1
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Sagear S, Ballard S. The orbital eccentricity distribution of planets orbiting M dwarfs. Proc Natl Acad Sci U S A 2023; 120:e2217398120. [PMID: 37252955 PMCID: PMC10265968 DOI: 10.1073/pnas.2217398120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 04/11/2023] [Indexed: 06/01/2023] Open
Abstract
We investigate the underlying distribution of orbital eccentricities for planets around early-to-mid M dwarf host stars. We employ a sample of 163 planets around early- to mid-M dwarfs across 101 systems detected by NASA's Kepler Mission. We constrain the orbital eccentricity for each planet by leveraging the Kepler lightcurve together with a stellar density prior, constructed using metallicity from spectroscopy, Ks magnitude from 2MASS, and stellar parallax from Gaia. Within a Bayesian hierarchical framework, we extract the underlying eccentricity distribution, assuming alternately Rayleigh, half-Gaussian, and Beta functions for both single- and multi-transit systems. We described the eccentricity distribution for apparently single-transiting planetary systems with a Rayleigh distribution with [Formula: see text], and for multitransit systems with [Formula: see text]. The data suggest the possibility of distinct dynamically warmer and cooler subpopulations within the single-transit distribution: The single-transit data prefer a mixture model composed of two distinct Rayleigh distributions with [Formula: see text] and [Formula: see text] over a single Rayleigh distribution, with 7:1 odds. We contextualize our findings within a planet formation framework, by comparing them to analogous results in the literature for planets orbiting FGK stars. By combining our derived eccentricity distribution with other M dwarf demographic constraints, we estimate the underlying eccentricity distribution for the population of early- to mid-M dwarf planets in the local neighborhood.
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Affiliation(s)
- Sheila Sagear
- Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL32611
| | - Sarah Ballard
- Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL32611
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2
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The Solar-Electric Sail: Application to Interstellar Migration and Consequences for SETI. UNIVERSE 2022. [DOI: 10.3390/universe8050252] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The Solar-Electric Sail accelerates by reflecting positively charged solar wind ions. If it is used to propel an interstellar migration mission, its interstellar cruise velocity relative to the home star cannot exceed the solar wind velocity. In an effort to analytically determine interstellar cruise velocity for a 107 kg generation ship, a constant solar wind velocity within the heliosphere of a Sun-like star of 600 km/s is assumed. The solar wind proton density at 1 AU is also considered constant at 10 protons per cubic centimeter. Solar wind density is assumed to decrease with the inverse square of solar distance. It is shown that, to maintain sufficient acceleration to achieve an interstellar cruise velocity about 70% of the solar wind velocity, the radius of the sail’s electric field is enormous—greater than 105 km. Because the solar wind velocity and density are not constant, field strength must be varied rapidly to compensate for solar wind variation. Although not competitive with the ultimate theoretical performance of solar-photon sail propelled migrations departing from Sun-like stars, the solar-electric sail might be superior in this application for migration from dim K and M main sequence stars. Such migrations conducted during close stellar encounters might have durations < 1000 terrestrial years. If only a tiny fraction of M dwarf stars host star-faring civilizations, a significant fraction of Milky Way galaxy planetary systems may have been inhabited, even if no major advances over currently postulated interstellar transportation systems are postulated. SETI theoreticians should consider this when estimating the effects of interstellar colonization.
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Coelho LF, Madden J, Kaltenegger L, Zinder S, Philpot W, Esquível MG, Canário J, Costa R, Vincent WF, Martins Z. Color Catalogue of Life in Ice: Surface Biosignatures on Icy Worlds. ASTROBIOLOGY 2022; 22:313-321. [PMID: 34964651 DOI: 10.1089/ast.2021.0008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
With thousands of discovered planets orbiting other stars and new missions that will explore our solar system, the search for life in the universe has entered a new era. However, a reference database to enable our search for life on the surface of icy exoplanets and exomoons by using records from Earth's icy biota is missing. Therefore, we developed a spectra catalogue of life in ice to facilitate the search for extraterrestrial signs of life. We measured the reflection spectra of 80 microorganisms-with a wide range of pigments-isolated from ice and water. We show that carotenoid signatures are wide-ranged and intriguing signs of life. Our measurements allow for the identification of such surface life on icy extraterrestrial environments in preparation for observations with the upcoming ground- and space-based telescopes. Dried samples reveal even higher reflectance, which suggests that signatures of surface biota could be more intense on exoplanets and moons that are drier than Earth or on environments like Titan where potential life-forms may use a different solvent. Our spectra library covers the visible to near-infrared and is available online. It provides a guide for the search for surface life on icy worlds based on biota from Earth's icy environments.
