanet observations. Producing an orbital HZ requires a large number of climate simulations to be run to investigate the parameter space - we achieve this using latitudinal energy balance models, which handle the insolation of the planet by both stars (including mutual eclipses), as well as the planetary atmosphere's ability to absorb, transfer and lose heat. We present orbital HZs for several known circumbinary planetary systems: Kepler-16, Kepler-34, Kepler-35, Kepler-47 and PH-1. Generally, the orbital HZs at zero eccentricity are consistent with spatial HZs derived by other authors, although we detect some signatures of variability that coincide with resonances between the binary and planet orbital periods. We confirm that Earth-like planets around Kepler-47 with Kepler-47c's orbital parameters could possess liquid water, despite current uncertainties regarding its eccentricity. Kepler-16b is found to be outside the HZ, as well as the other circumbinary planets investigated.

Forgan, Duncan

2014-01-01

53

The habitable-zone planet finder calibration system  

NASA Astrophysics Data System (ADS)

We present the design concept of the wavelength calibration system for the Habitable-zone Planet Finder instrument (HPF), a precision radial velocity (RV) spectrograph designed to detect terrestrial-mass planets around M-dwarfs. HPF is a stabilized, fiber-fed, R~50,000 spectrograph operating in the near-infrared (NIR) z/Y/J bands from 0.84 to 1.3 microns. For HPF to achieve 1 m s-1 or better measurement precision, a unique calibration system, stable to several times better precision, will be needed to accurately remove instrumental effects at an unprecedented level in the NIR. The primary wavelength calibration source is a laser frequency comb (LFC), currently in development at NIST Boulder, discussed separately in these proceedings. The LFC will be supplemented by a stabilized single-mode fiber Fabry-Perot interferometer reference source and Uranium-Neon lamp. The HPF calibration system will combine several other new technologies developed by the Penn State Optical-Infrared instrumentation group to improve RV measurement precision including a dynamic optical coupling system that significantly reduces modal noise effects. Each component has been thoroughly tested in the laboratory and has demonstrated significant performance gains over previous NIR calibration systems.

Halverson, Samuel; Mahadevan, Suvrath; Ramsey, Lawrence; Terrien, Ryan; Roy, Arpita; Schwab, Christian; Bender, Chad; Hearty, Fred; Levi, Eric; Osterman, Steve; Ycas, Gabe; Diddams, Scott

2014-08-01

54

Extrasolar "Earths" in habitable zones- targets of opportunity  

E-print Network

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 102 main-sequence exoplanetary systems confirmed by 25 September 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a half of these systems could have had an Earth-mass planet confined to the HZ for at least the most recent 1000 Ma. The HZ migrates outwards during the main-sequence lifetime, and so this proportion varies with stellar age; about two thirds of the systems could have such a planet confined to the HZ for at least 1000 Ma at sometime during the main-sequence lifetime. Clearly, these systems should be high on the target list for exploration for terrestrial planets. We have reached this conclusion by launching putative Earth-mass planets in various orbits and following their fate with mixed-variable symplectic and hybrid integrators. Whether the Earth-mass planets could form in the HZs of the exoplanetary systems is an urgent question that needs further study.

B. W. Jones; D. R. Underwood; P. N. Sleep

2003-10-10

55

Kepler Mission: Detecting Earth-sized Planets in Habitable Zones  

NASA Technical Reports Server (NTRS)

The Kepler Mission, which is presently in Phase A, is being proposed for launch in 5 years for a 4-year mission to determine the frequency of Earth-sized or larger planets in habitable zones in our galaxy. Kepler will be placed in an Earth-trailing orbit to provide stable physical environments for the sensitive scientific instruments. The satellite is equipped with a photometric system with the precision of 10E-5, which should be sufficient for detecting the transits of Earth-sized or larger planets in front of dwarf stars similar to the Sun. Approximately 100,000 or more sun-like stars brighter than the 14th apparently magnitude will be monitored continuously for 4 years in a preselected region of the sky, which is about 100 square degrees in size. In addition, Kepler will have a participating scientist program that will enable research in intrinsic variable stars, interacting binaries including cataclysmic stars and X-ray binaries, and a large number of solar analogs in our galaxy. Several ten thousand additional stars may be investigated in the guest observer program open to the whole world.

Kondo, Yoji; Fisher, Richard R. (Technical Monitor)

2001-01-01

56

The Orbits of Terrestrial Planets in the Habitable Zones of Known Exoplanetary Systems  

E-print Network

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002, and thus there are many known systems worth searching for terrestrial planets in habitable zones. We reach our conclusions by launching putative Earth-mass planets in various orbits and following their fate with a mixed-variable symplectic integrator.

Barrie W Jones; P Nick Sleep

2002-11-01

57

Microlensing Sensitivity to Earth-mass Planets in the Habitable Zone  

E-print Network

Microlensing is one of the most powerful methods that can detect extrasolar planets and a future space-based survey with a high monitoring frequency is proposed to detect a large sample of Earth-mass planets. In this paper, we examine the sensitivity of the future microlensing survey to Earth-mass planets located in the habitable zone. For this, we estimate the fraction of Earth-mass planets that will be located in the habitable zone of their parent stars by carrying out detailed simulation of microlensing events based on standard models of the physical and dynamic distributions and the mass function of Galactic matter. From this investigation, we find that among the total detectable Earth-mass planets from the survey, those located in the habitable zone would comprise less than 1% even under a less-conservative definition of the habitable zone. We find the main reason for the low sensitivity is that the projected star-planet separation at which the microlensing planet detection efficiency becomes maximum (lensing zone) is in most cases substantially larger than the median value of the habitable zone. We find that the ratio of the median radius of the habitable zone to the mean radius of the lensing zone is roughly expressed as $d_{\\rm HZ}/r_{\\rm E}\\sim 0.2(m/0.5 M_\\odot)^{1/2}$.

Byeong-Gon Park; Young-Beom Jeon; Chung-Uk Lee; Cheongho Han

2006-01-31

58

HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES  

SciTech Connect

Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO{sub 2} atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H{sub 2}O and CO{sub 2} absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T{sub eff} {approx}< 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest that conservative estimates of the HZ (water-loss and maximum greenhouse limits) should be used for current RV surveys and Kepler mission to obtain a lower limit on {eta}{sub Circled-Plus }, so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); Eymet, Vincent [Laboratoire d'Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France); Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria [NASA Astrobiology Institute's Virtual Planetary Laboratory (United States); Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States)

2013-03-10

59

Optimizing Coronagraphic Surveys for the detection of Habitable-Zone Extrasolar Planets  

Microsoft Academic Search

The direct detection of an extrasolar planet in the habitable zone around a nearby star would be a historic achievement for astronomers. It would pave the way for astrobiologists to begin looking for biosignatures in the spectra of potentially habitable planets. Using analytical scalings for coronagraphic searches for extrasolar planets we study the prospects for detecting Earth-like planets in the

Praveen Kundurthy; E. Agol

2009-01-01

60

Thermal Evolution and Lifetime of Intrinsic Magnetic Fields of Super-Earths in Habitable Zones  

Microsoft Academic Search

We have numerically studied the thermal evolution of different-mass terrestrial planets in habitable zones, focusing on the duration of dynamo activity to generate their intrinsic magnetic fields, which may be one of the key factors in habitability of the planets. In particular, we are concerned with super-Earths, observations of which are rapidly developing. We calculated the evolution of temperature distributions

C. Tachinami; H. Senshu; S. Ida

2011-01-01

61

Determination of habitable zones in extrasolar planetary systems: Where are Gaia's sisters?  

Microsoft Academic Search

A general modeling scheme for assessing the suitability for life of extrasolar planets is presented. The scheme focuses on the identification of the ``habitable zone'' in main sequence star planetary systems accommodating Earth-like components. Our definition of habitability is based on the long-term possibility of photosynthetic biomass production under geodynamic conditions. Therefore all the pertinent astrophysical, climatological, biogeochemical, and geodynamic

Siegfried Franck; Werner von Bloh; Christine Bounama; Matthias Steffen; Detlef Schönberner; Hans-Joachim Schellnhuber

2000-01-01

62

Considerations for the habitable zone of super-Earth planets in Gliese 581  

E-print Network

We assess the possibility that planets Gliese 581 c and d are within the habitable zone. In analogy with our solar system, we use an empirical definition of the habitable zone. We include assumptions such as planetary climates, and atmospheric circulation on gravitationally locked synchronous rotation. Based on the different scenarios, we argue that both planets in Gliese 581 could develop conditions for a habitable zone. In an Earth-like environment planet d could be within a habitable zone, if an atmosphere producing greenhouse effect of 100K could have developed. If the planets are gravitationally locked-in, planet c could develop atmospheric circulation that would allow it to reach temperatures consistent with the existence of surface liquid water, which in turn could support life.

P. Chylek; M. R. Perez

2007-09-10

63

Earth-Sized Planets in the Habitable Zones of Cool Stars  

NASA Astrophysics Data System (ADS)

The primary goal of the Kepler mission is to determine the frequency of Earth-sized planets in the habitable zone of their parent star. Great strides have been made towards achieving this goal, including the discoveries of Earth-sized planets interior to the habitable zone and several super-Earth-sized planets in the habitable zone. A planet that is both Earth-sized and has an orbit within the habitable zone of a main-sequence star, however, has remained elusive. We present updates several promising multi-planet systems that have Earth-sized, and possibly sub-Earth-sized, candidates in the habitable zone of cool low-mass stars in the Kepler field of view. We will present our methods of combining ground-based observations with transit modeling in our quest to confirm these planets and discuss their potential habitability. More than 70% of the stars in our galaxy are M stars, thus confirming these planets will have profound implications on the number of potentially habitable worlds beyond our Solar System.

Quintana, Elisa V.; Barclay, Thomas

2014-06-01

64

Direct Imaging of Extrasolar Giant Planets in the Habitable Zone  

NASA Astrophysics Data System (ADS)

Young extrasolar giant planets (EGPs) are initially very luminous as they radiate away gravitational potential energy from formation (Burrows et al., 2001), but they rapidly cool and after a few tens of MYr (depending on mass) are essentially undetectable with typical direct imaging capabilities. Ground-based direct imaging is limited by adaptive optics (AO) performance. As a result of these restrictions direct imaging searches for EGPs have mainly focused on young stars (<~100 MYr) and wide orbital separations (>~10 AU). As AO performance improves we will begin searching for EGPs at much closer separations. Stellar irradiation sets the minimum temperature of a planet atmosphere (depending on albedo), regardless of mass and age. At wide separations this minimum temperature is too low to maintain planet brightness, but closer to the star this minimum temperature is much higher. Furthermore, old EGPs are all roughly the same radius regardless of mass (Fortney et al., 2007). Taken together, these arguments mean that in the habitable zone (HZ) minimum EGP luminosity (proportional to R2T4) is nearly independent of mass and age. We show that this has exciting implications for the thermal-infrared (IR) detectability of EGPs in the HZs of older stars. Similar arguments apply to visible wavelengths as well: in the HZ water clouds significantly increase geometric albedo making EGPs very bright in reflected light. The high performance of second generation adaptive secondary AO systems, employed at the LBT and Magellan, has allowed us to begin searching for EGPs in the HZs of nearby bright stars with current telescopes. The coming generation of giant telescopes will allow us to expand this search to many more stars. Here we present detailed calculations of EGP detectability in the HZ in both the thermal IR and in reflected visible light, describe our observing strategy, and present preliminary results of our search. We also discuss the future of direct imaging in the HZ with giant telescoes.

Males, J. R.; Close, L. M.; Guyon, O.; Barman, T. S.

2014-03-01

65

TERRESTRIAL, HABITABLE-ZONE EXOPLANET FREQUENCY FROM KEPLER  

SciTech Connect

Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and host-star spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitable-zone (HZ) exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude <14.0) having transiting planets >0.5 Earth radius and periods <42 days. It is also assumed that the size distribution of planets is independent of orbital period and that there are no hidden biases in the data. Six significant statistical results are found: there is a paucity of small planet detections around faint target stars, probably an instrumental effect; the frequency of mid-size planet detections is independent of whether the host star is bright or faint; there are significantly fewer planets detected with periods <3 days, compared to longer periods, almost certainly an astrophysical effect; the frequency of all planets in the population with periods <42 days is 29%, broken down as terrestrials 9%, ice giants 18%, and gas giants 3%; the population has a planet frequency with respect to period which follows a power-law relation dN/dP {approx} P{sup {beta}-1}, with {beta} {approx_equal} 0.71 {+-} 0.08; and an extrapolation to longer periods gives the frequency of terrestrial planets in the HZs of FGK stars as {eta}{sub Circled-Plus} {approx_equal} (34 {+-} 14)%. Thus about one-third of FGK stars are predicted to have at least one terrestrial, HZ planet.

Traub, Wesley A., E-mail: wtraub@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2012-01-20

66

The Orbits of Terrestrial Planets in the Habitable Zones of Known Exoplanetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted\\u000aregions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho\\u000aCoronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon\\u000aAndromedae. The first three systems between them are representative of a large\\u000aproportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

Barrie W Jones; P. Nick Sleep

2002-01-01

67

Habitable Evaporated Cores: Converting Mini-Neptunes into Super-Earths in the Habitable Zone of M Dwarfs  

NASA Astrophysics Data System (ADS)

We show that photoevaporation and Roche lobe overflow of small gaseous exoplanets (“mini-Neptunes”) in the habitable zone (HZ) of young late M dwarfs can remove several Earth masses of hydrogen/helium from these planets and transform them into potentially habitable worlds, which we call “habitable evaporated cores.” We couple a simple model for the evolution of inflated planets that are partly overflowing their Roche lobes with evaporation due to strong extreme ultraviolet (XUV) irradiation. We also couple the orbital effects of anisotropic mass loss with tidal evolution and show that this coupling can lead to unexpected behavior, such as a net increase of the eccentricity and an outward-then-inward evolution of the semi-major axis, significantly enhancing the mass loss rate. Habitable evaporated cores are most likely to form from planets with up to about 40% gas by mass orbiting M4 stars and later. As terrestrial planet formation by accumulation of local material is likely to form sub-Earth mass planets, evaporation of mini-Neptunes could be the dominant formation mechanism for volatile-rich super-Earths around M dwarfs. Such habitable evaporated cores are likely to be detected in upcoming surveys.

Luger, Rodrigo; Barnes, R.; Lopez, E.; Fortney, J. J.; Jackson, B. K.; Meadows, V.

2014-01-01

68

VizieR Online Data Catalog: Habitable zone code (Valle+, 2014)  

NASA Astrophysics Data System (ADS)

A C computation code that provide in output the distance dm (i for which the duration of habitability is longest, the corresponding duration tm (in Gyr), the width W (in AU) of the zone for which the habitability lasts tm/2, the inner (Ri) and outer (Ro) boundaries of the 4Gyr continuously habitable zone. The code read the input file HZ-input.dat, containing in each row the mass of the host star (range: 0.70-1.10M?), its metallicity (either Z (range: 0.005-0.004) or [Fe/H]), the helium-to-metal enrichment ratio (range: 1-3, standard value = 2), the equilibrium temperature for habitable zone outer boundary computation (range: 169-203K) and the planet Bond Albedo (range: 0.0-1.0, Earth = 0.3). The output is printed on-screen. Compilation: just use your favorite C compiler: gcc hz.c -lm -o HZ (2 data files).

Valle, G.; Dell'Omodarme, M.; Prada Moroni, P. G.; Degl'Innocenti, S.

2014-06-01

69

Habitable Evaporated Cores: Converting Mini-Neptunes into Super- Earths in the Habitable Zone of M Dwarfs  

NASA Astrophysics Data System (ADS)

The low masses and luminosities of M dwarfs make them ideal targets for thedetection of terrestrial planets in the habitable zone (HZ). However, studies suggest that planets formed only from material in the HZs of these stars are likely to be small and dry (e.g., Raymond et al. 2007). As a result, many of the planets that will be detected in the HZ by upcoming missions are probably the result of migration from beyond the snow line, and may have formed with large H/He envelopes (so-called mini-Neptunes). Here we show that photoevaporation and Roche lobe overflow of these planets can lead to the complete loss of their gaseous envelopes, transforming them into potentially habitable worlds, which we call “habitable evaporated cores”. We couple the planet structure models of Lopez et al. (2012) with a simple Roche lobe overflow scheme and the X-ray/extreme ultraviolet (XUV)-induced mass loss model of Erkaev et al. (2007). We also couple the orbital effects of anisotropic mass loss with tidal evolution and show that this coupling can lead to orbital changes that significantly enhance the mass loss rate.Habitable evaporated cores are most likely to form from small mini-Neptunes (?4 M?) with large (?50%) initial hydrogen fractions orbiting M4 stars and later. Given the steep decrease in stellar XUV flux with time (Ribas et al. 2005), mass loss is negligible after ~1 Gyr, at which point a habitable evaporated core is capable of degassing and maintaining a secondary atmosphere. This process may be the dominant formation mechanism for habitable planets around M dwarfs, and may be discovered by missions such as TESS and PLATO.

Luger, R.; Barnes, R.; Lopez, E.; Fortney, J.; Jackson, B.; Meadows, V.

2014-03-01

70

Astrophysical, Geochemical, Geophysical and Biological Limits on Planet Habitability  

NASA Astrophysics Data System (ADS)

For life forms like us, the most important feature of the Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. Over the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabited regions on Earth tell us that temperature and the presence of water are the main constraints that can be used in a habitability classification scheme for rocky planets. Our compilation and review of recent exoplanet detections suggests that the fraction of stars with planets is ~ 100%, and that the fraction with rocky planets may be comparably large. We review extensions to the circumstellar habitable zone including an abiogenesis habitable zone and the galactic habitable zone.

Lineweaver, C.

2014-03-01

71

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable Zone Planets  

E-print Network

The remarkable discovery of many planets and candidates using the Kepler telescope even includes ten planets orbiting eight binaries. Three out of the eight, Kepler 16, Kepler 47, and KIC 9632895, have at least one planet in the circumbinary habitable zone (BHZ). In previous work (Mason et al. 2013), we investigated the potential habitability of Earth-like circumbinary planets. In particular, we highlighted the role of mutual stellar tidal interaction and the resulting impact on terrestrial planet habitability. The Kepler binaries with planets in the BHZ are studied in order to constrain the high energy radiation and plasma environment of potentially habitable circumbinary planets. The limits of the BHZ in these binaries as a function of time are estimated and the habitability lifetime is calculated. A self-consistent model of the evolution of stellar rotation including the effect of tidal interaction is key to establishing the plasma and radiation environment. A comprehensive model of the evolution of stella...

Zuluaga, Jorge I; Cuartas, Pablo A

2015-01-01

72

The Habitability of Our Earth and Other Earths: Astrophysical, Geochemical, Geophysical, and Biological Limits on Planet Habitability  

NASA Astrophysics Data System (ADS)

For life-forms like us, the most important feature of Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. During the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabited regions on Earth tell us that temperature and the presence of water are the main constraints that can be used in a habitability classification scheme for rocky planets. Our compilation and review of recent exoplanet detections suggests that the fraction of stars with planets is ˜100%, and that the fraction with rocky planets may be comparably large. We review extensions to the circumstellar habitable zone (HZ), including an abiogenesis habitable zone and the galactic habitable zone.

Lineweaver, Charles H.; Chopra, Aditya

2012-05-01

73

Thermal Escape from Super Earth Atmospheres in the Habitable Zones of M Stars  

Microsoft Academic Search

A fundamental question for exoplanet habitability is the long-term stability of the planet's atmosphere. We numerically solve a one-dimensional multi-component hydrodynamic thermosphere\\/ionosphere model to examine the thermal and chemical responses of the primary CO2 atmospheres of heavy super Earths (6-10 Earth masses) in the habitable zones of typical low-mass M stars to the enhanced soft X-ray and ultraviolet (XUV) fluxes

Feng Tian

2009-01-01

74

Transit Surveys for Earths in the Habitable Zones of White Dwarfs  

Microsoft Academic Search

To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from ≈0.005 to 0.02 AU for white dwarfs with masses from 0.4

Eric Agol

2011-01-01

75

The habitable zone of Earth-like planets around 47 UMa  

Microsoft Academic Search

The system of 47 UMa consists of two Jupiter-size planets beyond the outer edge of the stellar habitable zone, and thus resembles our own Solar System rather closely. The habitability of this system for Earth-like planets is investigated following a concept, which assumes the long-term possibility of photosynthetic biomass production under geodynamic conditions. In particular, the stellar luminosity and the

Werner von Bloh; Manfred Cuntz; Christine Bounama; Siegfried Franck

2002-01-01

76

EXPLORING THE HABITABLE ZONE FOR KEPLER PLANETARY CANDIDATES  

SciTech Connect

This Letter outlines a simple approach to evaluate habitability of terrestrial planets by assuming different types of planetary atmospheres and using corresponding model calculations. Our approach can be applied for current and future candidates provided by the Kepler mission and other searches. The resulting uncertainties and changes in the number of planetary candidates in the HZ for the Kepler 2011 February data release are discussed. To first order, the HZ depends on the effective stellar flux distribution in wavelength and time, the planet albedo, and greenhouse gas effects. We provide a simple set of parameters which can be used for evaluating future planet candidates from transit searches.

Kaltenegger, L. [MPIA, Koenigstuhl 17, 69117 Heidelberg (Germany); Sasselov, D., E-mail: lkaltene@cfa.harvard.edu [Harvard Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

2011-08-01

77

Habitable evaporated cores: transforming mini-Neptunes into super-Earths in the habitable zones of M dwarfs.  

PubMed

We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ?1 M? solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars. PMID:25590532

Luger, R; Barnes, R; Lopez, E; Fortney, J; Jackson, B; Meadows, V

2015-01-01

78

Habitable Evaporated Cores: Transforming Mini-Neptunes into Super-Earths in the Habitable Zones of M Dwarfs  

E-print Network

We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with $\\sim 1 M_\\oplus$ solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars.

Luger, Rodrigo; Lopez, Eric; Fortney, Jonathan; Jackson, Brian; Meadows, Victoria

2015-01-01

79

Can Life develop in the expanded habitable zones around Red Giant Stars?  

E-print Network

We present some new ideas about the possibility of life developing around sub-giant and red giant stars. Our study concerns the temporal evolution of the habitable zone. The distance between the star and the habitable zone, as well as its width, increases with time as a consequence of stellar evolution. The habitable zone moves outward after the star leaves the main sequence, sweeping a wider range of distances from the star until the star reaches the tip of the asymptotic giant branch. If life could form and evolve over time intervals from $5 \\times 10^8$ to $10^9$ years, then there could be habitable planets with life around red giant stars. For a 1 M$_{\\odot}$ star at the first stages of its post main-sequence evolution, the temporal transit of the habitable zone is estimated to be of several 10$^9$ years at 2 AU and around 10$^8$ years at 9 AU. Under these circumstances life could develop at distances in the range 2-9 AU in the environment of sub-giant or giant stars and in the far distant future in the environment of our own Solar System. After a star completes its first ascent along the Red Giant Branch and the He flash takes place, there is an additional stable period of quiescent He core burning during which there is another opportunity for life to develop. For a 1 M$_{\\odot}$ star there is an additional $10^9$ years with a stable habitable zone in the region from 7 to 22 AU. Space astronomy missions, such as proposed for the Terrestrial Planet Finder (TPF) and Darwin should also consider the environments of sub-giants and red giant stars as potentially interesting sites for understanding the development of life.

Bruno Lopez; Jean Schneider; William C. Danchi

2005-03-23

80

Evolution of the Habitable Zone and Search for Life Around Giant Stars Part II: Feasibility with Darwin\\/TPF  

Microsoft Academic Search

We discuss the evolution of the habitable zone around low mass and intermediate mass stars as they evolve off the main sequence. This work shows that this new class of stars should be included in the search for life because if planets could be found in their habitable zones, and these planets showed evidence for life, it is possible to

W. C. Danchi; B. Lopez; J. Schneider; A. Belu; R. Barry; J. Rajagopal; L. J. Richardson

2006-01-01

81

Evolution of the Habitable Zone and Search for Life Around Red Giant Stars, Part I: Interest of the Study  

Microsoft Academic Search

We discuss the evolution of the habitable zone around low mass and intermediate mass stars as they evolve off the main sequence. This work shows that this class of stars should be included in the search for life because if planets could be found in their habitable zones, they will allow to test different hypothesis concerning the conditions of life

B. Lopez; W. C. Danchi; J.-L. Menut; J. Rajagopal; J. Schneider; A. Belu; R. Barry

2006-01-01

82

Habitable zones for earth-like planets around main sequence stars  

Microsoft Academic Search

As stars evolve and brighten, the radial zone within which liquid water can exist at the surface of an Earth-like planet expands outward. Using a new planetary climate model we have calculated the evolution of these habitable zones around several main sequence stars of masses between 0.50 and 1.25 solar masses. This evolution is presented in the form of a

D. P. Whitmire; R. T. Reynolds; J. F. Kasting

83

Habitable Zones for Earth-like Planets Around Main Sequence Stars  

Microsoft Academic Search

As stars evolve and brighten, the radial zone within which liquid water can exist at the surface of an Earth-like planet expands outward. Using a new planetary climate model we have calculated the evolution of these habitable zones around several main sequence stars of masses between 0.50 and 1.25 solar masses. This evolution is presented in the form of a

D. P. Whitmire; R. T. Reynolds; J. F. Kasting

1991-01-01

84

Estimations of Dynamic Parameters and Possible Habitable Zones for Selected Stars of Pulkovo Program  

NASA Astrophysics Data System (ADS)

We give the results of a study of selected stars located in the neighborhood of the Sun. Their observations have been made by means of Pulkovo 26-inch refractor. An interest to these objects is raised in connection with expected results of the planned space missions.. We have made an estimation of habitable zones for possible planets rotating around of these stars.

Shakht, N. A.; Romanenko, L. G.

85

Stability of Earth-Mass Planets in the Habitable Zones of Extrasolar Planetary Systems  

E-print Network

Stability of Earth-Mass Planets in the Habitable Zones of Extrasolar Planetary Systems Dr. Ravi Kumar Kopparapu Dept. of Geosciences, College of Earth and Mineral Science Over 500 planets orbiting and Saturn but in the last couple of years several "super-earths", planets with mass less than 10 times Earth

Bjørnstad, Ottar Nordal

86

Planets Formed in Habitable Zones of M Dwarf Stars Probably Are Deficient in Volatiles  

Microsoft Academic Search

Dynamical considerations, presented herein via analytic scalings and numerical experiments, imply that Earth-mass planets accreting in regions that become habitable zones of M dwarf stars form within several million years. Temperatures in these regions during planetary accretion are higher than those encountered by the material that formed the Earth. Collision velocities during and after the prime accretionary epoch are larger

Jack J. Lissauer

2007-01-01

87

Dynamical Stability of Terrestrial Mass Planets in and around the Habitable Zones of Single Planet Systems  

Microsoft Academic Search

We discuss the dynamical stability of hypothetical terrestrial mass planets (1 -10 Earth masses) in the habitable zone (HZ) of systems which have an additional massive planet. We consider arbitrary masses and orbits, which cover the range of observed planetary system architectures. We determine stability through N-body simulations which we compare to the analytic \\

Ravi Kumar Kopparapu; R. Barnes

2010-01-01

88

Validating the First Habitable-Zone Planet Candidates Identified by the NASA Kepler Mission  

Microsoft Academic Search

At the beginning of Cycle 8, the NASA Kepler Mission will have completed two years of science observations, the minimum baseline sufficient to identify candidate transiting exoplanets orbiting within the habitable-zones of Sun-like stars. The principal task that lies ahead is to reject from this sample the false positives (blends of eclipsing binaries that precisely mimic the signal of a

David Charbonneau; Jean-Michel Desert; Francois Fressin; Sarah Ballard; William Borucki; David Latham; Ronald Gilliland; Sara Seager; Heather Knutson; Jonathan Fortney; Timothy Brown; Eric Ford; Drake Deming; Guillermo Torres

2011-01-01

89

Earth-like worlds on eccentric orbits: excursions beyond the habitable zone  

Microsoft Academic Search

any of the recently discovered extrasolar giant planets move around their stars on highly eccentric orbits, and some with e => 0.7. Systems with planets within or near the habitable zone (HZ) will possibly harbour life on terrestrial-type moons if the seasonal temperature extremes resulting from the large orbital eccentricities of the planets are not too severe. Here we use

Darren M. Williams; David Pollard

2002-01-01

90

Dynamical stability of terrestrial mass planets in and around the habitable zones of single planet systems  

Microsoft Academic Search

We discuss the dynamical stability of hypothetical terrestrial mass planets (1 -10 Earth masses) in the habitable zone (HZ) of systems which have an additional massive planet. We consider arbitrary masses and orbits, which cover the range of observed planetary system architectures. We determine stability through N-body simulations which we compare to the analytic \\

R. Kopparapu; R. Barnes

2009-01-01

91

The Potential for Archaeology Within and Beyond the Habitable Zones (HZ) of the Milky Way  

Microsoft Academic Search

As archaeology is established on Earth and we are actively exploring the Solar System and beyond, there is the potential to develop a number of forms of exo-archaeology. The archaeology of the things intelligent species do in theory could be practised anywhere, provided one can detect the evidence. Sites are being created by us elsewhere within our star's habitable zone

John B. Campbell

2004-01-01

92

TERRESTRIAL PLANET FORMATION AROUND THE CIRCUMBINARY HABITABLE ZONE: INWARD MIGRATION IN THE PLANETESIMAL SWARM  

SciTech Connect

According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, a significant amount of small planetesimals must exist in the inner zone when embryos form outside this CSMA. Thus, embryo migration induced by the planetesimal swarm is possible after gas disk depletion. Through numerical simulations, we found that (1) the scattering-driven inward migration of embryos is robust and planets can form in the habitable zone if we adopt a mass distribution of an MMSN-like disk; (2) the total mass of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations; and (3) the scattering-driven migration of embryos is a natural water-delivery mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.

Gong Yanxiang; Zhou Jilin; Xie Jiwei, E-mail: yxgong@nju.edu.cn, E-mail: zhoujl@nju.edu.cn [Department of Astronomy and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093 (China)

2013-01-20

93

Habitable zones around low mass stars and the search for extraterrestrial life.  

PubMed

Habitable planets are likely to exist around stars not too different from the Sun if current theories about terrestrial climate evolution are correct. Some of these planets may have evolved life, and some of the inhabited planets may have evolved O2-rich atmospheres. Such atmospheres could be detected spectroscopically on planets around nearby stars using a space-based interferometer to search for the 9.6 micron band of O3. Planets with O2-rich atmospheres that lie within the habitable zone around their parent star are, in all probability, inhabited. PMID:9150578

Kasting, J F

1997-06-01

94

The Lick-Carnegie Exoplanet Survey: A 3.1 M Planet in the Habitable Zone of the Nearby M3V Star Gliese 581  

E-print Network

research, the detection of Earth-size planets orbiting in the habitable zones (HZ) of stars. Nearby K and MThe Lick-Carnegie Exoplanet Survey: A 3.1 M Planet in the Habitable Zone of the Nearby M3V Star it squarely in the middle of the habitable zone of the star and offering a very compelling case

95

Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars  

NASA Astrophysics Data System (ADS)

Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets’ rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar mass. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere.

Leconte, Jérémy; Wu, Hanbo; Menou, Kristen; Murray, Norman

2015-02-01

96

Asynchronous rotation of Earth-like planets in the habitable zone of lower-mass stars  

E-print Network

Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets' rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than 0.5-0.7Msun. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere.

Leconte, Jérémy; Menou, Kristen; Murray, Norman

2015-01-01

97

TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS  

SciTech Connect

To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from {approx}0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 M{sub sun}, temperatures less than {approx}10{sup 4} K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, and rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.

Agol, Eric, E-mail: agol@uw.edu [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)] [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States)

2011-04-20

98

ASTROPHYSICAL PARAMETERS AND HABITABLE ZONE OF THE EXOPLANET HOSTING STAR GJ 581  

SciTech Connect

GJ 581 is an M dwarf host of a multiplanet system. We use long-baseline interferometric measurements from the CHARA Array, coupled with trigonometric parallax information, to directly determine its physical radius to be 0.299 {+-} 0.010 R{sub sun}. Literature photometry data are used to perform spectral energy distribution fitting in order to determine GJ 581's effective surface temperature T{sub EFF} = 3498 {+-} 56 K and its luminosity L = 0.01205 {+-} 0.00024 L{sub sun}. From these measurements, we recompute the location and extent of the system's habitable zone and conclude that two of the planets orbiting GJ 581, planets d and g, spend all or part of their orbit within or just on the edge of the habitable zone.

Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Boyajian, Tabetha S.; McAlister, Harold A.; Henry, Todd J.; Jao, Wei-Chun; Riedel, Adric R. [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Van Belle, Gerard T. [European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching (Germany); Lopez-Morales, Mercedes [Institut de Ciencies de L'Espai (CSIC-IEEC), Campus UAB, Facultat Ciencies, Torre C5 parell 2, 08193 Bellaterra, Barcelona (Spain); Subasavage, John P. [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Mazingue, Jude; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J. [CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Ridgway, Stephen, E-mail: kaspar@caltech.edu [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

2011-03-10

99

Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581  

NASA Astrophysics Data System (ADS)

The M dwarf star Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet—GJ 581g—is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the H? line, we measure a stellar rotation period of 130 ± 2 days and a correlation for H? modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5 standard deviations) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g.

Robertson, Paul; Mahadevan, Suvrath; Endl, Michael; Roy, Arpita

2014-07-01

100

Strong starlight suppression sufficient to enable direct detection of exoplanets in the habitable zone  

Microsoft Academic Search

Direct detection of photons from exoplanets in the habitable zone around nearby stars is challenging because of the much higher photon flux and close angular proximity of the star. At mid-infrared wavelengths, around 10 mum, the flux contrast ratio between a sun-like star and an earth-size planet is several million to one, favorable compared to the visible range, while the

S. R. Martin; A. J. Booth

2010-01-01

101

KEPLER: Search for Earth-Size Planets in the Habitable Zone  

Microsoft Academic Search

The Kepler Mission is a space-based mission whose primary goal is to determine the frequency of Earth-size and larger planets in the habitable zone of solar-like stars. The mission will monitor more than 100,000 stars for patterns of transits with a differential photometric precision of 20 ppm at V = 12 for a 6.5 hour transit. It will also provide

William Borucki; David Koch; Natalie Batalha; Douglas Caldwell; Jorgen Christensen-Dalsgaard; William D. Cochran; Edward Dunham; Thomas N. Gautier; John Geary; Ronald Gilliland; Jon Jenkins; Hans Kjeldsen; Jack J. Lissauer; Jason Rowe

2009-01-01

102

Finding Earth-size planets in the habitable zone: the Kepler Mission  

Microsoft Academic Search

The Kepler Mission is a space-based mission whose primary goal is to detect Earth-size and smaller planets in the habitable zone of solar-like stars. The mission will monitor more than 100,000 stars for transits with a differential photometric precision of 20 ppm at V=12 for a 6.5 hour transit. It will also provide asteroseismic results on several thousand dwarf stars.

William Borucki; David Koch; Gibor Basri; Natalie Batalha; Timothy Brown; Douglas Caldwell; Jørgen Christensen-Dalsgaard; William Cochran; Edward Dunham; Thomas N. Gautier; John Geary; Ronald Gilliland; Jon Jenkins; Yoji Kondo; David Latham; Jack J. Lissauer; David Monet

2008-01-01

103

Microlensing Sensitivity to Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

Microlensing is one of the most powerful methods that can detect extrasolar planets, and a future space-based survey with a high monitoring frequency is proposed to detect a large sample of Earth-mass planets. In this paper, we examine the sensitivity of the future microlensing survey to Earth-mass planets located in the habitable zone. For this, we estimate the fraction of

Byeong-Gon Park; Young-Beom Jeon; Chung-Uk Lee; Cheongho Han

2006-01-01

104

A Search For Earth-Sized Planets In Habitable Zones Using Photometry  

Microsoft Academic Search

Several methods have been suggested for the detection of extra-solar planets. In the habitable zone, the radial velocity and astrometric methods are only sensitive to the detection of massive planets (greater than about ten to one-hundred Earth masses). However, the photometric method is sensitive to Earth-sized planets in inner orbits about solar-like stars. The methodology for conducting a photometric space-based

David Koch; William Borucki

1996-01-01

105

Habitable zones for Earth-mass planets in multiple planetary systems  

Microsoft Academic Search

We perform numerical simulations to study the Habitable zones (HZs) and dynamical structure for Earth-mass planets in multiple planetary systems. For example, in the HD 69830 system, we extensively explore the planetary configuration of three Neptune-mass companions with one massive terrestrial planet residing in 0.07 AU <= a <= 1.20 AU, to examine the asteroid structure in this system. We

Jianghui Ji; Lin Liu; Hiroshi Kinoshita; Guangyu Li

2008-01-01

106

Thermal evolution and lifetime of intrinsic magnetic fields of Super Earths in habitable zones  

Microsoft Academic Search

We have numerically studied the thermal evolution of various-mass terrestrial\\u000aplanets in habitable zones, focusing on duration of dynamo activity to generate\\u000atheir intrinsic magnetic fields, which may be one of key factors in\\u000ahabitability on the planets. In particular, we are concerned with super-Earths,\\u000aobservations of which are rapidly developing. We calculated evolution of\\u000atemperature distributions in planetary interior,

Chihiro Tachinami; Hiroki Senshu; Shigeru Ida

2010-01-01

107

Enabling the Ground-based Detection of Transiting Habitable-zone Earths  

Microsoft Academic Search

The small radii and cool temperatures of M dwarfs make them favorable targets for transiting planet surveys of habitable-zone Earth and super-Earth planets. The MEarth survey has detected a super-Earth orbiting the nearby M5 star GJ 1214 and estimated the planetary mass and radius precisely. Despite this success, the MEarth survey encounters photometric noise larger than expected based upon Poisson

Christopher J. Burke

2011-01-01

108

The Inner Boundary of the Habitable Zone for Earth-like Planets  

Microsoft Academic Search

The orbital region around a star where liquid water could exist on the surface of a terrestrial planet is usually defined as the Habitable Zone (HZ). We investigate the inner boundary of the HZ for different planetary scenarios with a one-dimensional radiative-convective model of the atmosphere. Our modeling approach involves the step-by-step increase of the incoming stellar flux and the

B. Stracke; J. L. Grenfell; P. von Paris; A. B. C. Patzer; H. Rauer

2010-01-01

109

Prospects for `Earths' in the Habitable Zones of Known Exoplanetary Systems  

Microsoft Academic Search

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 104 main-sequence exoplanetary systems confirmed by mid-November 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a half of these systems could have had an Earth-mass planet

Barrie W. Jones; David R. Underwood; P. Nick Sleep

2004-01-01

110

Orbital Stability of Earth-like Planets in Stellar Habitable Zones  

Microsoft Academic Search

Long-term orbital stability of Earth-like planets in stellar habitable zones (HZs) is necessary for the evolution of any form of life. It is then interesting to ask whether Earth-like planets can exist in stable orbits around single stars with giant planets and in multiple stellar systems? The main conclusion from previous studies is that orbits of terrestrial planets in the

M. Noble; Z. E. Musielak; M. Cuntz

2001-01-01

111

Exomoon Habitability Constrained by Illumination and Tidal Heating  

PubMed Central

Abstract The detection of moons orbiting extrasolar planets (“exomoons”) has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local climates on exomoons by reducing stellar illumination. In addition to radiative heating, tidal heating can be very large on exomoons, possibly even large enough for sterilization. We identify combinations of physical and orbital parameters for which radiative and tidal heating are strong enough to trigger a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define a circumplanetary “habitable edge.” We apply our model to hypothetical moons around the recently discovered exoplanet Kepler-22b and the giant planet candidate KOI211.01 and describe, for the first time, the orbits of habitable exomoons. If either planet hosted a satellite at a distance greater than 10 planetary radii, then this could indicate the presence of a habitable moon. Key Words: Astrobiology—Extrasolar planets—Habitability—Habitable zone—Tides. Astrobiology 13, 18–46. PMID:23305357

2013-01-01

112

The Habitable Zone of Earth-like Planets with Different Levels of Atmospheric Pressure  

NASA Astrophysics Data System (ADS)

As a contribution to the study of the habitability of extrasolar planets, we implemented a one-dimensional energy balance model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p = 1/3 to 3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the efficiency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar-type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.

Vladilo, Giovanni; Murante, Giuseppe; Silva, Laura; Provenzale, Antonello; Ferri, Gaia; Ragazzini, Gregorio

2013-04-01

113

THE HABITABLE ZONE OF EARTH-LIKE PLANETS WITH DIFFERENT LEVELS OF ATMOSPHERIC PRESSURE  

SciTech Connect

As a contribution to the study of the habitability of extrasolar planets, we implemented a one-dimensional energy balance model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p = 1/3 to 3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the efficiency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar-type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.

Vladilo, Giovanni; Murante, Giuseppe; Silva, Laura [INAF-Trieste Astronomical Observatory, Trieste (Italy)] [INAF-Trieste Astronomical Observatory, Trieste (Italy); Provenzale, Antonello [Institute of Atmospheric Sciences and Climate-CNR, Torino (Italy)] [Institute of Atmospheric Sciences and Climate-CNR, Torino (Italy); Ferri, Gaia; Ragazzini, Gregorio, E-mail: vladilo@oats.inaf.it [Department of Physics, University of Trieste, Trieste (Italy)] [Department of Physics, University of Trieste, Trieste (Italy)

2013-04-10

114

MOA-2011-BLG-293Lb: First Microlensing Planet Possibly in the Habitable Zone  

NASA Astrophysics Data System (ADS)

We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation r = 1.1 ± 0.1 AU from its ML = 0.86 ± 0.06 M ? host, being the highest microlensing mass definitely identified. The planet has a mass mp = 4.8 ± 0.3 M Jup, and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: DL = 7.72 ± 0.44 kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model. These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is HL = 19.16 ± 0.13. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions and the uncertainties on the semimajor axis.