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Affiliation(s)
- Lígia F Coelho
- Centro de Química Estrutural, Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
- Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - Jack Madden
- Department of Astronomy, Cornell University, Ithaca, New York, USA
- Carl Sagan Institute, Ithaca, New York, USA
| | - Lisa Kaltenegger
- Department of Astronomy, Cornell University, Ithaca, New York, USA
- Carl Sagan Institute, Ithaca, New York, USA
| | - Stephen Zinder
- Carl Sagan Institute, Ithaca, New York, USA
- Department of Microbiology, Cornell University, Ithaca, New York, USA
| | - William Philpot
- Carl Sagan Institute, Ithaca, New York, USA
- School of Civil and Environmental Engineering, Cornell University, Ithaca, New York, USA
| | - M Glória Esquível
- Landscape, Environment, Agriculture and Food-LEAF Centre, Instituto Superior de Agronomia, Universidade de Lisboa, Lisboa, Portugal
| | - João Canário
- Centro de Química Estrutural, Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - Rodrigo Costa
- Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - Warwick F Vincent
- Centre for Northern Studies (CEN), Takuvik & Biology Department, Université Laval, Québec, Canada
| | - Zita Martins
- Centro de Química Estrutural, Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
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4
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Trifonov T, Caballero JA, Morales JC, Seifahrt A, Ribas I, Reiners A, Bean JL, Luque R, Parviainen H, Pallé E, Stock S, Zechmeister M, Amado PJ, Anglada-Escudé G, Azzaro M, Barclay T, Béjar VJS, Bluhm P, Casasayas-Barris N, Cifuentes C, Collins KA, Collins KI, Cortés-Contreras M, de Leon J, Dreizler S, Dressing CD, Esparza-Borges E, Espinoza N, Fausnaugh M, Fukui A, Hatzes AP, Hellier C, Henning T, Henze CE, Herrero E, Jeffers SV, Jenkins JM, Jensen ELN, Kaminski A, Kasper D, Kossakowski D, Kürster M, Lafarga M, Latham DW, Mann AW, Molaverdikhani K, Montes D, Montet BT, Murgas F, Narita N, Oshagh M, Passegger VM, Pollacco D, Quinn SN, Quirrenbach A, Ricker GR, Rodríguez López C, Sanz-Forcada J, Schwarz RP, Schweitzer A, Seager S, Shporer A, Stangret M, Stürmer J, Tan TG, Tenenbaum P, Twicken JD, Vanderspek R, Winn JN. A nearby transiting rocky exoplanet that is suitable for atmospheric investigation. Science 2021; 371:1038-1041. [PMID: 33674491 DOI: 10.1126/science.abd7645] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Accepted: 02/02/2021] [Indexed: 11/02/2022]
Abstract
Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet's short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy.
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Affiliation(s)
- T Trifonov
- Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany.
| | - J A Caballero
- Centro de Astrobiología (Consejo Superior de Investigaciones Científicas - Instituto Nacional de Técnica Aeroespacial), E-28692 Villanueva de la Cañada, Madrid, Spain
| | - J C Morales
- Institut de Ciències de l'Espai (Consejo Superior de Investigaciones Científicas), E-08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, E-08034 Barcelona, Spain
| | - A Seifahrt
- Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
| | - I Ribas
- Institut de Ciències de l'Espai (Consejo Superior de Investigaciones Científicas), E-08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, E-08034 Barcelona, Spain
| | - A Reiners
- Institut für Astrophysik, Georg-August-Universität, D-37077 Göttingen, Germany
| | - J L Bean
- Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
| | - R Luque
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - H Parviainen
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - E Pallé
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - S Stock
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - M Zechmeister
- Institut für Astrophysik, Georg-August-Universität, D-37077 Göttingen, Germany
| | - P J Amado
- Instituto de Astrofísica de Andalucía (Consejo Superior de Investigaciones Científicas), E-18008 Granada, Spain
| | - G Anglada-Escudé
- Institut de Ciències de l'Espai (Consejo Superior de Investigaciones Científicas), E-08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, E-08034 Barcelona, Spain
| | - M Azzaro
- Centro Astronómico Hispano-Alemán, Observatorio de Calar Alto, E-04550 Gérgal, Almería, Spain
| | - T Barclay
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.,University of Maryland, Baltimore County, Baltimore, MD 21250, USA
| | - V J S Béjar
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - P Bluhm
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - N Casasayas-Barris
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - C Cifuentes
- Centro de Astrobiología (Consejo Superior de Investigaciones Científicas - Instituto Nacional de Técnica Aeroespacial), E-28692 Villanueva de la Cañada, Madrid, Spain
| | - K A Collins
- Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA 02138, USA
| | - K I Collins
- Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA
| | - M Cortés-Contreras
- Centro de Astrobiología (Consejo Superior de Investigaciones Científicas - Instituto Nacional de Técnica Aeroespacial), E-28692 Villanueva de la Cañada, Madrid, Spain
| | - J de Leon
- Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
| | - S Dreizler
- Institut für Astrophysik, Georg-August-Universität, D-37077 Göttingen, Germany
| | - C D Dressing
- Astronomy Department, University of California at Berkeley, Berkeley, CA 94720, USA
| | - E Esparza-Borges
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - N Espinoza
- Space Telescope Science Institute, Baltimore, MD 21218, USA
| | - M Fausnaugh
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - A Fukui
- Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan.,Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
| | - A P Hatzes
- Thüringer Landessternwarte Tautenburg, D-07778 Tautenburg, Germany
| | - C Hellier
- Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
| | - Th Henning
- Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany
| | - C E Henze
- NASA Ames Research Center, Moffett Field, CA 94035, USA
| | - E Herrero
- Institut de Ciències de l'Espai (Consejo Superior de Investigaciones Científicas), E-08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, E-08034 Barcelona, Spain
| | - S V Jeffers
- Institut für Astrophysik, Georg-August-Universität, D-37077 Göttingen, Germany.,Max-Planck-Institut für Sonnensystemforschung, D-37077, Göttingen, Germany
| | - J M Jenkins
- NASA Ames Research Center, Moffett Field, CA 94035, USA
| | - E L N Jensen
- Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
| | - A Kaminski
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - D Kasper
- Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
| | - D Kossakowski
- Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany
| | - M Kürster
- Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany
| | - M Lafarga
- Institut de Ciències de l'Espai (Consejo Superior de Investigaciones Científicas), E-08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, E-08034 Barcelona, Spain
| | - D W Latham
- Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA 02138, USA
| | - A W Mann
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - K Molaverdikhani
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - D Montes
- Departamento de Física de la Tierra y Astrofísica and Instituto de Física de Partículas y del Cosmos, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
| | - B T Montet
- School of Physics, University of New South Wales, Sydney NSW 2052, Australia
| | - F Murgas
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - N Narita
- Komaba Institute for Science, University of Tokyo, Tokyo 153-8902, Japan.,Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Tokyo 153-8902, Japan.,Astrobiology Center, Tokyo 181-8588, Japan.,Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
| | - M Oshagh
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - V M Passegger
- Hamburger Sternwarte, Universität Hamburg, D-21029 Hamburg, Germany.,Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA
| | - D Pollacco
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK
| | - S N Quinn
- Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA 02138, USA
| | - A Quirrenbach
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - G R Ricker
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - C Rodríguez López
- Instituto de Astrofísica de Andalucía (Consejo Superior de Investigaciones Científicas), E-18008 Granada, Spain
| | - J Sanz-Forcada
- Centro de Astrobiología (Consejo Superior de Investigaciones Científicas - Instituto Nacional de Técnica Aeroespacial), E-28692 Villanueva de la Cañada, Madrid, Spain
| | - R P Schwarz
- Patashnick Voorheesville Observatory, Voorheesville, NY 12186, USA
| | - A Schweitzer
- Hamburger Sternwarte, Universität Hamburg, D-21029 Hamburg, Germany
| | - S Seager
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - A Shporer
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - M Stangret
- Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
| | - J Stürmer
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, D-69117 Heidelberg, Germany
| | - T G Tan
- Perth Exoplanet Survey Telescope, Perth WA 6010, Australia
| | - P Tenenbaum
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J D Twicken
- Search for Extraterrestrial Intelligence Institute, Mountain View, CA 94043, USA.,NASA Ames Research Center, Moffett Field, CA 94035, USA
| | - R Vanderspek
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J N Winn
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
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Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab. Life (Basel) 2020; 11:life11010010. [PMID: 33374408 PMCID: PMC7823553 DOI: 10.3390/life11010010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 12/18/2020] [Accepted: 12/18/2020] [Indexed: 11/26/2022] Open
Abstract
In a few years, space telescopes will investigate our Galaxy to detect evidence of life, mainly by observing rocky planets. In the last decade, the observation of exoplanet atmospheres and the theoretical works on biosignature gasses have experienced a considerable acceleration. The most attractive feature of the realm of exoplanets is that 40% of M dwarfs host super-Earths with a minimum mass between 1 and 30 Earth masses, orbital periods shorter than 50 days, and radii between those of the Earth and Neptune (1–3.8 R⊕). Moreover, the recent finding of cyanobacteria able to use far-red (FR) light for oxygenic photosynthesis due to the synthesis of chlorophylls d and f, extending in vivo light absorption up to 750 nm, suggests the possibility of exotic photosynthesis in planets around M dwarfs. Using innovative laboratory instrumentation, we exposed different cyanobacteria to an M dwarf star simulated irradiation, comparing their responses to those under solar and FR simulated lights. As expected, in FR light, only the cyanobacteria able to synthesize chlorophyll d and f could grow. Surprisingly, all strains, both able or unable to use FR light, grew and photosynthesized under the M dwarf generated spectrum in a similar way to the solar light and much more efficiently than under the FR one. Our findings highlight the importance of simulating both the visible and FR light components of an M dwarf spectrum to correctly evaluate the photosynthetic performances of oxygenic organisms exposed under such an exotic light condition.