Batista, V.; Beaulieu, J.-P.; Gould, A.; Bennett, D. P.; Yee, J. C.; Fukui, A.; Gaudi, B. S.; Sumi, T.; Udalski, A.

2014-01-01

115

On the ejection of Earth-mass planets from the habitable zones of the solar twins HD 20782 and HD 188015  

Microsoft Academic Search

We provide a detailed statistical study of the ejection of fictitious Earth-mass planets from the habitable zones of the solar twins HD 20782 and HD 188015. These systems possess a giant planet that crosses into the stellar habitable zone, thus effectively thwarting the possibility of habitable terrestrial planets. In the case of HD 188015, the orbit of the giant planet

K. E. Yeager; J. Eberle; M. Cuntz

2011-01-01

116

Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass.  

PubMed

Stellar astrospheres--the plasma cocoons carved out of the interstellar medium by stellar winds--are one of several buffers that partially screen planetary atmospheres and surfaces from high-energy radiation. Screening by astrospheres is continually influenced by the passage of stars through the fluctuating density field of the interstellar medium (ISM). The most extreme events occur inside dense interstellar clouds, where the increased pressure may compress an astrosphere to a size smaller than the liquid-water habitable-zone distance. Habitable planets then enjoy no astrospheric buffering from exposure to the full flux of galactic cosmic rays and interstellar dust and gas, a situation we call "descreening" or "astrospheric collapse." Under such conditions the ionization fraction in the atmosphere and contribution to radiation damage of putative coding organisms at the surface would increase significantly, and a series of papers have suggested a variety of global responses to descreening. These possibilities motivate a more careful calculation of the frequency of descreening events. Using a ram-pressure balance model, we compute the size of the astrosphere in the apex direction as a function of parent-star mass and velocity and ambient interstellar density, emphasizing the importance of gravitational focusing of the interstellar flow. The interstellar densities required to descreen planets in the habitable zone of solar- and subsolar-mass stars are found to be about 600(M/M[middle dot in circle])(-2) cm(-3) for the Sun's velocity relative to the local ISM. Such clouds are rare and small, indicating that descreening encounters are rare. We use statistics from two independent catalogues of dense interstellar clouds to derive a dependence of descreening frequency on the parent-star mass that decreases strongly with decreasing stellar mass, due to the weaker gravitational focusing and smaller habitable-zone distances for lower-mass stars. We estimate an uncertain upper limit to the absolute frequency of descreening encounters as 1-10 Gyr(-1) for solar-type stars and 10(2) to 10(9) times smaller for stars between 0.5 and 0.1 M[middle dot in circle]. Habitable-zone planets orbiting late-K to M stars are virtually never exposed to the severe consequences that have been proposed for astrospheric descreening events, but descreening events at a moderate rate may occur for stars with the Sun's mass or larger. PMID:19778278

Smith, David S; Scalo, John M

2009-09-01

117

The galactic habitable zone of the Milky Way and M31 from chemical evolution models with gas radial flows  

NASA Astrophysics Data System (ADS)

The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems. We apply detailed chemical evolution models including radial gas flows to study the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with `classical' (independent ring) models, where no gas inflows were included. For both the Milky Way and Andromeda, the main effect of the gas radial inflows is to enhance the number of stars hosting a habitable planet with respect to the `classical' model results, in the region of maximum probability for this occurrence, relative to the classical model results. These results are obtained by taking into account the supernova destruction processes. In particular, we find that in the Milky Way the maximum number of stars hosting habitable planets is at 8 kpc from the Galactic Centre, and the model with radial flows predicts a number which is 38 per cent larger than what was predicted by the classical model. For Andromeda we find that the maximum number of stars with habitable planets is at 16 kpc from the centre and that in the case of radial flows this number is larger by 10 per cent relative to the stars predicted by the classical model.

Spitoni, E.; Matteucci, F.; Sozzetti, A.

2014-05-01

118

AN ANALYTIC METHOD TO DETERMINE HABITABLE ZONES FOR S-TYPE PLANETARY ORBITS IN BINARY STAR SYSTEMS  

SciTech Connect

With more and more extrasolar planets discovered in and around binary star systems, questions concerning the determination of the classical habitable zone have arisen. Do the radiative and gravitational perturbations of the second star influence the extent of the habitable zone significantly, or is it sufficient to consider the host star only? In this article, we investigate the implications of stellar companions with different spectral types on the insolation a terrestrial planet receives orbiting a Sun-like primary. We present time-independent analytical estimates and compare them to insolation statistics gained via high precision numerical orbit calculations. Results suggest a strong dependence of permanent habitability on the binary's eccentricity, as well as a possible extension of habitable zones toward the secondary in close binary systems.

Eggl, Siegfried; Pilat-Lohinger, Elke; Gyergyovits, Markus; Funk, Barbara [Institute for Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Georgakarakos, Nikolaos, E-mail: siegfried.eggl@univie.ac.at, E-mail: elke.pilat-lohinger@univie.ac.at [128 V. Olgas str., Thessaloniki 546 45 (Greece)

2012-06-10

119

THERMAL EVOLUTION AND LIFETIME OF INTRINSIC MAGNETIC FIELDS OF SUPER-EARTHS IN HABITABLE ZONES  

SciTech Connect

We have numerically studied the thermal evolution of different-mass terrestrial planets in habitable zones, focusing on the duration of dynamo activity to generate their intrinsic magnetic fields, which may be one of the key factors in habitability of the planets. In particular, we are concerned with super-Earths, observations of which are rapidly developing. We calculated the evolution of temperature distributions in the planetary interior using Vinet equations of state, the Arrhenius-type formula for mantle viscosity, and the astrophysical mixing-length theory for convective heat transfer modified for mantle convection. After calibrating the model with terrestrial planets in the solar system, we apply it for 0.1-10 M{sub +} rocky planets with a surface temperature of 300 K (in habitable zones) and Earth-like compositions. With the criterion of heat flux at the core-mantle boundary (CMB), the lifetime of the magnetic fields is evaluated from the calculated thermal evolution. We found that the lifetime slowly increases with planetary mass (M{sub p} ), independent of the initial temperature gap at the CMB ({Delta}T{sub CMB}), but beyond the critical value M{sub c,p} ({approx}O(1) M{sub +}) it abruptly declines from the mantle viscosity enhancement due to the pressure effect. We derived M{sub c,p} as a function of {Delta}T{sub CMB} and a rheological parameter (activation volume, V*). Thus, the magnetic field lifetime of super-Earths with M{sub p} >M{sub p,c} sensitively depends on {Delta}T{sub CMB}, which reflects planetary accretion, and V*, which has uncertainty at very high pressure. More advanced high-pressure experiments and first-principle simulation, as well as planetary accretion simulation, are needed to discuss the habitability of super-Earths.

Tachinami, C.; Ida, S. [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 1528551 (Japan); Senshu, H., E-mail: ctchnm@geo.titech.ac.jp [Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Chiba 2750016 (Japan)

2011-01-10

120

A New Paradigm for Habitability in Planetary Systems: the Extremophilic Zone  

NASA Astrophysics Data System (ADS)

More than a thousand exoplanets have been discovered so far. Planetary surface temperature may strongly depends on its albedo and geodynamic conditions. We have fed exoplanets from the Encyclopedia database with a comprehensive model of Earth's atmosphere and plate tectonics. As CO2 is the main agent responsible for the greenhouse effect, its partial pressure has been taken as a free parameter to estimate the surface temperature of some known planets. We also investigated the possible presence of "exomoons" belonging to giant planets in the Habitable Zone capable of harbour dynamic stability, to retain an atmosphere and to keep geodynamic activity for long time spans. Biological data on earthly micro-organisms classified as "extremophiles" indicate that such kind of microbial species could dwell on the surface of many exoplanets and exomoons. We thus propose an extension of the mainly astronomically defined "Habitable Zone" concept into the more astrobiologically one, the "Extremophililic Zone", that takes into account other parameters allowing survival of more robust life forms. This contribution comes from an ongoing project developed by a French-Brazilian colaboration in Astrophysics and Biophysics to search for living fingerprints in astrobiologically promising exoplanets.

Janot-Pacheco, E., Bernardes, L., Lage, C. A. S.

2014-03-01

121

The Inner Boundary of the Habitable Zone for Earth-like Planets  

NASA Astrophysics Data System (ADS)

The orbital region around a star where liquid water could exist on the surface of a terrestrial planet is usually defined as the Habitable Zone (HZ). We investigate the inner boundary of the HZ for different planetary scenarios with a one-dimensional radiative-convective model of the atmosphere. Our modeling approach involves the step-by-step increase of the incoming stellar flux and the subsequent iterative calculation of resulting changes in the atmospheric water vapour content and the radiative properties. Modeling results are presented for the influence of various planetary and atmospheric conditions on the inner boundary (water loss limit) of the HZs around a Sun-type star.

Stracke, B.; Grenfell, J. L.; von Paris, P.; Patzer, A. B. C.; Rauer, H.

2010-10-01

122

The Properties of Exomoons Around the Habitable Zone Planet, Kepler 22b  

NASA Astrophysics Data System (ADS)

As part of a larger study to understand the formation, evolution, and stability of satellites around exoplanets, we have examined the Kepler 22 system. A single planet of mass 2 × 1026 kg, Kepler 22b orbits within the habitable zone (Kopparapu et al. 2013) at 0.85 AU. While Kepler 22b may be habitable, there also exists the possibility that any satellites of the planet may also be life sustaining.A series of N-body simulations were performed to examine the most probable configuration of moons orbiting Kepler 22b. Initially, a moonlet disk of 100 bodies (mdisk = 4.29 × 1022 kg) was randomly placed around Kepler 22b. The moonlet disk spanned 10 - 80% of Kepler 22b's Hill sphere (Kasting et al. 1993). Simulations were run for 500 kyrs, with the star, planet, and moonlets allowed to gravitationally evolve.The Kepler 22b system was able to retain three to four moons in 96% of the simulations. . The remaining simulations produced systems of two moons on highly eccentric orbits. It is unlikely that the two-moon configuration would remain stable for a significant amount of time. We present the properties of the stable satellites. We have run an additional set of simulations examining the rotational effects satellites will have on Kepler 22b, given the high likelihood that the planet possesses a system of moons. We were specifically investigating if the presence of moons reduces the precession of Kepler 22b, increasing the planet's habitability.

Fuse, Christopher R.; Bokorney, Jake

2015-01-01

123

A METHOD FOR COUPLING DYNAMICAL AND COLLISIONAL EVOLUTION OF DUST IN CIRCUMSTELLAR DISKS: THE EFFECT OF A DEAD ZONE  

SciTech Connect

Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics are size-dependent (because of gas drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid Lagrangian/Eulerian code is presented that overcomes some of these difficulties. The particles representing 'dust clouds' are tracked individually in a Lagrangian way. This system is then mapped on an Eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete Lagrangian particles, keeping their number constant. An application example of dust growth in a turbulent protoplanetary disk at 1 AU is presented. First, the growth of dust is considered in the absence of a dead zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of a millimeter in size. Then the same case with an embedded dead zone is investigated and it is found that coagulation is much more efficient and produces, in a short timescale, 1-10 cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryo-sized objects inside large-scale turbulent structures as shown recently.

Charnoz, Sebastien; Taillifet, Esther, E-mail: charnoz@cea.fr [Laboratoire AIM, Universite Paris Diderot/CEA/CNRS, 91191 Gif-sur-Yvette Cedex (France)

2012-07-10

124

GJ 832c: A Super-Earth in the Habitable Zone  

NASA Astrophysics Data System (ADS)

We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18 ± 0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a "super-Venus," featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system. This paper includes data gathered with the 6.5 m Magellan Telescopes located at the Las Campanas Observatory, Chile.

Wittenmyer, Robert A.; Tuomi, Mikko; Butler, R. P.; Jones, H. R. A.; Anglada-Escudé, Guillem; Horner, Jonathan; Tinney, C. G.; Marshall, J. P.; Carter, B. D.; Bailey, J.; Salter, G. S.; O'Toole, S. J.; Wright, D.; Crane, J. D.; Schectman, S. A.; Arriagada, P.; Thompson, I.; Minniti, D.; Jenkins, J. S.; Diaz, M.

2014-08-01

125

GJ 832c: A super-earth in the habitable zone  

E-print Network

We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly-circular 9.4-year orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68+/-0.03 days and minimum mass (m sin i) of 5.4+/-1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e=0.18+/-0.13) towards the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a "super-Venus," featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own Solar system.

Wittenmyer, R A; Butler, R P; Jones, H R A; Anglada-Escude, Guillem; Horner, Jonathan; Tinney, C G; Marshall, J P; Carter, B D; Bailey, J; Salter, G S; O'Toole, S J; Wright, D; Crane, J D; Schectman, S A; Arriagada, P; Thompson, I; Minniti, D; Jenkins, J S; Diaz, M

2014-01-01

126

Direct imaging of exoplanets in the habitable zone with adaptive optics  

E-print Network

One of the primary goals of exoplanet science is to find and characterize habitable planets, and direct imaging will play a key role in this effort. Though imaging a true Earth analog is likely out of reach from the ground, the coming generation of giant telescopes will find and characterize many planets in and near the habitable zones (HZs) of nearby stars. Radial velocity and transit searches indicate that such planets are common, but imaging them will require achieving extreme contrasts at very small angular separations, posing many challenges for adaptive optics (AO) system design. Giant planets in the HZ may even be within reach with the latest generation of high-contrast imagers for a handful of very nearby stars. Here we will review the definition of the HZ, and the characteristics of detectable planets there. We then review some of the ways that direct imaging in the HZ will be different from the typical exoplanet imaging survey today. Finally, we present preliminary results from our observations of t...

Males, Jared R; Guyon, Olivier; Morzinski, Katie M; Puglisi, Alfio; Hinz, Philip; Follette, Katherine B; Monnier, John D; Tolls, Volker; Rodigas, Timothy J; Weinberger, Alycia; Boss, Alan; Kopon, Derek; Wu, Ya-lin; Esposito, Simone; Riccardi, Armando; Xompero, Marco; Briguglio, Runa; Pinna, Enrico

2014-01-01

127

The ultraviolet radiation environment in the habitable zones around low-mass exoplanet host stars  

NASA Astrophysics Data System (ADS)

The EUV (200-911 Å), FUV (912-1750 Å), and NUV (1750-3200 Å) spectral energy distribution of exoplanet host stars has a profound influence on the atmospheres of Earth-like planets in the habitable zone. The stellar EUV radiation drives atmospheric heating, while the FUV (in particular, Ly ?) and NUV radiation fields regulate the atmospheric chemistry: the dissociation of H2O and CO2, the production of O2 and O3, and may determine the ultimate habitability of these worlds. Despite the importance of this information for atmospheric modeling of exoplanetary systems, the EUV/FUV/NUV radiation fields of cool (K and M dwarf) exoplanet host stars are almost completely unconstrained by observation or theory. We present observational results from a Hubble Space Telescope survey of M dwarf exoplanet host stars, highlighting the importance of realistic UV radiation fields for the formation of potential biomarker molecules, O2 and O3. We conclude by describing preliminary results on the characterization of the UV time variability of these sources.

France, Kevin; Linsky, Jeffrey L.; Parke Loyd, R. O.

2014-11-01

128

GLIESE 581D IS THE FIRST DISCOVERED TERRESTRIAL-MASS EXOPLANET IN THE HABITABLE ZONE  

SciTech Connect

It has been suggested that the recently discovered exoplanet GJ581d might be able to support liquid water due to its relatively low mass and orbital distance. However, GJ581d receives 35% less stellar energy than Mars and is probably locked in tidal resonance, with extremely low insolation at the poles and possibly a permanent night side. Under such conditions, it is unknown whether any habitable climate on the planet would be able to withstand global glaciation and/or atmospheric collapse. Here we present three-dimensional climate simulations which demonstrate that GJ581d will have a stable atmosphere and surface liquid water for a wide range of plausible cases, making it the first confirmed super-Earth (exoplanet of 2-10 Earth masses) in the habitable zone. We find that atmospheres with over 10 bar CO{sub 2} and varying amounts of background gas (e.g., N{sub 2}) yield global mean temperatures above 0{sup 0}C for both land and ocean-covered surfaces. Based on the emitted IR radiation calculated by the model, we propose observational tests that will allow these cases to be distinguished from other possible scenarios in the future.

Wordsworth, Robin D.; Forget, Francois; Millour, Ehouarn; Charnay, Benjamin; Madeleine, Jean-Baptiste [Laboratoire de Meteorologie Dynamique, Institut Pierre Simon Laplace, Paris (France); Selsis, Franck [CNRS, UMR 5804, Laboratoire d'Astrophysique de Bordeaux, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France)

2011-06-01

129

STABILITY ANALYSIS OF SINGLE-PLANET SYSTEMS AND THEIR HABITABLE ZONES  

SciTech Connect

We study the dynamical stability of planetary systems consisting of one hypothetical terrestrial-mass planet (1 or 10 M{sub +}) and one massive planet (10 M{sub +}-10 M{sub jup}). We consider masses and orbits that cover the range of observed planetary system architectures (including non-zero initial eccentricities), determine the stability limit through N-body simulations, and compare it to the analytic Hill stability boundary. We show that for given masses and orbits of a two-planet system, a single parameter, which can be calculated analytically, describes the Lagrange stability boundary (no ejections or exchanges) but diverges significantly from the Hill stability boundary. However, we do find that the actual boundary is fractal, and therefore we also identify a second parameter which demarcates the transition from stable to unstable evolution. We show the portions of the habitable zones (HZs) of {rho} CrB, HD 164922, GJ 674, and HD 7924 that can support a terrestrial planet. These analyses clarify the stability boundaries in exoplanetary systems and demonstrate that, for most exoplanetary systems, numerical simulations of the stability of potentially habitable planets are only necessary over a narrow region of the parameter space. Finally, we also identify and provide a catalog of known systems that can host terrestrial planets in their HZs.

Kopparapu, Ravi Kumar [Department of Physics, 104 Davey Lab, Pennsylvania State University, University Park, PA 16802-6300 (United States); Barnes, Rory, E-mail: ravi@gravity.psu.ed [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States)

2010-06-20

130

Direct imaging of exoplanets in the habitable zone with adaptive optics  

NASA Astrophysics Data System (ADS)

One of the primary goals of exoplanet science is to find and characterize habitable planets, and direct imaging will play a key role in this effort. Though imaging a true Earth analog is likely out of reach from the ground, the coming generation of giant telescopes will find and characterize many planets in and near the habitable zones (HZs) of nearby stars. Radial velocity and transit searches indicate that such planets are common, but imaging them will require achieving extreme contrasts at very small angular separations, posing many challenges for adaptive optics (AO) system design. Giant planets in the HZ may even be within reach with the latest generation of high-contrast imagers for a handful of very nearby stars. Here we will review the definition of the HZ, and the characteristics of detectable planets there. We then review some of the ways that direct imaging in the HZ will be different from the typical exoplanet imaging survey today. Finally, we present preliminary results from our observations of the HZ of ? Centauri A with the Magellan AO system's VisAO and Clio2 cameras.

Males, Jared R.; Close, Laird M.; Guyon, Olivier; Morzinski, Katie; Puglisi, Alfio; Hinz, Philip; Follette, Katherine B.; Monnier, John D.; Tolls, Volker; Rodigas, Timothy J.; Weinberger, Alycia; Boss, Alan; Kopon, Derek; Wu, Ya-lin; Esposito, Simone; Riccardi, Armando; Xompero, Marco; Briguglio, Runa; Pinna, Enrico

2014-07-01

131

CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. II. P-TYPE BINARIES  

SciTech Connect

We have developed a comprehensive methodology for calculating the circumbinary habitable zone (HZ) in planet-hosting P-type binary star systems. We present a general formalism for determining the contribution of each star of the binary to the total flux received at the top of the atmosphere of an Earth-like planet and use the Sun's HZ to calculate the inner and outer boundaries of the HZ around a binary star system. We apply our calculations to the Kepler's currently known circumbinary planetary systems and show the combined stellar flux that determines the boundaries of their HZs. We also show that the HZ in P-type systems is dynamic and, depending on the luminosity of the binary stars, their spectral types, and the binary eccentricity, its boundaries vary as the stars of the binary undergo their orbital motion. We present the details of our calculations and discuss the implications of the results.

Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Kaltenegger, Lisa [MPIA, Koenigstuhl 17, Heidelberg, D-69117 (Germany)

2013-11-10

132

Radiative Convective Transfer Calculations for Effective Stellar Fluxes of Habitable and Life Supporting Zones  

NASA Astrophysics Data System (ADS)

Recent fields of interest in exoplanetary research include studies of potentially habitable planets orbiting stars outside of our Solar System. Habitable Zones (HZs) are currently defined by calculating the inner and the outer limits of the mean distance between exoplanets and their central stars based on effective solar fluxes that allow for maintaining liquid water on the planet's surface. Kasting et al. (1993), Selsis et al. (2007), and recently Kopparapu et al. (2013) provided stellar flux limits for such scenarios. We compute effective solar fluxes for Earth-like planets using Earth-like and other atmospheric scenarios including atmospheres with high level and low level clouds. Furthermore we provide habitability limits for solvents other than water, i.e. limits for the so called Life Supporting Zone, introduced by Leitner et al. (2010). The Life Supporting Zone (LSZ) encompasses many habitable zones based on a variety of liquid solvents. Solvents like ammonia and sulfuric acid have been identified for instance by Leitner et al (2012) as possibly life supporting. Assuming planets on circular orbits, the extent of the individual HZ is then calculated via the following equation, d(i,o) = [L/Lsun*1/S(i,o)]**0.5 au, where L is the star's luminosity, and d(i,o) and S(i,o) are the distances to the central star for the inner and the outer edge and effective insolation for inner and the outer edge of the HZ, respectively. After generating S(i,o) values for a selection of solvents, we provide the means to determine LSZ boundaries for main sequence stars. Effective flux calculations are done using a one dimensional radiative convective model (Neubauer et al. 2011) based on a modified version of the open source radiative transfer software Streamer (Key and Schweiger, 1998). Modifications include convective adjustments, additional gases for absorption and the use of an offline cloud model, which allow us to observe the influence of clouds on effective stellar fluxes. Kasting, J.F., Whitmire, D.P., & Reynolds, R.T. 1993, Icar, 101, 108 Key JR, Schweiger AJ (1998) Geosci 24:443-451. Kopparapu, R.J., et al. 2013 ApJ 765, 131 Leitner, J. J., Schwarz, R., Firneis, M. G., Hitzenberger, R., and Neubauer, D., Astrobiology Science Conference 2010, 26-29 April 2010, League City, USA, 2010 Leitner, J.J., Schulze-Makuch, D., Firneis, M.G., Hitzenberger, R., Neubauer, D., 2012 Paleontology Journal 46 (9), 1091 Neubauer, D., Vrtala, A., Leitner, J.J., Firneis, M.G., Hitzenberger, R., 2011 Origins of Life and Evolution of Biospheres, 41, 545-552 Selsis, F., Kasting, J.F., Levrard, B., et al. 2007b, A&A, 476, 137

Ludwig, Wolfgang; Eggl, Siegfried; Neubauer, David; Leitner, Johannes; Firneis, Maria; Hitzenberger, Regina

2014-05-01

133

An Earth-sized planet in the habitable zone of a cool star.  

PubMed

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form. PMID:24744370

Quintana, Elisa V; Barclay, Thomas; Raymond, Sean N; Rowe, Jason F; Bolmont, Emeline; Caldwell, Douglas A; Howell, Steve B; Kane, Stephen R; Huber, Daniel; Crepp, Justin R; Lissauer, Jack J; Ciardi, David R; Coughlin, Jeffrey L; Everett, Mark E; Henze, Christopher E; Horch, Elliott; Isaacson, Howard; Ford, Eric B; Adams, Fred C; Still, Martin; Hunter, Roger C; Quarles, Billy; Selsis, Franck

2014-04-18

134

An Earth-sized Planet in the Habitable Zone of a Cool Star  

E-print Network

The quest for Earth-like planets represents a major focus of current exoplanet research. While planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surface. We present the detection of Kepler-186f, a 1.11+\\-0.14 Earth radius planet that is the outermost of five planets - all roughly Earth-sized - that transit a 0.47+\\-0.05 Rsun star. The intensity and spectrum of the star's radiation places Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and H2O at its surface, then some of this H2O is likely to be in liquid form.

Quintana, Elisa V; Raymond, Sean N; Rowe, Jason F; Bolmont, Emeline; Caldwell, Douglas A; Howell, Steve B; Kane, Stephen R; Huber, Daniel; Crepp, Justin R; Lissauer, Jack J; Ciardi, David R; Coughlin, Jeffrey L; Everett, Mark E; Henze, Christopher E; Horch, Elliott; Isaacson, Howard; Ford, Eric B; Adams, Fred C; Still, Martin; Hunter, Roger C; Quarles, Billy; Selsis, Franck

2014-01-01

135

Can there be additional rocky planets in the Habitable Zone of tight binary stars with a known gas giant?  

NASA Astrophysics Data System (ADS)

Locating planets in Habitable Zones (HZs) around other stars is a growing field in contemporary astronomy. Since a large percentage of all G-M stars in the solar neighbourhood are expected to be part of binary or multiple stellar systems, investigations of whether habitable planets are likely to be discovered in such environments are of prime interest to the scientific community. As current exoplanet statistics predicts that the chances are higher to find new worlds in systems that are already known to have planets, we examine four known extrasolar planetary systems in tight binaries in order to determine their capacity to host additional habitable terrestrial planets. Those systems are Gliese 86, ? Cephei, HD 41004 and HD 196885. In the case of ? Cephei, our results suggest that only the M dwarf companion could host additional potentially habitable worlds. Neither could we identify stable, potentially habitable regions around HD 196885 A. HD 196885 B can be considered a slightly more promising target in the search for Earth-twins. Gliese 86 A turned out to be a very good candidate, assuming that the system's history has not been excessively violent. For HD 41004, we have identified admissible stable orbits for habitable planets, but those strongly depend on the parameters of the system. A more detailed investigation shows that for some initial conditions stable planetary motion is possible in the HZ of HD 41004 A. In spite of the massive companion HD 41004 Bb, we found that HD 41004 B, too, could host additional habitable worlds.

Funk, B.; Pilat-Lohinger, E.; Eggl, S.

2015-04-01

136

Atmospheric Erosion Caused by Stellar Coronal Plasma Flows on Terrestrial Exoplanets within Close-In Habitable Zones of Low Mass Stars  

Microsoft Academic Search

Since low mass M stars show a higher level of stellar activity compared to solar-like stars, and because of the closer orbital distance of their habitable zones compared to that of the Solar System, terrestrial exoplanets within M star habitable zones are expected to be much more strongly influenced by stellar winds and dense plasma ejected from the host star

H. Lammer; N. Terada; Yu. N. Kulikov; H. I. M. Lichtenegger; M. L. Khodachenko; T. Penz

2008-01-01

137

55 CANCRI: STELLAR ASTROPHYSICAL PARAMETERS, A PLANET IN THE HABITABLE ZONE, AND IMPLICATIONS FOR THE RADIUS OF A TRANSITING SUPER-EARTH  

SciTech Connect

The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 {+-} 0.010 R{sub sun}, T{sub EFF} = 5196 {+-} 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 {+-} 2.5 Gyr, implying a stellar mass of 0.905 {+-} 0.015 M{sub sun}. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period {approx}260 days and Msin i = 0.155 M{sub Jupiter}, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ({approx}2.05 {+-} 0.15 R{sub +}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 {rho}{sub +} or 1.07 {rho}{sub +}.

Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Tabetha, S. Boyajian; McAlister, Harold A.; White, Russel [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P. O. Box 4106, Atlanta, GA 30302-4106 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J. [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Van Belle, Gerard T. [European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching (Germany); Raymond, Sean N. [Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France); Lopez-Morales, Mercedes [Institut de Ciencies de L'Espai (CSIC-IEEC), Campus UAB, Facultat Ciencies, Torre C5 parell 2, 08193 Bellaterra, Barcelona (Spain); Ridgway, Stephen T., E-mail: kaspar@caltech.edu [National Optical Astronomy Observatory, P. O. Box 26732, Tucson, AZ 85726-6732 (United States)

2011-10-10

138

Exomoon habitability constrained by illumination and tidal heating.  

PubMed

The detection of moons orbiting extrasolar planets ("exomoons") has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local climates on exomoons by reducing stellar illumination. In addition to radiative heating, tidal heating can be very large on exomoons, possibly even large enough for sterilization. We identify combinations of physical and orbital parameters for which radiative and tidal heating are strong enough to trigger a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define a circumplanetary "habitable edge." We apply our model to hypothetical moons around the recently discovered exoplanet Kepler-22b and the giant planet candidate KOI211.01 and describe, for the first time, the orbits of habitable exomoons. If either planet hosted a satellite at a distance greater than 10 planetary radii, then this could indicate the presence of a habitable moon. PMID:23305357

Heller, René; Barnes, Rory

2013-01-01

139

Astrometric Detection of Terrestrial Planets in the Habitable Zones of Nearby Stars with SIM PlanetQuest  

Microsoft Academic Search

SIM PlanetQuest is a space-borne Michelson interferometer with a 9 m baseline, currently slated for launch in 2016. One of the principal science goals of the mission is the astrometric detection and orbital characterization of terrestrial planets in the habitable zones of nearby stars. Differential astrometry of the target star against a set of reference stars lying within a degree

Joseph Catanzarite; Michael Shao; Angelle Tanner; Stephen Unwin; Jeffrey Yu

2006-01-01

140

BinHab: A Numerical Tool for the Calculation of S/P-Type Habitable Zones in Binary Systems  

NASA Astrophysics Data System (ADS)

The aim of this contribution is to introduce the numerical tool BinHab, a publicly accessible code, available at The University of Texas at Arlington, that allows the calculation of S-type and P-type habitable zones of general binary systems.

Cuntz, M.; Bruntz, R.

2015-01-01

141

The stability of the orbits of Earth-mass planets in and near the habitable zones of known exoplanetary systems  

Microsoft Academic Search

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 93 main-sequence exoplanetary systems confirmed by May 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a third of the 93 systems might be able to have

Barrie W. Jones; David R. Underwood; P. Nick Sleep

2003-01-01

142

WISE Detections of Dust in the Habitable Zones of Planet-Bearing Stars  

NASA Technical Reports Server (NTRS)

We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 microns (T(sub dust) approx.300 and/or approx.150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopedia as of 2012 January 31, 350 are robustly detected by WISE at > or = 5(sigma) level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 microns at > or = 3(sigma) level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of approx.2.6% for stars of all evolutionary stages, but approx.1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

Morales, Farisa Y.; Padgett, Deborah L.; Bryden, Geoffrey; Werner, M. W.; Furlan, E.

2012-01-01

143

WISE DETECTIONS OF DUST IN THE HABITABLE ZONES OF PLANET-BEARING STARS  

SciTech Connect

We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 {mu}m (T{sub dust} {approx} 300 and/or {approx}150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopaedia as of 2012 January 31, 350 are robustly detected by WISE at {>=}5{sigma} level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 {mu}m at {>=}3{sigma} level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of {approx}2.6% for stars of all evolutionary stages, but {approx}1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

Morales, Farisa Y.; Bryden, G.; Werner, M. W. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Padgett, D. L. [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Furlan, E., E-mail: Farisa@jpl.nasa.gov [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)

2012-09-20

144

Toward detection of terrestrial planets in the habitable zone of our closest neighbor: Proxima Centauri  

E-print Network

The precision of radial velocity (RV) measurements to detect indirectly planetary companions of nearby stars has improved to enable the discovery of extrasolar planets in the Neptune and Super-Earth mass range. Discoveries of Earth-like planets by means of ground-based RV programs will help to determine the parameter Eta_Earth, the frequency of potentially habitable planets around other stars. In search of low-mass planetary companions we monitored Proxima Centauri (M5V) as part of our M dwarf program. In the absence of a significant detection, we use these data to demonstrate the general capability of the RV method in finding terrestrial planets. For late M dwarfs the classic liquid surface water habitable zone (HZ) is located close to the star, in which circumstances the RV method is most effective. We want to demonstrate that late M dwarfs are ideal targets for the search of terrestrial planets with the RV technique. We obtained differential RV measurements of Proxima Cen over a time span of 7 years with the UVES spectrograph at the ESO VLT. We determine upper limits to the masses of companions in circular orbits by means of numerical simulations. The RV data of Proxima Cen have a total rms scatter of 3.1 m/s and a period search does not reveal any significant signals. As a result of our companion limit calculations, we find that we successfully recover all test signals with RV amplitudes corresponding to planets with m sin i > 2 - 3 M_Earth residing inside the HZ of Proxima Cen with a statistical significance of >99%. Over the same period range, we can recover 50% of the test planets with masses of m sin i > 1.5 - 2.5 M_Earth. Based on our simulations, we exclude the presence of any planet in a circular orbit with m sin i > 1 M_Neptune at separations of a < 1 AU.

Michael Endl; Martin Kuerster

2008-07-09

145

Water transport to the habitable zone and impact probabilities in the early phases of planetary systems in binary star systems  

NASA Astrophysics Data System (ADS)

By now, observations of exoplanets have found more than 50 binary star systems hosting 71 planets. We expect these numbers to increase as more than 70% of the main sequence stars in the solar neighbourhood are members of binary or multiple systems. The planetary motion in binary star systems depends strongly on both the parameters of the stellar system (stellar separation and eccentricity) and the architecture of the planetary system (number of planets and their orbital behaviour). In case a terrestrial planet moves in the so-called habitable zone (HZ) of its host star, the habitability of such a planet depend on many parameters. A crucial factor is certainly the amount of water. We present here a statistical study to assess the water transport of icy bodies to the habitable zone for various binary system characteristics (binary separation, eccentricity and stellar star type of the secondary). We aim to highlight the most efficicient systems for the migration of asteroids located beyond the snow-line to the habitable zone and therefore, the water delivery into planets.

Bancelin, D.; Pilat-Lohinger, E.; Eggl, S.

2014-04-01

146

The Mt John University Observatory search for Earth-mass planets in the habitable zone of ? Centauri  

NASA Astrophysics Data System (ADS)

The `holy grail' in planet hunting is the detection of an Earth-analogue: a planet with similar mass as the Earth and an orbit inside the habitable zone. If we can find such an Earth-analogue around one of the stars in the immediate solar neighbourhood, we could potentially even study it in such great detail to address the question of its potential habitability. Several groups have focused their planet detection efforts on the nearest stars. Our team is currently performing an intensive observing campaign on the ? Centauri system using the High Efficiency and Resolution Canterbury University Large Échelle Spectrograph (Hercules) at the 1 m McLellan telescope at Mt John University Observatory in New Zealand. The goal of our project is to obtain such a large number of radial velocity (RV) measurements with sufficiently high temporal sampling to become sensitive to signals of Earth-mass planets in the habitable zones of the two stars in this binary system. Over the past few years, we have collected more than 45 000 spectra for both stars combined. These data are currently processed by an advanced version of our RV reduction pipeline, which eliminates the effect of spectral cross-contamination. Here we present simulations of the expected detection sensitivity to low-mass planets in the habitable zone by the Hercules programme for various noise levels. We also discuss our expected sensitivity to the purported Earth-mass planet in a 3.24-day orbit announced by Dumusque et al. (2012).

Endl, Michael; Bergmann, Christoph; Hearnshaw, John; Barnes, Stuart I.; Wittenmyer, Robert A.; Ramm, David; Kilmartin, Pam; Gunn, Fraser; Brogt, Erik

2015-04-01

147

Exoplanet dynamics. Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars.  

PubMed

Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets' rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar mass. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere. PMID:25592420

Leconte, Jérémy; Wu, Hanbo; Menou, Kristen; Murray, Norman

2015-02-01

148

Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution.  

PubMed

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy. PMID:14577880

Stern, S Alan

2003-01-01

149

DIRECT IMAGING IN THE HABITABLE ZONE AND THE PROBLEM OF ORBITAL MOTION  

SciTech Connect

High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 {mu}m) and used exposure times of {approx}1 hr to search for planets with semi-major axes of {approx}> 10 AU. We are beginning to plan for surveys using extreme-AO systems on the next generation of 30 m class telescopes, where we hope to begin probing the habitable zones (HZs) of nearby stars. Here we highlight a heretofore ignorable problem in direct imaging: planets orbit their stars. Under the parameters of current surveys, orbital motion is negligible over the duration of a typical observation. However, this motion is not negligible when using large diameter telescopes to observe at relatively close stellar distances (1-10 pc), over the long exposure times (10-20 hr) necessary for direct detection of older planets in the HZ. We show that this motion will limit our achievable signal-to-noise ratio and degrade observational completeness. Even on current 8 m class telescopes, orbital motion will need to be accounted for in an attempt to detect HZ planets around the nearest Sun-like stars {alpha} Cen A and B, a binary system now known to harbor at least one planet. Here we derive some basic tools for analyzing this problem, and ultimately show that the prospects are good for de-orbiting a series of shorter exposures to correct for orbital motion.

Males, Jared R.; Skemer, Andrew J.; Close, Laird M., E-mail: jrmales@as.arizona.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

2013-07-01

150

Direct Imaging in the Habitable Zone and the Problem of Orbital Motion  

E-print Network

High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 microns) and used exposure times of ~1 hr to search for planets with semi-major axes of > ~10 AU. We are beginning to plan for surveys using extreme-AO systems on the next generation of 30-meter class telescopes, where we hope to begin probing the habitable zones (HZs) of nearby stars. Here we highlight a heretofore ignorable problem in direct imaging: planets orbit their stars. Under the parameters of current surveys, orbital motion is negligible over the duration of a typical observation. However, this motion is not negligible when using large diameter telescopes to observe at relatively close stellar distances (1-10pc), over the long exposure times (10-20 hrs) necessary for direct detection of older planets in the HZ. We show that this motion will limit our achievable signal-to-noise ratio and degrade observational completeness. Even on current 8m class telescopes, orbital motion will need to ...

Males, Jared R; Close, Laird M

2013-01-01

151

Direct Imaging in the Habitable Zone and the Problem of Orbital Motion  

NASA Astrophysics Data System (ADS)

High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 ?m) and used exposure times of ~1 hr to search for planets with semi-major axes of >~ 10 AU. We are beginning to plan for surveys using extreme-AO systems on the next generation of 30 m class telescopes, where we hope to begin probing the habitable zones (HZs) of nearby stars. Here we highlight a heretofore ignorable problem in direct imaging: planets orbit their stars. Under the parameters of current surveys, orbital motion is negligible over the duration of a typical observation. However, this motion is not negligible when using large diameter telescopes to observe at relatively close stellar distances (1-10 pc), over the long exposure times (10-20 hr) necessary for direct detection of older planets in the HZ. We show that this motion will limit our achievable signal-to-noise ratio and degrade observational completeness. Even on current 8 m class telescopes, orbital motion will need to be accounted for in an attempt to detect HZ planets around the nearest Sun-like stars ? Cen A&B, a binary system now known to harbor at least one planet. Here we derive some basic tools for analyzing this problem, and ultimately show that the prospects are good for de-orbiting a series of shorter exposures to correct for orbital motion.

Males, Jared R.; Skemer, Andrew J.; Close, Laird M.

2013-07-01

152

CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. I. S-TYPE BINARIES  

SciTech Connect

We have developed a comprehensive methodology for calculating the boundaries of the habitable zone (HZ) of planet-hosting S-type binary star systems. Our approach is general and takes into account the contribution of both stars to the location and extent of the binary HZ with different stellar spectral types. We have studied how the binary eccentricity and stellar energy distribution affect the extent of the HZ. Results indicate that in binaries where the combination of mass-ratio and orbital eccentricity allows planet formation around a star of the system to proceed successfully, the effect of a less luminous secondary on the location of the primary's HZ is generally negligible. However, when the secondary is more luminous, it can influence the extent of the HZ. We present the details of the derivations of our methodology and discuss its application to the binary HZ around the primary and secondary main-sequence stars of an FF, MM, and FM binary, as well as two known planet-hosting binaries ? Cen AB and HD 196886.

Kaltenegger, Lisa [MPIA, Koenigstuhl 17, D-69117 Heidelberg (Germany); Haghighipour, Nader, E-mail: kaltenegger@mpia.de [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States)

2013-11-10

153

Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone  

NASA Astrophysics Data System (ADS)

We report on the work to validate twelve candidate-transiting planets from Kepler with orbital periods ranging from 34 to 207 days initially identified in the pipeline search of three years of Kepler data from quarters 1 to 12. The candidates were selected based on pipeline Data Validation models indicating that they are small and potentially in the habitable zone (HZ) of their parent stars. As their expected Doppler signals are too small for a direct measure of their masses, we verify their planetary nature by validating them statistically using the BLENDER technique. BLENDER simulates large numbers of false-positive scenarios and compares the resulting light curves with the Kepler photometry, taking into account additional information from the analysis of Kepler flux centroids and new follow-up observations, including high-resolution optical and NIR spectroscopy, adaptive optics imaging, and speckle imaging. For eleven of the candidates we show that the likelihood they are true planets is far greater than that of a false positive, to a 99.73% confidence level. For the twelfth candidate, the planet confidence level is about 99.2%. Using improved stellar parameters for the host stars, we derive planetary radii ranging from 1.12 to 2.73 R?. All twelve objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of the candidates that have been previously validated by others, our study doubles the number of known potentially rocky planets in the HZ.

Caldwell, Douglas A.; Torres, Guillermo; Kipping, David M.; Ballard, Sarah; Batalha, Natalie; Borucki, William J.; Bryson, Steve; Ciardi, David R.; Crepp, Justin R.; Everett, Mark; Fressin, Francois; Henze, Christopher; Horch, Elliott; Howard, Andrew; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon Michael; Kolbl, Rea; Marcy, Geoffrey W.; McCauliff, Sean D.; Muirhead, Philip Steven; Newton, Elizabeth; Petigura, Erik; Twicken, Joseph D.; Quintana, Elisa V.; Barclay, Thomas

2015-01-01

154

Habitable Zones around Main-sequence Stars: Dependence on Planetary Mass  

NASA Astrophysics Data System (ADS)

The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M ? and 5 M ?. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (~10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (~7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

Kopparapu, Ravi Kumar; Ramirez, Ramses M.; SchottelKotte, James; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

2014-06-01

155

Scrambling and modal noise mitigation in the Habitable Zone Planet Finder fiber feed  

NASA Astrophysics Data System (ADS)

We present the baseline fiber feed design for the Habitable-zone Planet Finder (HPF), a precision radial velocity (RV) spectrograph designed to detect Earth analogs around M-dwarfs. HPF is a stabilized, fiber-fed, R˜50,000 spectrograph operating in the near-infrared (NIR) from 0.82 to 1.3 µm, and will be deployed on the Hobby- Eberly Telescope (HET) in Texas. While the essential function of the optical fibers is to deliver high throughput, this mode of light transport also provides the opportunity to introduce radial and azimuthal scrambling, which boosts instrument stability and thereby RV precision. Based on the unique requirements of HPF on the HET, we present initial tests showing very high scrambling gains via a compact scrambler in conjunction with octagonal fibers. Conversely, the propagation of light through the fibers injects modal noise, which can limit achievable RV precision. Laboratory tests of a custom-built mechanical agitator show significant gains over a static fiber feed. Overall, the fiber feed is designed to provide high relative throughput, excellent scrambling, and reliable modal noise suppression. We will also attempt to minimize focal ratio degradation (FRD) to the extent possible with the chosen configuration. HPF inculcates several other new technologies developed by the Penn State Optical-Infrared instrumentation group, including a rigorous calibration system, which are discussed separately in these proceedings.

Roy, Arpita; Halverson, Samuel; Mahadevan, Suvrath; Ramsey, Lawrence W.

2014-07-01

156

Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone  

E-print Network

We present an investigation of twelve candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For eleven of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false po...

Torres, Guillermo; Fressin, Francois; Caldwell, Douglas A; Twicken, Joseph D; Ballard, Sarah; Batalha, Natalie M; Bryson, Stephen T; Ciardi, David R; Henze, Christopher E; Howell, Steve B; Isaacson, Howard T; Jenkins, Jon M; Muirhead, Philip S; Newton, Elisabeth R; Petigura, Erik A; Barclay, Thomas; Borucki, William J; Crepp, Justin R; Everett, Mark E; Horch, Elliott P; Howard, Andrew W; Kolbl, Rea; Marcy, Geoffrey W; McCauliff, Sean; Quintana, Elisa V

2015-01-01

157

Transit and Radial Velocity Survey Efficiency Comparison for a Habitable Zone Earth  

NASA Astrophysics Data System (ADS)

Transit and radial velocity searches are two techniques for identifying nearby extrasolar planets to Earth that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution. We estimate the observing time required for a transit survey to find a transiting Earth-sized exoplanet in the habitable zone (HZ) with an emphasis on late-type stars. We also estimate the radial velocity precision necessary to detect the equivalent HZ Earth-mass exoplanet that also transits when using an equal amount of observing time as the transit survey. We find that a radial velocity survey with ?rv ~ 0.6 m s-1 precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision ?phot ~ 300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M dwarfs. For super-Earths, a ?rv ~ 2.0 m s-1 precision radial velocity survey has comparable efficiency to a transit survey with ?phot ~ 2300 ppm.

Burke, Christopher J.; McCullough, P. R.

2014-09-01

158

Exoplanet detection. Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581.  

PubMed

The M dwarf star Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet--GJ 581g--is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the H? line, we measure a stellar rotation period of 130 ± 2 days and a correlation for H? modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5 standard deviations) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g. PMID:24993348

Robertson, Paul; Mahadevan, Suvrath; Endl, Michael; Roy, Arpita

2014-07-25

159

WATER-PLANETS IN THE HABITABLE ZONE: ATMOSPHERIC CHEMISTRY, OBSERVABLE FEATURES, AND THE CASE OF KEPLER-62e AND -62f  

SciTech Connect

Planets composed of large quantities of water that reside in the habitable zone are expected to have distinct geophysics and geochemistry of their surfaces and atmospheres. We explore these properties motivated by two key questions: whether such planets could provide habitable conditions and whether they exhibit discernable spectral features that distinguish a water-planet from a rocky Earth-like planet. We show that the recently discovered planets Kepler-62e and -62f are the first viable candidates for habitable zone water-planets. We use these planets as test cases for discussing those differences in detail. We generate atmospheric spectral models and find that potentially habitable water-planets show a distinctive spectral fingerprint in transit depending on their position in the habitable zone.

Kaltenegger, L. [Max Planck Institute of Astronomy, Koenigstuhl 17, D-69115 Heidelberg (Germany)] [Max Planck Institute of Astronomy, Koenigstuhl 17, D-69115 Heidelberg (Germany); Sasselov, D.; Rugheimer, S., E-mail: kaltenegger@mpia.de [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2013-10-01

160

THE HUNT FOR EXOMOONS WITH KEPLER (HEK). III. THE FIRST SEARCH FOR AN EXOMOON AROUND A HABITABLE-ZONE PLANET  

SciTech Connect

Kepler-22b is the first transiting planet to have been detected in the habitable zone of its host star. At 2.4 R{sub ?}, Kepler-22b is too large to be considered an Earth analog, but should the planet host a moon large enough to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric world. Aside from being within the habitable zone, the target is attractive due to the availability of previously measured precise radial velocities and low intrinsic photometric noise, which has also enabled asteroseismology studies of the star. For these reasons, Kepler-22b was selected as a target-of-opportunity by the 'Hunt for Exomoons with Kepler' (HEK) project. In this work, we conduct a photodynamical search for an exomoon around Kepler-22b leveraging the transits, radial velocities, and asteroseismology plus several new tools developed by the HEK project to improve exomoon searches. We find no evidence for an exomoon around the planet and exclude moons of mass M{sub S} > 0.5 M{sub ?} to 95% confidence. By signal injection and blind retrieval, we demonstrate that an Earth-like moon is easily detected for this planet even when the time-correlated noise of the data set is taken into account. We provide updated parameters for the planet Kepler-22b, including a revised mass of M{sub P} < 53 M{sub ?} to 95% confidence and an eccentricity of 0.13{sub -0.13}{sup +0.36} by exploiting Single-body Asterodensity Profiling. Finally, we show that Kepler-22b has a >95% probability of being within the empirical habitable zone but a <5% probability of being within the conservative habitable zone.

Kipping, D. M. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Forgan, D. [Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Hartman, J.; Bakos, G. Á. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 05844 (United States); Nesvorný, D. [Department of Space Studies, Southwest Research Institute, Boulder, CO 80302 (United States); Schmitt, A.; Buchhave, L., E-mail: dkipping@cfa.harvard.edu [Niels Bohr Institute, Copenhagen University (Denmark)

2013-11-10

161

The Hunt for Exomoons with Kepler (HEK). III. The First Search for an Exomoon around a Habitable-zone Planet  

NASA Astrophysics Data System (ADS)

Kepler-22b is the first transiting planet to have been detected in the habitable zone of its host star. At 2.4 R ?, Kepler-22b is too large to be considered an Earth analog, but should the planet host a moon large enough to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric world. Aside from being within the habitable zone, the target is attractive due to the availability of previously measured precise radial velocities and low intrinsic photometric noise, which has also enabled asteroseismology studies of the star. For these reasons, Kepler-22b was selected as a target-of-opportunity by the "Hunt for Exomoons with Kepler" (HEK) project. In this work, we conduct a photodynamical search for an exomoon around Kepler-22b leveraging the transits, radial velocities, and asteroseismology plus several new tools developed by the HEK project to improve exomoon searches. We find no evidence for an exomoon around the planet and exclude moons of mass MS > 0.5 M ? to 95% confidence. By signal injection and blind retrieval, we demonstrate that an Earth-like moon is easily detected for this planet even when the time-correlated noise of the data set is taken into account. We provide updated parameters for the planet Kepler-22b, including a revised mass of MP < 53 M ? to 95% confidence and an eccentricity of 0.13_{-0.13}^{+0.36} by exploiting Single-body Asterodensity Profiling. Finally, we show that Kepler-22b has a >95% probability of being within the empirical habitable zone but a <5% probability of being within the conservative habitable zone. Based on archival data of the Kepler telescope.

Kipping, D. M.; Forgan, D.; Hartman, J.; Nesvorný, D.; Bakos, G. Á.; Schmitt, A.; Buchhave, L.

2013-11-01

162

Delayed Gratification Habitable Zones: When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution  

Microsoft Academic Search

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with

S. Alan Stern

2003-01-01

163

The stability of the orbits of Earth-mass planets in the habitable zone of 47 Ursae Majoris  

Microsoft Academic Search

We have investigated whether Earth-mass planets could survive in the habitable zone (HZ) of the 47 Ursae Majoris system. Mixed-variable symplectic numerical integration has been used to investigate the orbits of putative Earth-mass planets. Whereas the 47 UMa system as previously known, with just one giant planet, could have Earth-mass planets that remain confined to the HZ for a fairly

B. W. Jones; P. N. Sleep

2002-01-01

164

On atmospheric erosion of Earth-like exoplanets induced by stellar radiation and plasma in close-in habitable zones  

Microsoft Academic Search

The efficiency of atmospheric erosion of CO2 -rich exoplanets, with sizes and masses similar to that of the Earth, due to Coronal Mass Ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since active flare M-stars are also active at the X-ray and EUV radiation wavelengths over long time periods, we have applied

H. Lammer; H. I. M. Lichtenegger; Yu. N. Kulikov; M. L. Khodachenko; J.-M. Griessmeier; N. Terada; I. Ribas

2006-01-01

165

How Close Are We To Detecting Earth-like Planets in the Habitable Zone Using the Radial Velocity Technique?  

Microsoft Academic Search

Discovering an Earth-like exoplanet in habitable zone is an important milestone for astronomers in search of extra-terrestrial life. While the radial velocity (RV) technique remains one the most powerful tools in detecting and characterizing exo-planetary sys- tems, we calculate the uncertainties in precision RV measurements considering stellar spectral quality factors, RV calibration sources, stellar noise and telluric contamination in different

Ji Wang; Jian Ge

2011-01-01

166

Astrobiological Effects of Stellar Radiation in Circumstellar Environments  

NASA Astrophysics Data System (ADS)

The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

2006-10-01

167

A SUPER-EARTH-SIZED PLANET ORBITING IN OR NEAR THE HABITABLE ZONE AROUND A SUN-LIKE STAR  

SciTech Connect

We present the discovery of a super-Earth-sized planet in or near the habitable zone of a Sun-like star. The host is Kepler-69, a 13.7 mag G4V-type star. We detect two periodic sets of transit signals in the 3-year flux time series of Kepler-69, obtained with the Kepler spacecraft. Using the very high precision Kepler photometry, and follow-up observations, our confidence that these signals represent planetary transits is >99.3%. The inner planet, Kepler-69b, has a radius of 2.24{sup +0.44}{sub -0.29} R{sub Circled-Plus} and orbits the host star every 13.7 days. The outer planet, Kepler-69c, is a super-Earth-sized object with a radius of 1.7{sup +0.34}{sub -0.23} R{sub Circled-Plus} and an orbital period of 242.5 days. Assuming an Earth-like Bond albedo, Kepler-69c has an equilibrium temperature of 299 {+-} 19 K, which places the planet close to the habitable zone around the host star. This is the smallest planet found by Kepler to be orbiting in or near the habitable zone of a Sun-like star and represents an important step on the path to finding the first true Earth analog.

Barclay, Thomas; Burke, Christopher J.; Howell, Steve B.; Rowe, Jason F.; Huber, Daniel; Jenkins, Jon M.; Quintana, Elisa V.; Still, Martin; Twicken, Joseph D.; Bryson, Stephen T.; Borucki, William J.; Caldwell, Douglas A.; Clarke, Bruce D.; Christiansen, Jessie L; Coughlin, Jeffrey L. [NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States); Isaacson, Howard; Kolbl, Rea; Marcy, Geoffrey W. [Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720 (United States); Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Fischer, Debra A. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); and others

2013-05-10

168

Effect of Metallicity on the Evolution of the Habitable Zone from the Pre-Main Sequence to the Asymptotic Giant Branch and the Search for Life  

E-print Network

During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M$_{\\odot}$ for metallicities ranging from Z=0.0001 to Z=0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well a...

Danchi, William C

2013-01-01

169

Volatile-rich Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

A small planet is not necessarily a terrestrial planet. Planets that form beyond the snow line with too little mass to seed rapid gas accretion (<~10 M?) should be rich in volatile ices like H2O and NH3. Some of these planets should migrate inward by interacting with a circumstellar disk or with other planets. Such objects can retain their volatiles

Marc J. Kuchner

2003-01-01

170

Volatile-Rich Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

A small planet is not necessarily a terrestrial planet. Planets that form beyond the snow line with too little mass to seed rapid gas accretion (< ˜ 10 M \\\\bigoplus ) should be rich in volatile ices like H2O and NH3. Some of these planets should migrate inward by interacting with a circumstellar disk or with other planets. Such objects

M. J. Kuchner

2003-01-01

171

Validation of 12 Small Kepler Transiting Planets in the Habitable Zone  

NASA Astrophysics Data System (ADS)

We present an investigation of 12 candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. Few of these objects are known. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For 11 of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false positive, to a confidence level of 99.73% (3?) or higher. For KOI-4427.01 the confidence level is about 99.2% (2.6?). With our accurate characterization of the GKM host stars, the derived planetary radii range from 1.1 to 2.7 R ?. All 12 objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of them that have been previously validated by others, our study doubles the number of known rocky planets in the HZ. KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most similar to the Earth discovered to date when considering their size and incident flux jointly.

Torres, Guillermo; Kipping, David M.; Fressin, Francois; Caldwell, Douglas A.; Twicken, Joseph D.; Ballard, Sarah; Batalha, Natalie M.; Bryson, Stephen T.; Ciardi, David R.; Henze, Christopher E.; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon M.; Muirhead, Philip S.; Newton, Elisabeth R.; Petigura, Erik A.; Barclay, Thomas; Borucki, William J.; Crepp, Justin R.; Everett, Mark E.; Horch, Elliott P.; Howard, Andrew W.; Kolbl, Rea; Marcy, Geoffrey W.; McCauliff, Sean; Quintana, Elisa V.

2015-02-01

172

Observations of Interstellar Formamide: Availability of a Prebiotic Precursor in the Galactic Habitable Zone  

PubMed Central

Abstract We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12?m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250?GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×1012 to 9.1×1013 cm?2, with rotational temperatures of 70–177?K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10?11 to 1×10?10. It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ?0.1?mol/km2/yr or 0.18?mmol/m2 in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. Key Words: Formamide—Astrobiology—Radioastronomy—ISM—Comets—Meteorites. Astrobiology 13, 439–453. PMID:23654214

Adande, Gilles R.; Woolf, Neville J.

2013-01-01

173

Observations of interstellar formamide: availability of a prebiotic precursor in the galactic habitable zone.  

PubMed

We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×10(12) to 9.1×10(13) cm(-2), with rotational temperatures of 70-177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10(-11) to 1×10(-10). It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ~0.1 mol/km(2)/yr or 0.18 mmol/m(2) in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. PMID:23654214

Adande, Gilles R; Woolf, Neville J; Ziurys, Lucy M

2013-05-01

174

Cosmic ray impact on extrasolar earth-like planets in close-in habitable zones.  

PubMed

Because of their different origins, cosmic rays can be subdivided into galactic cosmic rays and solar/stellar cosmic rays. The flux of cosmic rays to planetary surfaces is mainly determined by two planetary parameters: the atmospheric density and the strength of the internal magnetic moment. If a planet exhibits an extended magnetosphere, its surface will be protected from high-energy cosmic ray particles. We show that close-in extrasolar planets in the habitable zone of M stars are synchronously rotating with their host star because of the tidal interaction. For gravitationally locked planets the rotation period is equal to the orbital period, which is much longer than the rotation period expected for planets not subject to tidal locking. This results in a relatively small magnetic moment. We found that an Earth-like extrasolar planet, tidally locked in an orbit of 0.2 AU around an M star of 0.5 solar masses, has a rotation rate of 2% of that of the Earth. This results in a magnetic moment of less than 15% of the Earth's current magnetic moment. Therefore, close-in extrasolar planets seem not to be protected by extended Earth-like magnetospheres, and cosmic rays can reach almost the whole surface area of the upper atmosphere. Primary cosmic ray particles that interact with the atmosphere generate secondary energetic particles, a so-called cosmic ray shower. Some of the secondary particles can reach the surface of terrestrial planets when the surface pressure of the atmosphere is on the order of 1 bar or less. We propose that, depending on atmospheric pressure, biological systems on the surface of Earth-like extrasolar planets at close-in orbital distances can be strongly influenced by secondary cosmic rays. PMID:16225432

Griessmeier, J-M; Stadelmann, A; Motschmann, U; Belisheva, N K; Lammer, H; Biernat, H K

2005-10-01

175

Kepler Mission: A Mission to Find Earth-size Planets in the Habitable Zone  

NASA Technical Reports Server (NTRS)

The Kepler Mission is a Discovery-class mission designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. It is a wide field of view photometer Schmidt-type telescope with an array of 42 CCDs. It has a 0.95 m aperture and 1.4 m primary and is designed to attain a photometric precision of 2 parts in 10(exp 5) for 12th magnitude solar-like stars for a 6 hr transit duration. It will continuously observe 100,000 main-sequence stars from 9th to 14th magnitude in the Cygnus constellation for a period of four years with a cadence of 4/hour. An additional 250 stars can be monitored at a cadence of l/minute to do astro-seismology of stars brighter than 11.5 mv. The photometer is scheduled to be launched into heliocentric orbit in 2007. When combined with ground-based spectrometric observations of these stars, the positions of the planets relative to the habitable zone can be found. The spectra of the stars are also used to determine the relationships between the characteristics of terrestrial planets and the characteristics of the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. Based on the results of the current Doppler-velocity discoveries, over a thousand giant planets will also be found. Information on the albedos and densities of those giants showing transits will be obtained. At the end of the four year mission, hundreds of Earth-size planets should be discovered in and near the HZ of their stars if such planets are common. A null result would imply that terrestrial planets in the HZ are very rare and that life might also be quite rare.

Borucki, W. J.

2003-01-01

176

The Mt John University Observatory Search For Earth-mass Planets In The Habitable Zone Of Alpha Centauri  

E-print Network

The "holy grail" in planet hunting is the detection of an Earth-analog: a planet with similar mass as the Earth and an orbit inside the habitable zone. If we can find such an Earth-analog around one of the stars in the immediate solar neighborhood, we could potentially even study it in such great detail to address the question of its potential habitability. Several groups have focused their planet detection efforts on the nearest stars. Our team is currently performing an intensive observing campaign on the alpha Centauri system using the Hercules spectrograph at the 1-m McLellan telescope at Mt John University Observatory (MJUO) in New Zealand. The goal of our project is to obtain such a large number of radial velocity measurements with sufficiently high temporal sampling to become sensitive to signals of Earth-mass planets in the habitable zones of the two stars in this binary system. Over the past years, we have collected more than 45,000 spectra for both stars combined. These data are currently processed ...

Endl, M; Hearnshaw, J; Barnes, S I; Wittenmyer, R A; Ramm, D; Kilmartin, P; Gunn, F; Brogt, E

2014-01-01

177

Volatile-Rich Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

A small planet is not necessarily a terrestrial planet. Planets that form\\u000abeyond the snow line with too little mass to seed rapid gas accretion (<~ 10\\u000aEarth masses) should be rich in volatile ices like water and ammonia. Some of\\u000athese planets should migrate inward by interacting with a circumstellar disk or\\u000awith other planets. Such objects can retain

Marc J. Kuchner

2003-01-01

178

EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE  

SciTech Connect

During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

Danchi, William C. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Lopez, Bruno, E-mail: william.c.danchi@nasa.gov, E-mail: bruno.lopez@oca.eu [Observatoire de la Cote d'Azur, Laboratoire Lagrange UMR 7293, BP 4229, F-06034 Nice Cedex 4 (France)

2013-05-20

179

Effect of Metallicity on the Evolution of the Habitable Zone from the Pre-main Sequence to the Asymptotic Giant Branch and the Search for Life  

NASA Astrophysics Data System (ADS)

During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M ? for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M ? star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and ~4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

Danchi, William C.; Lopez, Bruno

2013-05-01

180

Extreme water loss and abiotic o2 buildup on planets throughout the habitable zones of m dwarfs.  

PubMed

We show that terrestrial planets in the habitable zones of M dwarfs older than ?1?Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ?5 bar/Myr on Earth-mass planets and up to ?25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars. Key Words: Astrobiology-Biosignatures-Extrasolar terrestrial planets-Habitability-Planetary atmospheres. Astrobiology 15, 119-143. PMID:25629240

Luger, R; Barnes, R

2015-02-01

181

Extreme Water Loss and Abiotic O2 Buildup on Planets Throughout the Habitable Zones of M Dwarfs  

PubMed Central

Abstract We show that terrestrial planets in the habitable zones of M dwarfs older than ?1?Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ?5 bar/Myr on Earth-mass planets and up to ?25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars. Key Words: Astrobiology—Biosignatures—Extrasolar terrestrial planets—Habitability—Planetary atmospheres. Astrobiology 15, 119–143. PMID:25629240

Barnes, R.

2015-01-01

182

Volatile-Rich Earth-Mass Planets in the Habitable Zone  

E-print Network

A small planet is not necessarily a terrestrial planet. Planets that form beyond the snow line with too little mass to seed rapid gas accretion (Earth masses) should be rich in volatile ices like water and ammonia. Some of these planets should migrate inward by interacting with a circumstellar disk or with other planets. Such objects can retain their volatiles for billions of years or longer at ~1 AU as their atmospheres undergo slow hydrodynamic escape. These objects could appear in future surveys for extrasolar Earth analogs.

Marc J. Kuchner

2003-08-28

183

Extreme Water Loss and Abiotic O2 Buildup On Planets Throughout the Habitable Zones of M Dwarfs  

NASA Astrophysics Data System (ADS)

We show that terrestrial planets in the habitable zones of M dwarfs older than ~1 Gyr could have been in runaway greenhouses for several hundred Myr following their formation due to the star's extended pre-main sequence phase. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone. We find that the amount of water lost roughly scales with the planet mass: super-Earths, which lose water primarily via the escape of hydrogen, lose more water than Earth-mass planets, which lose water more slowly via the escape of both hydrogen and oxygen. If the surface is able to absorb most of the photolytically produced oxygen, planets around low mass M dwarfs can be completely desiccated for initial inventories of up to several tens of Earth oceans. On the other hand, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bars of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate of ~5 bars/Myr on Earth-mass planets and up to ~25 bars/Myr on super- Earths. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low mass stars.

Luger, Rodrigo; Barnes, Rory

2015-01-01

184

Direct Detection of Nearby Habitable Zone Planets Using Slicer Based Integral Field Spectrographs and EPICS on the E-ELT  

NASA Astrophysics Data System (ADS)

Early design studies for the future Exo-Planet Imaging Camera and Specrotgraph (EPICS) on the European Extremely Large Telescope (E-ELT) show the ability to probe the region of super-Earths in the habitable zone of stars within 5pc (including Gilese 581d). However, these planets will be lost to us if the correct choice of integral field spectrograph (IFS) technology is not selected for such an instrument the ability to fit and remove the speckle noise that remains is crucial to reaching these contrasts. We conclusively demonstrate, though the use of an experimental setup producing an artificial speckle, that slicer based IFSs and post-processing using spectral deconvolution can achieve speckle rejection factors exceeding 103. Contrary to popular belief, we do not find any evidence that this choice of IFS technology limits the achievable contrast. Coupled with extreme adaptive optics and high performance coronographs, a slicer based integral field spectrograph could achieve contrasts exceeding 109, enabling these super-Earths to be detected in the habitable zone of nearby stars, making it an attractive option for the next generation of instruments being designed for the direct detection of extra solar planets.

Salter, Graeme S.; Thatte, Niranjan A.; Tecza, Matthias; Clarke, Fraser; Kasper, Markus E.

2014-04-01

185

Astrometric Detection of Terrestrial Planets in the Habitable Zones of Nearby Stars with SIM PlanetQuest  

E-print Network

SIM PlanetQuest (Space Interferometry Mission) is a space-borne Michelson interferometer for precision stellar astrometry, with a nine meter baseline, currently slated for launch in 2015. One of the principal science goals is the astrometric detection and orbit characterization of terrestrial planets in the habitable zones of nearby stars. Differential astrometry of the target star against a set of reference stars lying within a degree will allow measurement of the target star's reflex motion with astrometric accuracy of 1 micro-arcsecond in a single measurement. We assess SIM's capability for detection (as opposed to characterization by orbit determination) of terrestrial planets in the habitable zones of nearby solar-type stars. We compare SIM's performance on target lists optimized for the SIM and Terrestrial Planet Finder Coronograph (TPF-C) missions. Performance is quantified by three metrics: minimum detectable planet mass, number and mass distribution of detected planets, and completeness of detections in each mass range. Finally, we discuss the issue of confidence in detections and non-detections, and show how information from SIM's planet survey can enable TPF to increase its yield of terrestrial planets.

Joseph Catanzarite; Michael Shao; Angelle Tanner; Stephen Unwin; Jeffrey Yu

2006-05-04

186

Planet Hunters Update: Many New Planet Candidates Identified by Citizen Scientists from Kepler Data, Including Several in the Habitable Zone  

NASA Astrophysics Data System (ADS)

Since December, 2010, more than 250,000 public volunteers have searched through more than 19 million Kepler light curves hunting for transiting planets. The Kepler light curves are shown in 30 day sections, and with ~160,000 Kepler target stars, the users have contributed the equivalent of 180 years of work hours. This vetting process has resulted in over 40 new planet candidates and two new confirmed planets, including several not identified through the Kepler pipeline. Many of our candidate planets lie within their host star's habitable zone. We review the recent large release of new PH candidates in Wang et al. (2013), including one confirmed planet, and give preliminary results for our next PH candidate release.

Schmitt, Joseph; Wang, Ji

2013-07-01

187

The Stability of the Orbits of Earth-mass Planets in and near the Habitable Zones of Known Exoplanetary Systems  

E-print Network

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 93 main-sequence exoplanetary systems confirmed by May 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a third of the 93 systems might be able to have Earth-mass planets in stable, confined orbits somewhere in their HZs. Clearly, these systems should be high on the target list for exploration for terrestrial planets. We have reached this conclusion by launching putative Earth-mass planets in various orbits and following their fate with a mixed-variable symplectic integrator.

Barrie W Jones; David R Underwood; P Nick Sleep

2003-05-27

188

The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)  

NASA Astrophysics Data System (ADS)

We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary circumstellar disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 ?/D IWA or 0.14” with a wavefront control system utilizing a 2000-element MEMS DM and fast steering mirror. EXCEDE will provide 0.12” spatial resolution at 0.4 ?m with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead.

Guyon, Olivier; Schneider, Glenn; Belikov, Ruslan; Tenerelli, Domenick J.

2012-09-01

189

Whitewashed ground or real clouds? Explicit representation of the radiative properties of clouds brings the outer edge of the habitable zone inward and cools the early Earth  

Microsoft Academic Search

Since the work of Kasting (1984) it has been customary to omit clouds from climate models addressing the habitable zone and early Earth climate and to balance the planetary energy budget with a high surface albedo. We compare models with explicit clouds to Kasting's whitewashed surface. We show that the whitewashed surface leads to a systematic bias in the calculated

C. Goldblatt; K. J. Zahnle

2009-01-01

190

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  

Microsoft Academic Search

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

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

2007-01-01

191

Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks  

NASA Astrophysics Data System (ADS)

Context: As accretion in protoplanetary disks is enabled by turbulent viscosity, the border between active and inactive (dead) zones constitutes a location where there is an abrupt change in the accretion flow. The gas accumulation that ensues triggers the Rossby wave instability, which in turn saturates into anticyclonic vortices. It has been suggested that the trapping of solids within them leads to a burst of planet formation on very short timescales. Aims: We study in the formation and evolution of the vortices in greater detail, focusing on the implications for the dynamics of embedded solid particles and planet formation. Methods: We performed two-dimensional global simulations of the dynamics of gas and solids in a non-magnetized thin protoplanetary disk with the Pencil code. We used multiple particle species of radius 1, 10, 30, and 100 cm. We computed the particles' gravitational interaction by a particle-mesh method, translating the particles' number density into surface density and computing the corresponding self-gravitational potential via fast Fourier transforms. The dead zone is modeled as a region of low viscosity. Adiabatic and locally isothermal equations of state are used. Results: The Rossby wave instability is triggered under a variety of conditions, thus making vortex formation a robust process. Inside the vortices, fast accumulation of solids occurs and the particles collapse into objects of planetary mass on timescales as short as five orbits. Because the drag force is size-dependent, aerodynamical sorting ensues within the vortical motion, and the first bound structures formed are composed primarily of similarly-sized particles. In addition to erosion due to ram pressure, we identify gas tides from the massive vortices as a disrupting agent of formed protoplanetary embryos. We find evidence that the backreaction of the drag force from the particles onto the gas modifies the evolution of the Rossby wave instability, with vortices being launched only at later times if this term is excluded from the momentum equation. Even though the gas is not initially gravitationally unstable, the vortices can grow to Q ? 1 in locally isothermal runs, which halts the inverse cascade of energy towards smaller wavenumbers. As a result, vortices in models without self-gravity tend to rapidly merge towards a m = 2 or m =1 mode, while models with self-gravity retain dominant higher order modes (m = 4 or m = 3) for longer times. Non-selfgravitating disks thus show fewer and stronger vortices. We also estimate the collisional velocity history of the particles that compose the most massive embryo by the end of the simulation, finding that the vast majority of them never experienced a collision with another particle at speeds faster than 1 m s-1. This result lends further support to previous studies showing that vortices provide a favorable environment for planet formation.

Lyra, W.; Johansen, A.; Zsom, A.; Klahr, H.; Piskunov, N.

2009-04-01

192

The habitable-zone planet finder: a stabilized fiber-fed NIR spectrograph for the Hobby-Eberly Telescope  

NASA Astrophysics Data System (ADS)

We present the scientific motivation and conceptual design for the recently funded Habitable-zone Planet Finder (HPF), a stabilized fiber-fed near-infrared (NIR) spectrograph for the 10 meter class Hobby-Eberly Telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The HPF will cover the NIR Y and J bands to enable precise radial velocities to be obtained on mid M dwarfs, and enable the detection of low mass planets around these stars. The conceptual design is comprised of a cryostat cooled to 200K, a dual fiber-feed with a science and calibration fiber, a gold coated mosaic echelle grating, and a Teledyne Hawaii-2RG (H2RG) *NIR detector with a 1.7?m cutoff. A uranium-neon hollow-cathode lamp is the baseline wavelength calibration source, and we are actively testing laser frequency combs to enable even higher radial velocity precision. We will present the overall instrument system design and integration with the HET, and discuss major system challenges, key choices, and ongoing research and development projects to mitigate risk. We also discuss the ongoing process of target selection for the HPF survey.

Mahadevan, Suvrath; Ramsey, Lawrence; Bender, Chad; Terrien, Ryan; Wright, Jason T.; Halverson, Sam; Hearty, Fred; Nelson, Matt; Burton, Adam; Redman, Stephen; Osterman, Steven; Diddams, Scott; Kasting, James; Endl, Michael; Deshpande, Rohit

2012-09-01

193

The Habitable-zone Planet Finder (HPF): Achieving high precision radial velocities and mitigating stellar activity noise  

NASA Astrophysics Data System (ADS)

HPF is a stabilized, fiber-fed, near infrared (NIR) spectrograph currently being built at Penn State for the 10m Hobby-Eberly Telescope (HET). HPF will be capable of discovering low mass planets in the Habitable Zones of mid-late M dwarfs via radial velocity (RV). We discuss the development of critical sub-systems like our high-stability temperature control system, vacuum cryostat, and implementation of new wavelength calibration techniques. The design of the HET enables queue-scheduled operation, but its variable pupil requires attention to both near- and far-field fiber scrambling, which we accomplish with double scramblers and octagonal fibers.HPF will provide partial bandwith coverage of the information-rich z, Y and J NIR bands at a spectral resolving power of R˜50,000. While stellar activity induced RV noise is lower in the NIR than at visible wavelengths, we have carefully included NIR activity indicators in our spectral bandpass to help discriminate stellar activity from real planet signals, as has been recently demonstrated for Gliese 581 and Gliese 667C systems.

Mahadevan, Suvrath; Ramsey, Lawrence W.; Terrien, Ryan; Robertson, Paul; Marchwinski, Robert C.; Hearty, Fred; Levi, Eric; Kári Stefánsson, Gudmundur; Bender, Chad F.; Halverson, Samuel; Roy, Arpita; Nelson, Matt; Schwab, Christian

2015-01-01

194

Conditions for Oceans on Earth-like Planets Orbiting within the Habitable Zone: Importance of Volcanic CO2 Degassing  

NASA Astrophysics Data System (ADS)

Earth-like planets in the habitable zone (HZ) have been considered to have warm climates and liquid water on their surfaces if the carbonate-silicate geochemical cycle is working as on Earth. However, it is known that even the present Earth may be globally ice-covered when the rate of CO2 degassing via volcanism becomes low. Here we discuss the climates of Earth-like planets in which the carbonate-silicate geochemical cycle is working, with focusing particularly on insolation and the CO2 degassing rate. The climate of Earth-like planets within the HZ can be classified into three climate modes (hot, warm, and snowball climate modes). We found that the conditions for the existence of liquid water should be largely restricted even when the planet is orbiting within the HZ and the carbonate-silicate geochemical cycle is working. We show that these conditions should depend strongly on the rate of CO2 degassing via volcanism. It is, therefore, suggested that thermal evolution of the planetary interiors will be a controlling factor for Earth-like planets to have liquid water on their surface.

Kadoya, S.; Tajika, E.

2014-08-01

195

The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs  

Microsoft Academic Search

We present radial velocity (RV) measurements of our sample of 40 M dwarfs from our planet search programme with VLT+UVES begun in 2000. Although with our RV precision down to 2-2.5 m\\/s and timebase line of up to 7 years, we are capable of finding planets of a few Earth masses in the close-in habitable zones of M dwarfs, there

M. Zechmeister; M. Kürster; M. Endl

2009-01-01

196

The HARPS search for Earth-like planets in the habitable zone. I. Very low-mass planets around HD 20794, HD 85512, and HD 192310  

Microsoft Academic Search

Context. In 2009 we started an intense radial-velocity monitoring of a few nearby, slowly-rotating and quiet solar-type stars within the dedicated HARPS-Upgrade GTO program. Aims: The goal of this campaign is to gather very-precise radial-velocity data with high cadence and continuity to detect tiny signatures of very-low-mass stars that are potentially present in the habitable zone of their parent stars.

F. Pepe; C. Lovis; D. Ségransan; W. Benz; F. Bouchy; X. Dumusque; M. Mayor; D. Queloz; N. C. Santos; S. Udry

2011-01-01

197

The EXoplanetary Circumstellar Disk Environments and Disk Explorer  

NASA Astrophysics Data System (ADS)

We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary CS disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 lambda/D IWA of 0.14” with a wavefront control system utilizing a 64x64 element MEMS DM and fast steering mirror. EXCEDE will provide 144 mas spatial resolution at 0.4 microns with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead.

Schneider, Glenn; Guyon, O.; Science Mission, EXCEDE; Technology Team

2012-01-01

198

A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS  

SciTech Connect

Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing and Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15{sup +0.13}{sub -0.06} per star for Earth-size planets (0.5-1.4 R{sub Circled-Plus }). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effective temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R{sub Circled-Plus }, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48{sup +0.12}{sub -0.24} and 0.53{sup +0.08}{sub -0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R{sub Circled-Plus }, the frequency increases to 0.51{sup +0.10}{sub -0.20} per star for the conservative estimate and to 0.61{sup +0.07}{sub -0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41{sup +0.54}{sub -0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.

Kopparapu, Ravi Kumar [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States)

2013-04-10

199

PLANET HUNTERS. V. A CONFIRMED JUPITER-SIZE PLANET IN THE HABITABLE ZONE AND 42 PLANET CANDIDATES FROM THE KEPLER ARCHIVE DATA  

SciTech Connect

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R{sub PL} = 10.12 ± 0.56 R{sub ?}) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false-positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least 3 transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between those of Neptune and Jupiter. These detections nearly double the number of gas-giant planet candidates orbiting at habitable-zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.

Wang, Ji; Fischer, Debra A.; Boyajian, Tabetha S.; Schmitt, Joseph R.; Giguere, Matthew J.; Brewer, John M. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Barclay, Thomas [NASA Ames Research Center, M/S 244-30, Moffett Field, CA 94035 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Schwamb, Megan E. [Department of Physics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Lintott, Chris; Simpson, Robert [Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Jek, Kian J.; Hoekstra, Abe J.; Jacobs, Thomas Lee; LaCourse, Daryll; Schwengeler, Hans Martin; Smith, Arfon M.; Parrish, Michael; Lynn, Stuart [Adler Planetarium, 1300 South Lake Shore Drive, Chicago, IL 60605 (United States); Schawinski, Kevin, E-mail: ji.wang@yale.edu [Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich (Switzerland); and others

2013-10-10

200

Planet Hunters. V. A Confirmed Jupiter-size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data  

NASA Astrophysics Data System (ADS)

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R PL = 10.12 ± 0.56 R ?) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false-positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least 3 transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between those of Neptune and Jupiter. These detections nearly double the number of gas-giant planet candidates orbiting at habitable-zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events. .

Wang, Ji; Fischer, Debra A.; Barclay, Thomas; Boyajian, Tabetha S.; Crepp, Justin R.; Schwamb, Megan E.; Lintott, Chris; Jek, Kian J.; Smith, Arfon M.; Parrish, Michael; Schawinski, Kevin; Schmitt, Joseph R.; Giguere, Matthew J.; Brewer, John M.; Lynn, Stuart; Simpson, Robert; Hoekstra, Abe J.; Jacobs, Thomas Lee; LaCourse, Daryll; Schwengeler, Hans Martin; Chopin, Mike; Herszkowicz, Rafal

2013-10-01

201

Atmospheric Chemistry on Planets in the Habitable Zone of F, G, K and M Main Sequence Stars (Invited)  

Microsoft Academic Search

The atmospheric chemistry of a planet is mainly driven by the UV radiation received from its parent star. Given a constant surface production of a biogenic compound (e.g. methane, nitrous oxide) on a planet, the concentration of that compound in the planetary atmosphere will mostly depend on the photochemistry. This is relevant for the characterization of habitable planets using planned

A. Segura; V. S. Meadows; J. F. Kasting; L. Walkowicz; M. Cohen

2009-01-01

202

Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208  

E-print Network

We have undertaken a thorough dynamical investigation of five extrasolar planetary systems using extensive numerical experiments. The systems Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of whether they could host terrestrial like planets in their habitable zones (=HZ). First we investigated the mean motion resonances between fictitious terrestrial planets and the existing gas giants in these five extrasolar systems. Then a fine grid of initial conditions for a potential terrestrial planet within the HZ was chosen for each system, from which the stability of orbits was then assessed by direct integrations over a time interval of 1 million years. The computations were carried out using a Lie-series integration method with an adaptive step size control. This integration method achieves machine precision accuracy in a highly efficient and robust way, requiring no special adjustments when the orbits have large eccentricities. The stability of orbits was examined with a determination of the Renyi entropy, estimated from recurrence plots, and with a more straight forward method based on the maximum eccentricity achieved by the planet over the 1 million year integration. Additionally, the eccentricity is an indication of the habitability of a terrestrial planet in the HZ; any value of e>0.2 produces a significant temperature difference on a planet's surface between apoapse and periapse. The results for possible stable orbits for terrestrial planets in habitable zones for the five systems are summarized as follows: for Gl 777 A nearly the entire HZ is stable, for 47 Uma, HD 72659 and HD 4208 terrestrial planets can survive for a sufficiently long time, while for Gl 614 our results exclude terrestrial planets moving in stable orbits within the HZ.

N. Asghari; C. Broeg; L. Carone; R. Casas-Miranda; J. C. Castro Palacio; I. Csillik; R. Dvorak; F. Freistetter; G. Hadjivantsides; H. Hussmann; A. Khramova; M. Khristoforova; I. Khromova; I. Kitiashivilli; S. Kozlowski; T. Laakso; T. Laczkowski; D. Lytvinenko; O. Miloni; R. Morishima; A. Moro-Martin; V. Paksyutov; A. Pal; V. Patidar; B. Pecnik; O. Peles; J. Pyo; T. Quinn; A. Rodriguez; C. Romano; E. Saikia; J. Stadel; M. Thiel; N. Todorovic; D. Veras; E. Vieira Neto; J. Vilagi; W. von Bloh; R. Zechner; E. Zhuchkova

2004-03-05

203

The habitable zone of Earth-mass planets around 47 UMa: results for land and water worlds  

Microsoft Academic Search

In a previous paper, we showed that Earth-type habitable planets around 47 UMa are in principle possible if a distinct set of conditions is warranted. These conditions include that the Earth-type planets have successfully formed and are orbitally stable and, in addition, that the 47 UMa star-planet system is relatively young ([less, similar]6 Gyr). We now extend this study by

S. Franck; M. Cuntz; W. von Bloh; C. Bounama

2003-01-01

204

Formation, habitability, and detection of extrasolar moons.  