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Abstract
Most definitions of life assume that, at a minimum, life is a physical form of matter distinct from its environment at a lower state of entropy than its surroundings, using energy from the environment for internal maintenance and activity, and capable of autonomous reproduction. These assumptions cover all of life as we know it, though more exotic entities can be envisioned, including organic forms with novel biochemistries, dynamic inorganic matter, and self-replicating machines. The probability that any particular form of life will be found on another planetary body depends on the nature and history of that alien world. So the biospheres would likely be very different on a rocky planet with an ice-covered global ocean, a barren planet devoid of surface liquid, a frigid world with abundant liquid hydrocarbons, on a rogue planet independent of a host star, on a tidally locked planet, on super-Earths, or in long-lived clouds in dense atmospheres. While life at least in microbial form is probably pervasive if rare throughout the Universe, and technologically advanced life is likely much rarer, the chance that an alternative form of life, though not intelligent life, could exist and be detected within our Solar System is a distinct possibility.
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7
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Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab4f7e] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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8
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Abstract
Lower heating of our planet by the young Sun was compensated by higher warming from factors such as greater greenhouse gas concentrations or reduced albedo. Earth's climate history has therefore been one of increasing solar forcing through time roughly cancelled by decreasing forcing due to geological and biological processes. The current generation of coupled carbon-cycle/climate models suggests that decreasing geological forcing-due to falling rates of outgassing, continent growth, and plate spreading-can account for much of Earth's climate history. If Earth-like planets orbiting in the habitable zone of red dwarfs experience a similar history of decreasing geological forcing, their climates will cool at a faster rate than is compensated for by the relatively slow evolution of their smaller stars. As a result, they will become globally glaciated within a few billion years. The results of this paper therefore suggest that coupled carbon-cycle/climate models account, parsimoniously, for both the faint young Sun paradox and the puzzle of why Earth orbits a relatively rare and short-lived star-type.
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Affiliation(s)
- David Waltham
- Department of Earth Sciences, Royal Holloway, Egham, UK
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9
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Kreidberg L, Koll DDB, Morley C, Hu R, Schaefer L, Deming D, Stevenson KB, Dittmann J, Vanderburg A, Berardo D, Guo X, Stassun K, Crossfield I, Charbonneau D, Latham DW, Loeb A, Ricker G, Seager S, Vanderspek R. Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b. Nature 2019; 573:87-90. [DOI: 10.1038/s41586-019-1497-4] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 07/22/2019] [Indexed: 11/09/2022]
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10
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How to Constrain Your M Dwarf. II. The Mass–Luminosity–Metallicity Relation from 0.075 to 0.70 Solar Masses. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/aaf3bc] [Citation(s) in RCA: 148] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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11
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12
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Tilley MA, Segura A, Meadows V, Hawley S, Davenport J. Modeling Repeated M Dwarf Flaring at an Earth-like Planet in the Habitable Zone: Atmospheric Effects for an Unmagnetized Planet. ASTROBIOLOGY 2019; 19:64-86. [PMID: 30070900 PMCID: PMC6340793 DOI: 10.1089/ast.2017.1794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Understanding the impact of active M dwarf stars on the atmospheric equilibrium and surface conditions of a habitable zone Earth-like planet is key to assessing M dwarf planet habitability. Previous modeling of the impact of electromagnetic (EM) radiation and protons from a single large flare on an Earth-like atmosphere indicated that significant and long-term reductions in ozone were possible, but the atmosphere recovered. However, these stars more realistically exhibit frequent flaring with a distribution of different total energies and cadences. Here, we use a coupled 1D photochemical and radiative-convective model to investigate the effects of repeated flaring on the photochemistry and surface UV of an Earth-like planet unprotected by an intrinsic magnetic field. As input, we use time-resolved flare spectra obtained for the dM3 star AD Leonis, combined with flare occurrence frequencies and total energies (typically 1030.5 to 1034 erg) from the 4-year Kepler light curve for the dM4 flare star GJ1243, with varied proton event impact frequency. Our model results show that repeated EM-only flares have little effect on the ozone column depth but that multiple proton events can rapidly destroy the ozone column. Combining the realistic flare and proton event frequencies with nominal CME/SEP geometries, we find the ozone column for an Earth-like planet can be depleted by 94% in 10 years, with a downward trend that makes recovery unlikely and suggests further destruction. For more extreme stellar inputs, O3 depletion allows a constant ∼0.1-1 W m-2 of UVC at the planet's surface, which is likely detrimental to organic complexity. Our results suggest that active M dwarf hosts may comprehensively destroy ozone shields and subject the surface of magnetically unprotected Earth-like planets to long-term radiation that can damage complex organic structures. However, this does not preclude habitability, as a safe haven for life could still exist below an ocean surface.