PubMed

The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1-0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology. PMID:25147963

Heller, René; Williams, Darren; Kipping, David; Limbach, Mary Anne; Turner, Edwin; Greenberg, Richard; Sasaki, Takanori; Bolmont, Emeline; Grasset, Olivier; Lewis, Karen; Barnes, Rory; Zuluaga, Jorge I

2014-09-01

205

Formation, Habitability, and Detection of Extrasolar Moons  

NASA Astrophysics Data System (ADS)

The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1-0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology.

Heller, René; Williams, Darren; Kipping, David; Limbach, Mary Anne; Turner, Edwin; Greenberg, Richard; Sasaki, Takanori; Bolmont, Émeline; Grasset, Olivier; Lewis, Karen; Barnes, Rory; Zuluaga, Jorge I.

2014-09-01

206

THE LICK-CARNEGIE EXOPLANET SURVEY: A 3.1 M{sub +} PLANET IN THE HABITABLE ZONE OF THE NEARBY M3V STAR GLIESE 581  

SciTech Connect

We present 11 years of HIRES precision radial velocities (RVs) of the nearby M3V star Gliese 581, combining our data set of 122 precision RVs with an existing published 4.3-year set of 119 HARPS precision RVs. The velocity set now indicates six companions in Keplerian motion around this star. Differential photometry indicates a likely stellar rotation period of {approx}94 days and reveals no significant periodic variability at any of the Keplerian periods, supporting planetary orbital motion as the cause of all the RV variations. The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and 67-day planets previously announced by Bonfils et al., Udry et al., and Mayor et al.. The observations also indicate a fifth planet in the system, GJ 581f, a minimum-mass 7.0 M{sub +} planet orbiting in a 0.758 AU orbit of period 433 days, and a sixth planet, GJ 581g, a minimum-mass 3.1 M{sub +} planet orbiting at 0.146 AU with a period of 36.6 days. The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star. That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of precision RV surveys, indicates that {eta}{sub +}, the fraction of stars with potentially habitable planets, is likely to be substantial. This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume-limited samples of stars in the immediate solar neighborhood, suggests that {eta}{sub +} could well be on the order of a few tens of percent. If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets.

Vogt, Steven S.; Rivera, E. J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Butler, R. Paul [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States); Haghighipour, N. [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Henry, Gregory W.; Williamson, Michael H. [Tennessee State University, Center of Excellence in Information Systems, 3500 John A. Merritt Blvd., Box 9501, Nashville, TN 37209-1561 (United States)

2010-11-01

207

Comets and circumstellar dust  

Microsoft Academic Search

Since comets are pristine solar-system objects, they must abound in the circumstellar disks which surround young stellar objects. Infrared spectroscopy is by excellence the tool to explore the composition of these disks, and the field has received a substantial boost from the possibilities offered by the Infrared Space Observatory ISO. We present ISO results for the circumstellar disks of several

C. Waelkens; L. B. F. M. Waters; Anton Pannekoek

2000-01-01

208

Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.  

PubMed

M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 ?m, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought. PMID:22181553

Joshi, Manoj M; Haberle, Robert M

2012-01-01

209

Searching for HabitableSearching for Habitable Worlds and Life in theWorlds and Life in the  

E-print Network

Earth #12;What makes planets habitable ? The planet must be in the habitable zone of its star need to take spectra of habitable planets Spectra of Earth (taken by looking at Earthshine) shows1 Searching for HabitableSearching for Habitable Worlds and Life in theWorlds and Life

Guyon, Olivier

210

A Joint Approach to the Study of S-Type and P-Type Habitable Zones in Binary Systems: New Results in the View of 3-D Planetary Climate Models  

NASA Astrophysics Data System (ADS)

In two previous papers, given by Cuntz (2014a,b) [ApJ 780, A14 (19 pages); arXiv:1409.3796], a comprehensive approach has been provided for the study of S-type and P-type habitable zones in stellar binary systems, P-type orbits occur when the planet orbits both binary components, whereas in case of S-type orbits, the planet orbits only one of the binary components with the second component considered a perturbator. The selected approach considers a variety of aspects, including (1) the consideration of a joint constraint including orbital stability and a habitable region for a possible system planet through the stellar radiative energy fluxes; (2) the treatment of conservative (CHZ), general (GHZ) and extended zones of habitability (EHZ) [see Paper I for definitions] for the systems as previously defined for the Solar System; (3) the provision of a combined formalism for the assessment of both S-type and P-type habitability; in particular, mathematical criteria are devised for which kind of system S-type and P-type habitability is realized; and (4) the applications of the theoretical approach to systems with the stars in different kinds of orbits, including elliptical orbits (the most expected case). Particularly, an algebraic formalism for the assessment of both S-type and P-type habitability is given based on a higher-order polynomial expression. Thus, an a prior specification for the presence or absence of S-type or P-type radiative habitable zones is - from a mathematical point of view - neither necessary nor possible, as those are determined by the adopted formalism. Previously, numerous applications of the method have been given encompassing theoretical star-panet systems and and observations. Most recently, this method has been upgraded to include recent studies of 3-D planetary climate models. Originally, this type of work affects the extent and position of habitable zones around single stars; however, it has also profound consequence for the habitable regions in binary systems (both S-type and P-type), the topic of the intended presentation.

Cuntz, Manfred

2015-01-01

211

A rapid method for investigating the confinement in habitable zones of Earth-mass planets in exoplanetary systems  

Microsoft Academic Search

We have carried out lengthy investigations of seven exoplanetary systems, to obtain an estimate of the distance D from the giant planet in each system within which orbital stability is unlikely for a planet of order of Earth mass (EMP). Distances less than D define the disaster zone. For orbits interior (alternatively exterior) to the giant orbit, D is measured

B. W. Jones; D. R. Underwood; P. N. Sleep

2005-01-01

212

Quantitative habitability.  

PubMed

A framework is proposed for a quantitative approach to studying habitability. Considerations of environmental supply and organismal demand of energy lead to the conclusions that power units are most appropriate and that the units for habitability become watts per organism. Extreme and plush environments are revealed to be on a habitability continuum, and extreme environments can be quantified as those where power supply only barely exceeds demand. Strategies for laboratory and field experiments are outlined that would quantify power supplies, power demands, and habitability. An example involving a comparison of various metabolisms pursued by halophiles is shown to be well on the way to a quantitative habitability analysis. PMID:18163866

Shock, Everett L; Holland, Melanie E

2007-12-01

213

What makes a planet habitable ?  

E-print Network

edge of the habitable zone, probably with a Venus-like greenhouse effect. 581 d is a super-Earth (~10 decades, we will finally be able to probe for life on exoplanets not too different from Earth #12;What makes a planet habitable ? #12;#12;How to detect planets ? #12;Radial velocity #12;Transits

Guyon, Olivier

214

EXOPLANET CHARACTERIZATION BY PROXY: A TRANSITING 2.15 R{sub Circled-Plus} PLANET NEAR THE HABITABLE ZONE OF THE LATE K DWARF KEPLER-61  

SciTech Connect

We present the validation and characterization of Kepler-61b: a 2.15 R{sub Circled-Plus} planet orbiting near the inner edge of the habitable zone of a low-mass star. Our characterization of the host star Kepler-61 is based upon a comparison with a set of spectroscopically similar stars with directly measured radii and temperatures. We apply a stellar prior drawn from the weighted mean of these properties, in tandem with the Kepler photometry, to infer a planetary radius for Kepler-61b of 2.15 {+-} 0.13 R{sub Circled-Plus} and an equilibrium temperature of 273 {+-} 13 K (given its period of 59.87756 {+-} 0.00020 days and assuming a planetary albedo of 0.3). The technique of leveraging the physical properties of nearby ''proxy'' stars allows for an independent check on stellar characterization via the traditional measurements with stellar spectra and evolutionary models. In this case, such a check had implications for the putative habitability of Kepler-61b: the planet is 10% warmer and larger than inferred from K-band spectral characterization. From the Kepler photometry, we estimate a stellar rotation period of 36 days, which implies a stellar age of >1 Gyr. We summarize the evidence for the planetary nature of the Kepler-61 transit signal, which we conclude is 30,000 times more likely to be due to a planet than a blend scenario. Finally, we discuss possible compositions for Kepler-61b with a comparison to theoretical models as well as to known exoplanets with similar radii and dynamically measured masses.

Ballard, Sarah; Charbonneau, David; Fressin, Francois; Torres, Guillermo; Irwin, Jonathan; Newton, Elisabeth [University of Washington, Seattle, WA 98195 (United States); Desert, Jean-Michel; Crepp, Justin R.; Shporer, Avi [California Institute of Technology, Pasadena, CA 91125 (United States); Mann, Andrew W. [Institute for Astronomy, University of Hawai'i, Honolulu, HI 96822 (United States); Ciardi, David R. [NASA Exoplanet Science Institute/Caltech, Pasadena, CA 91125 (United States); Henze, Christopher E.; Bryson, Stephen T.; Howell, Steven B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Horch, Elliott P. [Southern Connecticut State University, New Haven, CT 06515 (United States); Everett, Mark E., E-mail: sarahba@uw.edu [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)

2013-08-20

215

Dynamical Habitability of Known Extrasolar Planetary Systems  

Microsoft Academic Search

Habitability is usually defined as the requirement for a terrestrial planet's atmosphere to sustain liquid water. This definition can be complemented by the dynamical requirement that other planets in the system do not gravitationally perturb terrestrial planets outside of their habitable zone, the orbital region allowing the existence of liquid water. We quantify the dynamical habitability of 85 known extrasolar

Kristen Menou; Serge Tabachnik

2003-01-01

216

Exomoon habitability and tidal evolution in low-mass star systems  

NASA Astrophysics Data System (ADS)

Current technology and theoretical methods are allowing for the detection of sub-Earth sized extrasolar planets. In addition, the detection of massive moons orbiting extrasolar planets ("exomoons'') has become feasible and searches are currently underway. Several extrasolar planets have now been discovered in the habitable zone (HZ) of their parent star. This naturally leads to questions about the habitability of moons around planets in the HZ. Red dwarf stars present interesting targets for habitable planet detection. Compared to the Sun, red dwarfs are smaller, fainter, lower mass, and much more numerous. Due to their low luminosities, the HZ is much closer to the star than for Sun-like stars. For a planet-moon binary in the HZ, the close proximity of the star presents dynamical restrictions on the stability of the moon, forcing it to orbit close to the planet to remain gravitationally bound. Under these conditions the effects of tidal heating, distortion torques, and stellar perturbations become important considerations to the habitability of an exomoon. Utilizing an evolution model that considers both dynamical and tidal interactions, I performed a computational investigation into long-term evolution of exomoon systems. My study focused on satellite systems in the HZ of red dwarf stars and the dependence of exomoon habitability on the mass of the central star. Results show that dwarf stars with masses less than about 0.2 solar masses cannot host habitable exomoons within the stellar HZ due to extreme tidal heating in the moon. These results suggest that a host planet could be located outside the stellar HZ to where higher tidal heating rates could act to promote habitability for an otherwise uninhabitable moon. Perturbations from a central star may continue to have deleterious effects in the HZ up to about 0.5 solar masses, depending on the host planet's mass and its location in the HZ. In cases with lower intensity tidal heating, stellar perturbations may have a positive influence on exomoon habitability by promoting long-term heating rates above a minimum for habitable terrestrial environments. In addition to heating concerns, torques due to tidal and spin distortion can lead to the relatively rapid inward spiraling of a moon. The effects of torque and stability constraints also make it unlikely that long-term resonances between two massive moons will develop in the HZs around red dwarf stars. My study showed that moons in the circumstellar HZ are not necessarily habitable by definition. In addition, the HZ for an exomoon may extend beyond the HZ for an exoplanet. Therefore, an extended model is required when considering exomoon habitability in comparison to exoplanet habitability.

Zollinger, Rhett R.

217

THE LICK-CARNEGIE EXOPLANET SURVEY: A SATURN-MASS PLANET IN THE HABITABLE ZONE OF THE NEARBY M4V STAR HIP 57050  

SciTech Connect

Precision radial velocities (RV) from Keck/HIRES reveal a Saturn-mass planet orbiting the nearby M4V star HIP 57050. The planet has a minimum mass of Msin i {approx} 0.3 M{sub J}, an orbital period of 41.4 days, and an orbital eccentricity of 0.31. V-band photometry reveals a clear stellar rotation signature of the host star with a period of 98 days, well separated from the period of the RV variations and reinforcing a Keplerian origin for the observed velocity variations. The orbital period of this planet corresponds to an orbit in the habitable zone of HIP 57050, with an expected planetary temperature of {approx}230 K. The star has a metallicity of [Fe/H] = 0.32 {+-} 0.06 dex, of order twice solar and among the highest metallicity stars in the immediate solar neighborhood. This newly discovered planet provides further support that the well-known planet-metallicity correlation for F, G, and K stars also extends down into the M-dwarf regime. The a priori geometric probability for transits of this planet is only about 1%. However, the expected eclipse depth is {approx}7%, considerably larger than that yet observed for any transiting planet. Though long on the odds, such a transit is worth pursuing as it would allow for high quality studies of the atmosphere via transmission spectroscopy with Hubble Space Telescope. At the expected planetary effective temperature, the atmosphere may contain water clouds.

Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Vogt, Steven S.; Rivera, Eugenio J.; Laughlin, Greg; Meschiari, Stefano [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Paul Butler, R. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, Washington, DC 20015 (United States); Henry, Gregory W. [Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209 (United States)

2010-05-20

218

Loss of nebula-captured hydrogen envelopes from 'sub'- to 'super-Earths' in the habitable zone of Sun-like stars  

NASA Astrophysics Data System (ADS)

We investigate the escape of captured hydrogen envelopes from protoplanets having masses in a range between `sub-Earth'-like bodies of 0.1 Earth-mass and `super-Earths' with a mass of 5 Earth-masses in the habitable zone at 1 AU of a Sun like G star, assuming that their rocky cores had formed before the nebula gas dissipated. For studying the escape of these accumulated hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high soft-X-ray and extreme ultraviolet (XUV) flux of the young Sun/star. The results of our study indicate that under most nebula conditions `sub-Earth' and Earth-mass planets can lose their captured hydrogen envelopes by thermal escape during the first 100 Myr after the disk dissipated. Depending on nebula properties and protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, more massive `super-Earths' that can accumulate a huge amount of nebula gas, lose only tiny fractions of their primordial hydrogen envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density `super-Earths' that most likely could not get rid of their dense protoatmospheres.

Lammer, Helmut; Erkaev, Nikolai V.; Odert, Petra; Kulikov, Yuri N.; Kislyakova, Kristina G.; Stoekl, Alexander; Dorfi, Ernst A.; Guedel, Manuel; Leitzinger, Martin

2014-05-01

219

CHARACTERIZING HABITABLE EXOMOONS  

SciTech Connect

We discuss the possibility of screening the atmosphere of exomoons for habitability. We concentrate on Earth-like satellites of extrasolar giant planets (EGPs) that orbit in the Habitable Zone (HZ) of their host stars. The detectability of exomoons for EGPs in the HZ has recently been shown to be feasible with the Kepler Mission or equivalent photometry using transit duration observations. Transmission spectroscopy of exomoons is a unique potential tool to screen them for habitability in the near future, especially around low mass stars. Using the Earth itself as a proxy we show the potential and limits of spectroscopy to detect biomarkers on an Earth-like exomoon and discuss effects of tidal locking for such potential habitats.

Kaltenegger, L. [Harvard University, 60 Garden Street, 02138 MA, Cambridge (United States)], E-mail: lkaltene@cfa.harvard.edu

2010-04-01

220

Habitable Trinity  

NASA Astrophysics Data System (ADS)

We propose a new concept of a habitable environment in the search for life beyond Earth that goes beyond the follow-the-water paradigm, newly named Habitable Trinity. Habitable Trinity is the coexistence of an atmosphere (consisting largely of C and N), an ocean (H and O), and a landmass (supplier of nutrients). It is the minimum requirement for the beginning of life to satisfy (1) formation of membrane, (2) metabolism, and (3) self-replication as we know it. A habitable planet, which has largely been defined as having an adequate climate, a sufficient atmosphere, and the presence of liquid water on its surface, is insufficient to meet the requirements to bear life. Also, material circulation driven by the Sun must be maintained with Habitable Trinity to continue the supply of elements necessary to sustain organic radical reactions that is the basis of life. The Sun is the major engine that links the three components primarily through hydrological cycling, including weathering, erosion, and transport of nutrient-enriched landmass materials to the ocean via far-reaching river systems. Habitable Trinity can be applied to other planets and moons to discuss the presence of extraterrestrial life. Mars is considered to be the best target to test the hypothesis of whether life exists elsewhere in our solar system, as it records an ancient Habitable Trinity (i.e., lakes and oceans which interacted with a landmass (cratered southern highlands) and an atmosphere). Other terrestrial planets, as well as satellites of the gaseous giants such as Europa and Titan, have little chance to harbor life as we know it because they lack Habitable Trinity. Going beyond 'the-follow-the-water-approach', the Habitable-Trinity concept provides an index in the quest for life-containing planetary bodies beyond our solar system as the reconnaissance systems become increasingly autonomous and at higher resolution, affording greater perspective during this golden age of international and interdisciplinary exploration and discovery.

Dohm, J. M.; Maruyama, S.

2013-12-01

221

Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR  

SciTech Connect

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 {+-} 0.060 M{sub Sun} and 0.979 {+-} 0.020 R{sub Sun }. The depth of 492 {+-} 10 ppm for the three observed transits yields a radius of 2.38 {+-} 0.13 Re for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities (RVs) obtained with the High Resolution Echelle Spectrometer on Keck I over a one-year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3{sigma} upper limit of 124 M{sub Circled-Plus }, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other than the Sun.

Borucki, William J.; Koch, David G.; Bryson, Stephen T.; Howell, Steve B.; Lissauer, Jack J. [NASA-Ames Research Center, Moffett Field, CA 94035-0001 (United States); Batalha, Natalie [Department of Physics and Astronomy, San Jose State University, San Jose, CA, 95192 (United States); Rowe, Jason; Caldwell, Douglas A.; DeVore, Edna; Jenkins, Jon M. [SETI Institute, Mountain View, CA 94043 (United States); Fressin, Francois; Torres, Guillermo; Geary, John C.; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Christensen-Dalsgaard, Jorgen [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Cochran, William D. [McDonald Observatory, University of Texas at Austin, Austin, TX 78712 (United States); Gautier, Thomas N. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA, 91109 (United States); Gilliland, Ronald [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Gould, Alan [Lawrence Hall of Science, University of California, Berkeley, CA 94720 (United States); Marcy, Geoffrey W., E-mail: William.J.Borucki@nasa.gov [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); and others

2012-02-01

222

A PLANETARY SYSTEM AROUND THE NEARBY M DWARF GJ 667C WITH AT LEAST ONE SUPER-EARTH IN ITS HABITABLE ZONE  

SciTech Connect

We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the European Southern Observatory public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/Planet Finder Spectrograph and Keck/High Resolution Echelle Spectrometer spectrometers reveals three additional signals beyond the previously reported 7.2 day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (period {approx}10 years). The 28 day signal implies a planet candidate with a minimum mass of 4.5 M{sub Circled-Plus} orbiting well within the canonical definition of the star's liquid water habitable zone (HZ), that is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition, and interior dynamics. The 75 day signal is less certain, being significantly affected by aliasing interactions among a potential 91 day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal-poor compared to the Sun. The presence of a super-Earth in the HZ of a metal-poor M dwarf in a triple star system supports the evidence that such worlds should be ubiquitous in the Galaxy.

Anglada-Escude, Guillem; Butler, R. Paul [Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Rd. NW, Washington, DC 20015 (United States); Arriagada, Pamela; Minniti, Dante [Department of Astronomy, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Vogt, Steven S.; Rivera, Eugenio J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B. [Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101-1292 (United States); Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Monoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Carter, Brad D. [Faculty of Sciences, University of Southern Queensland, Toowoomba 4350 (Australia); Tinney, C. G.; Wittenmyer, Robert A.; Bailey, Jeremy A. [Department of Astrophysics, School of Physics, University of New South Wales, Sydney 2052 (Australia); O'Toole, Simon J. [Australian Astronomical Observatory, P.O. Box 296, Epping 1710 (Australia); Jones, Hugh R. A. [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts, AL10 9AB (United Kingdom); Jenkins, James S., E-mail: anglada@dtm.ciw.edu [Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile)

2012-05-20

223

Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars  

PubMed Central

The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet’s atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, “Dune” planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, Seff, the recently recalculated HZ boundaries are: recent Venus—1.78; runaway greenhouse—1.04; moist greenhouse—1.01; maximum greenhouse—0.35; and early Mars—0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4–0.5. PMID:24277805

Kasting, James F.; Kopparapu, Ravikumar; Ramirez, Ramses M.; Harman, Chester E.

2014-01-01

224

Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars.  

PubMed

The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, "Dune" planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, S(eff), the recently recalculated HZ boundaries are: recent Venus--1.78; runaway greenhouse--1.04; moist greenhouse--1.01; maximum greenhouse--0.35; and early Mars--0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4-0.5. PMID:24277805

Kasting, James F; Kopparapu, Ravikumar; Ramirez, Ramses M; Harman, Chester E

2014-09-01

225

Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars  

NASA Astrophysics Data System (ADS)

The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. Historically, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, 'Dune' planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, Seff, the recently recalculated HZ boundaries are: recent Venus-1.78, runaway greenhouse-1.04, moist greenhouse-1.01, maximum greenhouse-0.35, early Mars-0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late-K and M stars observed by Kepler is in the range of 0.4-0.5.

Kasting, J. F.; Kopparapu, R.; Ramirez, R. M.; Harman, C. E.

2014-09-01

226

The structure of circumstellar shells  

NASA Technical Reports Server (NTRS)

This document provides a report on research activities carried out with the support of NASA grant NAG 5-1174, the Structure of Circumstellar Shells, funded under the Astrophysics Data Program. The research carried out with the support of this grant is a study of the properties of circumstellar dust shells for which spectra are available through IRAS low resolution spectrometry (LRS). This research consisted of the development and application of models of axisymmetric circumstellar shells and a preliminary survey of the applicability of neural nets for analysis of the IRAS LRS spectra of circumstellar dust shells.

Fix, John D.

1993-01-01

227

Exoplanet Habitability: Effects of Planetesimal Carbon Chemistry  

NASA Astrophysics Data System (ADS)

We explore the effects of reported differences in C/O values for exoplanet host stars on the composition of planetesimals formed beyond the snow line in these systems. Since the value of C/O in a planet forming nebula has a strong effect on amount of oxygen available for water ice in an oxidizing nebula, exoplanet systems for host stars with C/O greater than the solar value may have planetesimals with very little or no water ice. We have estimated the composition of volatile and refractory material in extrasolar planetesimals using a set of stars with a wide range of measured C/O abundances (Johnson et al. ApJ. 757(2), 192, 2012). The volatile ice content of planetesimals in these systems varies significantly with C/O, controlled primarily by the availability of O for H2O ice condensation. Systems with C/O less than the solar value (C/O = 0.55) should have very water ice rich planetesimals, while water ice mass fraction decreases rapidly with increasing C/O until only ices of CO and CO2 are left in significant proportions. If a significant fraction of C is in the form of refractory CHON particles, C and O are removed from the gas phase and the condensates for super-solar C/O values will be water-poor mixtures of silicates and metal, carbon, and carbon-bearing volatile ices, depending on temperature. For very carbon-rich systems, oxidizing conditions cannot be sustained beyond about C/O=1, due to the oxygen sequestered in solid silicates, oxides and CHON, for refractory C fractions within the Pollack et al. range of 0.4 - 0.7 (ApJ. 421, 615, 1994). These results have implications for assessing the habitability of exoplanets since they constrain the amount of water available beyond the snow line for dynamical delivery to inner planets, depending on the host star's C/O in the circumstellar nebula. Thus one the key chemical ingredients for habitability may be in short supply in carbon-rich, oxygen-poor systems even if planets exist in the 'habitable zone'. TVJ acknowledges government support at JPL/Caltech, under a contract with NASA. NM acknowledges support from Yale University. JIL was supported by the JWST Project through NASA. O.M. acknowledges support from CNES.

Johnson, Torrence; Mousis, Olivier; Lunine, Jonathan; Madhusudhan, Nikku

2014-05-01

228

Origin and loss of nebula-captured hydrogen envelopes from `sub'- to `super-Earths' in the habitable zone of Sun-like stars  

NASA Astrophysics Data System (ADS)

We investigate the origin and loss of captured hydrogen envelopes from protoplanets having masses in a range between `sub-Earth'-like bodies of 0.1 M? and `super-Earths' with 5 M? in the habitable zone at 1 au of a Sun-like G star, assuming that their rocky cores had formed before the nebula gas dissipated. We model the gravitational attraction and accumulation of nebula gas around a planet's core as a function of protoplanetary luminosity during accretion and calculate the resulting surface temperature by solving the hydrostatic structure equations for the protoplanetary nebula. Depending on nebular properties, such as the dust grain depletion factor, planetesimal accretion rates, and resulting luminosities, for planetary bodies of 0.1-1 M? we obtain hydrogen envelopes with masses between ˜2.5 × 1019 and 1.5 × 1026 g. For `super-Earths' with masses between 2 and 5 M? more massive hydrogen envelopes within the mass range of ˜7.5 × 1023-1.5 × 1028 g can be captured from the nebula. For studying the escape of these accumulated hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high soft-X-ray and extreme ultraviolet (XUV) flux of the young Sun/star. The results of our study indicate that under most nebula conditions `sub-Earth' and Earth-mass planets can lose their captured hydrogen envelopes by thermal escape during the first ˜100 Myr after the disc dissipated. However, if a nebula has a low dust depletion factor or low accretion rates resulting in low protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, more massive `super-Earths', which can accumulate a huge amount of nebula gas, lose only tiny fractions of their primordial hydrogen envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density `super-Earths' that most likely could not get rid of their dense protoatmospheres.

Lammer, H.; Stökl, A.; Erkaev, N. V.; Dorfi, E. A.; Odert, P.; Güdel, M.; Kulikov, Yu. N.; Kislyakova, K. G.; Leitzinger, M.

2014-04-01

229

Habitable exoplanets statistics in the Milky Way  

NASA Astrophysics Data System (ADS)

We present an exoplanet statistical analysis into the Milky Way. We use the Becanson galactic synthetic model to simulate the Milky Way and the galactic and stellar habitable zones to calculate habitable planets. To assess habitability on the Galactic scale, we model supernova rates and planet formation. Our study, models the SNII and SNIa sterilizations by selecting them from within this preexisting stellar population. Furthermore, we consider habitability on tidally locked and non-tidally locked planets separately, and study habitability as a function of height above and below the Galactic mid-plane. The number of total habitable planets makes Milky Way practically empty of habitable planets. Our results, from these simulations, agree very well with Kepler's discoveries. Finally, we apply our results to the PLATO future space mission.

Anagnos, Th.

2013-09-01

230

UV Habitability of Possible Exomoons in Observed F-star Planetary Systems  

E-print Network

In the present study we explore the astrobiological significance of F-type stars of spectral type between F5 V and F9.5 V, which possess Jupiter-type planets within or close to their climatological habitable zones. These planets, or at least a subset of them, may also possess rocky exomoons, which potentially offer habitable environments. Our work considers eight selected systems. The Jupiter-type planets in these systems are in notably different orbits with eccentricities ranging from 0.08 to 0.72. Particularly, we consider the stellar UV environments provided by the photospheric stellar radiation in regard to the circumstellar habitability of the system. According to previous studies, DNA is taken as a proxy for carbon-based macromolecules following the paradigm that extraterrestrial biology might be based on hydrocarbons. Thus, the DNA action spectrum is utilized to represent the impact of the stellar UV radiation. Atmospheric attenuation is taken into account based on parameterized attenuation functions. ...

Sato, Satoko

2015-01-01

231

Lifestyle Habits  

PubMed Central

Objectives: This study aimed to investigate the lifestyle habits—physical activity (PA), eating habits (EH), and sleep duration (SD)—of Omani adolescents, and to examine gender differences in such variables. Methods: 802 Omani adolescents (442 females and 360 males), aged 15–18 years were randomly recruited. Anthropometric indices, PA level, and EH and SD were evaluated by the Arab Teenage Lifestyle questionnaire. A semi-quantitative food frequency questionnaire for dietary assessment was also administered. Results: The results showed that although the study subjects had a sedentary lifestyle (lack of PA, average of 6.7 hours sleep, and consumption of high calorie foods), they maintained a normal body mass (less than 25 Kg/m2). Males were more than twice as active as females. With respect to EH, there were few gender differences, except in dairy and meat consumption where 62.5% and 55.5% of males consumed more than 3 servings, respectively, compared to 18.78 % and 35.2% of females, respectively. In addition, waist/height ratio, height, reasons for being active, energy drinks, potato consumption, eating sweets, vigorous PA and breakfast EHs were statistically significant independent predictors for BMI, P <0.05 for both males and females. Conclusion: This study revealed a high prevalence of sedentary behaviors and a low level of physical activity, especially among females. Unhealthy dietary habits were also widely found among both genders. There is an urgent need for more research as well as a national policy promoting active living and healthy eating and discouraging sedentary behaviour among Omani adolescents. PMID:24273660

Kilani, Hashem; Al-Hazzaa, Hazzaa; Waly, Mostafa I.; Musaiger, Abdulrahman

2013-01-01

232

Exoplanet habitability.  

PubMed

The search for exoplanets includes the promise to eventually find and identify habitable worlds. The thousands of known exoplanets and planet candidates are extremely diverse in terms of their masses or sizes, orbits, and host star type. The diversity extends to new kinds of planets, which are very common yet have no solar system counterparts. Even with the requirement that a planet's surface temperature must be compatible with liquid water (because all life on Earth requires liquid water), a new emerging view is that planets very different from Earth may have the right conditions for life. The broadened possibilities will increase the future chances of discovering an inhabited world. PMID:23641111

Seager, Sara

2013-05-01

233

The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs  

Microsoft Academic Search

We present radial velocity (RV) measurements of our sample of 40 M dwarfs\\u000afrom our planet search programme with VLT+UVES begun in 2000. Although with our\\u000aRV precision down to 2 - 2.5 m\\/s and timebase line of up to 7 years, we are\\u000acapable of finding planets of a few Earth masses in the close-in habitable\\u000azones of M

M. Zechmeister; M. Kürster; M. Endl

2009-01-01

234

Dynamics and stability of telluric planets within the habitable zone of extrasolar planetary systems. Numerical simulations of test particles within the HD 4208 and HD 70642 systems  

Microsoft Academic Search

Aims: We study gravitational perturbation effects of observed giant extrasolar planets on hypothetical Earth-like planets in the context of the three-body problem. This paper considers a large parameter survey of different orbital configuration of two extrasolar giant planets (HD 70642b and HD 4208b) and compares their dynamical effect on Earth-mass planetary orbits initially located within the respective habitable terrestrial region.

T. C. Hinse; R. Michelsen; U. G. Jørgensen; K. Gozdziewski; S. Mikkola

2008-01-01

235

Tides and the Evolution of Planetary Habitability  

E-print Network

Tides raised on a planet by its host star's gravity can reduce a planet's orbital semi-major axis and eccentricity. This effect is only relevant for planets orbiting very close to their host stars. The habitable zones of low-mass stars are also close-in and tides can alter the orbits of planets in these locations. We calculate the tidal evolution of hypothetical terrestrial planets around low-mass stars and show that tides can evolve planets past the inner edge of the habitable zone, sometimes in less than 1 billion years. This migration requires large eccentricities (>0.5) and low-mass stars (<0.35 M_Sun). Such migration may have important implications for the evolution of the atmosphere, internal heating and the Gaia hypothesis. Similarly, a planet detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently-discovered, ~5 M_Earth planet, Gliese 581 c. We find that it could have been habitable for reasonable choices of orbital and physical properties as recently as 2 Gyr ago. However, when we include constraints derived from the additional companions, we see that most parameter choices that predict past habitability require the two inner planets of the system to have crossed their mutual 3:1 mean motion resonance. As this crossing would likely have resulted in resonance capture, which is not observed, we conclude that Gl 581 c was probably never habitable.

Rory Barnes; Sean N. Raymond; Brian Jackson; Richard Greenberg

2008-07-04

236

Atmospheric escape, redox evolution, and planetary habitability  

NASA Astrophysics Data System (ADS)

Through the greenhouse effect, the presence and composition of an atmosphere is critical for defining a (conventional) circumstellar habitable zone in terms of planetary surface temperatures suitable for liquid water. Lack of knowledge of planetary atmospheres is likely to frustrate attempts to say with any certainty whether detected terrestrial-sized exoplanets may or may not be habitable. Perhaps an underappreciated role in such considerations is the evolutionary effect of atmospheric escape for determining atmospheric composition or whether an atmosphere exists in the first place. Whether atmospheres exist at all on planets is demonstrably connected to the effect of integrated atmospheric escape. When we observe our own Solar System and transiting exoplanets, the existence of an atmosphere is clearly delineated by a relative vulnerability to thermal escape and impact erosion. The prevalence of thermal escape as a key evolutionary determinant for the presence of planetary atmosphere is shown by a relationship between the relative solar (or stellar) heating and the escape velocity. Those bodies with too much stellar heating and too smaller escape velocity end up devoid of atmospheres. Impact erosion is evident in the relationship between impact velocity and escape velocity. Escape due to impacts is particularly important for understanding the large differences in the atmospheres of giant planet moons, such as Ganymede versus Titan. It is also significant for Mars-sized planets. The oxidation state of atmospheres is important for some theories of the origin of life (where an early reducing atmosphere is helpful for organic synthesis) and the evolution of advanced life (where free molecular oxygen is the best source of high energy metabolism). Surfaces on some relatively small planets and moons are observed to have evolved to an oxidized state, which theory and observation can explain through atmospheric escape. There are several examples in the Solar System where a net escape of hydrogen relative to heavier oxygen is the generally accepted explanation for the present oxidation state: Venus and Mars amongst the planets, and Ganymede, Europa, and Rhea amongst bodies with extremely tenuous atmospheres. We also argue that hydrogen escape was the key factor for oxidizing the Earth and facilitating the increase of photosynthetically-produced oxygen in the Proterozoic atmosphere. Our view about the primacy of hydrogen escape with regard to the Earth's atmospheric oxygenation is perhaps less widely accepted. However, it was inevitable that hydrogen escaped from Earth's early anoxic atmosphere at a significant rate. The result was a very big integrated oxidation consistent with what is observed in the Earth's crust in addition to some export to the mantle. In conclusion, a better understanding of atmospheric escape processes appears critical for understanding the suitability of planets for harboring life from simple to advanced forms.

Catling, D. C.; Zahnle, K. J.

2011-12-01

237

Promoting habit formation  

Microsoft Academic Search

Habits are automatic behavioural responses to environmental cues, thought to develop through repetition of behaviour in consistent contexts. When habit is strong, deliberate intentions have been shown to have a reduced influence on behaviour. The habit concept may provide a mechanism for establishing new behaviours, and so healthy habit formation is a desired outcome for many interventions. Habits also however

Phillippa Lally; Benjamin Gardner

2011-01-01

238

HABEBEE: habitability of eyeball-exo-Earths.  

PubMed

Extrasolar Earth and super-Earth planets orbiting within the habitable zone of M dwarf host stars may play a significant role in the discovery of habitable environments beyond Earth. Spectroscopic characterization of these exoplanets with respect to habitability requires the determination of habitability parameters with respect to remote sensing. The habitable zone of dwarf stars is located in close proximity to the host star, such that exoplanets orbiting within this zone will likely be tidally locked. On terrestrial planets with an icy shell, this may produce a liquid water ocean at the substellar point, one particular "Eyeball Earth" state. In this research proposal, HABEBEE: exploring the HABitability of Eyeball-Exo-Earths, we define the parameters necessary to achieve a stable icy Eyeball Earth capable of supporting life. Astronomical and geochemical research will define parameters needed to simulate potentially habitable environments on an icy Eyeball Earth planet. Biological requirements will be based on detailed studies of microbial communities within Earth analog environments. Using the interdisciplinary results of both the physical and biological teams, we will set up a simulation chamber to expose a cold- and UV-tolerant microbial community to the theoretically derived Eyeball Earth climate states, simulating the composition, atmosphere, physical parameters, and stellar irradiation. Combining the results of both studies will enable us to derive observable parameters as well as target decision guidance and feasibility analysis for upcoming astronomical platforms. PMID:23510083

Angerhausen, Daniel; Sapers, Haley; Citron, Robert; Bergantini, Alexandre; Lutz, Stefanie; Queiroz, Luciano Lopes; da Rosa Alexandre, Marcelo; Araujo, Ana Carolina Vieira

2013-03-01

239

Submillimeter observations of circumstellar dust  

NASA Astrophysics Data System (ADS)

Five late-type stars with circumstellar envelopes were observed with the James Clerk Maxwell Telescope (JCMT) on 1988 February 7-8. The stars IK Tauri, Alpha Orionis, VY Canis Majoris, CW Leonis, and RW Leonis Minoris were observed in the 450, 800, and 1100 micron wavebands. These data were combined with existing measurements at shorter wavelengths for each star. The combined data were fitted to a circumstellar-dust-shell model based on the computer code by Leung (1975). Derived parameters, including mass-loss rates, are presented for the observed stars.

Marshall, Caroline R.; Leahy, Denis A.; Kwok, Sun

1992-06-01

240

The habitability and detection of Earth-like planets orbiting cool white L. Fossati1  

E-print Network

The habitability and detection of Earth-like planets orbiting cool white dwarfs. L. Fossati1 remain in the Continuous Habitable Zone (CHZ) for 8 Gyr. We show that photosynthetic pro- cesses can is 102 (104 ) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star

241

Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps)  

Microsoft Academic Search

Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone\\u000a (IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments\\u000a in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons\\u000a in the associated leucosomes. The primary morphology and Th-U

Gerhard Vavra; Rolf Schmid; Dieter Gebauer

1999-01-01

242

Living with an Old Red Dwarf: X-ray-UV Emissions of Kapteyn’s Star - Effects of X-UV radiation on Habitable Zone Planets hosted by old Red Dwarf Stars  

NASA Astrophysics Data System (ADS)

Red dwarfs (dM) stars make up over 75% of the local stellar population and a significant fraction (~40-50%) are older than the Sun. Because of the high frequency of red dwarfs and their longevity (> 50 Gyr), there is a greater possibility of more advanced life in red dwarf-exoplanet systems. MEarths, UVES, SDSS-III, and the upcoming TESS mission are some surveys that are targeting red dwarfs in the search for hosted potentially habitalble planets. As part of Villanova's 'Living with a Red Dwarf' program, we have obtained HST-COS Ultraviolet spectra (1150-3000A) and Chandra X-ray observations of Kapteyn's star (GJ 191; M1 V, V = 8.85 mag , d = 12.76 +/- 0.05 ly). Kapyteyn's Star is important for the study of old red dwarfs because it is the nearest (Pop II) halo star with a radial velocity of +245.2 km/s and an estimated age of 11.2 +/-0.9 Gyrs. Recently Kapteyn's Star was found to host two super-Earth mass planets - one of these is orbiting inside the star's Habitable Zone (Anglada-Escude' 2014: MNRAS 443, L89). In our program, Kapteyn's star is the oldest red dwarf and as such serves as an anchor for our age, rotation, and activity relations. The spectra obtained from HST/COS provide one of the cleanest measurements of the important HI Lyman-alpha 1215.6 A emission flux for red dwarfs. This is due to the large Doppler shift from the high radial velocity, separating the stellar Ly-alpha emission from by the Ly-alpha ISM and local geo-coronal sources. These observations further provide calibrations at the old age/low rotation/low activity extremes for our relations. As the nearest and brightest old red dwarf star, Kapteyn's Star also provides insights into its magnetic properties to investigae coronal x-ray and UV emission for the large population of old, slowly rotating red dwarf stars. Kapteyn's star also serves as a proxy for the numerous metal-poor old disk - Pop II M dwarfs by providing information about X-UV emissions. This information is crucial for determining X-ray-UV irradiances for habitable zone planets hosted by these old numerous, cool low luminosity stars.We gratefully acknowledge the support from NSF/RUI Grant AST-1009903, NASA/Chandra Grants GO2-13020X, and HST-GO-13020

Guinan, Edward F.; Durbin, Allyn J.; Engle, Scott G.

2015-01-01

243

Response of atmospheric biomarkers to NO(x)-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of M dwarf stars.  

PubMed

Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N(2)), which leads to production of nitrogen oxides (NO(x)) in the planetary atmosphere, hence affecting biomarkers such as ozone (O(3)). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NO(x) production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O(3) formation proceeds via the reaction O+O(2)+M?O(3)+M. At high NO(x) abundances, the O atoms arise mainly from NO(2) photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O(2)). For the flaring case, O(3) is mainly destroyed via direct titration, NO+O(3)?NO(2)+O(2), and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O(3), Rayleigh scattering by the main atmospheric gases (O(2), N(2), and CO(2)) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O(3) survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker nitrous oxide (N(2)O) could survive in the planetary atmosphere under all conditions of stellar activity considered here, which clearly has important implications for missions that aim to detect spectroscopic biomarkers. PMID:23215581

Grenfell, John Lee; Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A Beate C; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

2012-12-01

244

Response of Atmospheric Biomarkers to NOx-Induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M Dwarf Stars  

PubMed Central

Abstract Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides (NOx) in the planetary atmosphere, hence affecting biomarkers such as ozone (O3). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NOx production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O3 formation proceeds via the reaction O+O2+M?O3+M. At high NOx abundances, the O atoms arise mainly from NO2 photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O2). For the flaring case, O3 is mainly destroyed via direct titration, NO+O3?NO2+O2, and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O3, Rayleigh scattering by the main atmospheric gases (O2, N2, and CO2) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O3 survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker nitrous oxide (N2O) could survive in the planetary atmosphere under all conditions of stellar activity considered here, which clearly has important implications for missions that aim to detect spectroscopic biomarkers. Key Words: M dwarf—Atmosphere—Earth-like—Biomarkers—Stellar cosmic rays. Astrobiology 12, 1109–1122. PMID:23215581

Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A. Beate C.; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

2012-01-01

245

Tides, Planetary Companions, and Habitability  

NASA Astrophysics Data System (ADS)

Earth-scale planets in the classical habitable zone (HZ) are more likely to be habitable if they possess active geophysics to drive processes that regulate their atmosphere. Without a constant internal energy source, planets cool as they age, eventually terminating tectonic activity. Planets orbiting low-mass stars can be very old, due to the longevity of such stars, so they may be rendered sterile to life in this way. However, the presence of an outer companion could generate enough tidal heat in the HZ planet to prevent such cooling. The range of mass and orbital parameters for the companion that give adequate long-term heating of the inner HZ planet, while avoiding very early total desiccation, is substantial. We locate the ideal location for the outer of a pair of planets, under the assumption that the inner planet has the same incident flux as Earth, orbiting example stars: a generic late M dwarf and the M9V/L0 dwarf DEN1048. We also analyze the extent to which systems with ideal parameters for heating will evolve over time. Thus discoveries of Earth-scale planets in the HZ zone of old small stars should be followed by searches for outer companion planets that might be essential for current habitability.

Van Laerhoven, Christa L.; Barnes, Rory; Greenberg, Richard

2014-05-01

246

Energy Balance Models of planetary climate as a tool for investigating the habitability of terrestrial planets and its evolution  

NASA Astrophysics Data System (ADS)

The study of the habitability and potential for life formation of terrestrial planets requires a considerable work of modelization owing to the limited amount of experimental constraints typical of this type of research. As an example, the paucity of experimental Archean data severely limits the study of the habitability of the primitive Earth at the epoch of the origin of life. In the case of exoplanets the amount of experimental information available is quite limited and the need for modelization strong. Here we focus on the modelization of the surface planetary temperature, a key thermodynamical quantity used to define the habitability. Energy Balance Models (EBM) of planetary climate provide a simple way to calculate the temperature-latitude profile of terrestrial planets with a small amount of computing resources. Thanks to this fact EBMs offer an excellent tool to exploring a wide range of parameter space and therefore testing the effects of variations of physical/chemical quantities unconstrained by experimental data. In particular, one can easily probe possible scenarios of habitability at different stages of planetary evolution. We have recently implemented one-dimensional EBMs featuring the possibility of probing variations of astronomical and geophysical parameters, such as stellar luminosity, orbital semi-major axis and eccentricity, obliquity of the planetary axis, planet rotational velocity, land/ocean surface fractions and thermal capacities, and latitudinal heat diffusion. After testing our models against results obtained in previous work (Williams & Kasting 1997, Icarus, 129, 254; Spiegel et al. 2008, ApJ, 681, 1609), we introduced a novel parametrization of the diffusion coefficient as a function of the stellar zenith distance. Our models have been validated using the mean temperature-latitude profiles of the present Earth and its seasonal variations; the global albedo has been used as an additional constraint. In this work we present specific examples of application of our EBMs to studies of habitability of terrestrial planets. In the first part we focus on the primitive Earth, taking into account the effects of the higher speed of Earth rotation and reduced solar luminosity at the epoch of life formation. In the second part we provide examples of habitability studies of planetary systems discovered in surveys of exoplanets. These examples allow us to critically discuss the concept of circumstellar habitable zone.

Ferri, G.; Murante, G.; Provenzale, A.; Silva, L.; Vladilo, G.

2012-04-01

247

The Habitable-zone Planet Finder: A status update on the development of a stabilized fiber-fed near-infrared spectrograph for the for the Hobby-Eberly telescope  

NASA Astrophysics Data System (ADS)

The Habitable-Zone Planet Finder is a stabilized, fiber-fed, NIR spectrograph being built for the 10m Hobby- Eberly telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The optical design of the HPF is a white pupil spectrograph layout in a vacuum cryostat cooled to 180 K. The spectrograph uses gold-coated mirrors, a mosaic echelle grating, and a single Teledyne Hawaii-2RG (H2RG) NIR detector with a 1.7-micron cutoff covering parts of the information rich z, Y and J NIR bands at a spectral resolution of R˜50,000. The unique design of the HET requires attention to both near and far-field fiber scrambling, which we accomplish with double scramblers and octagonal fibers. In this paper we discuss and summarize the main requirements and challenges of precision RV measurements in the NIR with HPF and how we are overcoming these issues with technology, hardware and algorithm developments to achieve high RV precision and address stellar activity.

Mahadevan, Suvrath; Ramsey, Lawrence W.; Terrien, Ryan; Halverson, Samuel; Roy, Arpita; Hearty, Fred; Levi, Eric; Stefansson, Gudmundur K.; Robertson, Paul; Bender, Chad; Schwab, Chris; Nelson, Matt

2014-07-01

248

EXoplanetary Circumstellar Environments and Disk Explorer technology demonstration: Experimental results in air and vacuum  

NASA Astrophysics Data System (ADS)

Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting and spatially resolving low surface brightness circumstellar debris disks as well as imaging giant planets as close as in the habitable zones of their host stars. One proposed mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development A (Category Ill). EXCEDE is a 0.7 m space telescope concept designed to achieve raw contrasts of 1e-6 at an inner working angle of 1.2 l/D and 1e-7 at 2 l/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular the achievement of the first major milestone in our technology development program (1e-6 median raw contrast between a 1.2 l/D inner working angle and 2 l/D, simultaneously with 1e-7 median raw contrast between 2 l/D and 4 l/D, in monochromatic light and in a controlled and repeatable fashion). In addition, we will describe the upgrades to our system, such as (a) the Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (b) efficient model-based wavefront control algorithms; (c) a reconfiguration of our DM to be upstream of the coronagraph and the addition of the "inverse PIAA" system that enables better outer working angles. Finally, we report on preliminary demonstrations in a vacuum chamber. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging spacebased telescopes because of the many challenges common to different coronagraph architectures and mission requirements.

Lozi, J.; Belikov, R.; Bendek, E.; Davis, P. K.; Duncan, A.; Greene, T. P.; Guyon, O.; Hix, T.; Irwin, W.; Kendrick, R.; Lynch, D.; Mihara, R.; PIuzhnik, E.; Schneider, G.; Smith, E.; Thomas, S.; Witteborn, F. C.

2014-03-01

249

Geophysical and atmospheric evolution of habitable planets.  

PubMed

The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere. PMID:20307182

Lammer, Helmut; Selsis, Frank; Chassefière, Eric; Breuer, Doris; Griessmeier, Jean-Mathias; Kulikov, Yuri N; Erkaev, Nikolai V; Khodachenko, Maxim L; Biernat, Helfried K; Leblanc, Francois; Kallio, Esa; Lundin, Richard; Westall, Frances; Bauer, Siegfried J; Beichman, Charles; Danchi, William; Eiroa, Carlos; Fridlund, Malcolm; Gröller, Hannes; Hanslmeier, Arnold; Hausleitner, Walter; Henning, Thomas; Herbst, Tom; Kaltenegger, Lisa; Léger, Alain; Leitzinger, Martin; Lichtenegger, Herbert I M; Liseau, René; Lunine, Jonathan; Motschmann, Uwe; Odert, Petra; Paresce, Francesco; Parnell, John; Penny, Alan; Quirrenbach, Andreas; Rauer, Heike; Röttgering, Huub; Schneider, Jean; Spohn, Tilman; Stadelmann, Anja; Stangl, Günter; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

2010-01-01

250

Habitability of Planets in Binaries  

E-print Network

A survey of currently known extrasolar planets indicates that close to 20% of their hosting stars are members of binary systems. While the majority of these binaries are wide (i.e., with separations between 250 and 6500 AU), the detection of Jovian-type planets in the three binaries of Gamma Cephei (separation of 18.5 AU), GL 86 (separation of 21 AU), and HD 41004 (separation of 23 AU) have brought to the forefront questions on the formation of giant planets and the possibility of the existence of smaller bodies in moderately close binary star systems. This paper discusses the late stage of the formation of habitable planets in binary systems that host Jovian-type bodies, and reviews the effects of the binary companion on the formation of Earth-like planets in the system's habitable zone. The results of a large survey of the parameter-space of binary-planetary systems in search of regions where habitable planets can form and have long-term stable orbits are also presented.

Nader Haghighipour

2007-10-03

251

Microbial habitability of the Hadean Earth during the late heavy bombardment  

E-print Network

shows that there is no plausible situation in which the habitable zone was fully sterilized on EarthLETTERS Microbial habitability of the Hadean Earth during the late heavy bombardment Oleg Abramov1 in the effort to recreate the effect of the LHB on the Earth as a whole; outputs were used to assess habitable

Mojzsis, Stephen J.

252

Habitable planets around the star Gl 581?  

E-print Network

Radial velocity surveys are now able to detect terrestrial planets at habitable distance from M-type stars. Recently, two planets with minimum masses below 10 Earth masses were reported in a triple system around the M-type star Gliese 581. Using results from atmospheric models and constraints from the evolution of Venus and Mars, we assess the habitability of planets Gl 581c and Gl 581d and we discuss the uncertainties affecting the habitable zone (HZ) boundaries determination. We provide simplified formulae to estimate the HZ limits that may be used to evaluate the astrobiological potential of terrestrial exoplanets that will hopefully be discovered in the near future. Planets Gl 581c and 'd' are near, but outside, what can be considered as the conservative HZ. Planet 'c' receives 30% more energy from its star than Venus from the Sun, with an increased radiative forcing caused by the spectral energy distribution of Gl 581. Its habitability cannot however be positively ruled out by theoretical models due to uncertainties affecting cloud properties. Irradiation conditions of planet 'd' are comparable with those of early Mars. Thanks to the warming effect of CO2-ice clouds planet 'd' might be a better candidate for the first exoplanet known to be potentially habitable. A mixture of various greenhouse gases could also maintain habitable conditions on this planet.

Franck Selsis; J. F. Kasting; B. Levrard; J. Paillet; I. Ribas; X. Delfosse

2007-11-21

253

TIDAL LIMITS TO PLANETARY HABITABILITY  

SciTech Connect

The habitable zones (HZs) of main-sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurfaces the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO{sub 2} may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with the range of the traditional HZ for main-sequence, low-mass stars. We propose a revised HZ that incorporates both stellar insolation and tidal heating. We apply these criteria to GJ 581 d and find that it is in the traditional HZ, but its tidal heating alone may be insufficient for plate tectonics.

Barnes, Rory [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Jackson, Brian; Greenberg, Richard [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Raymond, Sean N. [Virtual Planetary Laboratory (United States)

2009-07-20

254

Dynamical habitability of planetary systems.  

PubMed

The problem of the stability of planetary systems, a question that concerns only multiplanetary systems that host at least two planets, is discussed. The problem of mean motion resonances is addressed prior to discussion of the dynamical structure of the more than 350 known planets. The difference with regard to our own Solar System with eight planets on low eccentricity is evident in that 60% of the known extrasolar planets have orbits with eccentricity e > 0.2. We theoretically highlight the studies concerning possible terrestrial planets in systems with a Jupiter-like planet. We emphasize that an orbit of a particular nature only will keep a planet within the habitable zone around a host star with respect to the semimajor axis and its eccentricity. In addition, some results are given for individual systems (e.g., Gl777A) with regard to the stability of orbits within habitable zones. We also review what is known about the orbits of planets in double-star systems around only one component (e.g., gamma Cephei) and around both stars (e.g., eclipsing binaries). PMID:20307181

Dvorak, Rudolf; Pilat-Lohinger, Elke; Bois, Eric; Schwarz, Richard; Funk, Barbara; Beichman, Charles; Danchi, William; Eiroa, Carlos; Fridlund, Malcolm; Henning, Thomas; Herbst, Tom; Kaltenegger, Lisa; Lammer, Helmut; Léger, Alain; Liseau, René; Lunine, Jonathan; Paresce, Francesco; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Selsis, Frank; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

2010-01-01

255

Dynamical Habitability of Planetary Systems  

NASA Astrophysics Data System (ADS)

The problem of the stability of planetary systems, a question that concerns only multiplanetary systems that host at least two planets, is discussed. The problem of mean motion resonances is addressed prior to discussion of the dynamical structure of the more than 350 known planets. The difference with regard to our own Solar System with eight planets on low eccentricity is evident in that 60% of the known extrasolar planets have orbits with eccentricity e > 0.2. We theoretically highlight the studies concerning possible terrestrial planets in systems with a Jupiter-like planet. We emphasize that an orbit of a particular nature only will keep a planet within the habitable zone around a host star with respect to the semimajor axis and its eccentricity. In addition, some results are given for individual systems (e.g., Gl777A) with regard to the stability of orbits within habitable zones. We also review what is known about the orbits of planets in double-star systems around only one component (e.g., gamma Cephei) and around both stars (e.g., eclipsing binaries).

Dvorak, Rudolf; Pilat-Lohinger, Elke; Bois, Eric; Schwarz, Richard; Funk, Barbara; Beichman, Charles; Danchi, William; Eiroa, Carlos; Fridlund, Malcolm; Henning, Thomas; Herbst, Tom; Kaltenegger, Lisa; Lammer, Helmut; Léger, Alain; Liseau, René; Lunine, Jonathan; Paresce, Francesco; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Selsis, Frank; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J.

2010-01-01

256

Tidal Limits to Planetary Habitability  

E-print Network

The habitable zones of main sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurface the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO_2 may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with th...

Barnes, Rory; Greenberg, Richard; Raymond, Sean N

2009-01-01

257

Stellar Activity Masking and Mimicking Habitable Exoplanets  

NASA Astrophysics Data System (ADS)

Future generations of precise radial velocity (RV) surveys aim to attain a sensitivity sufficient to detect Earth mass planets orbiting in their host star's habitable zones. The RV semi-amplitude of such a planet can be significantly smaller than RV variations caused by stellar "jitter". Some RV variations, in particular those caused by starspots rotating in and out of view and those caused by magnetic activity cycles can be periodic in nature and can mimic planetary RV signals. We calculate and compare the relative timescales and amplitudes of RV variations due to activity and habitable planetary companions as a function of stellar mass, and discuss the ramifications for RV surveys.

Vanderburg, Andrew; Plavchan, Peter; Johnson, John A.

2014-06-01

258

Circumstellar interaction of the type Ia supernova 2002ic  

E-print Network

We propose a model to account for the bolometric light curve, quasi-continuum and the Ca II emission features of the peculiar type Ia supernova (SN) 2002ic, which exploded in a dense circumstellar envelope. The model suggests that the SN Ia had the maximum possible kinetic energy and that the ejecta expand in an approximately spherically symmetric (possibly clumpy) circumstellar environment. The Ca II and quasi-continuum are emitted by shocked SN ejecta that underwent deformation and fragmentation in the intershock layer. Modeling of the Ca II triplet implies that the contribution of the O I 8446 A line is about 25% of the 8500 A feature on day 234, which permits us to recover the flux in the Ca II 8579 A triplet from the flux of 8500 A blend reported by Deng et al. (2004). We use the Ca II doublet and triplet fluxes on day 234 to derive the electron temperature (~4400 K) in the Ca II line-emitting zone and the ratio of the total area of dense fragments to the area of the shell, S/S_0 ~ 100. We argue that Ca II bands and quasi-continuum originate from different zones of the shocked ejecta that reflect the abundance stratification of the supernova.

N. N. Chugai; R. A. Chevalier; P. Lundqvist

2004-08-26

259

Circumstellar Nebulae in Young Supernova Remnants  

E-print Network

Supernovae descendent from massive stars explode in media that have been modified by their progenitors' mass loss and UV radiation. The supernova ejecta will first interact with the circumstellar material shed by the progenitors at late evolutionary stages, and then interact with the interstellar material. Circumstellar nebulae in supernova remnants can be diagnosed by their small expansion velocities and high [N II]/H$\\alpha$ ratios. The presence of circumstellar nebulae appears ubiquitous among known young supernova remnants. These nebulae can be compared to those around evolved massive stars to assess the nature of their supernova progenitors. Three types of archeological artifacts of supernova progenitors have been observed in supernovae and/or young supernova remnants: (1) deathbed ejecta, (2) circumstellar nebulae, and (3) interstellar bubbles. Examples of these three types are given.

Y. -H. Chu

2000-12-29

260

Circumstellar Material Around Evolved Massive Stars  

E-print Network

I review multiwavelength observations of material seen around different types of evolved massive stars (i.e. red supergiants, yellow hypergiants, luminous blue variables, B[e] supergiants, and Wolf-Rayet stars), concentrating on diagnostics of mass, composition, and kinetic energy in both local and distant examples. Circumstellar material has significant implications for the evolutionary state of the star, the role of episodic mass loss in stellar evolution, and the roles of binarity and rotation in shaping the ejecta. This mass loss determines the type of supernova that results via the stripping of the star's outer layers, but the circumstellar gas can also profoundly influence the immediate pre-supernova environment. Dense circumstellar material can actually change the type of supernova that is seen when it is illuminated by the supernova or heated by the blast wave. As such, unresolved circumstellar material illuminated by distant supernovae can provide a way to study mass loss in massive stars in distant ...

Smith, Nathan

2010-01-01

261

WHERE TO FIND HABITABLE ''EARTHS'' IN CIRCUMBINARY SYSTEMS  

SciTech Connect

Six P-type planets have been found thus far around five binary systems, i.e., Kepler-16b, 34b, 35b, 38b, and 47b and c, which are all Neptune- or Jupiter-like planets. The stability of planets and the habitable zones are influenced by the gravitational and radiative perturbations of binary companions. In this Letter, we check the stability of an additional habitable Earth-mass planet in each system. Based on our simulations in 10 Myr, a habitable ''Earth'' is hardly stable in Kepler-16, while a stable ''Earth'' in Kepler-47 close to the boundaries of the habitable zone is possible. In contrast, Kepler-34, 35, and 38 seem to have high probabilities of being able to tolerante a stable ''Earth'' in their habitable zones. The affects of transit time variations are quite small due to the small mass of an undetected ''Earth,'' except that of Kepler-16b. With a time precision of 10{sup -3} day ({approx}88 s), an ''Earth'' in the corotational resonance with Kepler-16b can be detected in three years, while habitable ''Earths'' in the Kepler-34 and 38 systems can be detected in 10 yr. Habitable ''Earths'' in Kepler-35 and 47 are not likely to be detected in 10 yr under this precision.

Liu Huigen; Zhang Hui; Zhou Jilin, E-mail: huigen@nju.edu.cn [School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093 (China)

2013-04-20

262

The Role of Tides in Planetary Habitability  

NASA Astrophysics Data System (ADS)

Terrestrial planets in the classic "habitable zone" (Kasting et al. 1993) of stars may be influenced by tides. Tidal evolution is poorly constrained and multiple acceptable models exist which, although qualitatively similar, predict different rates of evolution. Using different models, we examine how tides may modify several key properties of planets in the habitable zone: semi-major axis, eccentricity, obliquity and rotation rate. Tides can lock the rotation rate and erode the obliquity (to 0 or 180 degrees) in 103-1010 years, depending on the stellar mass and eccentricity. Some tidal models even predict significant obliquity evolution for planets in the habitable zones of solar-mass stars. This evolution dissipates energy in the planet's interior (at the expense of the orbit) and leads to "tidal heating." In extreme cases of high eccentricity and very low mass stars, the heating may initiate a runaway greenhouse, and/or total evaporation of potential surface water, eliminating any hope of habitability. After the spin properties have equilibrated, the planet is said to be "tidally locked" and further evolution primarily changes the orbital angular momentum. For exoplanets, tides tend to reduce eccentricities and semi-major axes, and can also change the rotation period, eventually reaching synchroneity with the orbit when both eccentricity and obliquity reach zero. Orbital circularization requires millions to trillions of years, depending on the planet's initial conditions and the tidal model assumed. Tidal heating also occurs during circularization and planets may pass through a "super-Io" phase prior to reaching internal heating rates similar to the modern day Earth. Tides clearly have the potential to impact habitability and may lead to planets with evolutionary paths markedly different from the Earth. These issues are presented and discussed for the simple case of one planet orbiting one star.

Barnes, Rory; Heller, R.; Jackson, B.; Leconte, J.; Greenberg, R.; Mullins, K.; Raymond, S. N.

2011-01-01

263

Effects of Extreme Obliquity Variations on the Habitability of Exoplanets  

PubMed Central

Abstract We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 108 years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes. Key Words: Exoplanets—Habitable zone—Energy balance models. Astrobiology 14, 277–291. PMID:24611714

Barnes, R.; Domagal-Goldman, S.; Breiner, J.; Quinn, T.R.; Meadows, V.S.

2014-01-01

264

Circumstellar gas in beta Pic  

NASA Astrophysics Data System (ADS)

From the very early observations completed in 1984, it was clear that some gas was present in the circumstellar environment. In particular the CaII lines were showing very strong absorption signatures never observed in the local ISM toward similarly nearby stars. From the comparison of the two first observations of these lines it became also clear that these lines were time variable. This lead to numerous observational campaigns showing that stable gas as well as infalling gas was present in the system. The concept of falling and evaporating bodies (FEBs) was born: unexpectedly, exocomets were observed before exoplanets ! The lifetime of the continuously produced gas being very short, it lead to a needed additional concept of a stable braking gas at rest relative to the system and able to stop all other species through collisions. The nature of this braking gas is still debated and its location unclear. The distance of the gas is shown to be very extended, some of it being at less than 1 AU, mainly from absorption studies and some at more than 100 AU from the star, mainly from the observation of emissions signatures. The nature, origin and composition of the gas seem to be due to either the evaporation of FEBs for the closer gas or to the evaporation of distant orbiting and evaporating bodies (OEBs) of all sizes including grains, for the more remote gas.

Vidal-Majar, A.

2014-09-01

265

Your Child's Habits  

MedlinePLUS

... don't scold or lecture. Punishment, ridicule, or criticism could cause the behavior to increase. Involve your ... good behavior, it will disappear over time. The new, positive habit must be firmly established before the ...

266

Changing your sleep habits  

MedlinePLUS

... these patterns over many years, they become habits. Insomnia is difficulty falling asleep or staying asleep. In many cases, you can relieve insomnia by making a few simple lifestyle changes. However, ...

267

Habitability design for spacecraft  

NASA Technical Reports Server (NTRS)

Habitability is understood to mean those spacecraft design elements that involve a degree of comfort, quality or necessities to support man in space. These elements are environment, architecture, mobility, clothing, housekeeping, food and drink, personal hygiene, off-duty activities, each of which plays a substantial part in the success of a mission. Habitability design for past space flights is discussed relative to the Mercury, Gemini, Apollo, and Skylab spacecraft, with special emphasis on an examination of the Shuttle Orbiter cabin design from a habitability standpoint. Future projects must consider the duration and mission objectives to meet their habitability requirements. Larger ward rooms, improved sleeping quarters and more complete hygiene facilities must be provided for future prolonged space flights

Franklin, G. C.

1978-01-01

268

Habitability: CAMELOT 4  

NASA Technical Reports Server (NTRS)

During 1988 to 1989 the NASA/USRA Advanced Design Program sponsored research and design efforts aimed at developing habitability criteria and at defining a habitability concept as a useful tool in understanding and evaluating dwellings for prolonged stays in extraterrestrial space. The Circulating Auto sufficient Mars-Earth Luxurious Orbital Transport (CAMELOT) was studied as a case in which the students would try to enhance the quality of life of the inhabitants by applying architectural design methodology. The study proposed 14 habitability criteria considered necessary to fulfill the defined habitability concept, which is that state of equilibrium that results from the interaction between components of the Individual Architecture Mission Complex, which allows a person to sustain physiological homeostatis, adequate performance, and acceptable social relationships. Architecture, design development, refinements and revisions to improve the quality of life, new insights on artificial gravity, form and constitution problems, and the final design concept are covered.

Alequin, W.; Barragan, A.; Carro, M.; Garcia, F.; Gonzalez, I.; Mercado, J. A.; Negron, N.; Lopez, D.; Rivera, L. A.; Rivera, M.

1990-01-01

269

Habitability study shuttle orbiter  

NASA Technical Reports Server (NTRS)

Studies of the habitability of the space shuttle orbiter are briefly summarized. Selected illustrations and descriptions are presented for: crew compartment, hygiene facilities, food system and galley, and storage systems.

1972-01-01

270

NASA: Habitable Worlds  

NSDL National Science Digital Library

NASA's Habitable Worlds website encourages visitors to "search the solar system for signs of life," by selecting a "World to Explore." This creatively designed website smartly displays our solar system's colorful planets or worlds amidst the dark background of space. In order to gain in-depth information specific to each planet, users simply click on the world of their choosing. Each planet page provides beautiful images and information about habitability, moons, and more.

271

Kepler Mission: A Search for Habitable Planets  

NASA Technical Reports Server (NTRS)

The Kepler Mission was selected by NASA as one of the next two Discovery Missions. The mission design is based on the search for Earth-size planets in the habitable zone of solar-like stars, but does not preclude the discovery of larger or smaller planets in other orbits of non-solar-like stars. An overview of the mission, the scientific goals and the anticipated results will be presented.

Koch, David; Fonda, Mark (Technical Monitor)

2002-01-01

272

ABUNDANT CIRCUMSTELLAR SILICA DUST AND SiO GAS CREATED BY A GIANT HYPERVELOCITY COLLISION IN THE {approx}12 MYR HD172555 SYSTEM  

SciTech Connect

The fine dust detected by infrared (IR) emission around the nearby {beta} Pic analog star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, nonequilibrium materials, with approximately three quarters of the Si atoms in silica (SiO{sub 2}) species. Tektite and obsidian lab thermal emission spectra (nonequilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a {sup -3.95{+-}}{sup 0.10}. While IR photometry of the system has stayed stable since the 1983 IRAS mission, this steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 {+-} 0.6 AU (equivalent to 1.9 {+-} 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 10{sup 19}-2 x 10{sup 20} kg, equivalent to a 150-200 km radius asteroid. Significant emission features centered at 4 and 8 {mu}m due to fluorescing SiO gas are also found. Roughly 10{sup 22} kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 10{sup 21}-10{sup 22} kg and equivalent to the largest sized asteroid currently found in the solar system's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong stellar X-ray activity, and an extended disk of {beta} meteoroids argues that the source of the observed circumstellar materials is a giant hypervelocity (>10 km s{sup -1}) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

Lisse, C. M. [JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723 (United States); Chen, C. H. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Wyatt, M. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Morlok, A. [Open University, Milton Keynes, MK7 6AA (United Kingdom); Song, I. [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States); Bryden, G. [Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Sheehan, P. [Department of Physics and Astronomy, University of Rochester, Rochester, NY (United States)], E-mail: carey.lisse@jhuapl.edu, E-mail: cchen@stsci.edu, E-mail: wyatt@ast.cam.ac.uk, E-mail: A.Morlok@open.ac.uk, E-mail: song@uga.edu, E-mail: Geoffrey.Bryden@jpl.nasa.gov, E-mail: psheeha2@mail.rochester.edu

2009-08-20

273

The Detectability of Habitable Exomoons with Kepler  

NASA Astrophysics Data System (ADS)

Now that more than 400 exoplanets have been discovered, focus has moved from finding planets to characterise these alien worlds. As well as detecting the atmospheres of these exoplanets, part of the characterisation process undoubtedly involves the search for extrasolar moons. We explore the motivations for undergoing such a search, review some of the proposed detection techniques and introduce a model for the Transit Time Variation (TTV) and Transit Duration Variation (TDV) signals which permits not only the identification of exomoons but also the derivation of some of their characteristics. The detectability of a habitable-zone exomoon around various configurations of exoplanetary systems with the Kepler Mission or photometry of approximately equal quality is investigated. We calculate both the predicted transit timing signal amplitudes and the estimated uncertainty on such measurements in order to calculate the confidence in detecting such bodies across a broad spectrum of orbital arrangements. The effects of photon noise, stellar variability and instrument noise are all accounted for in the analysis. We validate our methodology by simulating synthetic lightcurves and we find that habitable-zone exomoons down to 0.2 Earth masses may be detected and 25,000 stars could be surveyed for habitable-zone exomoons within Kepler`s field-of-view. Finally, we predict how a further characterisation of these bodies can be carried out.

Campanella, Giammarco; Kipping, David; Fossey, Stephen

274

Technology Demonstration Milestone #1 for the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) I. Laboratory/Experimental Results  

NASA Astrophysics Data System (ADS)

Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting and spatially resolving low surface brightness circumstellar debris disks as well as imaging giant planets as close as in the habitable zones of their host stars. One proposed mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 1e6 at an inner working angle of 1.2 l/D and 1e7 at 2 l/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular the achievement of the first major milestone in our technology development program (1e6 median raw contrast between a 1.2 l/D inner working angle and 2 l/D, simultaneously with 1e7 median raw contrast between 2 l/D and 4 l/D, in monochromatic light and in a controlled and repeatable fashion - see companion paper by Schneider et al. for science drivers). In addition, we will describe the upgrades to our system, such as (a) the Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (b) efficient model-based wavefront control algorithms; (c) a reconfiguration of our DM to be upstream of the coronagraph and the addition of the “inverse PIAA” system that enables better outer working angles. Finally, we report on preliminary demonstrations in a vacuum chamber. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging space-based telescopes because of the many challenges common to different coronagraph architectures and mission requirements. This work was supported in part by the NASA Explorer program and Ames Research Center, University of Arizona, and Lockheed Martin SSC.

Belikov, Ruslan; Bendek, E.; Davis, P.; Duncan, A.; Greene, T. P.; Guyon, O.; Hix, T.; Irwin, W.; Kendrick, R.; Lozi, J.; Lynch, D.; Mihara, R.; Pluzhnik, E.; Schneider, G.; Smith, E.; Thomas, S.; Witteborn, F. C.

2014-01-01

275

Habitability of Planets Orbiting Binaries Consisting of Solar Mass Twins  

NASA Astrophysics Data System (ADS)

An important problem in astrobiology is the study of the potential habitability of planets orbiting binary stars. Theoretical and observational studies of circumbinary planets indicate that it is not uncommon for circumbinary planets to be located in the habitable zones surrounding main sequence binaries. However, it is also clear that the time evolution of stellar activity of the individual stars in close binaries is of primary concern for the habitability of planets. For example, planets orbiting active stars may lose the entirety of their water budget due to atmospheric mass loss; despite being in the standard radiative habitable zone. Alternatively, stars in some binaries may undergo a reduction in stellar activity due to tidal effects that cause the rotation of the stars to slow faster than single stars. Thereby, magneto-coronal activity is reduced to less aggressive levels, allowing circumbinary planets to maintain surface water. We summarize these effects, which we call the Binary Habitability Mechanism (BHM). We performed orbital integrations of circumbinary, Earth-like, planets and find that resonances play a particularly important role in the stability of habitable zone planets orbiting solar twin binaries in the 20-60 day period range, allowing for the possibility of several habitable planets orbiting some binaries. We present numerical simulations of the effects of colliding winds in binaries containing solar mass twins. We used stellar wind parameters based on solar like conditions for our 3D hydrodynamic simulations. We find devastating effects for close in planets, yet relatively mild stellar wind conditions exist within the circumbinary habitable zone.

Mason, Paul A.; Zuluaga, Jorge I.; Zhilkin, Andrey G.; Bisikalo, Dmitry V.

2015-01-01

276

A Quick Study of Science Return from Direct Imaging Exoplanet Missions: Detection and Characterization of Circumstellar Material with an AFTA or EXO-C/S CGI  

E-print Network

The capabilities of a high (~ 10^-9 resel^-1) contrast, narrow-field, coronagraphic instrument (CGI) on a space-based AFTA-C or probe-class EXO-C/S mission, conceived to study the diversity of exoplanets now known to exist into stellar habitable zones, are particularly and importantly germane to symbiotic studies of the systems of circumstellar (CS) material from which planets have emerged and interact with throughout their lifetimes. The small particle populations in "disks" of co-orbiting materials can trace the presence of planets through dynamical interactions that perturb the spatial distribution of the light-scattering debris, detectable at optical wavelengths and resolvable with an AFTA-C or EXO-S/C CGI. Herein we: (1) present the science case to study the formation, evolution, architectures, diversity, and properties of the material in the planet-hosting regions of nearby stars, (2) discuss how a CGI under current conception can uniquely inform and contribute to those investigations, (3) consider the ...

Schneider, Glenn

2014-01-01

277

Physics and Chemistry of Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

Part I. Setting the Stage: 1. Introduction; 2. Evolutionary status of dust-enshrouded objects; Part II. Theoretical Description of Circumstellar Dust Shells: 3. Theory of circumstellar dust shells; 4. The energy equation for matter; 5. Radiative transfer; 6. Interaction between gas and dust particles; 7. Extinction by dust grains and gas; 8. Approaches to the temperature equations; 9. Chemistry in thermodynamic equilibrium; 10. Gas-phase chemical composition; 11. Gas-solid chemical equilibria; 12. Growth of dust grains; 13. Formation of seed nuclei; 14. Moment equations; Part III. Applications: 15. Modeling of circumstellar dust shells; 16. Miras and long-period variables; 17. Mass loss formulae; 18. R Coronae Borealis stars; Part IV. Appendices; Bibliography; Index.

Gail, Hans-Peter; Sedlmayr, Erwin

2013-12-01

278

Possible Habitability of Ocean Worlds  

NASA Astrophysics Data System (ADS)

In the last decade, the number of detected exoplanets has increased to over thousand confirmed planets and more as yet unconfirmed planet candidates. The scientific community mainly concentrates on terrestrial planets (up to 10 Earth masses) in the habitable zone, which describes the distance from the host star where liquid water can exist at the surface (Kasting et al., 1993). Another target group of interest are ocean worlds, where a terrestrial-like body (i.e. with an iron core and a silicate mantle) is covered by a thick water-ice layer - similar to the icy moons of our solar system but with several Earth masses (e.g. Grasset et al., 2009). When an exoplanet is detected and confirmed as a planet, typically the radius and the mass of it are known, leading to the mean density of the planet that gives hints to possible interior structures. A planet with a large relative iron core and a thick ocean on top of the silicate mantle for example would have the same average planet density as a planet with a more Earth-like appearance (where the main contributor to the mass is the silicate mantle). In this study we investigate how the radius and mass of a planet depend on the amount of water, silicates and iron present (after Wagner et al., 2011) the occurence of high-pressure-ice in the water-ice layer (note: we only consider surface temperatures at which liquid water exists at the surface) if the ocean layer influences the initiation of plate tectonics We assume that ocean worlds with a liquid ocean layer (and without the occurence of high-pressure ice anywhere in the water layer) and plate tectonics (especially the occurence of subduction zones, hydrothermal vents and continental formation) may be called habitable (Class III/IV habitats after Lammer et al., 2009). References: Kasting, J.F., Whitmire, D.P., and Reynolds, R.T. (1993). Habitable Zones around Main Sequence Stars. Icarus 101, 108-128. Grasset, O., Schneider, J., and Sotin, C. (2009). A study of the accuracy of mass-radius relationships for silicate-rich and ice-rich planets up to 100 Earth masses. The Astrophysical Journal 693, 722-733. Wagner, F.W., Sohl, F., Hussmann, H., Grott, M., and Rauer, H. (2011). Interior structure models of solid exoplanets using material laws in the infinite pressure limit. Icarus 214, 366-376. Lammer, H., Bredehöft, J.H., Coustenis, A., Khodachenko, M.L., Kaltenegger, L., Grasset, O., Prieur, D., Raulin, F., Ehrenfreund, P., Yamauchi, M., Wahlund, J.-E., Grießmeier, J.-M., Stangl, G., Cockell, C.S., Kulikov, Yu.N., Grenfell, J.L., and Rauer, H. (2009). What makes a planet habitable? Astron Astrophys Rev 17, 181-249.

Noack, Lena; Höning, Dennis; Bredehöft, Jan H.; Lammer, Helmut

2014-05-01

279

MAGNETIC SHIELDING OF EXOMOONS BEYOND THE CIRCUMPLANETARY HABITABLE EDGE  

SciTech Connect

With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. However, formation models predict that moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt could also have detrimental effects on exomoon habitability. Here we synthesize models for the evolution of the magnetic environment of giant planets with thresholds from the runaway greenhouse (RG) effect to assess the habitability of exomoons. For modest eccentricities, we find that satellites around Neptune-sized planets in the center of the HZ around K dwarf stars will either be in an RG state and not be habitable, or they will be in wide orbits where they will not be affected by the planetary magnetosphere. Saturn-like planets have stronger fields, and Jupiter-like planets could coat close-in habitable moons soon after formation. Moons at distances between about 5 and 20 planetary radii from a giant planet can be habitable from an illumination and tidal heating point of view, but still the planetary magnetosphere would critically influence their habitability.

Heller, René [McMaster University, Department of Physics and Astronomy, Hamilton, ON L8S 4M1 (Canada)] [McMaster University, Department of Physics and Astronomy, Hamilton, ON L8S 4M1 (Canada); Zuluaga, Jorge I., E-mail: rheller@physics.mcmaster.ca, E-mail: jzuluaga@fisica.udea.edu.co [FACom - Instituto de Física - FCEN, Universidad de Antioquia, Calle 70 No. 52-21, Medellín (Colombia)

2013-10-20

280

Trajectories of Martian Habitability  

PubMed Central

Abstract Beginning from two plausible starting points—an uninhabited or inhabited Mars—this paper discusses the possible trajectories of martian habitability over time. On an uninhabited Mars, the trajectories follow paths determined by the abundance of uninhabitable environments and uninhabited habitats. On an inhabited Mars, the addition of a third environment type, inhabited habitats, results in other trajectories, including ones where the planet remains inhabited today or others where planetary-scale life extinction occurs. By identifying different trajectories of habitability, corresponding hypotheses can be described that allow for the various trajectories to be disentangled and ultimately a determination of which trajectory Mars has taken and the changing relative abundance of its constituent environments. Key Words: Mars—Habitability—Liquid water—Planetary science. Astrobiology 14, 182–203. PMID:24506485

2014-01-01

281

Discovery and Study of Nearby Habitable Planets with Mesolensing  

E-print Network

We demonstrate that gravitational lensing can be used to discover and study planets in the habitable zones of nearby dwarf stars. If appropriate software is developed, a new generation of monitoring programs will automatically conduct a census of nearby planets in the habitable zones of dwarf stars. In addition, individual nearby dwarf stars can produce lensing events at predictable times; careful monitoring of these events can discover any planets located in the zone of habitability. Because lensing can discover planets (1) in face-on orbits, and (2) in orbit around the dimmest stars, lensing techniques will provide complementary information to that gleaned through Doppler and/or transit investigations. The ultimate result will be a comprehensive understanding of the variety of systems with conditions similar to those that gave rise to life on Earth.

Rosanne Di Stefano; Christopher Night

2008-01-09

282

The Habitability of Mars  

Microsoft Academic Search

INASMUCH as Dr. Wallace has sent me his book through his publishers, as I gather from the wrapper-though it is not so expressed-I suppose it is incumbent on me to acknowledge it, since he clearly expects some sort of reply. The effect of its perusal is to show me again how cogent is the argument for the habitability of Mars,

Percival Lowell

1908-01-01

283

Temperature Variations and Habitability  

NSDL National Science Digital Library

These are the student pages for a two part lesson plan that will teach students about observing, describing, and adapting to temperature variations and relating factors that influence planetary temperature and habitability. The class will decide upon a plan for describing indoor and outdoor environments and compare them with the data on environmental conditions at other Earth locales and planets in our solar system. These will be used to discuss temperature ranges, their relation to habitability, and ways to adapt to these conditions. In the second activity, students will give three examples of how humans modify the environment to improve livability, identify three factors that may determine the average temperature of a planet, identify a minimum of five factors that may determine the habitability of a planet, state the importance of maintaining habitable temperature on a planet, and briefly describe the links between two sets of factors of their choosing. The site provides a list of materials, objectives, and worksheets. Teachers' notes are also included.

284

Learning How to Change Habits  

MedlinePLUS

... to get ready. Then write the steps here. ___________________________________________ ___________________________________________ ___________________________________________ Learning How to Change Habits American Diabetes Association? ? 1– ... Diabetes Association, Inc. 10/13 Toolkit No. 4: Learning How to Change Habits continued Things to Do ...

285

HABITABILITY OF EXOMOONS AT THE HILL OR TIDAL LOCKING RADIUS  

SciTech Connect

Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets {mu} Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated flux on a moon at its furthest, stable distance from the planet achieves its largest flux gradient, which places a limit on the flux ranges expected for subsequent (observed) moons closer in orbit to the planet. We have also analyzed the effect of planetary eccentricity on the flux on the moon, examining planets that traverse the habitable zone either fully or partially during their orbit. Looking solely at the stellar contributions, we find that moons around planets that are totally within the habitable zone experience thermal equilibrium temperatures above the runaway greenhouse limit, requiring a small heat redistribution efficiency. In contrast, exomoons orbiting planets that only spend a fraction of their time within the habitable zone require a heat redistribution efficiency near 100% in order to achieve temperatures suitable for habitability. This means that a planet does not need to spend its entire orbit within the habitable zone in order for the exomoon to be habitable. Because the applied systems comprise giant planets around bright stars, we believe that the transit detection method is most likely to yield an exomoon discovery.