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Affiliation(s)
- Matt A. Tilley
- Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Address correspondence to: Matt A. Tilley, University of Washington, Johnson Hall Rm-070, Box 351310, Seattle, WA 98195-1310
| | - Antígona Segura
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, México
| | - Victoria Meadows
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Department of Astronomy, University of Washington, Seattle, Washington, USA
| | - Suzanne Hawley
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Department of Astronomy, University of Washington, Seattle, Washington, USA
| | - James Davenport
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Department of Physics and Astronomy, Western Washington University, Bellingham, Washington, USA
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14
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Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aae36a] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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15
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Abstract
As evident from the nearby examples of Proxima Centauri and TRAPPIST-1, Earth-sized planets in the habitable zone of low-mass stars are common. Here, we focus on such planetary systems and argue that their (oceanic) tides could be more prominent due to stronger tidal forces. We identify the conditions under which tides may exert a significant positive influence on biotic processes including abiogenesis, biological rhythms, nutrient upwelling, and stimulating photosynthesis. We conclude our analysis with the identification of large-scale algal blooms as potential temporal biosignatures in reflectance light curves that can arise indirectly as a consequence of strong tidal forces. Key Words: Tidal effects-Abiogenesis-Biological clocks-Planetary habitability-Temporal biosignatures. Astrobiology 18, 967-982.
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Affiliation(s)
- Manasvi Lingam
- 1 Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
- 2 John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts
| | - Abraham Loeb
- 1 Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
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16
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Gebauer S, Grenfell JL, Lehmann R, Rauer H. Evolution of Earth-like Planetary Atmospheres around M Dwarf Stars: Assessing the Atmospheres and Biospheres with a Coupled Atmosphere Biogeochemical Model. ASTROBIOLOGY 2018; 18:856-872. [PMID: 30035637 DOI: 10.1089/ast.2017.1723] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Earth-like planets orbiting M dwarfs are prominent targets when searching for life outside the Solar System. We apply our Coupled Atmosphere Biogeochemical model to investigate the coupling between the biosphere, geosphere, and atmosphere in order to gain insight into the atmospheric evolution of Earth-like planets orbiting M dwarfs and to understand the processes affecting biosignatures and climate on such worlds. This is the first study applying an automated chemical pathway analysis quantifying the production and destruction pathways of molecular oxygen (O2) for an Earth-like planet with an Archean O2 concentration orbiting in the habitable zone of the M dwarf star AD Leonis, which we take as a type-case of an active M dwarf. The main production arises in the upper atmosphere from carbon dioxide photolysis followed by catalytic hydrogen oxide radical (HOx) reactions. The strongest destruction does not take place in the troposphere, as was the case in Gebauer et al. ( 2017 ) for an early Earth analog planet around the Sun, but instead in the middle atmosphere where water photolysis is the strongest. Results further suggest that these atmospheres are in absolute terms less destructive for O2 than for early Earth analog planets around the Sun despite higher concentrations of reduced gases such as molecular hydrogen, methane, and carbon monoxide. Hence smaller amounts of net primary productivity are required to oxygenate the atmosphere due to a change in the atmospheric oxidative capacity, driven by the input stellar spectrum resulting in shifts in the intrafamily HOx partitioning. Under the assumption that an atmosphere of an Earth-like planet survived and evolved during the early high-activity phase of an M dwarf to an Archean-type composition, a possible "Great Oxidation Event," analogous to that on Early Earth, would have occurred earlier in time after the atmospheric composition was reached, assuming the same atmospheric O2 sources and sinks as on early Earth. Key Words: Earth-like-Oxygen-M dwarf stars-Atmosphere-Biogeochemistry-Photochemistry-Biosignatures-Earth-like planets. Astrobiology 18, 856-872.