Hinkel, Natalie R.; Kane, Stephen R., E-mail: natalie.hinkel@gmail.com [NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States)

2013-09-01

286

Habitability of Exomoons at the Hill or Tidal Locking Radius  

NASA Astrophysics Data System (ADS)

Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets ? Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated flux on a moon at its furthest, stable distance from the planet achieves its largest flux gradient, which places a limit on the flux ranges expected for subsequent (observed) moons closer in orbit to the planet. We have also analyzed the effect of planetary eccentricity on the flux on the moon, examining planets that traverse the habitable zone either fully or partially during their orbit. Looking solely at the stellar contributions, we find that moons around planets that are totally within the habitable zone experience thermal equilibrium temperatures above the runaway greenhouse limit, requiring a small heat redistribution efficiency. In contrast, exomoons orbiting planets that only spend a fraction of their time within the habitable zone require a heat redistribution efficiency near 100% in order to achieve temperatures suitable for habitability. This means that a planet does not need to spend its entire orbit within the habitable zone in order for the exomoon to be habitable. Because the applied systems comprise giant planets around bright stars, we believe that the transit detection method is most likely to yield an exomoon discovery.

Hinkel, Natalie R.; Kane, Stephen R.

2013-09-01

287

Effects of extreme obliquity variations on the habitability of exoplanets.  

PubMed

We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 10(8) years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes. PMID:24611714

Armstrong, J C; Barnes, R; Domagal-Goldman, S; Breiner, J; Quinn, T R; Meadows, V S

2014-04-01

288

Habitable Planet Formation in Binary Planetary Systems  

NASA Astrophysics Data System (ADS)

Recent radial velocity observations have indicated that Jovian-type planets can exist in moderately close binary star systems. Numerical simulations of the dynamical stability of terrestrial-class planets in such environments have shown that, in addition to their giant planets, these systems can also harbor Earth-like objects. In this paper we study the late stage of terrestrial planet formation in such binary planetary systems, and present the results of the simulations of the formation of Earth-like bodies in their habitable zones. We consider a circumprimary disk of Moon- to Mars-sized objects and numerically integrate the orbits of these bodies at the presence of the Jovian-type planet of the system and for different values of the mass, semimajor axis, and orbital eccentricity of the secondary star. Results indicate that Earth-like objects, with substantial amounts of water, can form in the habitable zone of the primary star. Simulations also indicate that by transferring angular momentum from the secondary star to protoplanetary objects, the giant planet of the system plays a key role in the radial mixing of these bodies and the water contents of the final terrestrial planets. We will discuss the results of our simulation and show that the formation of habitable planets in binary planetary systems is more probable in binaries with moderate to large perihelia.

Haghighipour, Nader; Raymond, Sean N.

2007-09-01

289

Isothermal Circumstellar Dust Shell Model for Teaching  

ERIC Educational Resources Information Center

We introduce a model of radiative transfer in circumstellar dust shells. By assuming that the shell is both isothermal and its thickness is small compared to its radius, the model is simple enough for students to grasp and yet still provides a quantitative description of the relevant physical features. The isothermal model can be used in a…

Robinson, G.; Towers, I. N.; Jovanoski, Z.

2009-01-01

290

Fullerenes in Circumstellar and Interstellar Environments  

NASA Astrophysics Data System (ADS)

In recent years, the fullerene species C60 (and to a lesser extent also C70) has been reported in the mid-IR spectra of various astronomical objects. Cosmic fullerenes form in the circumstellar material of evolved stars, and survive in the interstellar medium (ISM). It is not entirely clear how they form or what their excitation mechanism is.

Cami, Jan

2015-03-01

291

Radiological Habits Survey: Devonport, 2011  

E-print Network

Radiological Habits Survey: Devonport, 2011 2012 Environment Report RL 01/12 Cefas contract report Radiological Habits Survey: Devonport, 2011 F.J. Clyne, C.J. Garrod, V.E. Ly and P. Rumney Peer reviewed by G.J., Garrod, C.J., Ly, V.E. and Rumney, P., 2012. Radiological Habits Survey: Devonport, 2011. RL 01/12. Cefas

292

Radiological Habits Survey: Dungeness, 2010  

E-print Network

Radiological Habits Survey: Dungeness, 2010 2011 Environment Report RL 11/11 Cefas contract report Radiological Habits Survey: Dungeness, 2010 F.J. Clyne, C.J. Garrod, V.E. Ly, P. Rumney and J. Elliott Peer: Clyne, F.C., Garrod, C.J., Ly, V.E., Rumney, P., and Elliott, J., 2011. Radiological Habits Survey

293

Radiological Habits Survey: Heysham, 2011  

E-print Network

Radiological Habits Survey: Heysham, 2011 2012 Environment Report RL 02/12 Cefas contract report C Radiological Habits Survey: Heysham, 2011 C.J. Garrod, F.J. Clyne, V.E. Ly and P. Rumney Peer reviewed by G, C.J., Clyne, F.J., Ly, V.E. and Rumney, P., 2012. Radiological Habits Survey: Heysham, 2011. RL 02

294

Radiological Habits Survey: Amersham, 2009  

E-print Network

Radiological Habits Survey: Amersham, 2009 2010 Environment Report RL 04/10 Cefas contract report C Radiological Habits Survey: Amersham, 2009 F.J. Clyne, C.J. Garrod and J. Elliott Peer reviewed by G.J. Hunt.C., Garrod, C.J. and Elliott, J., 2010. Radiological Habits Survey: Amersham, 2009. RL 04/10. Cefas

295

Radiological Habits Survey: Wylfa, 2013  

E-print Network

Radiological Habits Survey: Wylfa, 2013 2014 Environment Report RL 03/14 Cefas contract report C6028 #12;This page has been intentionally left blank #12;Cefas Document Control Radiological Habits blank #12;Environment Report RL 03/14 Final report Radiological Habits Survey: Wylfa, 2013 C.J. Garrod

296

Radiological Habits Survey: Derby, 2009  

E-print Network

Radiological Habits Survey: Derby, 2009 2010 Environment Report RL 05/10 Cefas contract report C Radiological Habits Survey: Derby, 2009 J. Elliott, F.J. Clyne and C.J. Garrod Peer reviewed by G.J. Hunt., Clyne, F.C. and Garrod, C.J., 2010. Radiological Habits Survey: Derby, 2009. RL 05/10. Cefas, Lowestoft

297

Radiological Habits Survey: Wylfa, 2009  

E-print Network

Radiological Habits Survey: Wylfa, 2009 2010 Environment Report RL 03/10 Cefas contract report C Radiological Habits Survey: Wylfa, 2009 C.J. Garrod, F.J. Clyne, J. Elliott and J.R. Tipple Peer reviewed by G, C. J., Clyne, F. C., Elliott, J., and Tipple, J.R., 2010. Radiological Habits Survey: Wylfa, 2009

298

Radiological Habits Survey: Sizewell, 2010  

E-print Network

Radiological Habits Survey: Sizewell, 2010 2011 Environment Report RL 12/11 Cefas contract report C Radiological Habits Survey: Sizewell, 2010 C.J. Garrod, F.J. Clyne, P. Rumney, J. Elliott, C.A. Smedley and V, J., Smedley, C., and Ly, V.E., 2011. Radiological Habits Survey: Sizewell, 2010. RL 12/11. Cefas

299

Habitable planets with high obliquities  

NASA Technical Reports Server (NTRS)

Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations.

Williams, D. M.; Kasting, J. F.

1997-01-01

300

Habitable planets with high obliquities.  

PubMed

Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations. PMID:11541242

Williams, D M; Kasting, J F

1997-01-01

301

The habitability of super-Earths in Gliese 581  

E-print Network

Aims: The planetary system around the M star Gliese 581 consists of a hot Neptune (Gl 581b) and two super-Earths (Gl 581c and Gl 581d). The habitability of this system with respect to the super-Earths is investigated following a concept that studies the long-term possibility of photosynthetic biomass production on a dynamically active planet. Methods: A thermal evolution model for a super-Earth is used to calculate the sources and sinks of atmospheric carbon dioxide. The habitable zone is determined by the limits of biological productivity on the planetary surface. Models with different ratios of land / ocean coverage are investigated. Results: The super-Earth Gl 581c is clearly outside the habitable zone, since it is too close to the star. In contrast, Gl 581d is a tidally locked habitable super-Earth near the outer edge of the habitable zone. Despite the adverse conditions on this planet, at least some primitive forms of life may be able to exist on its surface.Therefore, Gl 581d is an interesting target for the planned TPF/Darwin missions to search for biomarkers in planetary atmospheres.

W. von Bloh; C. Bounama; M. Cuntz; S. Franck

2007-10-12

302

The Solar Neighborhood: Habitable Real Estate Around Nearby Stars  

NASA Astrophysics Data System (ADS)

We have determined the amount of habitable "real estate" for 38 stars nearer than 5 parsecs. Using photometric spectral energy distributions (SEDs) derived using available and new UBVRIJHK photometry from the RECONS (Research Consortium on Nearby Stars) effort, we estimate the region around each target star in which liquid water may exist on any orbiting planet, i.e. the classical habitable zone. From the SEDs and parallax data from RECONS, we were able to estimate radii and temperatures for these stars using an IDL curve fitting function and GAIA models. These radii and temperatures were then used to estimate habitable area around each star, and the sums for each spectral type were found. Results indicate that spectral type A stars provide the most habitable real estate as a group, followed by the F stars. This research has been supported by NSF grant AST 05-07711, NASA's Space Interferometry Mission, and Georgia State University.

Cantrell, Justin R.; Jao, W.; Henry, T.; Monteiro, H.

2007-12-01

303

HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY  

SciTech Connect

In the outer regions of the habitable zone, the risk of transitioning into a globally frozen 'snowball' state poses a threat to the habitability of planets with the capacity to host water-based life. Here, we use a one-dimensional energy balance climate model (EBM) to examine how obliquity, spin rate, orbital eccentricity, and the fraction of the surface covered by ocean might influence the onset of such a snowball state. For an exoplanet, these parameters may be strikingly different from the values observed for Earth. Since, for a constant semimajor axis, the annual mean stellar irradiation scales with (1 - e {sup 2}){sup -1/2}, one might expect the greatest habitable semimajor axis (for fixed atmospheric composition) to scale as (1 - e {sup 2}){sup -1/4}. We find that this standard simple ansatz provides a reasonable lower bound on the outer boundary of the habitable zone, but the influence of both obliquity and ocean fraction can be profound in the context of planets on eccentric orbits. For planets with eccentricity 0.5, for instance, our EBM suggests that the greatest habitable semimajor axis can vary by more than 0.8 AU (78%) depending on obliquity, with higher obliquity worlds generally more stable against snowball transitions. One might also expect that the long winter at an eccentric planet's apoastron would render it more susceptible to global freezing. Our models suggest that this is not a significant risk for Earth-like planets around Sun-like stars, as considered here, since such planets are buffered by the thermal inertia provided by oceans covering at least 10% of their surface. Since planets on eccentric orbits spend much of their year particularly far from the star, such worlds might turnout to be especially good targets for direct observations with missions such as TPF-Darwin. Nevertheless, the extreme temperature variations achieved on highly eccentric exo-Earths raise questions about the adaptability of life to marginally or transiently habitable conditions.

Dressing, Courtney D.; Spiegel, David S. [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544 (United States); Scharf, Caleb A. [Columbia Astrobiology Center, Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Menou, Kristen [Kavli Institute for Theoretical Physics, UCSB, Santa Barbara, CA 93106-4030 (United States); Raymond, Sean N., E-mail: courtney@astro.princeton.ed, E-mail: dsp@astro.princeton.ed, E-mail: kristen@astro.columbia.ed, E-mail: caleb@astro.columbia.ed, E-mail: raymond@obs.u-bordeaux1.f [Universite Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France)

2010-10-01

304

Trajectories of martian habitability.  

PubMed

Beginning from two plausible starting points-an uninhabited or inhabited Mars-this paper discusses the possible trajectories of martian habitability over time. On an uninhabited Mars, the trajectories follow paths determined by the abundance of uninhabitable environments and uninhabited habitats. On an inhabited Mars, the addition of a third environment type, inhabited habitats, results in other trajectories, including ones where the planet remains inhabited today or others where planetary-scale life extinction occurs. By identifying different trajectories of habitability, corresponding hypotheses can be described that allow for the various trajectories to be disentangled and ultimately a determination of which trajectory Mars has taken and the changing relative abundance of its constituent environments. PMID:24506485

Cockell, Charles S

2014-02-01

305

Personality and health habits  

Microsoft Academic Search

Four hundred and fifty-five males and 523 females from a community sample participated in a study on the relationship between seven health practices (sleeping; breakfasting; snacking; being at good weight; smoking; alcohol consumption and physical activity) and seven personality factors (Neuroticism; Social Inadequacy; Rigidity; Hostility; Self-sufficiency; Dominance and Self-esteem).It was found that the seven health habits did not constitute a

A. J. J. M. Vingerhoets; M. Croon; A. J. Jeninga; L. J. Menges

1990-01-01

306

POST-CAPTURE EVOLUTION OF POTENTIALLY HABITABLE EXOMOONS  

SciTech Connect

The satellites of extrasolar planets (exomoons) have been recently proposed as astrobiological targets. Since giant planets in the habitable zone are thought to have migrated there, it is possible that they may have captured a former terrestrial planet or planetesimal. We therefore attempt to model the dynamical evolution of a terrestrial planet captured into orbit around a giant planet in the habitable zone of a star. We find that approximately half of loose elliptical orbits result in stable circular orbits over timescales of less than a few million years. We also find that those orbits are mostly at low inclination, but have no prograde/retrograde preference. In addition, we calculate the transit timing and duration variations for the resulting systems, and find that potentially habitable Earth-mass exomoons should be detectable.

Porter, Simon B.; Grundy, William M., E-mail: porter@lowell.edu [Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001 (United States)

2011-07-20

307

Delivery of Volatiles to Habitable Planets in Extrasolar Planetary Systems  

NASA Technical Reports Server (NTRS)

The Earth can support life because: (1) its orbit lies in the Sun's habitable zone', and (2) it contains enough volatile material (e.g. water and organics) for life to flourish. However, it seems likely that the Earth was drier when it formed because it accreted in a part of the Sun's protoplanetary nebula that was too hot for volatiles to condense. If this is correct, water and organics must have been delivered to the habitable zone, after dissipation of the solar nebula, from a 'wet zone' in the asteroid belt or the outer solar system, where the nebula was cool enough for volatiles to condense. Material from the wet zone would have been delivered to the Earth by Jupiter and Saturn. Gravitational perturbations from these giant planets made much of the wet zone unstable, scattering volatile-rich planetesimals and protoplanets across the Solar System. Some of these objects ultimately collided with the inner Planets which themselves lie in a stable part of the Solar System. Giant planets are now being discovered orbiting other sunlike stars. To date, these planets have orbits and masses very different from Jupiter and Saturn, such that few if any of these systems is likely to have terrestrial planets in the star's habitable zone. However, new discoveries are anticipated due to improved detector sensitivity and the increase in the timespan of observations. Here we present numerical experiments examining the range of giant-planet characteristics that: (1) allow stable terrestrial Planets to exist in a star's habitable zone, and (2) make a large part of the star's wet zone weakly unstable, thus delivering volatiles to the terrestrial planets over an extended period of time after the dissipation of the solar nebula.

Chambers, John E.; Kress, Monika E.; Bell, K. Robbins; Cash, Michele; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

308

Stellar masers, circumstellar envelopes, and supernova remnants  

E-print Network

This paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

Athol J. Kemball

2007-05-15

309

Circumstellar Material Around Evolved Massive Stars  

Microsoft Academic Search

I review multiwavelength observations of material seen around different types of evolved massive stars (i.e. red supergiants, yellow hypergiants, luminous blue variables, B[e] supergiants, and Wolf-Rayet stars), concentrating on diagnostics of mass, composition, and kinetic energy in both local and distant examples. Circumstellar material has significant implications for the evolutionary state of the star, the role of episodic mass loss

Nathan Smith

2011-01-01

310

Circumstellar Material Around Evolved Massive Stars  

Microsoft Academic Search

I review multiwavelength observations of material seen around different types\\u000aof evolved massive stars (i.e. red supergiants, yellow hypergiants, luminous\\u000ablue variables, B[e] supergiants, and Wolf-Rayet stars), concentrating on\\u000adiagnostics of mass, composition, and kinetic energy in both local and distant\\u000aexamples. Circumstellar material has significant implications for the\\u000aevolutionary state of the star, the role of episodic mass loss

Nathan Smith

2010-01-01

311

Computer codes for evaluation of control room habitability (HABIT)  

SciTech Connect

This report describes the Computer Codes for Evaluation of Control Room Habitability (HABIT). HABIT is a package of computer codes designed to be used for the evaluation of control room habitability in the event of an accidental release of toxic chemicals or radioactive materials. Given information about the design of a nuclear power plant, a scenario for the release of toxic chemicals or radionuclides, and information about the air flows and protection systems of the control room, HABIT can be used to estimate the chemical exposure or radiological dose to control room personnel. HABIT is an integrated package of several programs that previously needed to be run separately and required considerable user intervention. This report discusses the theoretical basis and physical assumptions made by each of the modules in HABIT and gives detailed information about the data entry windows. Sample runs are given for each of the modules. A brief section of programming notes is included. A set of computer disks will accompany this report if the report is ordered from the Energy Science and Technology Software Center. The disks contain the files needed to run HABIT on a personal computer running DOS. Source codes for the various HABIT routines are on the disks. Also included are input and output files for three demonstration runs.

Stage, S.A. [Pacific Northwest Lab., Richland, WA (United States)

1996-06-01

312

Longevity of moons around habitable planets  

NASA Astrophysics Data System (ADS)

We consider tidal decay lifetimes for moons orbiting habitable extrasolar planets using the constant Q approach for tidal evolution theory. Large moons stabilize planetary obliquity in some cases, and it has been suggested that large moons are necessary for the evolution of complex life. We find that the Moon in the Sun-Earth system must have had an initial orbital period of not slower than 20 h rev-1 for the moon's lifetime to exceed a 5 Gyr lifetime. We assume that 5 Gyr is long enough for life on planets to evolve complex life. We show that moons of habitable planets cannot survive for more than 5 Gyr if the stellar mass is less than 0.55 and 0.42 M ? for Q p=10 and 100, respectively, where Q p is the planetary tidal dissipation quality factor. Kepler-62e and f are of particular interest because they are two actually known rocky planets in the habitable zone. Kepler-62e would need to be made of iron and have Q p=100 for its hypothetical moon to live for longer than 5 Gyr. A hypothetical moon of Kepler-62f, by contrast, may have a lifetime greater than 5 Gyr under several scenarios, and particularly for Q p=100.

Sasaki, Takashi; Barnes, Jason W.

2014-10-01

313

Planetary habitability: lessons learned from terrestrial analogues  

NASA Astrophysics Data System (ADS)

Terrestrial analogue studies underpin almost all planetary missions and their use is essential in the exploration of our Solar system and in assessing the habitability of other worlds. Their value relies on the similarity of the analogue to its target, either in terms of their mineralogical or geochemical context, or current physical or chemical environmental conditions. Such analogue sites offer critical ground-truthing for astrobiological studies on the habitability of different environmental parameter sets, the biological mechanisms for survival in extreme environments and the preservation potential and detectability of biosignatures. The 33 analogue sites discussed in this review have been selected on the basis of their congruence to particular extraterrestrial locations. Terrestrial field sites that have been used most often in the literature, as well as some lesser known ones which require greater study, are incorporated to inform on the astrobiological potential of Venus, Mars, Europa, Enceladus and Titan. For example, the possibility of an aerial habitable zone on Venus has been hypothesized based on studies of life at high-altitudes in the terrestrial atmosphere. We also demonstrate why many different terrestrial analogue sites are required to satisfactorily assess the habitability of the changing environmental conditions throughout Martian history, and recommend particular sites for different epochs or potential niches. Finally, habitable zones within the aqueous environments of the icy moons of Europa and Enceladus and potentially in the hydrocarbon lakes of Titan are discussed and suitable analogue sites proposed. It is clear from this review that a number of terrestrial analogue sites can be applied to multiple planetary bodies, thereby increasing their value for astrobiological exploration. For each analogue site considered here, we summarize the pertinent physiochemical environmental features they offer and critically assess the fidelity with which they emulate their intended target locale. We also outline key issues associated with the existing documentation of analogue research and the constraints this has on the efficiency of discoveries in this field. This review thus highlights the need for a global open access database for planetary analogues.

Preston, Louisa J.; Dartnell, Lewis R.

2014-01-01

314

FUSE Observations of the ? Pic Circumstellar Environment  

NASA Astrophysics Data System (ADS)

We present the first far UV spectrum of Beta Pictoris obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Although the stellar continuum drops below detectability for wavelengths shorter than 1100 Å, the Ciii line at 977 Å and the Ovi doublet at 1032 and 1037 Å are clearly detected in emission. These emissions are believed to have a stellar origin. Because we did not detect H2 absorption in our spectrum, the coincidence of Ovi and H2 transitions allows us to set a very low upper limit on the H2 column density toward ? Pic. This is surprising, as Beta Pic has one of the largest circumstellar disks seen around a main-sequence star. From the comparison with HST observations, we obtain a CO/H2 ratio above the typical interstellar value of 10-4; this seems to confirm the circumstellar origin of the observed CO. Species observed in the ? Pic circumstellar gas at the stellar radial velocity, like Feii and Caii, feel strong radiation pressure from the star and should be ejected from the system. Lagrange et al. (1998) suggested that these species could be slowed down by a thick, colliding torus of massive gas; our non-detection of H2 toward Beta Pic leaves this dynamical problem unresolved. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U.S. participants has been provided by NASA contract NAS5-32985.

Lecavelier des Etangs, A.; Vidal-Madjar, A.; Ferlet, R.; Roberge, A.; Feldman, P. D.; Deleuil, M.; Bouret, J.-C.; André, M.; Blair, W. P.; Moos, H. W.; FUSE Science Team

2000-12-01

315

How Common are Habitable Planets?  

NASA Technical Reports Server (NTRS)

The Earth is teeming with life, which, occupies a diverse array of environments; other bodies in our Solar System offer fewer, if any, niches which are habitable by life as we know it. Nonetheless, astronomical studies suggest that a large number of habitable planets-are likely to be present within our Galaxy.

Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

2000-01-01

316

What Makes a Habitable Planet?  

NASA Astrophysics Data System (ADS)

Space missions help answer one of humanity's most profound questions: Are we alone in the universe? To begin to understand what makes a planet habitable, and thus where to look for life both within and outside of Earth's solar system, scientists need to understand what in planetary formation and what in its subsequent evolution combine to produce a habitable planet.

Elkins-Tanton, L.

2013-04-01

317

Language Habits of the Japanese.  

ERIC Educational Resources Information Center

Contrasts Japanese language habits with Western language habits, asserting that Japanese need to speak more concisely, express themselves clearly and frankly, and eliminate superfluous polite language and preliminaries in order to be successful in the efficiency-oriented civilization that is a product of Western culture. (RAE)

Kinosita, Koreo

1988-01-01

318

Radiological Habits Survey: Sellafield, 2013  

E-print Network

Radiological Habits Survey: Sellafield, 2013 2014 Environment Report RL 02/14 Cefas contract report C6028 #12;This page has been intentionally left blank #12; Cefas Document Control Radiological #12;This page has been intentionally left blank #12;Environment Report RL 02/14 Radiological Habits

319

The Beta Pictoris Circumstellar Disk (5202; 2ND Visit)  

NASA Astrophysics Data System (ADS)

We propose new methods to examine the circumstellar disk around Beta Pictoris in order to determine its radial profile, and hence (in combination with IRAS data) to fix its albedo and temperature profile. These observations will extend previous extensive ground based coronagraphic observations, and models by members of the science team. The data will enable us to understand better the central clearing in the disk and whether it is caused by sublimation or possible planet formation. They will also constrain the geometric propertie of the disk including its inclination angle, vertical thickness and radial profile. Such observations limit models for the dynamics of the disk, includin its velocity dispersion and hence mass distribution, and radial mass transport mechanisms. If density waves or clear zones are observed, they will give indirect evidence for the presence of massive bodies (planets) in the disk. Th observations involve a combination of roll deconvolution, polarizers and PSF modelling in order to allow the central stellar image and associated scattered light to be subtracted. Ultraviolet observations will constrain the particle size distribution and the composition of the disk. The observations require the new capabilities in WFPC2 provided by the absence of bleeding across columns, as well as its UV capabilities.

Trauger, John

1994-01-01

320

The Circumstellar Dust Disk of HD 100546  

NASA Astrophysics Data System (ADS)

We investigate the chemical composition, dust grain size range, and disk extent of the circumstellar disk surrounding the well-studied Herbig Ae star HD 100546. We model the spectrophotometric and multi-wavelength imaging observations using 2-Dust, a radiative transfer code, capable of producing spectral energy distributions (SEDs) and projected surface brightness maps. The SEDs and surface brightness maps are modeled using a passive disk in radiative and hydrostatic equilibrium, but with the addition of crystalline silicate forsterite grains, which are know to be present in the circumstellar dust composition of HD 100546 from spectroscopic observations. We compare the modeled SED to an observed SED constructed using spectra from the International Ultraviolet Explorer, the Infrared Space Observatory (ISO) Long-Wavelength and Short-Wavelength Spectrometer, photometric points from Infra-Red Astronomical Satellite (IRAS), and the literature. Likewise, we compare the modeled surface brightness images to near-IR ADONIS and NICMOS2 chronographic observations and ACS optical coronagraphic observations. We find that a layered passive disk used in some recent HD 1000546 SED models is not necessary to match its unusually large mid-IR excess. This research was funded by NASA/NAG5-12595.

Hedrick, C. H.; Doering, R.; Lee, K.-G.; Sosey, M.; Meixner, M.; Ardila, D.

2005-12-01

321

The Structure of Brown Dwarf Circumstellar Disks  

E-print Network

We present synthetic spectra for circumstellar disks that are heated by radiation from a central brown dwarf. Under the assumption of vertical hydrostatic equilibrium, our models yield scaleheights for brown dwarf disks in excess of three times those derived for classical T Tauri (CTTS) disks. If the near-IR excess emission observed from brown dwarfs is indeed due to circumstellar disks, then the large scaleheights we find could have a significant impact on the optical and near-IR detectability of such systems. Our radiation transfer calculations show that such highly flared disks around brown dwarfs will result in a large fraction of obscured sources due to extinction of direct starlight by the disk over a wide range of sightlines. The obscured fraction for a 'typical' CTTS is less than 20%. We show that the obscured fraction for brown dwarfs may be double that for CTTS, but this depends on stellar and disk mass. We also comment on possible confusion in identifying brown dwarfs via color-magnitude diagrams: edge-on CTTS display similar colors and magnitudes as a face-on brown dwarf plus disk systems.

Christina Walker; Kenneth Wood; C. J. Lada; Thomas Robitaille; J. E. Bjorkman; Barbara Whitney

2004-03-11

322

Circumstellar environment of close PMS binary systems  

NASA Astrophysics Data System (ADS)

Based on observations obtained on the 3.60m ESO telescope at La Silla, Chile, with the ADONIS adaptative optics system. We present preliminary results of a survey in the near IR domain (1-5 microns : in the JHKL&M filters) of a sample of tight PMS binary stars (0.2 - 2.6''). This survey has been carried out with the ADONIS ESO adaptive optics system equiped with the new near IR camera COMIC. All the CTTS systems in our list but one, show evidence of circumstellar disks around one or both components, while none but one of the WTTS systems do. In all the intrinsically reddened systems, the primary (defined as the brighter component) appears redder that the secondary (ie. with a larger H-K). The wider systems appear redder (larger H-K) than the tighter ones, a result consistent with the hypothesis that the presence of a companion tends to clear the inner circumstellar disk(s).

Monin, Jean-Louis; Geoffray, Herve; Menard, Francois

323

Assessing Habitability: Lessons from the Phoenix Mission  

NASA Technical Reports Server (NTRS)

The Phoenix mission's key objective was to search for a habitable zone. The Phoenix lander carried a robotic arm with digging scoop to collect soil and icy material for analysis with an instrument payload that included volatile mineral and organic analysis(3) and soil ionic chemistry analysis (4). Results from Phoenix along with theoretical modeling and other previous mission results were used to evaluate the habitability of the landing site by considering four factors that characterize the environments ability to support life as we know it: the presence of liquid water, the presence of an energy source to support metabolism, the presence of nutrients containing the fundamental building blocks of life, and the absence of environmental conditions that are toxic to or preclude life. Phoenix observational evidence for the presence of liquid water (past or present) includes clean segregated ice, chemical etching of soil grains, calcite minerals in the soil and variable concentrations of soluble salts5. The maximum surface temperature measured was 260K so unfrozen water can form only in adsorbed films or saline brines but warmer climates occur cyclically on geologically short time scales due to variations in orbital parameters. During high obliquity periods, temperatures allowing metabolism extend nearly a meter into the subsurface. Phoenix discovered 1%w/w perchlorate salt in the soil, a chemical energy source utilized by a wide range of microbes. Nutrient sources including C, H, N, O, P and S compounds are supplied by known atmospheric sources or global dust. Environmental conditions are within growth tolerance for terrestrial microbes. Summer daytime temperatures are sufficient for metabolic activity, the pH is 7.8 and is well buffered and the projected water activity of a wet soil will allow growth. In summary, martian permafrost in the north polar region is a viable location for modern life. Stoker et al. presented a formalism for comparing the habitability of various regions visited to date on Mars that involved computing a habitability probability, defined as the product of probabilities for the presence of liquid water (P(sub lw)), energy (P(sub e)), nutrients (P(sub ch)), and a benign environment (P(sub b)). Using this formalism, they argued that the Phoenix site was the most habitable of any site visited to date by landed missions and warranted a follow up mission to search for modern evidence of life. This paper will review that conclusion in view of more recent information from the Mars Exploration Rovers and Mars Science Lander missions.

Stoker, Carol R.

2013-01-01

324

ROTATIONAL SYNCHRONIZATION MAY ENHANCE HABITABILITY FOR CIRCUMBINARY PLANETS: KEPLER BINARY CASE STUDIES  

SciTech Connect

We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression toward planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of X-ray and ultraviolet (XUV) radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogs have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.

Mason, Paul A. [Department of Physics, University of Texas at El Paso, El Paso, TX 79968 (United States); Zuluaga, Jorge I.; Cuartas-Restrepo, Pablo A. [FACom-Instituto de Fisica-FCEN, Universidad de Antioquia, Calle 70 No. 52-21, Medellin (Colombia); Clark, Joni M. [Department of Mathematics and Physical Sciences, New Mexico State University-DACC, Las Cruces, NM 88003 (United States)

2013-09-10

325

Rotational Synchronization May Enhance Habitability for Circumbinary Planets: Kepler Binary Case Studies  

NASA Astrophysics Data System (ADS)

We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression toward planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of X-ray and ultraviolet (XUV) radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogs have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.

Mason, Paul A.; Zuluaga, Jorge I.; Clark, Joni M.; Cuartas-Restrepo, Pablo A.

2013-09-01

326

Obesity and Smoking Habits  

PubMed Central

A large-scale survey of steel workers in South Wales has shown a considerable difference between the body weights of smokers and of non-smokers. The difference increases with age so that men over 40 years who have never smoked are on average 13 lb (5·9 kg) heavier than smokers. Even so, smokers are about 15 lb (6·8 kg) heavier than the weight standard considered desirable by the Metropolitan Life Insurance Company, while non-smokers are nearly 30 lb (13·6 kg) heavier. About 20% of the men are attempting to give up the smoking habit. Ex-smokers who have given up smoking for more than eight years approach the body weight of men of the same age who have never smoked. Many reports have been published on the health consequences of smoking and of obesity. Because smoking and obesity are inversely related studies of the interrelation of these two health hazards and of their relative importance are needed. PMID:5096876

Khosla, T.; Lowe, C. R.

1971-01-01

327

Endolithic microniches support habitability  

NASA Astrophysics Data System (ADS)

Particular micro-niches on extreme environments give us some clues about the habitability potential under protected environments with important connotations from an astrobiological point of view [1]. The salts precipitation patters in extreme environments can contribute to biomineralization processes which could be of special interest for organics but also life preservation on environmental harsh conditions. These "oasys" for organics and/or life forms are of special as trobiological interest and should attract our attention in other planets and we should be looking for it during rover exploration missions. Endolithic micro niches in Rio Tinto salts precipitates determine controlled scenarios where phototrops develop under controlled conditions. Rio Tinto, 100 km river located at South West of Spain, is being taken as a well reported Mars analog due to the similarities in the mineralogy of the system which that reported by MER Opportunity Rover missions which landed in Meridiani Planum where sedimentary deposits have been identified in different craters [2]. Interesting multi layered salty deposits were identified in Rio Tinto source area where endolithic micro niches were settled [3]. Green layers appear included in brown stratified salt precipitates. The crust deposit was between 5 mm and 1 cm width. The layered structure is deposited over rocks or over man made structures as dam or mining tunnels walls but always in places with specific environmental characteristics. It appears in not direct Sun light exposed places (shadow side of walls) with thermal and pH stability.

Gómez, F.; Rodríguez, N.; Rodríguez-Manfredi, J. A.; Fernández-Sampedro, M.; Amils, R.

2013-09-01

328

Magnetic shielding of exomoons beyond the circumplanetary habitable edge  

E-print Network

With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants, rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. But formation models predict moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt could also have detrimental effects on exomoon habitability. We here synthesize models for the evolution of the magnetic environment of giant planets with thresholds from the runaway greenhouse (RG) effect to assess the habitability of exomoons. For modest eccentricities, we find that satellites around Neptune-sized planets in the center of the HZ around K dwarf stars will either be in an RG state and not be habitable, ...

Heller, René

2013-01-01

329

Prospects for the habitability of OGLE-2006-BLG-109L  

E-print Network

The extrasolar system OGLE-2006-BLG-109L is the first multiple-planet system to be discovered by gravitational microlensing (Gaudi et al., 2008); the two large planets that have been detected have mass ratios, semimajor axis ratios, and equilibrium temperatures that are similar to those of Jupiter and Saturn; the mass of the host star is only 0.5 M_sun, and the system is more compact than our own Solar system. We find that in the habitable zone of the host star, the two detected planets resonantly excite large orbital eccentricities on a putative earth-mass planet, driving such a planet out of the habitable zone. We show that an additional inner planet of ~>0.3M_earth at habitability of the system. Thus, the planetary architecture of a potentially habitable OGLE-2006-BLG-109L planetary system -- with two ``terrestrial'' planets and two jovian planets -- could bear very close resemblance to our own Solar system.

Renu Malhotra; David A. Minton

2008-06-27

330

Healthy habits for weight loss  

MedlinePLUS

... habits if your shelves are lined with sugary snacks. Rearrange the kitchen to make diet-boosting foods ... you feel hungry, you'll have a healthy snack close at hand. Reduce temptation. If you know ...

331

HL Tauri and its circumstellar disk  

NASA Technical Reports Server (NTRS)

New far infrared observations of HL Tau which support the identification of an edge-on disk surrounding the star are presented. A bolometric luminosity for the star of 7.2 solar luminosities and a ratio of infrared to optical luminosity of 630 are indicated. A circumstellar A(V) of about 7.0 mag is produced, consistent with the silicate optical depth to the star. Data on HL Tau's effective temperature and radius and its position on the HR diagram suggest that the star has recently completed its accretion phase and is only 100,000 yr old. The column masses of ice and silicates are combined with the disk dimensions to build a simple model of the disk for comparison with the primitive solar nebula. Estimates of the far-infrared emitting mass provide independent probes of the mass in larger grains around HL Tau.

Cohen, M.

1983-01-01

332

The interaction of supernovae with circumstellar bubbles  

NASA Technical Reports Server (NTRS)

This paper examines the interaction of a massive star supernova with the shell created by the fast wind from a blue supergiant, either in the main-sequence phase or in a late evolutionary phase. Making a number of idealizations, the general features of shell interaction are described by semianalytical solutions. The expected properties of the supernova and its environment are discussed, and the hydrodynamics of the interaction is described. It is found that, typically, the shock traversal occurs before the energy transfer is significant. Applications of the model to observed objects are considered, with special attention given to the interaction of SN 1987A with its circumstellar shell, which is expected to occur within decades.

Chevalier, Roger A.; Liang, Edison P.

1989-01-01

333

Constraints on planetary habitability from interior modelling  

NASA Astrophysics Data System (ADS)

The most interesting planetary bodies outside the Solar System regarding the search for life are potentially rocky extrasolar planets. Some of them may feature surface conditions that allow for liquid water, which is the elementary prerequisite for life as we know it. The amount of greenhouse gases, like e.g. carbon dioxide (CO2), plays an important role for the determination of the surface temperature, hence the habitability of an extrasolar planet. The amount of greenhouse gases is strongly influenced by their outgassing from the interior. In this study, we investigate under which conditions the planetary interior structure and dynamics allow for the build-up of planetary atmospheres which may lead to habitable surface conditions. We investigate the evolution of a secondary atmosphere for Earth-sized planets with different interior structures (i.e. iron-silicate mixing ratios) by applying a two-dimensional model of interior dynamics [1], which allows for the calculation of the production of partial melt [2]. From this, we estimate the amount of CO2 outgassing for Earth-sized planets with different core and mantle radii after adapting the total CO2 outgassing in 4.5 Gyr for a Venus reference simulation to the present-day atmosphere of Venus. We furthermore investigate the possible influence of plate tectonics on outgassing and the likelihood of plate tectonics depending on the interior structure of the planet. We find that the size of the iron core has a large impact on the production of partial melt, hence on the possible outgassing of CO2, which is due to the pressure-dependence of the melting temperature of silicate rocks: for planets with a large core the planetary mass is larger than for a planet with a small iron core, leading to larger melting temperatures in the upper mantle. Therefore only little outgassing from the interior can be expected. However, for the determination of the outer edge of the habitable zone it is typically assumed that enough greenhouse gas CO2 is available in the atmosphere to lead to liquid water at the surface - independent of the interior of the planet [3]. Our results on the other hand suggest that the outer boundary of the habitable zone may be constrained by the production of partial melt in the interior for planets with a large iron core and a thin silicate mantle. However, if plate tectonics initiates, several tens of bars of CO2 can be outgassed in a short time also for planets with a large iron core. In this case the outer boundary of the habitable zone would not be limited by outgassing as is the case for stagnant-lid planets. It is, however, questionable if planets with a very thin mantle are able to initiate plate tectonics. References [1] Hüttig, C. and Stemmer, K. (2008), PEPI, 171(1-4):137-146. [2] Plesa, A.-C. and Spohn, T. (2012), Transactions of the HLRS 2011, Springer, 551-565. [3] Kasting, J., Whitmire, D.P. and Reynolds, R.T. (1993), Icarus, 101:108-128.

Noack, Lena; Godolt, Mareike; von Paris, Philip; Plesa, Ana-Catalina; Stracke, Barbara; Breuer, Doris; Rauer, Heike

2013-04-01

334

Habitability: from stars to cells  

Microsoft Academic Search

To determine where to search for life in our solar system or in other extrasolar systems, the concept of habitability has\\u000a been developed, based on the only sample we have of a biological planet—the Earth. Habitability can be defined as the set\\u000a of the necessary conditions for an active life to exist, even if it does not exist. In astronomy,

Emmanuelle J. Javaux; Véronique Dehant

2010-01-01

335

Circumstellar dust: From protostars to planetary systems  

NASA Astrophysics Data System (ADS)

A combination of theoretical work and observational discoveries over the past three decades has led to significant advances in our understanding of the star and planet formation process. However, many important questions remain to be addressed, especially regarding the earliest phases of protostellar collapse and the transformation of circumstellar disks into planetary systems. In this thesis, I have undertaken a theoretical study of ``Class 0'' protostars and an observational investigation of the evolution of protoplanetary disks, diversity of planetary debris systems, and the kinship between dusty remnants and planets, using a new generation of infrared and sub- millimeter instruments. I present radiative transfer calculations of infalling envelopes surrounding Class 0 sources, compare them to the observed spectral energy distributions and radial intensity profiles, and derive mass infall rates. The rapid infall, probably inevitable given their dense environments, and the relatively flat inferred density distribution, perhaps due to contributions from external cloud material, lead us to suggest that many Class 0 sources could be the protostars of dense regions. It has been suggested that circumstellar disks evolve from massive, optically thick, actively accreting structures to low-mass, optically thin, passive remnants in about 10 Myr. That transition may mark the assembly of grains into planetesimals, or clearing of the disk by planets. I present mid infrared observation of the TW Hydrate Association, a recently identified nearby group of 10-Myr-old stars. The results suggest rapid evolution of inner disks as does our discovery of a spatially- resolved disk with a central cavity around the young A star HR 4796A. I also present the results of mid-infrared imaging of 11 other Vega-like stars, derive global properties of the dust disks, place constraints on their sizes, and discuss several interesting cases in detail. Finally, I report the detection of dust emission from a possible Kuiper Belt around 55 Cancri, a star with known planetary companion(s).