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Affiliation(s)
- S Gebauer
- 1 Zentrum für Astronomie und Astrophysik (ZAA), Technische Universität Berlin (TUB) , Berlin, Germany
- 2 Institut für Planetenforschung (PF) , Abteilung Eaxtrasolare Planeten und Atmosphären (EPA), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
| | - J L Grenfell
- 2 Institut für Planetenforschung (PF) , Abteilung Eaxtrasolare Planeten und Atmosphären (EPA), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
| | - R Lehmann
- 3 Alfred-Wegener Institut , Helmholtz-Zentrum für Polar- und Meeresforschung, Potsdam, Germany
| | - H Rauer
- 1 Zentrum für Astronomie und Astrophysik (ZAA), Technische Universität Berlin (TUB) , Berlin, Germany
- 2 Institut für Planetenforschung (PF) , Abteilung Eaxtrasolare Planeten und Atmosphären (EPA), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
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17
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Schwieterman EW, Kiang NY, Parenteau MN, Harman CE, DasSarma S, Fisher TM, Arney GN, Hartnett HE, Reinhard CT, Olson SL, Meadows VS, Cockell CS, Walker SI, Grenfell JL, Hegde S, Rugheimer S, Hu R, Lyons TW. Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life. ASTROBIOLOGY 2018; 18:663-708. [PMID: 29727196 PMCID: PMC6016574 DOI: 10.1089/ast.2017.1729] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 12/10/2017] [Indexed: 05/04/2023]
Abstract
In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. Key Words: Exoplanets-Biosignatures-Habitability markers-Photosynthesis-Planetary surfaces-Atmospheres-Spectroscopy-Cryptic biospheres-False positives. Astrobiology 18, 663-708.
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Affiliation(s)
- Edward W. Schwieterman
- Department of Earth Sciences, University of California, Riverside, California
- NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- Blue Marble Space Institute of Science, Seattle, Washington
| | - Nancy Y. Kiang
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Goddard Institute for Space Studies, New York, New York
| | - Mary N. Parenteau
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Ames Research Center, Exobiology Branch, Mountain View, California
| | - Chester E. Harman
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Goddard Institute for Space Studies, New York, New York
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York
| | - Shiladitya DasSarma
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland
- Institute of Marine and Environmental Technology, University System of Maryland, Baltimore, Maryland
| | - Theresa M. Fisher
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
| | - Giada N. Arney
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Hilairy E. Hartnett
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
- School of Molecular Sciences, Arizona State University, Tempe, Arizona
| | - Christopher T. Reinhard
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Stephanie L. Olson
- Department of Earth Sciences, University of California, Riverside, California
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
| | - Victoria S. Meadows
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Astronomy Department, University of Washington, Seattle, Washington
| | - Charles S. Cockell
- University of Edinburgh School of Physics and Astronomy, Edinburgh, United Kingdom
- UK Centre for Astrobiology, Edinburgh, United Kingdom
| | - Sara I. Walker
- Blue Marble Space Institute of Science, Seattle, Washington
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
- Beyond Center for Fundamental Concepts in Science, Arizona State University, Tempe, Arizona
- ASU-Santa Fe Institute Center for Biosocial Complex Systems, Arizona State University, Tempe, Arizona
| | - John Lee Grenfell
- Institut für Planetenforschung (PF), Deutsches Zentrum für Luft und Raumfahrt (DLR), Berlin, Germany
| | - Siddharth Hegde
- Carl Sagan Institute, Cornell University, Ithaca, New York
- Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York
| | - Sarah Rugheimer
- Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, United Kingdom
| | - Renyu Hu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
| | - Timothy W. Lyons
- Department of Earth Sciences, University of California, Riverside, California
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
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18
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Brun AS, Browning MK. Magnetism, dynamo action and the solar-stellar connection. LIVING REVIEWS IN SOLAR PHYSICS 2017; 14:4. [PMID: 31997984 PMCID: PMC6956918 DOI: 10.1007/s41116-017-0007-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 07/28/2017] [Indexed: 05/29/2023]
Abstract
The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism-e.g., its dependence on stellar age, mass, or rotation rate-that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief summary of what we have learned, and a sampling of issues that remain uncertain or unsolved.
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Affiliation(s)
- Allan Sacha Brun
- Laboratoire AIM, DRF/IRFU/Département d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette France
| | - Matthew K. Browning
- Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL UK
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The Surface UV Environment on Planets Orbiting M Dwarfs: Implications for Prebiotic Chemistry and the Need for Experimental Follow-up. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/aa773e] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Poch O, Frey J, Roditi I, Pommerol A, Jost B, Thomas N. Remote Sensing of Potential Biosignatures from Rocky, Liquid, or Icy (Exo)Planetary Surfaces. ASTROBIOLOGY 2017; 17:231-252. [PMID: 28282216 DOI: 10.1089/ast.2016.1523] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
To detect signs of life by remote sensing on objects of our Solar System and on exoplanets, the characterization of light scattered by surface life material could complement possible clues given by the atmospheric composition. We reviewed the reflectance spectra of a broad selection of major biomolecules that constitute terrestrial carbon-based life from 0.4 to 2.4 μm, and we discuss their detectability through atmospheric spectral windows. Biomolecule features in the near-infrared (0.8-2.4 μm) will likely be obscured by water spectral features and some atmospheric gases. The visible range (0.4-0.8 μm), including the strong spectral features of pigments, is the most favorable. We investigated the detectability of a pigmented microorganism (Deinococcus radiodurans) when mixed with silica sand, liquid water, and water-ice particles representative of diverse surfaces of potentially habitable worlds. We measured the visible to near-infrared reflectance spectra (0.4-2.4 μm) and the visible phase curves (at 0.45 and 0.75 μm) of the mixtures to assess how the surface medium and the viewing geometry affect the detectability of the microorganisms. The results show that ice appears to be the most favorable medium for the detection of pigments. Water ice is bright and featureless from 0.4 to 0.8 μm, allowing the absorption of any pigment present in the ice to be well noticeable. We found that the visible phase curve of water ice is the most strongly affected by the presence of pigments, with variations of the spectral slope by more than a factor of 3 with phase angles. Finally, we show that the sublimation of the ice results in the concentration of the biological material onto the surface and the consequent increase of its signal. These results have applications to the search for life on icy worlds, such as Europa or Enceladus. Key Words: Remote sensing-Biosignatures-Reflectance spectroscopy-Exoplanets-Spectroscopic biosignatures-Pigments. Astrobiology 17, 231-252.
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Affiliation(s)
- Olivier Poch
- 1 Center for Space and Habitability , Universität Bern, Bern, Switzerland
| | - Joachim Frey
- 2 Institute of Veterinary Bacteriology, University of Bern , Bern, Switzerland
| | - Isabel Roditi
- 3 Institut für Zellbiologie (IZB) , Bern, Switzerland
| | | | - Bernhard Jost
- 4 Physikalisches Institut, Universität Bern , Bern, Switzerland
| | - Nicolas Thomas
- 4 Physikalisches Institut, Universität Bern , Bern, Switzerland
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22
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Nava-Sedeño JM, Ortiz-Cervantes A, Segura A, Domagal-Goldman SD. Carbon Monoxide and the Potential for Prebiotic Chemistry on Habitable Planets around Main Sequence M Stars. ASTROBIOLOGY 2016; 16:744-754. [PMID: 27700137 DOI: 10.1089/ast.2015.1435] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Lifeless planets with CO2 atmospheres produce CO by CO2 photolysis. On planets around M dwarfs, CO is a long-lived atmospheric compound, as long as UV emission due to the star's chromospheric activity lasts, and the sink of CO and O2 in seawater is small compared to its atmospheric production. Atmospheres containing reduced compounds, like CO, may undergo further energetic and chemical processing to give rise to organic compounds of potential importance for the origin of life. We calculated the yield of organic compounds from CO2-rich atmospheres of planets orbiting M dwarf stars, which were previously simulated by Domagal-Goldman et al. (2014) and Harman et al. (2015), by cosmic rays and lightning using results of experiments by Miyakawa et al. (2002) and Schlesinger and Miller ( 1983a , 1983b ). Stellar protons from active stars may be important energy sources for abiotic synthesis and increase production rates of biological compounds by at least 2 orders of magnitude compared to cosmic rays. Simple compounds such as HCN and H2CO are more readily synthesized than more complex ones, such as amino acids and uracil (considered here as an example), resulting in higher yields for the former and lower yields for the latter. Electric discharges are most efficient when a reducing atmosphere is present. Nonetheless, atmospheres with high quantities of CO2 are capable of producing higher amounts of prebiotic compounds, given that CO is constantly produced in the atmosphere. Our results further support planetary systems around M dwarf stars as candidates for supporting life or its origin. Key Words: Prebiotic chemistry-M dwarfs-Habitable planets-Cosmic rays-Lightning-Stellar activity. Astrobiology 16, 744-754.
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Affiliation(s)
- J Manik Nava-Sedeño
- 1 Department for Innovative Methods of Computing, ZIH, Technische Universität Dresden , Dresden, Germany
| | - Adrian Ortiz-Cervantes
- 2 Structural Bioinformatics and Computational Biology, BIOTEC, Technische Universität Dresden , Dresden, Germany
| | - Antígona Segura
- 3 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México , México D.F., México
| | - Shawn D Domagal-Goldman
- 4 Planetary Environments Laboratory, NASA Goddard Space Flight Center , Greenbelt, Maryland, USA
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Cabrol NA. Alien Mindscapes-A Perspective on the Search for Extraterrestrial Intelligence. ASTROBIOLOGY 2016; 16:661-76. [PMID: 27383691 PMCID: PMC5111820 DOI: 10.1089/ast.2016.1536] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Accepted: 05/23/2016] [Indexed: 05/15/2023]
Abstract
UNLABELLED Advances in planetary and space sciences, astrobiology, and life and cognitive sciences, combined with developments in communication theory, bioneural computing, machine learning, and big data analysis, create new opportunities to explore the probabilistic nature of alien life. Brought together in a multidisciplinary approach, they have the potential to support an integrated and expanded Search for Extraterrestrial Intelligence (SETI (1) ), a search that includes looking for life as we do not know it. This approach will augment the odds of detecting a signal by broadening our understanding of the evolutionary and systemic components in the search for extraterrestrial intelligence (ETI), provide more targets for radio and optical SETI, and identify new ways of decoding and coding messages using universal markers. KEY WORDS SETI-Astrobiology-Coevolution of Earth and life-Planetary habitability and biosignatures. Astrobiology 16, 661-676.