Jayawardhana, Ray

2000-11-01

336

On the Inclination and Habitability of the HD 10180 System  

NASA Astrophysics Data System (ADS)

There are numerous multi-planet systems that have now been detected via a variety of techniques. These systems exhibit a range of both planetary properties and orbital configurations. For those systems without detected planetary transits, a significant unknown factor is the orbital inclination. This produces an uncertainty in the mass of the planets and their related properties, such as atmospheric scale height. Here we investigate the HD 10180 system, which was discovered using the radial velocity technique. We provide a new orbital solution for the system which allows for eccentric orbits for all planets. We show how the inclination of the system affects the mass/radius properties of the planets and how the detection of phase signatures may resolve the inclination ambiguity. We finally evaluate the Habitable Zone properties of the system and show that the g planet spends 100% of an eccentric orbit within the Habitable Zone.

Kane, Stephen R.; Gelino, Dawn M.

2014-09-01

337

Delegation: developing the habit.  

PubMed

Often, individuals take personal delegation skills for granted and assume the presence of expertise with the practice of delegation, which may not be the case. Those assumptions can be found at both ends of the process, with the manager and the employee. Every time a manager places an employee in a job and gives him or her a job description or a set of instructions, the manager has delegated. The manager has placed someone in a position to perform operations for which ultimately the manager is responsible. Delegation is both a process and a condition. The process is the act of assigning work to an employee; the condition of delegating a job is a thorough and mutual understanding between the supervisor and the employee of specific results and methods by which these results can be achieved. The condition goes far beyond the simple process of assigning a job. The point at which many managers fail in delegating is in neglecting to move past the process and take the required steps to establish a true condition of delegation. Failure to delegate is the leading cause of managers retarding their professional growth. In the case of a workaholic--someone who fails to learn the value of delegation--the job soon becomes too much, and the effectiveness of the department may suffer. By reducing the burden of technical duties and busy work, managers will find that it is possible to be more effective and actually spend more time managing. A number of the reasons why managers fail to delegate are complex and subconscious, such as insecurity, fear of competition and even fear of not being recognized for accomplishments achieved. Other reasons for failing to delegate are habit and shortages of staff members or time. Delegation is an investment in time. The eventual gain from such an investment, which may temporarily cause the department to fall further behind during a training period, outweighs the costs. The manager is the final authority in such duties as approval, recommendations and implementations. Remember that to delegate authority does not mean to delegate ultimate responsibility. Only the manager should bear the burden of responsibilities that directly affect his or her career. One of the most common mistakes in the process of delegating is to turn an employee loose on a job with inadequate instruction. Too often this is caused by lack of time. Strictly speaking, when managers assign tasks to employees, they are delegating the authority to perform the task. However, all responsibility for the completion of the task remains with the manager. In most instances, responsibility for the failure of a delegated project lies with the manager, not the employee. While some failure is to be expected, it can be minimized by proper evaluation of the situation and proper communication. Delegation is a calculated risk. The manager should be willing to take a risk to see if an employee does have the skills and ability to perform the specific task. How else will the manager ever know? Developing a strong habit of delegation will lead to development of an effective and efficient staff and department. Delegation will serve not only the organization well, but also managers throughout their careers. PMID:11499078

Duehring, G L

2001-01-01

338

Habitable moons around extrasolar giant planets  

NASA Astrophysics Data System (ADS)

Possible planetary objects have now been discovered1-9 orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone'10, where life-supporting liquid water11 could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere.

Williams, Darren M.; Kasting, James F.; Wade, Richard A.

1997-01-01

339

Habitable moons around extrasolar giant planets  

NASA Technical Reports Server (NTRS)

Possible planetary objects have now been discovered orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone', where life-supporting liquid water could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere.

Williams, D. M.; Kasting, J. F.; Wade, R. A.

1997-01-01

340

Habitable moons around extrasolar giant planets.  

PubMed

Possible planetary objects have now been discovered orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone', where life-supporting liquid water could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere. PMID:9000072

Williams, D M; Kasting, J F; Wade, R A

1997-01-16

341

Managing away bad habits.  

PubMed

We've all worked with highly competent people who are held back by a seemingly fatal personality flaw. One person takes on too much work; another sees the downside in every proposed change; a third pushes people out of the way. At best, people with these "bad habits" create their own glass ceilings, which limit their success and their contributions to the company. At worst, they destroy their own careers. Although the psychological flaws of such individuals run deep, their managers are not helpless. In this article, James Waldroop and Timothy Butler--both psychologists--examine the root causes of these flaws and suggest concrete tactics they have used to help people recognize and correct the following six behavior patterns: The hero, who always pushes himself--and subordinates--too hard to do too much for too long. The meritocrat, who believes that the best ideas can and will be determined objectively and ignores the politics inherent in most situations. The bulldozer, who runs roughshod over others in a quest for power. The pessimist, who always worries about what could go wrong. The rebel, who automatically fights against authority and convention. And the home run hitter, who tries to do too much too soon--he swings for the fences before he's learned to hit singles. Helping people break through their self-created glass ceilings is the ultimate win-win scenario: both the individual and the organization are rewarded. Using the tactics introduced in this article, managers can help their brilliantly flawed performers become spectacular achievers. PMID:11143157

Waldroop, J; Butler, T

2000-01-01

342

Exozodiacal Dust: Noise Source and Signpost for Habitable Planets  

NASA Astrophysics Data System (ADS)

Exozodiacal light, from debris material in other planetary systems, is both a noise source for future exoplanet imaging missions and a signpost of rocky material in, or near, the habitable zone. The LBT Interferometer has been designed to discover and characterize faint exozodiacal dust around nearby stars. This talk will summarize what we currently know about exozodiacal dust and what we aim to learn with the LBTI's survey, the Hunt for Observable Signatures of Terrestrial Planets (HOSTS).

Hinz, P.

2014-03-01

343

Exotic Earths: Forming Habitable Worlds with Giant Planet Migration  

E-print Network

Close-in giant planets (e.g. ``Hot Jupiters'') are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth mass planets also form interior to the migrating Jovian planet, analogous to recently-discovered ``Hot Earths''. Very water-rich, Earth-mass planets form from surviving material outside the giant planet's orbit, often in the Habitable Zone and with low orbital eccentricities. More than a third of the known systems of giant planets may harbor Earth-like planets.

Sean N. Raymond; Avi M. Mandell; Steinn Sigurdsson

2006-09-08

344

Exotic Earths: forming habitable worlds with giant planet migration.  

PubMed

Close-in giant planets (e.g., "hot Jupiters") are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth-mass planets also form interior to the migrating jovian planet, analogous to recently discovered "hot Earths." Very-water-rich, Earth-mass planets form from surviving material outside the giant planet's orbit, often in the habitable zone and with low orbital eccentricities. More than a third of the known systems of giant planets may harbor Earth-like planets. PMID:16960000

Raymond, Sean N; Mandell, Avi M; Sigurdsson, Steinn

2006-09-01

345

What Grain Alignment can Tell about Circumstellar Disks and Comets  

E-print Network

Grain alignment theory suggests that grains should be aligned in circumstellar regions and the observational data available supports this conclusion. We discuss the alignment of grains via (1) magnetic relaxation, (2) mechanical processes, and (3) radiative torques. We show that ferromagnetic relaxation is likely to be more important than superparamagnetic relaxation if the dust in circumstellar regions is similar to species recently captured in Earth atmosphere. Outflows and stellar winds provide grain streaming along magnetic field lines and therefore mechanical alignment competes with the ferromagnetic and radiative alignments. We estimate measures of grain alignment in circumstellar regions, comets and interplanetary space and conclude that in many circumstellar regions and in the interplanetary space radiative torques may constitue the major alignment mechanism which aligns grain longer axes perpendicular to the direction of magnetic field. Observations in submillimeter and microwave ranges are suggested as a means of disentangling effects of multiple scattering from those related to aligned grains.

Lazarian A

1998-11-03

346

The origin and formation of the circumstellar disc  

NASA Astrophysics Data System (ADS)

The formation and evolution of the circumstellar disc in the collapsing molecular cloud with and without magnetic field is investigated from the pre-stellar stage resolving both the molecular cloud core and the protostar itself. In the collapsing cloud core, the first (adiabatic) core appears prior to the protostar formation. Reflecting the thermodynamics of the collapsing gas, the first core is much more massive than the protostar. When the molecular cloud has no angular momentum, the first core falls on to the protostar and disappears a few years after the protostar formation. On the other hand, when the molecular cloud has an angular momentum, the first core does not disappear even after the protostar formation, and directly evolves into the circumstellar disc with a Keplerian rotation. There are two paths for the formation of the circumstellar disc. When the initial cloud has a considerably small rotational energy, two nested discs appear just after the protostar formation. During the early main accretion phase, the inner disc increases its size and merges with the outer disc (i.e. first core) to form a single circumstellar disc with a Keplerian rotation. On the other hand, when the molecular cloud has a rotational energy comparable to observations, a single centrifugally supported disc that corresponds to the first core already exists prior to the protostar formation. In such a cloud, the first core density gradually increases, maintaining the Keplerian rotation and forms the protostar inside it. The magnetic field rarely affects the early formation of the circumstellar disc because the magnetic field dissipates in the high-density gas region where the circumstellar disc forms. As a result, in any case, the protostar at its formation is already surrounded by a massive circumstellar disc. The circumstellar disc is about 10-100 times more massive than the protostar in the main accretion phase. Such discs are favourable sites for the formation of binary companions and gas-giant planets.

Machida, Masahiro N.; Matsumoto, Tomoaki

2011-06-01

347

The Warped Circumstellar Disk of HD100546  

E-print Network

We propose that the two armed spiral features seen in visible Hubble Space Telescope images of scattered light in HD100546's circumstellar disk are caused by the illumination of a warped outer disk. A tilt of 6-15 degrees from the symmetry plane can cause the observed surface brightness variations providing the disk is very twisted (highly warped) at radii greater than 200 AU where the spiral features are seen. Dust lanes are due in part to shadowing in the equatorial plane from the inner disk within a radius of 100 AU. HD100546's outer disk, if viewed edge-on, would appear similar to that of Beta Pictorus. A disk initially misaligned with a planetary system, becomes warped due to precession induced by planetesimal bodies and planets. However, the twistedness of HD100546's disk cannot be explained by precession during the lifetime of the system induced by a single Jovian mass planet within the clearing at ~13 AU. One possible explanation for the corrugated disk is that precession was induced by massive of bodies embedded in the disk at larger radius. This would require approximately a Jupiter mass of bodies well outside the central clearing at 13 AU and within the location of the spiral features or at radii approximately between 50-200 AU.

Alice C. Quillen

2005-10-17

348

Heating and Cooling in Circumstellar Disks  

NASA Astrophysics Data System (ADS)

We present two dimensional hydrodynamic simulations of massive disks around protostars using the `Smoothed Particle Hydrodynamic' (SPH) code. These simulations implement a simple model of the heating and cooling processes present in circumstellar disks in which heating is provided by artificial viscosity and shock dissipation and cooling is modelled locally as a black-body with a temperature defined by the disk photosphere. From these simulations we produce spectral energy distributions (SED's) which, in many respects, reproduce those observed around many T Tauri systems. In several other important respects, the SED's and the derived disk luminosities differ from observations. From these differences and the physical assumptions incorporated into our models, we deduce that 1) grain destruction in the midplane of the inner disk can have a pronounced effect on the observed character of the system and 2) large-scale shocks (generated for example by spiral structure) cannot be responsible for a large fraction of the thermal energy generated in the disk, except in the inner few AU.

Nelson, A.; Benz, W.; Ruzmaikina, T.

349

TEM studies of a circumstellar rock  

NASA Technical Reports Server (NTRS)

Reported here is the discovery of crystals of titanium carbide in a grain of silicon carbide which formed as a circumstellar dust particle in the atmosphere of a carbon-rich star. Just as in the case of terrestrial rocks, whose assemblage of minerals gives us clues to the composition and conditions of the environment in which they formed, the titanium carbide crystals and their textural relationship to the silicon carbide give us important clues to the nature of the stellar atmosphere in which they formed. From microscopic studies of the relationships between the atomic planes of the silicon carbide and the titanium carbide, we can show that the titanium carbide cannot have existed as already-formed crystals in a gas around which silicon carbide subsequently condensed. An alternative possibility is that both minerals grew quickly and simultaneously from condensing gas in the rapidly cooling and expanding stellar atmosphere. Other microscopic features of the silicon carbide, such as abundant atomic layer disorder and crystal twinning, similarly suggest rapid grain growth. However, another possibility is that the titanium carbide grew inside of the silicon carbide by diffusion of titanium atoms. Our calculations suggest that this scenario is less likely, given the relatively short times (a year or less) for which stellar condensates can be expected to be exposed to temperatures high enough to make diffusion sufficiently rapid.

Bernatowicz, Thomas J.; Amari, Sachiko; Lewis, Roy S.

1992-01-01

350

Circumstellar features in hot DA white dwarfs  

E-print Network

We present a phenomenological study of highly ionised, non-photospheric absorption features in high spectral resolution vacuum ultraviolet spectra of 23 hot DA white dwarfs. Prior to this study, four of the survey objects (Feige 24, REJ 0457-281, G191-B2B and REJ 1614-085) were known to possess these features. We find four new objects with multiple components in one or more of the principal resonance lines: REJ 1738+665, Ton 021, REJ 0558-373 and WD 2218+706. A fifth object, REJ 2156-546 also shows some evidence of multiple components, though further observations are required to confirm the detection. We discuss possible origins for these features including ionisation of the local interstellar environment, the presence of material inside the gravitational well of the white dwarf, mass loss in a stellar wind, and the existence of material in an ancient planetary nebula around the star. We propose ionisation of the local interstellar medium as the origin of these features in G191-B2B and REJ 1738+665, and demonstrate the need for higher resolution spectroscopy of the sample, to detect multiple ISM velocity components and to identify circumstellar features which may lie close to the photospheric velocity.

N. P. Bannister; M. A. Barstow; J. B. Holberg; F. C. Bruhweiler

2003-01-13

351

Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs  

E-print Network

By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 Earth radii in the habitable zones of their host stars. The MEarth Project, a future transit search, aims to employ a network of ground-based robotic telescopes to monitor M dwarfs in the northern hemisphere with sufficient precision and cadence to detect such planets. Here we investigate the design requirements for the MEarth Project. We evaluate the optimal bandpass, and the necessary field of view, telescope aperture, and telescope time allocation on a star-by-star basis, as is possible for the well-characterized nearby M dwarfs. Through these considerations, 1,976 late M dwarfs (R habitable zone orbits, we find that a network of ten 30 cm telescopes could survey these 1,976 M dwarfs in less than 3 years. A null result from this survey would set an upper limit (at 99% confidence) of 17% for the rate of occurrence of planets larger than 2 Earth radii in the habitable zones of late M dwarfs, and even stronger constraints for planets lying closer than the habitable zone. If the true occurrence rate of habitable planets is 10%, the expected yield would be 2.6 planets.

Philip Nutzman; David Charbonneau

2008-01-18

352

Exomoon habitability constrained by energy flux and orbital stability  

NASA Astrophysics Data System (ADS)

Context. Detecting massive satellites that orbit extrasolar planets has now become feasible, which led naturally to questions about the habitability of exomoons. In a previous study we presented constraints on the habitability of moons from stellar and planetary illumination as well as from tidal heating. Aims: Here I refine our model by including the effect of eclipses on the orbit-averaged illumination. I then apply an analytic approximation for the Hill stability of a satellite to identify the range of stellar and planetary masses in which moons can be habitable. Moons in low-mass stellar systems must orbit their planet very closely to remain bounded, which puts them at risk of strong tidal heating. Methods: I first describe the effect of eclipses on the stellar illumination of satellites. Then I calculate the orbit-averaged energy flux, which includes illumination from the planet and tidal heating to parametrize exomoon habitability as a function of stellar mass, planetary mass, and planet-moon orbital eccentricity. The habitability limit is defined by a scaling relation at which a moon loses its water by the runaway greenhouse process. As a working hypothesis, orbital stability is assumed if the moon's orbital period is less than 1/9 of the planet's orbital period. Results: Due to eclipses, a satellite in a close orbit can experience a reduction in orbit-averaged stellar flux by up to about 6%. The smaller the semi-major axis and the lower the inclination of the moon's orbit, the stronger the reduction. I find a lower mass limit of ? 0.2 M? for exomoon host stars that allows a moon to receive an orbit-averaged stellar flux comparable to the Earth's, with which it can also avoid the runaway greenhouse effect. Precise estimates depend on the satellite's orbital eccentricity. Deleterious effects on exomoon habitability may occur up to ? 0.5 M? if the satellite's eccentricity is ? 0.05. Conclusions: Although the traditional habitable zone lies close to low-mass stars, which allows for many transits of planet-moon binaries within a given observation cycle, resources should not be spent to trace habitable satellites around them. Gravitational perturbations by the close star, another planet, or another satellite induce eccentricities that likely make any moon uninhabitable. Estimates for individual systems require dynamical simulations that include perturbations among all bodies and tidal heating in the satellite.

Heller, R.

2012-09-01

353

Practicing Good Habits, Grade 2.  

ERIC Educational Resources Information Center

This illustrated primer, designed for second grade students in Vietnam, consists of stories depicting rural family life in Vietnam. The book is divided into the following six chapters: (1) Practicing Good Habits (health, play, helpfulness); (2) Duties at Home (grandparents, father and mother, servants, the extended family; (3) Duties in School…

Nguyen Van Quan; And Others

354

Teaching Your Child Healthy Hair Care Habits  

MedlinePLUS

... healthy hair care Teaching your child healthy hair care habits Many common hair care practices can lead ... a conditioner. Teaching your child other healthy hair care habits Many things that we do to style ...

355

Breastfeeding FAQs: Your Eating and Drinking Habits  

MedlinePLUS

... the Flu Pregnancy Precautions Checkups: What to Expect Breastfeeding FAQs: Your Eating and Drinking Habits KidsHealth > Parents > Growth & Development > Feeding & Eating > Breastfeeding FAQs: Your Eating and Drinking Habits Print A ...

356

Habitable Planet Formation in Binary-Planetary Systems  

E-print Network

Recent radial velocity observations have indicated that Jovian-type planets can exist in moderately close binary star systems. Numerical simulations of the dynamical stability of terrestrial-class planets in such environments have shown that, in addition to their giant planets, these systems can also harbor Earth-like objects. In this paper, we study the late stage of terrestrial planet formation in such binary-planetary systems, and present the results of the simulations of the formation of Earth-like bodies in their habitable zones. We consider a circumprimary disk of Moon- to Mars-sized objects and numerically integrate the orbits of these bodies at the presence of the Jovian-type planet of the system and for different values of the mass, semimajor axis, and orbital eccentricity of the secondary star. Results indicate that, Earth-like objects, with substantial amounts of water, can form in the habitable zone of the primary star. Simulations also indicate that, by transferring angular momentum from the secondary star to protoplanetary objects, the giant planet of the system plays a key role in the radial mixing of these bodies and the water contents of the final terrestrial planets. We will discuss the results of our simulation and show that the formation of habitable planets in binary-planetary systems is more probable in binaries with moderate to large perihelia.

Nader Haghighipour; Sean N. Raymond

2007-02-27

357

Circumstellar Surroundings of Young Stellar Objectse  

NASA Astrophysics Data System (ADS)

The close surroundings of young low mass stars hold a multitude of physical phenomena related to star formation. This thesis presents a set of works on theoretical, experimental, and observational issues connected with these phenomena. After a description of the properties of T Tauri, FU Orionis and Ae/Be Herbig stars, with a particular emphasis on their accretion disks, I study the vertical structure of such disks which results from the radiative transfer and the hydrostatic equilibrium. The energy dissipation comes from both the viscous friction of disk particles accreting onto the star and from the absorption of the stellar radiation. A disk ``chromosphere'' is shown to result from the grazing stellar radiation. In the following I study the possibility of detecting directly the circumstellar features (disk, binarity, planets, jets,...) thanks to the high angular resolution techniques (adaptive optics and interferometry). I then present the prototype of a coronagraph at high spatial resolution that I designed, modelized, built and tested for that kind of observations. Finally I describe the observations of the young stellar system Z Canis Majoris, which I obtained at the diffraction limit of the 3.6 meter ESO telescope in the near infrared. This object is shown to be composed of a binary system in addition to an elongated disk-like structure perpendicular to the known jet and illuminated not by the central source but by the infrared companion. [A copy of this thesis (which is mostly in french) can be obtained in binary mode by ftp. There is a file 'these_malbet.tar' in the directory '/pub/publications/' at the FTP node 'gag.observ-gr.fr (IP 130.190.200.11)'. By doing 'tar -xvf these_malbet.tar', you create a directory 'these_malbet/' where there is a 'readme' which gives all information.

Malbet, Fabien

1992-12-01

358

Habitability potential of icy moons: a comparative study  

NASA Astrophysics Data System (ADS)

Looking for habitable conditions in the outer solar system our research focuses on the natural satellites rather than the planets themselves. Indeed, the habitable zone as traditionally defined may be larger than originally con-ceived. The strong gravitational pull caused by the giant planets may produce enough energy to sufficiently heat the interiors of orbiting icy moons. The outer solar system satellites then provide a conceptual basis within which new theories for understanding habitability can be constructed. Measurements from the ground but also by the Voyager, Galileo and the Cassini spacecrafts revealed the potential of these satellites in this context, and our understanding of habitability in the solar system and beyond can be greatly enhanced by investigating several of these bodies together [1]. Their environments seem to satisfy many of the "classical" criteria for habitability (liquid water, energy sources to sustain metabolism and chemical compounds that can be used as nutrients over a period of time long enough to allow the development of life). Indeed, several of the moons show promising conditions for habitability and the de-velopment and/or maintenance of life. Europa, Callisto and Ganymede may be hiding, under their icy crust, putative undersurface liquid water oceans [3] which, in the case of Europa [2], may be in direct contact with a silicate mantle floor and kept warm by tidally generated heat [4]. Titan and Enceladus, Saturn's satellites, were found by the Cassini-Huygens mission to possess active organic chemistries with seasonal variations, unique geological features and possibly internal liquid water oceans. Titan's rigid crust and the probable existence of a subsurface ocean create an analogy with terrestrial-type plate tectonics, at least surficial [5], while Enceladus' plumes find an analogue in gey-sers. As revealed by Cassini the liquid hydrocarbon lakes [6] distributed mainly at polar latitudes on Titan are ideal isolated environments to look for biomarkers. Currently, for Titan and Enceladus, geophysical models try to explain the possible existence of an oceanic layer that decouples the mantle from the icy crust. If the silicate mantles of Eu-ropa and Ganymede and the liquid sources of Titan and Enceladus are geologically active as on Earth, giving rise to the equivalent of hydrothermal systems, the simultaneous presence of water, geodynamic interactions, chemical en-ergy sources and a diversity of key chemical elements may fulfill the basic conditions for habitability. Titan has been suggested to be a possible cryovolcanic world due to the presence of local complex volcanic-like geomorphol-ogy and the indications of surface albedo changes with time [7,8]. Such dynamic activity that would most probably include tidal heating, possible internal convection, and ice tectonics, is believed to be a pre-requisite of a habitable planetary body as it allows the recycling of minerals and potential nutrients and provides localized energy sources. In a recent study by Sohl et al. [2013], we have shown that tidal forces are a constant and significant source of inter-nal deformation on Titan and the interior liquid water ocean can be relatively warm for reasonable amounts of am-monia concentrations, thus completing the set of parameters needed for a truly habitable planetary body. Such habi-tability indications from bodies at distances of 10 AU, are essential discoveries brought to us by space exploration and which have recently revolutionized our perception of habitability in the solar system. In the solar system's neighborhood, such potential habitats can only be investigated with appropriate designed space missions, like JUICE-Laplace (JUpiter ICy moon Explorer) for Ganymede and Europa [9]. JUICE is an ESA mission to Jupiter and its icy moons, recently selected to launch in 2022. References: [1] Coustenis, A., Encrenaz, Th., in "Life Beyond Earth : the search for habitable worlds in the Universe", Cambridge Univ. Press, 2013. [2] Patterson, G.W., et al.: AGU P41F-09, 2011. [3]

Solomonidou, Anezina; Coustenis, Athena; Encrenaz, Thérèse; Sohl, Frank; Hussmann, Hauke; Bampasidis, Georgios; Wagner, Frank; Raulin, François; Schulze-Makuch, Dirk; Lopes, Rosaly

2014-05-01

359

First Circumstellar Disk around a Massive Star  

NASA Astrophysics Data System (ADS)

Observations with an infrared-sensitive instrument at the ESO 3.6-m telescope at La Silla have for the first time shown the presence of a disk around a hot and massive star, known as G339.88-1.26 . Until now, disks have only been found around less massive stars. Planets are formed in such disks. The new discovery may thus have important implications for our understanding of the formation of planetary systems around stars. TIMMI observations Observations at mid-infrared wavelengths were carried out in July 1997 by Bringfried Stecklum (Landessternwarte Thüringen, Tautenburg, Germany) and Hans-Ulrich Käufl (ESO), using the TIMMI instrument at the ESO 3.6-m telescope. Additional measurements were carried out in March 1998. TIMMI ( T hermal I nfrared M ulti M ode I nstrument) is a general-purpose camera spectrometer operating at a wavelength of 10 µm. To reach sufficient sensitivity, the camera must be cooled to approx. -260 o C, i.e. a few degrees above the absolute minimum, by use of liquid Helium. Astronomical objects whose temperatures are between -120 o C and 300 o C radiate most of their energy at this wavelength. In addition, dust and haze that are absolutely impenetrable for light visible to the human eye, are often found to be nearly transparent at this wavelength. This is why fire-fighters now use similar equipment to look through smoke. G339.88-1.26: A very special object ESO PR Photo 22a/98 ESO PR Photo 22a/98 [JPEG, 800k] This image is a true-color composite of near-infrared observations of the sky region around the radio source G339.88-1.26 with the ESO/MPI 2.2-m telescope at La Silla. In this image, the visible colors red, green and blue have been used to represent the infrared filters J, H and K (at 1.25, 1.63 and 2.2 µm wavelength, respectively). No object is visible at the position of the radio source, even at these near-infrared wavelengths. A dark band of absorbing dust is clearly visible, exactly at the position of the object (indicated by an arrow). Earlier observations with radio telescopes of the object G339.88-1.26 , deeply embedded in an interstellar nebula, had been interpreted in terms of the possible existence of a circumstellar disk around a high-mass star. It was concluded that the star responsible for heating the surrounding gas must be very hot and also that it must be intrinsically very bright. The star, most likely of spectral type O9, would have a luminosity 10,000 times higher than that of the Sun and a mass of about 20 times that of the Sun. From the measured velocity, the likely distance of this object is about 10,000 light-years. The object is associated with several "spots" of very strong radio emission from methanol molecules (methanol masers). Interestingly, they form a chain in the sky and the measured velocities of the individual spots are indicative for orbital motion in a rotating disk around the central star. The circumstellar disk ESO PR Photo 22/98 ESO PR Photo 22b/98 [JPEG, 640k] The TIMMI 10 µm image of the inclined dust disk around a hot O9 star at the G339.88-1.26 radio source. The diameter of the disk is of the order of 5 arcsec, i.e. at the most probable distance to the object (10,000 lightyears) it is 20,000 times larger than the diameter of the Earth's orbit around the Sun. The new TIMMI observations of G339.88-1.26 showed an elliptical object with strong infrared radiation. The peak of this radiation (as seen in the sky) coincides with the peak of the radio emission. Furthermore, the apparent orientation of the disk is well aligned with that of the methanol maser "spots". There is little doubt that this object is indeed the infrared image of a circumstellar disk, viewed at an angle. As far as known, this is the first direct image of a disk around a very massive star. At a wavelength of 10 µm, however, the central star that is responsible for heating the dust disc, cannot be seen in spite of its rather high luminosity. This is because it radiates mostly in the ultra-violet part of the spectrum. Moreover, the dust disk in which the hot star is

1998-06-01

360

Radiological Habits Survey: Sellafield Review, 2010  

E-print Network

Radiological Habits Survey: Sellafield Review, 2010 2011 Environment Report RL 13/11 Cefas contract Radiological Habits Survey: Sellafield Review, 2010 Shellfish consumption and intertidal occupancy review F, P., Smedley, C.A., and Ly, V.E., 2011. Radiological Habits Survey: Sellafield Review, 2010. RL 13

361

Radiological Habits Survey: Sellafield Review, 2011  

E-print Network

Radiological Habits Survey: Sellafield Review, 2011 2012 Environment Report RL 05/12 Cefas contract Radiological Habits Survey: Sellafield Review, 2011 Shellfish consumption and intertidal occupancy review F., 2012. Radiological Habits Survey: Sellafield Review, 2011. RL 05/12. Cefas, Lowestoft A copy can

362

University Students' Media Habits: A Lithuanian Study.  

ERIC Educational Resources Information Center

A study replicated a 1994 study, "College Students' Media Habits: A National Study." In the present study, Lithuanian university students' media habits relative to American students' media habits were gauged. A total of 1500 survey questionnaires were distributed to 7 of the 16 Lithuanian universities. Background biographical questions were asked,…

Kamalipour, Yahya R.; And Others

363

The Stability of Habitable Planetary Environments  

NASA Astrophysics Data System (ADS)

The recent discoveries of extrasolar planets have generated widespread anticipation of detecting a life-supporting environment, such as an Earth-like planet or moon, around a nearby solar-type star. Future observations will enable life on such worlds to be detected remotely through the spectral identification of CH4 and O3 in their atmospheres. This thesis addresses the climatic and dynamic factors affecting whether an Earth-like biosphere might exist around another star and, hence, the likelihood that extraterrestrial life will be discovered in the foreseeable future. To remain habitable for billions of years, a planetary body must be large enough to form and retain an atmosphere. Earth's Moon (~0.01M?) does not satisfy this basic criterion. Objects with atmospheres must orbit their stars within the habitable zone (HZ) for liquid water to exist on their surfaces. Otherwise habitable worlds can have their climates destabilized by the slow brightening of their-stars as the age, or by chaotic variability of their orbits and obliquities over time. Earth's 23.5o-obliquity is presently stable, but the spin-stability of extrasolar Earths will depend on the masses and proximity of satellites and neighboring planets. Climates of planets with high obliquities are investigated using an energy-balance climate model. At high obliquity, Earth's climatic zonation is reversed so that the lower latitudes are permanently frozen and the poles are subjected to extraordinary swings in seasonal temperature. Planets within the outer HZs around their stars are less affected by obliquity because they develop dense-CO2 atmospheres as a result of the carbonate-silicate geochemical cycle. Efficient heat transport within such atmospheres reduce latitudinal temperature gradients and limit the amplitudes of seasonal temperature extremes. Geologic evidence for low-latitude glaciation during the Precambrian era suggests that the obliquity of early-Earth may have been much higher than it is today. Earth's obliquity could have been reduced to its present value as a consequence of obliquity-oblateness feedback. In this process, obliquity-driven changes to continental ice volume and oblateness may have caused a secular downward drift in obliquity of ~30o between 600 Ma and 500 Ma. Such an event may account for the present non-zero inclination of the lunar orbit.

Williams, Darren Mark

1998-12-01

364

Habitability of extrasolar planets and tidal spin evolution.  

PubMed

Stellar radiation has conservatively been used as the key constraint to planetary habitability. We review here the effects of tides, exerted by the host star on the planet, on the evolution of the planetary spin. Tides initially drive the rotation period and the orientation of the rotation axis into an equilibrium state but do not necessarily lead to synchronous rotation. As tides also circularize the orbit, eventually the rotation period does equal the orbital period and one hemisphere will be permanently irradiated by the star. Furthermore, the rotational axis will become perpendicular to the orbit, i.e. the planetary surface will not experience seasonal variations of the insolation. We illustrate here how tides alter the spins of planets in the traditional habitable zone. As an example, we show that, neglecting perturbations due to other companions, the Super-Earth Gl581d performs two rotations per orbit and that any primordial obliquity has been eroded. PMID:22139513

Heller, René; Barnes, Rory; Leconte, Jérémy

2011-12-01

365

THE RICH CIRCUMSTELLAR CHEMISTRY OF SMP LMC 11  

SciTech Connect

Carbon-rich evolved stars from the asymptotic giant branch to the planetary nebula phase are characterized by a rich and complex carbon chemistry in their circumstellar envelopes. A peculiar object is the preplanetary nebula SMP LMC 11, whose Spitzer Infrared Spectrograph spectrum shows remarkable and diverse molecular absorption bands. To study how the molecular composition in this object compares to our current understanding of circumstellar carbon chemistry, we modeled this molecular absorption. We find high abundances for a number of molecules, perhaps most notably benzene. We also confirm the presence of propyne (CH{sub 3}C{sub 2}H) in this spectrum. Of all the cyanopolyynes, only HC{sub 3}N is evident; we can detect at best a marginal presence of HCN. From comparisons to various chemical models, we can conclude that SMP LMC 11 must have an unusual circumstellar environment (a torus rather than an outflow).

Malek, S. E.; Cami, J. [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Bernard-Salas, J., E-mail: smalek2@uwo.ca, E-mail: jcami@uwo.ca [Institut d'Astrophysique Spatiale, CNRS/Universite Paris-Sud 11, 91405 Orsay (France)

2012-01-01

366

Environmental control system for Habitable-zone Planet Finder (HPF)  

NASA Astrophysics Data System (ADS)

HPF is an ultra-stable, precision radial velocity near infrared spectrograph with a unique environmental control scheme. The spectrograph will operate at a mid-range temperature of 180K, approximately half way between room temperature and liquid nitrogen temperature; it will be stable to sub -milli-Kelvin(mK) levels over a calibration cycle and a few mK over months to years. HPF's sensor is a 1.7 micron H2RG device by Teledyne. The environmental control boundary is a 9 m2 thermal enclosure that completely surrounds the optical train and produces a near blackbody cavity for all components. A large, pressure - stabilized liquid nitrogen tank provides the heat sink for the system via thermal straps while a multichannel resistive heater control system provides the stabilizing heat source. High efficiency multi-layer insulation blanketing provides the outermost boundary of the thermal enclosure to largely isolate the environmental system from ambient conditions. The cryostat, a stainless steel shell derived from the APOGEE design, surrounds the thermal enclosure and provides a stable, high quality vacuum environment. The full instrument will be housed in a passive 'meat -locker' enclosure to add a degree of additional thermal stability and as well as protect the instrument. Effectiveness of this approach is being empirically demonstrated via long duration scale model testing. The full scale cryostat and environmental control system are being constructed for a 2016 delivery of the instrument to the Hobby-Eberly Telescope. This report describes the configuration of the hardware and the scale-model test results as well as projections for performance of the full system.

Hearty, Fred; Levi, Eric; Nelson, Matt; Mahadevan, Suvrath; Burton, Adam; Ramsey, Lawrence; Bender, Chad; Terrien, Ryan; Halverson, Samuel; Robertson, Paul; Roy, Arpita; Blank, Basil; Blanchard, Ken; Stefansson, Gudmundur

2014-07-01

367

Europa, tidally heated oceans, and habitable zones around giant planets  

Microsoft Academic Search

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. Europa could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such a case, sufficient solar energy could reach liquid water

R. T. Reynolds; C. P. McKay; J. F. Kasting

1987-01-01

368

Habitable zones for Earth like planets in the solar system  

Microsoft Academic Search

A new conceptual Earth system model is presented to investigate the long-term co-evolution of geosphere and biosphere from the geological past up to 1.5 billion years into the planet's future. The model is based on the global carbon cycle mediated by life and driven by increasing solar luminosity and plate tectonics. As a major result of our investigation we calculate

W. von Bloh; S. Franck; C. Bounama

2001-01-01

369

A model of habitability within the Milky Way galaxy.  

PubMed

We present a model of the galactic habitable zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favor the development of complex life. The Milky Way galaxy was modeled using a computational approach by populating stars and their planetary systems on an individual basis by employing Monte Carlo methods. We began with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We varied some of these properties and created four models to test the sensitivity of our assumptions. To assess habitability on the galactic scale, we modeled supernova rates, planet formation, and the time required for complex life to evolve. Our study has improved on other literature on the GHZ by populating stars on an individual basis and modeling Type II supernova (SNII) and Type Ia supernova (SNIa) sterilizations by selecting their progenitors from within this preexisting stellar population. Furthermore, we considered habitability on tidally locked and non-tidally locked planets separately and studied habitability as a function of height above and below the galactic midplane. In the model that most accurately reproduces the properties of the Galaxy, the results indicate that an individual SNIa is ?5.6× more lethal than an individual SNII on average. In addition, we predict that ?1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy. Of those stars with a habitable planet, ?75% of planets are predicted to be in a tidally locked configuration with their host star. The majority of these planets that may support complex life are found toward the inner Galaxy, distributed within, and significantly above and below, the galactic midplane. PMID:22059554

Gowanlock, M G; Patton, D R; McConnell, S M

2011-11-01

370

A Catalog of Stellar Evolution Profiles and the Effects of Variable Composition on Habitable Systems  

E-print Network

We present stellar evolution models for 0.5 - 1.2 \\Msol at scaled metallicities of 0.1 - 1.5 Z\\sol and O/Fe values of 0.44 - 2.28 O/Fe\\sol. The time dependent evolution of habitable zone boundaries are calculated for each stellar evolution track based on stellar mass, effective temperature, and luminosity parameterizations. The rate of change of stellar surface quantities and the surrounding habitable zone position are strong functions of all three quantities explored. The range of orbits that remain continuously habitable, or habitable for at least 2 Gyr, are provided. The results show that the detailed chemical characterization of exoplanet host stars and a consideration of their evolutionary history are necessary to assess the likelihood that a planet found in the instantaneous habitable zone has had sufficient time to develop a biosphere capable of producing detectable biosignatures. This model grid is designed for use by the astrobiology and exoplanet communities to efficiently characterize the time evol...

Truitt, Amanda; Spacek, Alexander; Probst, Luke; Dietrich, Jeremy

2015-01-01

371

Space Physics of Close-in Exoplanets and its Implications for Planet Habitability  

NASA Astrophysics Data System (ADS)

The search for habitable exoplanets is currently focused on planets orbiting M-dwarf stars, due to the close proximity of the habitable zone to the star. However, the traditional habitability definition does not account for the physical space environment near the planets, which can be extreme at close-in orbits, and can lead to erosion of te planetary atmosphere. In order to sustain their atmosphers, M-dwarf planets need to have either an intrinsic magnetic field, or a thick atmosphere. Here we present a set of numerical magnetohydrodynamic simulations of the interaction of an Earth-like magnetized planet and a Venus-like non-magnetized planet with the stellar wind of M-dwarf star. We study space physics aspects of these interactions and their implications for planet habitability

Cohen, Ofer

2015-04-01

372

The infrared spectrum of M8 E - Evidence for circumstellar CO  

NASA Technical Reports Server (NTRS)

High-resolution spectroscopic observations of the compact infrared source M8 E are reported in the region from 3 to 5 microns. Very prominent CO absorption lines are observed in the v = 1-0 band at 4.7 microns. The velocity width and rotational temperature suggest that this CO absorption occurs in a highly excited region. The high background continuum flux level and the prominent appearance of the CO features suggest that the CO line-forming region must be in front of the dust emission region. A blister model for M8 E, which places most of the dust continuum emission behind the source, satisfies this requirement. According to this picture, the observed circumstellar CO spectrum shows a high rotational temperature and a large velocity dispersion because of the combined effects of the strong stellar wind and possible shock heating near the dust zone as the wind encounters the ambient molecular cloud.

Larson, H. P.; Fink, U.; Hofmann, R.

1986-01-01

373

The Solar Neighborhood XXIX: The Habitable Real Estate of Our Nearest Stellar Neighbors  

NASA Astrophysics Data System (ADS)

We use the sample of known stars and brown dwarfs within 5 pc of the Sun, supplemented with AFGK stars within 10 pc, to determine which stellar spectral types provide the most habitable real estate—defined as locations where liquid water could be present on Earth-like planets. Stellar temperatures and radii are determined by fitting model spectra to spatially resolved broadband photometric energy distributions for stars in the sample. Using these values, the locations of the habitable zones are calculated using an empirical formula for planetary surface temperature and assuming the condition of liquid water, called here the empirical habitable zone (EHZ). Systems that have dynamically disruptive companions are considered not habitable. We consider companions to be disruptive if the separation ratio of the companion to the habitable zone is less than 5:1. We use the results of these calculations to derive a simple formula for predicting the location of the EHZ for main sequence stars based on V - K color. We consider EHZ widths as more useful measures of the habitable real estate around stars than areas because multiple planets are not expected to orbit stars at identical stellar distances. This EHZ provides a qualitative guide on where to expect the largest population of planets in the habitable zones of main sequence stars. Because of their large numbers and lower frequency of short-period companions, M stars provide more EHZ real estate than other spectral types, possessing 36.5% of the habitable real estate en masse. K stars are second with 21.5%, while A, F, and G stars offer 18.5%, 6.9%, and 16.6%, respectively. Our calculations show that three M dwarfs within 10 pc harbor planets in their EHZs—GJ 581 may have two planets (d with msin i = 6.1 M ? g with msin i = 3.1 M ?), GJ 667 C has one (c with msin i = 4.5 M ?), and GJ 876 has two (b with msin i = 1.89 M Jup and c with msin i = 0.56 M Jup). If Earth-like planets are as common around low-mass stars as recent Kepler results suggest, M stars will harbor more Earth-like planets in habitable zones than any other stellar spectral type.

Cantrell, Justin R.; Henry, Todd J.; White, Russel J.

2013-10-01

374

THE SOLAR NEIGHBORHOOD XXIX: THE HABITABLE REAL ESTATE OF OUR NEAREST STELLAR NEIGHBORS  

SciTech Connect

We use the sample of known stars and brown dwarfs within 5 pc of the Sun, supplemented with AFGK stars within 10 pc, to determine which stellar spectral types provide the most habitable real estate—defined as locations where liquid water could be present on Earth-like planets. Stellar temperatures and radii are determined by fitting model spectra to spatially resolved broadband photometric energy distributions for stars in the sample. Using these values, the locations of the habitable zones are calculated using an empirical formula for planetary surface temperature and assuming the condition of liquid water, called here the empirical habitable zone (EHZ). Systems that have dynamically disruptive companions are considered not habitable. We consider companions to be disruptive if the separation ratio of the companion to the habitable zone is less than 5:1. We use the results of these calculations to derive a simple formula for predicting the location of the EHZ for main sequence stars based on V – K color. We consider EHZ widths as more useful measures of the habitable real estate around stars than areas because multiple planets are not expected to orbit stars at identical stellar distances. This EHZ provides a qualitative guide on where to expect the largest population of planets in the habitable zones of main sequence stars. Because of their large numbers and lower frequency of short-period companions, M stars provide more EHZ real estate than other spectral types, possessing 36.5% of the habitable real estate en masse. K stars are second with 21.5%, while A, F, and G stars offer 18.5%, 6.9%, and 16.6%, respectively. Our calculations show that three M dwarfs within 10 pc harbor planets in their EHZs—GJ 581 may have two planets (d with msin i = 6.1 M {sub ?}; g with msin i = 3.1 M {sub ?}), GJ 667 C has one (c with msin i = 4.5 M {sub ?}), and GJ 876 has two (b with msin i = 1.89 M {sub Jup} and c with msin i = 0.56 M {sub Jup}). If Earth-like planets are as common around low-mass stars as recent Kepler results suggest, M stars will harbor more Earth-like planets in habitable zones than any other stellar spectral type.

Cantrell, Justin R.; Henry, Todd J.; White, Russel J., E-mail: cantrell@chara.gsu.edu, E-mail: thenry@chara.gsu.edu, E-mail: white@chara.gsu.edu [Georgia State University, Atlanta, GA 30302-4106 (United States)

2013-10-01

375

The feeding habits of Glossina*  

PubMed Central

The feeding habits of 15 species of Glossina have been studied by the identification of their blood meals. Representative samples of the blood meals from each of these species of tsetse fly and from different habitats were collected and 22 640 blood meals were identified. The feeding patterns are characteristic for each species of tsetse fly and do not appear to depend entirely on the availability of different hosts, suggesting that the feeding habits of Glossina are genetically determined. However, a broad grouping can be made into five categories: species feeding mainly on suids, those feeding on suids and bovids, those feeding mainly on bovids, those feeding mainly on mammals other than suids and bovids, and those feeding on most available hosts and on man. The possibility of control by selective elimination of the main hosts of these groups is discussed. PMID:13999790

Weitz, Bernard

1963-01-01

376

A search for circumstellar dust disks with ADONIS  

NASA Astrophysics Data System (ADS)

We present results of a coronographic imaging search for circumstellar dust disks with the Adaptive Optics Near Infrared System (ADONIS) at the ESO 3.6 m telescope in La Silla (Chile). 22 candidate stars, known to be orbited by a planet or to show infrared excess radiation, were examined for circumstellar material. In the PSF-subtracted images no clear disk was found. We further determine the detection sensitivities and outline how remaining atmospheric fluctuations still can hamper adaptive optics observations. Based on observations collected at the European Southern Observatory, La Silla, Chile (65.I-0098, 67.C-0240, 68.C-0070).

Schütz, O.; Böhnhardt, H.; Pantin, E.; Sterzik, M.; Els, S.; Hahn, J.; Henning, Th.

2004-09-01

377

Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and the Implications for Habitability  

Microsoft Academic Search

Planets within the habitable zones of M dwarfs are likely to be synchronous rotators; in other words, one side is permanently illuminated while the other side is in perpetual darkness. We present results of three-dimensional simulations of the atmospheres of such planets, and comment on their possible habitability. Near the ground, a thermally direct longitudinal cell exists, transporting heat from

M. M. Joshi; R. M. Haberle; R. T. Reynolds

1997-01-01

378

The origin and evolution of dust in interstellar and circumstellar environments  

NASA Technical Reports Server (NTRS)

This status report covers the period from the commencement of the research program on 1 Jul. 1992 through 30 Apr. 1993. Progress is reported for research in the following areas: (1) grain formation in circumstellar envelopes; (2) photochemistry in circumstellar envelopes; (3) modeling ice features in circumstellar envelopes; (4) episodic dust formation in circumstellar envelopes; (5) grain evolution in the diffuse interstellar medium; and (6) grain evolution in dense molecular clouds.

Whittet, Douglas C. B.; Leung, Chun M.

1993-01-01

379

Development of a Habitable Planet  

NSDL National Science Digital Library

In this lesson, students investigate the origin of the elements, the process of planet formation, the evolution of life on Earth, and the conditions necessary for life as we know it. Using multimedia resources and a classroom activity, students identify and sequence the major events that caused Earth to develop into the planet we know, understand where the ingredients for Earth originated, including the conditions necessary for life, and consider the likelihood of other habitable worlds.

2005-01-01

380

Using Optogenetics to Study Habits  

PubMed Central

It is now well documented that optogenetics brings to neuroscience a long sought-after foothold to study the causal role of millisecond-scale activity of genetically or anatomically defined populations of neurons. Progress is rapid, and, as evidenced by the work collected in this Special Issue, the possibilities of what can now be done are almost dizzying. Even for those concerned with complex phenomena, such as behavioral habits and flexibility, signs are that we could be on the threshold of a leap in scientific understanding. In this article, we note this special time in neuroscience by the example of our use of optogenetics to study habitual behavior. We present a basic sketch of the neural circuitry of habitual behavior built mainly on findings from experiments in which lesion and drug microinjection techniques were employed in combination with sophisticated behavioral analysis. We then outline the types of questions that now can be approached through the use of optogenetic approaches, and, as an example, we summarize the results of a recent study of ours in which we took this approach to probe the neural basis of habit formation. With optogenetic methods, we were able to demonstrate that a small site in the medial prefrontal cortex can control habits on-line during their execution, and we were able to control new habits when they competed with prior ones. The nearly immediate effect of disabling this site optogenetically suggests the existence of a mechanism for moment-to-moment monitoring of behaviors that long have been thought to be almost automatic and reflexive. This example highlights the kind of new knowledge that can be gained by the carefully timed use of optogenetic tools. PMID:23313580

Smith, Kyle S.; Graybiel, Ann M.

2013-01-01

381

Widen the belt of habitability!  

PubMed

Among the key-parameters to characterize habitability are presence or availability of liquid water, an appropriate temperature range, and the time scale of reference. These criteria for habitability are discussed and described from the point of view of water- and ice-physics, and it is shown that liquid water may exist in the sub-surfaces of planetary bodies like Mars, and possibly of inner asteroids and internally heated ice-moons. Water can remain fluid there also at temperatures far below the "canonical" 0 °C. This behaviour is made possible as a consequence of the freezing point depression due to salty solutes in water or "brines", as they can be expected to exist in nature more frequently than pure liquid water. On the other hand, low temperatures cause a slowing down of chemical processes, as can be described by Arrhenius's relation. The resulting smaller reaction rates probably will have the consequence to complicate the detection of low-temperature life processes, if they exist. Furthermore, the adaptation potential of life is to be mentioned in this context as a yet partially unknown process. Resulting recommendations are given to improve the use of criteria to characterize habitable conditions. PMID:22638839

Möhlmann, D

2012-06-01

382

Killer Whales in Hawaiian Waters: Information on Population Identity and Feeding Habits1  

E-print Network

523 Killer Whales in Hawaiian Waters: Information on Population Identity and Feeding Habits1 Robin been reported from Hawaiian waters, and most of what is known about killer whales world- wide comes the Hawaiian Exclusive Economic Zone between 1994 and 2004. Killer whales were recorded nine months of the year

Baird, Robin W.

383

Supernova spectra below strong circumstellar interaction  

NASA Astrophysics Data System (ADS)

We construct spectra of supernovae (SNe) interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum, and an emission-line spectrum. In a Monte Carlo simulation we vary a large number of parameters, such as the SN type, brightness and phase, the strength of the CSM interaction, the extinction, and the signal to noise ratio (S/N) of the observed spectrum. We generate more than 800 spectra, distribute them to ten different human classifiers, and study how the different simulation parameters affect the appearance of the spectra and their classification. The SNe IIn showing some structure over the continuum were characterized as "SNe IInS" to allow for a better quantification. We demonstrate that the flux ratio of the underlying SN to the continuum fV is the single most important parameter determining whether a spectrum can be classified correctly. Other parameters, such as extinction, S/N, and the width and strength of the emission lines, do not play a significant role. Thermonuclear SNe get progressively classified as Ia-CSM, IInS, and IIn as fV decreases. The transition between Ia-CSM and IInS occurs at fV ~ 0.2-0.3. It is therefore possible to determine that SNe Ia-CSM are found at the (un-extincted) magnitude range -19.5 >M> -21.6, in very good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The literature sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association can be attributed to a luminosity bias (91T-like being brighter than normal events). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors that are responsible for the CSM. Despite the spectroscopic similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was very small in our simulation and mostly at low S/N. Combined with the SN luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the H? profiles vary with fV. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A more advanced simulation, including radiative transfer, shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data.

Leloudas, G.; Hsiao, E. Y.; Johansson, J.; Maeda, K.; Moriya, T. J.; Nordin, J.; Petrushevska, T.; Silverman, J. M.; Sollerman, J.; Stritzinger, M. D.; Taddia, F.; Xu, D.

2015-02-01

384

Circumstellar Masers in the Galactic center Lor ant Sjouwerman  

E-print Network

Circumstellar Masers in the Galactic center Lor#19;ant Sjouwerman National Radio Astronomy surveys for maser emission (OH, H2O, and SiO) in the central degree (#20; 150 pc) of the Galactic center will be discussed, with the emphasis on masers in OH/IR stars. Using the masers, some recent clues about

Sjouwerman, Loránt

385

Structure and evolution of circumstellar disks: A Spitzer view  

Microsoft Academic Search

This dissertation is the sum of five studies of the structure and evolution of circumstellar disks, the birthplace of planets. These studies are all based on Infrared data from the Spitzer Space Telescope, and taken together trace the evolution of disks from the optically thick primordial stage to the optically thin debris disk stage. The five projects included in this

Lucas Alejo Cieza-Gonzalez

2007-01-01

386

On the Classification of Infrared Spectra from Circumstellar Dust Shells  

NASA Technical Reports Server (NTRS)

We present results from an ongoing effort to classify the infrared spectra produced by circumstellar dust shells. Earlier efforts concentrated on oxygen-rich dust shells from sources associated with the asymptotic giant branch (AGB). Here, we describe the expansion of our classification to include S stars, supergiants, and carbon stars.

Sloan, G. C.; Little-Marenin, I. R.; Price, S. D.

1996-01-01

387

Habitable worlds with no signs of life  

E-print Network

'Most habitable worlds in the cosmos will have no remotely detectable signs of life' is proposed as a biological hypothesis to be tested in studies of exoplanets. Habitable planets could be discovered elsewhere in the Universe, yet there are many hypothetical scenarios whereby the search for life on them could yield negative results. Scenarios for habitable worlds with no remotely detectable signatures of life include: planets that are habitable, but have no biosphere (Uninhabited Habitable Worlds); planets with life, but lacking any detectable surface signatures of that life (laboratory examples are provided) and planets with life, where the concentration of atmospheric gases produced or removed by biota are impossible to disentangle from abiotic processes because of the lack of detailed knowledge of planetary conditions (the 'problem of exoplanet thermodynamic uncertainty'). A rejection of the hypothesis would require that the origin of life usually occurs on habitable planets, that spectrally detectable pi...

Cockell, Charles S

2013-01-01

388

The MEarth Project to Detect Habitable SuperEarth Exoplanets  

NASA Astrophysics Data System (ADS)

By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 Earth radii in the habitable zones of their host stars. The discovery of such planets is important for two reasons: First, their transiting geometries permit direct estimates of the planetary masses and radii, and hence provide fundamental constraints on the physical structure of planets that are primarily rock and ice in composition. Second, by differencing spectra gathered when the planet is in view from those when it is occulted by the star, we can study the atmospheric chemistry of potentially habitable worlds. The MEarth Project will consist of 8 identical, automated 16-inch telescopes in a single enclosure at Mt Hopkins, AZ. Two of these telescopes have been in operation since January 2008. We will describe the target sample, survey design, and the current photometric precision, with the goal of demonstrating the feasibility of the ground-based detection of habitable exoplanets. We acknowledge funding from the David and Lucile Packard Fellowship for Science and Engineering.

Charbonneau, David; Irwin, J.; Nutzman, P.; Falco, E. E.

2008-05-01

389

Habitable periglacial landscapes in martian mid-latitudes  

NASA Astrophysics Data System (ADS)

Subsurface permafrost environments on Mars are considered to be zones where extant life could have survived. For the identification of possible habitats it is important to understand periglacial landscape evolution and related subsurface and environmental conditions. Many landforms that are interpreted to be related to ground ice are located in the martian mid-latitudinal belts. This paper summarizes the insights gained from studies of terrestrial analogs to permafrost landforms on Mars. The potential habitability of martian mid-latitude periglacial landscapes is exemplarily deduced for one such landscape, that of Utopia Planitia, by a review and discussion of environmental conditions influencing periglacial landscape evolution. Based on recent calculations of the astronomical forcing of climate changes, specific climate periods are identified within the last 10 Ma when thaw processes and liquid water were probably important for the development of permafrost geomorphology. No periods could be identified within the last 4 Ma which met the suggested threshold criteria for liquid water and habitable conditions. Implications of past and present environmental conditions such as temperature variations, ground-ice conditions, and liquid water activity are discussed with respect to the potential survival of highly-specialized microorganisms known from terrestrial permafrost. We conclude that possible habitable subsurface niches might have been developed in close relation to specific permafrost landform morphology on Mars. These would have probably been dominated by lithoautotrophic microorganisms (i.e. methanogenic archaea).

Ulrich, M.; Wagner, D.; Hauber, E.; de Vera, J.-P.; Schirrmeister, L.

2012-05-01

390

The Astrophysical Journal Letters, 734:L13 (5pp), 2011 June 10 doi:10.1088/2041-8205/734/1/L13 C 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.  

E-print Network

In the circumstellar habitable zone (HZ), an Earth-like planet has surface temperatures permissive of liquid water PLANETS BEYOND THE HABITABLE ZONE Raymond Pierrehumbert1 and Eric Gaidos2 1 Department of the Geophysical the "classical" habitable zone defined for CO2 greenhouse atmospheres. Using a one- dimensional radiative

Pierrehumbert, Raymond

391

Radiological Habits Survey: Hinkley Point, 2010  

E-print Network

Radiological Habits Survey: Hinkley Point, 2010 2011 Environment Report RL 01/11 Cefas contract Radiological Habits Survey: Hinkley Point, 2010 F.J. Clyne, C.J. Garrod, P. Rumney, L.M. Hughes and V.E. Ly be cited as: Clyne, F.C., Garrod, C.J., Rumney, P., Hughes, L.M., and Ly, V.E., 2011. Radiological Habits

392

Space station group activities habitability module study  

NASA Technical Reports Server (NTRS)

This study explores and analyzes architectural design approaches for the interior of the Space Station Habitability Module (originally defined as Habitability Module 1 in Space Station Reference Configuration Decription, JSC-19989, August 1984). In the Research Phase, architectural program and habitability design guidelines are specified. In the Schematic Design Phase, a range of alternative concepts is described and illustrated with drawings, scale-model photographs and design analysis evaluations. Recommendations are presented on the internal architectural, configuration of the Space Station Habitability Module for such functions as the wardroom, galley, exercise facility, library and station control work station. The models show full design configurations for on-orbit performance.

Nixon, David

1986-01-01

393

The set of habitable planets and astrobiological regulation mechanisms  

NASA Astrophysics Data System (ADS)

The number of habitable planets in the Milky Way and its temporal variation are major unknowns in the nascent fields of astrobiology and Search for ExtraTerrestrial Intelligence studies. All numerical models developed thus far have suffered from large uncertainties in the input data, in addition to our lack of understanding of the processes of astrobiological dynamics. Here, we argue that at least the input data can now be specified with more confidence, and use a simple Monte Carlo model of the Galactic Habitable Zone (GHZ) as a flexible platform for their elucidation. Previous papers have described some of the major results of this class of models; in this paper we present its mechanics and input parameters, notably the number of the habitable planets in the GHZ and their temporal distribution, based on the results of Lineweaver et al. (Lineweaver, C.H., Fenner, Y. & Gibson, B.K. (2004). Science 303, 59-62.) Regulation mechanisms (such as gamma-ray bursts or supernovae) and their temporal evolution, assumed to be main agents responsible for large-scale correlation effects, are modelled as type ? (which can sterilize part of or the entire GHZ) and type ? (which are of local importance) events with decreasing mean temporal frequency over the cosmological timescale. The considered global risk function implies as an upper limit that about one out of a hundred habitable sites will achieve high astrobiological complexity. The preliminary results of numerical modelling presented here and elsewhere imply that the lack of a sudden change from an essentially dead Galaxy to a Galaxy filled with complex life - the astrobiological phase transition - in our past (a version of Fermi's paradox) may be understood as a consequence of global astrobiological disequilibrium, strongly indicating such a transitional epoch in our future.

Vukoti?, Branislav

2010-04-01

394

Make peak flow a habit!  

MedlinePLUS

... peak flow at home with a small, plastic meter. Some peak flow meters have tabs on the side that you can ... action plan zones (green, yellow, red). If your meter does not have these, you can mark them ...

395

A Re-appraisal of the Habitability of Planets Around M Dwarf Stars  

E-print Network

Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.

Jill C. Tarter; Peter R. Backus; Rocco L. Mancinelli; Jonathan M. Aurnou; Dana E. Backman; Gibor S. Basri; Alan P. Boss; Andrew Clarke; Drake Deming; Laurance R. Doyle; Eric D. Feigelson; Friedmann Freund; David H. Grinspoon; Robert M. Haberle; Steven A. Hauck II; Martin J. Heath; Todd J. Henry; Jeffery L. Hollingsworth; Manoj M. Joshi; Steven Kilston; Michael C. Liu; Eric Meikle; I. Neill Reid; Lynn J. Rothschild; John M. Scalo; Antigona Segura; Carol M. Tang; James M. Tiedje; Margaret C. Turnbull; Lucianne M. Walkowicz; Arthur L. Weber; Richard E. Young

2006-11-20

396

Trace Element Condensation in Circumstellar Envelopes of Carbon Stars  

NASA Astrophysics Data System (ADS)

It is now well established that meteorites contain reduced presolar grains, such as graphite and silicon carbide (SiC), which are probably formed by condensation of dust in the circumstellar envelopes of carbon-rich AGB stars. Here we model condensation in envelopes of carbon stars, with an emphasis on trace elements. Since absolute elemental abundances in stellar atmospheres are generally not known, we assume solar abundances (Anders and Grevesse 1989), except for carbon. A C/O ratio of 2, consistent with the mean and median values of 2.1 and 1.8 respectively, for 61 carbon stars (Gow 1977) was used. The C/O ratio was increased by adding carbon because astrophysicists believe that carbon produced in helium-burning zones may be mixed to the surfaces of C stars (e.g. Lucy 1976). We used physical parameters for the circumstellar shell of the high mass-loss rate, prototypical carbon star IRC +10216 (e.g. Keady et al. 1988, Dominik et al. 1990) and theoretical considerations by Salpeter (1974a,b) to construct a P-T-model of the envelope (see Fig. 1). Thermodynamic equilibrium condensation calculations for a reduced gas include ~600 gaseous and solid compounds of the elements H, C, N, O, S, P, F, Cl, Fe, Mg, Al, Ti, Si, Ca, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and REE. Refractory oxides, sulfides, nitrides, and carbides were considered as condensates. The calculations were done from T = 800 to 2500 K, and P= 10^-5 to 10^-13 bars. The effects of nucleation on condensation temperatures were calculated using the nucleation model discussed by Salpeter (1974a,b) and Cameron and Fegley (1982). The temperature drop required for condensation depends on (P,T, density) in the expanding envelope and also on the abundance, density, and surface energy (Es) of the nucleating compound. The range of E(sub)s values for NaCl-type carbides are about 800-1700 erg/cm^2 (Livey & Murray 1956); however, these data are generally poorly known. Another important variable is the sticking coefficient (s), taken = 10^-3 here. Results of the equilibrium condensation calculations as a function of pressure at C/O = 2 are shown in Table 1 and Fig. 1. The initial major element condensates are graphite, TiC, SiC, Fe3C, AlN, and CaS (Table 1). The data for C(sub)GR TiC, and SiC are also shown in Fig. 1, together with the P-T profile for the carbon star IRC +10216. Also included are the condensation temperatures if nucleation constraints are applied (dotted lines). Neglecting nucleation effects, C(sub)Gr, TiC, and SiC would be present within 2-3 stellar radii from the photosphere (r/R = 1). With nucleation constraints, TiC and SiC form at lower T at a distance of about 5 stellar radii. The T-drop required for graphite condensation is only about 100 K lower than the equilibrium condensation temperatures at higher P. Therefore, graphite grains would be stable at r/R >1.5. We note that at r = 3-5 R there is observational evidence for SiC, graphite and amorphous carbon in the envelope of the C star IRC +10216 (e.g. Keady et al. 1988, Ridgway and Keady 1988). Of the nitrides, AlN is the only which forms initially. Because of its structural similarity to SiC and TiC one could expect formation of AlN solid solutions with NaCl-type carbides. Most trace elements initially form carbides. The most refractory carbides are TaC, WC, NbC, ZrC, and HfC, condensing about 100-250 K higher than TiC. E(sub)s data are available for TaC and ZrC. Nucleation constraints show that only ZrC would form prior to TiC. Other trace element carbides (Mo(sub)2C, MoC, VC(sub)0.88, YC(sub)2, Cr(sub)3C(sub)2) condense as pure compounds below the equilibrium condensation temperatures of C(sub)Gr, TiC, and SiC. However, they may condense in solid solution in TiC or SiC or in both if allowed by their crystal structures. In any case, nitrides are not initial condensates for these trace elements. However, because the carbides and nitrides can form solid solutions, one could expect carbide-nitride solutions. References: Anders E. and Grevesse N. (1989) Geochim. Cosmochim. Acta 53, 197-214. Cameron A.G.W

Lodders, K.; Fegley, B., Jr.

1992-07-01

397

Technological Zones  

Microsoft Academic Search

This article provides an overview of the analysis of technological zones. A technological zone can be understood as a space within which differences between technical practices, procedures and forms have been reduced, or common standards have been established. Such technological zones take broadly one of three forms: (1) metrological zones associated with the development of common forms of measurement; (2)

Andrew Barry

2006-01-01

398

Computer Technology and College Students' Reading Habits  

Microsoft Academic Search

The purposes of this study were to determine if computer technology had an impact on EFL college students' reading habits and if students' online reading habits and their demographic variables, such as gender, age, CJEE scores, employment status, and online hours were related. 124 valid survey questionnaires were collected from college students in a university in southern Taiwan. The results

Li-Bi Shen

2006-01-01

399

Radiological Habits Survey: Cumbrian coast beach occupancy,  

E-print Network

Radiological Habits Survey: Cumbrian coast beach occupancy, 2009 2010 Cefas contract report C3635 Environment Report RL 01/10 #12;1 Environment Report RL 01/10 Radiological Habits Survey: Cumbrian coast beach. Survey area 9 Map 1 The Cumbrian coast beach occupancy survey area 10 3.1 General observations 11 3

400

The Leisure Reading Habits of Urban Adolescents  

ERIC Educational Resources Information Center

Research indicates that there is a strong relationship between leisure reading and school achievement, but the leisure reading habits of urban adolescents have rarely been studied. From their investigation of the leisure reading habits of 584 urban minority middle school students, the authors identify these key findings: (1) More than two-thirds…

Hughes-Hassell, Sandra; Rodge, Pradnya

2007-01-01

401

Genetic Influences on Adolescent Eating Habits  

Microsoft Academic Search

Behavioral genetic research shows that variation in eating habits and food consumption is due to genetic and environmental factors. The current study extends this line of research by examining the genetic contribution to adolescent eating habits. Analysis of sibling pairs drawn from the National Longitudinal Study of Adolescent Health (Add Health) revealed significant genetic influences on variance in an unhealthy

Kevin M. Beaver; Tori Flores; Brian B. Boutwell; Chris L. Gibson

2012-01-01

402

Genetic Influences on Adolescent Eating Habits  

ERIC Educational Resources Information Center

Behavioral genetic research shows that variation in eating habits and food consumption is due to genetic and environmental factors. The current study extends this line of research by examining the genetic contribution to adolescent eating habits. Analysis of sibling pairs drawn from the National Longitudinal Study of Adolescent Health (Add Health)…

Beaver, Kevin M.; Flores, Tori; Boutwell, Brian B.; Gibson, Chris L.

2012-01-01

403

Detection of circumstellar material in a normal type Ia supernova.  

PubMed

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion. PMID:17626848

Patat, F; Chandra, P; Chevalier, R; Justham, S; Podsiadlowski, Ph; Wolf, C; Gal-Yam, A; Pasquini, L; Crawford, I A; Mazzali, P A; Pauldrach, A W A; Nomoto, K; Benetti, S; Cappellaro, E; Elias-Rosa, N; Hillebrandt, W; Leonard, D C; Pastorello, A; Renzini, A; Sabbadin, F; Simon, J D; Turatto, M

2007-08-17

404

Circumstellar discs around solar-mass stars in NGC 6611  

E-print Network

We have performed IZJHKL' observations in NGC 6611, the young cluster that ionises the Eagle Nebula. We have discovered a rich pre-main sequence concentrated around the O-stars in the cluster. As measured by their L'-band excesses, at least 58% +/- 5% of the pre-main sequence objects (0.45 Msun < M < 2 Msun) have circumstellar discs. By comparing this disc frequency with frequencies determined for regions where the pre-main sequence stars are subject to less ionising radiation, we find no evidence that the harsher environment of NGC 6611 (approximately an order of magnitude more ionising Lyman continuum radiation than the Trapezium cluster) significantly hastens the dissipation of circumstellar discs around solar-mass stars.

J. M. Oliveira; R. D. Jeffries; J. Th. van Loon; S. P Littlefair; T. Naylor

2005-01-12

405

CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE  

SciTech Connect

Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

Shen, Ken J. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Guillochon, James [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Foley, Ryan J., E-mail: kenshen@astro.berkeley.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-06-20

406

The chemistry of molecular anions in circumstellar sources  

NASA Astrophysics Data System (ADS)

The detection of negatively charged molecules in the interstellar and circumstellar medium in the past four years has been one of the most impacting surprises in the area of molecular astrophysics. It has motivated the interest of astronomers, physicists, and chemists on the study of the spectroscopy, chemical kinetics, and prevalence of molecular anions in the different astronomical regions. Up to six different molecular anions have been discovered in space to date, the last one being the small ion CN-, which has been observed in the envelope of the carbon star IRC +10216 and which contrary to the other larger anions is not formed by electron attachment to CN, but through reactions of large carbon anions with nitrogen atoms. Here we briefly review the current status of our knowledge of the chemistry of molecular anions in space, with particular emphasis on the circumstellar source IRC +10216, which to date is the astronomical source harboring the largest variety of anions.

Agúndez, Marcelino; Cernicharo, José; Guélin, Michel

2015-01-01

407

Circumstellar shells resolved in IRAS survey data. II - Analysis  

NASA Technical Reports Server (NTRS)

IRAS survey data for 512 red giant stars and young planetary nebulae were processed using a computer program which fitted the data to an idealized model of a circumstellar shell. Seventy-six of these stars were found to have circumstellar shells resolved in the 60-micron survey data. Forty pct of the 76 stars are carbon stars. Thirteen are Mira variables. The evolution of these shells, involving the interaction of the expelled material with the ISM, is modeled, and the results suggest that the period during which Mira variables lose mass lasts for approximately 10 exp 5 yr. Carbon stars are found to shed mass for about 2 x 10 exp 5 yr. The expansion velocity of the outer shell for the largest shells will normally be lower by a factor of 3-5 than the expansion velocity obtained from CO observations.

Young, K.; Phillips, T. G.; Knapp, G. R.

1993-01-01

408

Dust mineralogy in the circumstellar envelope of SVS13  

NASA Astrophysics Data System (ADS)

It is of great interest to study the mineralogy of circumstellar dust around young stars as it represents the original constituents of planetesimals, hence of the rocky planets like our own Earth. To this end, we have obtained an N-band (8-13 µm) spectrum of a pre-main-sequence star SVS13, using the facility mid-infrared imaging spectrometer COMICS on the Japanese 8.2-m Subaru Telescope atop the summit of Mauna Kea, Hawaii. We have fitted various emissivities/absorption coefficients of dust species to the spectrum to examine dust mineralogy in the circumstellar envelope of this remarkable young star. In this presentation, we outline the modelling and highlight some of our findings.

Fujiyoshi, T.; Wright, C.; Moore, T.

409

Hot circumstellar material resolved around ? Pic with VLTI/PIONIER  

NASA Astrophysics Data System (ADS)

Aims: We aim at resolving the circumstellar environment around ? Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results: We detected near-infrared circumstellar emission around ? Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (?1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of ? Pic with an unprecedented accuracy (?LD= 0.736 ± 0.019 mas). Conclusions: The presence of a small H-band excess originating in the vicinity of ? Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded. Based on data collected at the ESO Paranal Observatory under commissioning time and programme 088.C-0266.

Defrère, D.; Lebreton, J.; Le Bouquin, J.-B.; Lagrange, A.-M.; Absil, O.; Augereau, J.-C.; Berger, J.-P.; di Folco, E.; Ertel, S.; Kluska, J.; Montagnier, G.; Millan-Gabet, R.; Traub, W.; Zins, G.

2012-10-01

410

NASA plans relevant to the study of circumstellar matter  

NASA Astrophysics Data System (ADS)

The Astrophysics program of the National Aeronautics and Space Administration of the United States emphasizes use of vehicles to obtain above-the-atmosphere observational advantages, including expanded electromagnetic frequency access, enhanced sensitivity resulting from reduced or eliminated atmospheric absorption of light and image smearing. Space technology provides a superior means for astrophysical inquiry, particularly in the case of circumstellar material. Much of the flight program is undergoing intensive review following the Space Shuttle disaster of January 1986.

Stencel, Robert E.

411

Possible Tracers of Circumstellar Gas in the Disk Around ? Pictoris  

NASA Astrophysics Data System (ADS)

The nature of the circumstellar disk around ? Pictoris has been extensively discussed in the literature during the past ten years. CO is in general a poor tracer for the gas content of such low-mass disks. Based on recent disk models (Kamp & van Zadelhoff 2001), which include a self-consistent calculation of the gas temperature, we find that C and C+ are very promising tracers for the gas around ? Pictoris.

Kamp, I.; van Zadelhoff, G.-D.; van Dishoeck, E.

2004-12-01

412

The Habitable Planet: Ecology Lab  

NSDL National Science Digital Library

The Annenberg Media project continues to bring interesting and engaging educational materials to teachers and students, and the ball keeps on rolling with this particular feature. The ecology lab feature here is designed to be used in conjunction with "The Habitable Planet" series, which is also available on the site. Teachers and others will note that the site includes an ecology simulator, and visitors can toggle the various settings to learn how the addition or removal of different species will affect their self-designed ecosystem. The simulator is fairly easy to understand, and there's a "HELP" section designed to provide assistance. Additionally, the site also includes a glossary of relevant ecosystem terms, videos, and an online textbook.

413

Additional constraints on circumstellar disks in the Trapezium Cluster  

NASA Technical Reports Server (NTRS)

We discuss new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new HST Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the circumstellar disk model is the most likely one for the majority of sources, although it remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a circumstellar disk. Our estimate of 25-75 percent is comparable to that found for PMS stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of disks seen around pre-main sequence stars.

Stauffer, John R.; Prosser, Charles F.; Hartmann, Lee; Mccaughrean, Mark J.

1994-01-01

414

Circumstellar Environments of Southern M Dwarfs in the Solar Neighborhood  

NASA Astrophysics Data System (ADS)

We present the first results from SIRENS, the Search for InfraRed Excesses around Nearby Stars. Our goal is to characterize the circumstellar environments of the most common and closest stars in the Universe, the ubiquitous red dwarfs. In this phase of the study, we search 1404 southern M dwarfs within 25 parsecs of the Sun, as reported in Winters et. al 2014, using (Johnson-Kron-Cousins) optical, (2MASS) near-infrared, and (WISE) mid-infrared photometry for circumstellar disks and low-mass companions. Several studies have recently used WISE photometry to detect circumstellar disks and companions --- searches around members of the nearby young moving groups, objects with parallaxes from Hipparcos, and many northern M stars in the SDSS. However, no work has yet been done that focuses on the nearest red dwarfs, which account for at least 75% of all stars. This study, a volume-limited search around M dwarfs in the southern sky, includes statistical conclusions applicable to a majority of the stars in the universe, and opens potential gateways to a better understanding of star and planet formation.

Silverstein, Michele L.; Henry, Todd J.; Jao, Wei-Chun; Winters, Jennifer G.; Recons Team

2015-01-01

415

The fraction of circumstellar debris at white dwarfs  

NASA Astrophysics Data System (ADS)

We present results of the first unbiased Spitzer IRAC survey of a homogeneous and well-defined sample of 134 single white dwarfs in search of infrared excesses compatible with the presence of circumstellar dust formed from the disruption of planetesimals. The stars were selected without regard to atmospheric metal content but were chosen to have 1) hydrogen rich atmospheres, 2) 17 000K < Teff < 20 000K and correspondingly young post main-sequence ages of 20-120 Myr, and 3) sufficient far-ultraviolet brightness for a corresponding Hubble Space Telescope COS Snapshot. We find five white dwarfs that host an infrared bright dust disc, three previously known, and two reported here for the first time, yielding a nominal 3.7% of white dwarfs in this post-main sequence age range with detectable circumstellar material. Remarkably, our complementary HST observations indicate this fraction is almost certainly an order of magnitude higher, with the bulk of circumstellar discs currently hidden in the infrared. The presence of narrow and attenuated dust rings, and especially atmospheric pollution, corroborate this interpretation as do the distribution of LIR/L* values as a function of cooling age.

Rocchetto, M.; Farihi, J.; Gänsicke, B. T.; Bergfors, C.

2014-04-01

416

Cosmological Aspects of Habitability of Exoplanets  

NASA Astrophysics Data System (ADS)

Habitable zone (HZ) defines the region around a start within which planets may support liquid water at their surfaces, which is supposed to be the necessary factor for origination and development of life on the planet. Currently we know about 30 planets inside HZ. The most interesting question is that of possibility of existence of complex life on the planets. As several space-based project aimed at searching of traces of life at exoplanets are presently being worked out, the problem of elaboration of criteria for selection out of the list of planets inside HZ those which most probably host life acquires supreme importance. It is usually implicitly assumed that planets inside HZ may host life, not taking into consideration such an important factor as the planet age. On the other hand the crucial importance of the factor meets the eye immediately. In fact, if we consider a life similar to that on the Earth, it is obvious, that planets younger than 1 Gyr can hardly bear even primitive life-forms because life needs time to originate and develop. Moreover, as a part of biochemical and metabolic processes are endothermic, and, therefore, threshold, the process of life origination may prove extremely sensitive even to tiny HZ parameter variations. Still a most of the discovered planets are known to orbit young stars (stellar population I), no older than several mullions of years. So a considerable number of planets sure HZ inhabitants may prove too young to be really inhabitable. On the other hand, 12-13 Gyr old planetary systems (population II) may happen to be more probable bearers of life. In spite of the fact that such systems are, in the average more distant from us that the population I stars, estimations of possibility of direct detection of traces of metabolism on those systems are quite optimistic, if we bear in mind planetary systems of old law-mass K-stars.

Shchekinov, Yu. A.; Safonova, M.; Murphy, J.

2014-10-01

417

Circumstellar Disks and Sub-Stellar Objects  

NASA Astrophysics Data System (ADS)

This proposal consists of two parts related to the study of low-mass sub-stellar objects. In the first part, intend to obtain low-resolution IRS spectra and MIPS 50-160um data of a nearby young star surrounded by a newly-discovered debris disk, containing an embedded point source at 50 AU - a candidate planet. The system was discovered recently in the course of a ground- based adaptive optics survey for sub-stellar companions to young solar analogs. The AO images detect the disk in scattered light over 30-50 AU from the star. Through 5-38 micron IRS spectroscopy, sensitive to material at 1-20 AU from this sun-like star, I will be able to constrain the amount of dust and its composition at separations inaccessible through direct imaging. The MIPS 50-95um SED and 160um imaging data, combined with 24um and 70um GTO data, will constrain the temperature and amount of material in the resolved scattered light disk. The combination of imaging, spectroscopic and SED data over 1-160um will thus offer a unified picture of this intriguing system over orbital separations spanning the equivalents of the terrestrial and the ice giant zones in the Solar System. In the second part of the proposal, I will use 3-9 micron IRAC imaging to study the photospheres of newly-found candidate free-floating planetary-mass objects. I have identified such candidates from a positional and color cross-match between the SDSS and 2MASS surveys, aimed at discovering objects beyond the bottom of the T dwarf sequence, so-called Y dwarfs. All of the selected candidates are seen only in the SDSS z- and 2MASS J-bands, and thus have very red (i-z>3.0) optical and blue (J-Ks<1.0) near-IR colors, as is characteristic for late T dwarfs and as may also be expected for early Y dwarfs. If Y dwarfs are confirmed in the sample, their mid-IR colors of will constrain the abundances of the dominant molecular species (methane, ammonia, water) in their photospheres, and will allow a quantitative classification of this new spectral type.

Metchev, Stanimir

2005-04-01

418

Infrared interferometry and spectroscopy of circumstellar envelopes  

NASA Astrophysics Data System (ADS)

This thesis reports on two experiments designed to reveal fundamentally new information about the inner dust and gas envelopes around mass-losing stars. The mid-infrared Infrared Spatial Interferometer was outfitted with an RF filterbank to allow interferometric observations of molecular absorption features (NH3 and SiH4) with very high spectral resolution ( / ~ 105). These new data permitted the molecular stratification around carbon star IRC +10216 and red supergiant VY CMa to be investigated. For IRC +10216, it was determined that both ammonia and silane form in the dusty outflow significantly beyond both the dust formation and gas acceleration zones ( >~ 20 R* ). More specifically, ammonia was found to form before silane in a region of decaying gas turbulence, while the silane is produced in a region of relatively smooth gas flow much further from the star ( >~ 80 R* ). The depletion of SiS on grains soon after dust formation may fuel silane-producing reactions on the grain surfaces. For VY CMa, a combination of interferometric and spectral observations suggest that NH3 is forming near the termination of the gas acceleration phase in a region of high gas turbulence (~40 R* ). The second half of the thesis describes a novel aperture masking experiment which converted the Keck-I 10-m primary mirror into a separate-element interferometric array. High signal-to-noise images were reconstructed of bright near-infrared sources at the diffraction limit (~ 0.050'' at 2 m m) using VLBI techniques. The inner dust shells of IRC +10216 and VY CMa are shown to be highly clumpy and inhomogeneous, a finding inconsistent with current (simple) models of mass-loss. For IRC +10216, spatial resolution on the scale of the star itself was attained, and proper motion of dust clumps within 10 R* was detected, revealing the dynamics of the outflow directly. Unexpectedly, carbon-rich dust shells around some late- type Wolf-Rayet stars were resolved into highly- collimated, spinning ``pinwheel'' nebulae, formed from the interacting winds of embedded short- period (~1 yr) binaries. Precise orbital parameters and wind velocities are determined from the multi-epoch spiral morphology; important implications on binary and stellar evolution are discussed.

Monnier, John David

419

Habitable Planets Around White and Brown Dwarfs: The Perils of a Cooling Primary  

PubMed Central

Abstract White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time; hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern that tidal heating may also be strong enough to trigger a runaway greenhouse, even for orbital eccentricities as small as 10?6. Water loss occurs due to photolyzation by UV photons in the planetary stratosphere, followed by hydrogen escape. Young white dwarfs emit a large amount of these photons, as their surface temperatures are over 104 K. The situation is less clear for brown dwarfs, as observational data do not constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable. Key Words: Extrasolar terrestrial planets—Habitability—Habitable zone—Tides—Exoplanets. Astrobiology 13, 279–291. PMID:23537137

Heller, René

2013-01-01

420

An IDL Code for Automatically Modelling Infrared Circumstellar Emission of Dust (ICED)  

NASA Astrophysics Data System (ADS)

Circumstellar dust is of prime importance for the evolution of Asymptotic Giant Branch (AGB) and Red Supergiant (RSG) stars, and it can be used to study/constrain their (circum)stellar parameters and evolution. The dust shows spectral features at infrared (IR) wavelengths, which are sensitive to the dust (grain) properties. Modeling IR spectra can be tedious and time consuming. Often there are many (circum)stellar parameters to be fitted, and the solutions are not unique. Here I present the IDL code ICED, which automatically and objectively fits the IR emission of circumstellar dust, with an application to the IR spectrum of IRC+10216.

Dijkstra, C.

2007-11-01

421

Habitability design elements for a space station  

NASA Technical Reports Server (NTRS)

Habitability in space refers to the components, characteristics, conditions, and design parameters that go beyond but include the basic life sustaining requirements. Elements of habitability covered include internal environment, architecture, mobility and restraint, food, clothing, personal hygiene, housekeeping, communications, and crew activities. All elements are interrelated and need to be treated as an overall discipline. Designing for a space station is similar to designing on earth but with 'space rules' instead of ground rules. It is concluded that some habitability problems require behavioral science solutions.

Dalton, M. C.

1983-01-01