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THE MUSCLES TREASURY SURVEY. II. INTRINSIC LYαAND EXTREME ULTRAVIOLET SPECTRA OF K AND M DWARFS WITH EXOPLANETS. ACTA ACUST UNITED AC 2016. [DOI: 10.3847/0004-637x/824/2/101] [Citation(s) in RCA: 152] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Heller R, Pudritz RE. The Search for Extraterrestrial Intelligence in Earth's Solar Transit Zone. ASTROBIOLOGY 2016; 16:259-270. [PMID: 26967201 DOI: 10.1089/ast.2015.1358] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Over the past few years, astronomers have detected thousands of planets and candidate planets by observing their periodic transits in front of their host stars. A related method, called transit spectroscopy, might soon allow studies of the chemical imprints of life in extrasolar planetary atmospheres. Here, we address the reciprocal question, namely, from where is Earth detectable by extrasolar observers using similar methods. We explore Earth's transit zone (ETZ), the projection of a band around Earth's ecliptic onto the celestial plane, where observers can detect Earth transits across the Sun. ETZ is between 0.520° and 0.537° wide due to the noncircular Earth orbit. The restricted Earth transit zone (rETZ), where Earth transits the Sun less than 0.5 solar radii from its center, is about 0.262° wide. We first compile a target list of 45 K and 37 G dwarf stars inside the rETZ and within 1 kpc (about 3260 light-years) using the Hipparcos catalogue. We then greatly enlarge the number of potential targets by constructing an analytic galactic disk model and find that about 10(5) K and G dwarf stars should reside within the rETZ. The ongoing Gaia space mission can potentially discover all G dwarfs among them (several 10(4)) within the next 5 years. Many more potentially habitable planets orbit dim, unknown M stars in ETZ and other stars that traversed ETZ thousands of years ago. If any of these planets host intelligent observers, they could have identified Earth as a habitable, or even as a living, world long ago, and we could be receiving their broadcasts today. The K2 mission, the Allen Telescope Array, the upcoming Square Kilometer Array, or the Green Bank Telescope might detect such deliberate extraterrestrial messages. Ultimately, ETZ would be an ideal region to be monitored by the Breakthrough Listen Initiatives, an upcoming survey that will constitute the most comprehensive search for extraterrestrial intelligence so far.
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Affiliation(s)
- René Heller
- 1 Max Planck Institute for Solar System Research , Göttingen, Germany
| | - Ralph E Pudritz
- 2 Origins Institute , McMaster University , Hamilton, Canada
- 3 Department of Physics and Astronomy, McMaster University , Hamilton, Canada
- 4 Max Planck Institute for Astronomy , Heidelberg, Germany
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Horneck G, Walter N, Westall F, Grenfell JL, Martin WF, Gomez F, Leuko S, Lee N, Onofri S, Tsiganis K, Saladino R, Pilat-Lohinger E, Palomba E, Harrison J, Rull F, Muller C, Strazzulla G, Brucato JR, Rettberg P, Capria MT. AstRoMap European Astrobiology Roadmap. ASTROBIOLOGY 2016; 16:201-43. [PMID: 27003862 PMCID: PMC4834528 DOI: 10.1089/ast.2015.1441] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Accepted: 01/27/2016] [Indexed: 05/07/2023]
Abstract
The European AstRoMap project (supported by the European Commission Seventh Framework Programme) surveyed the state of the art of astrobiology in Europe and beyond and produced the first European roadmap for astrobiology research. In the context of this roadmap, astrobiology is understood as the study of the origin, evolution, and distribution of life in the context of cosmic evolution; this includes habitability in the Solar System and beyond. The AstRoMap Roadmap identifies five research topics, specifies several key scientific objectives for each topic, and suggests ways to achieve all the objectives. The five AstRoMap Research Topics are • Research Topic 1: Origin and Evolution of Planetary Systems • Research Topic 2: Origins of Organic Compounds in Space • Research Topic 3: Rock-Water-Carbon Interactions, Organic Synthesis on Earth, and Steps to Life • Research Topic 4: Life and Habitability • Research Topic 5: Biosignatures as Facilitating Life Detection It is strongly recommended that steps be taken towards the definition and implementation of a European Astrobiology Platform (or Institute) to streamline and optimize the scientific return by using a coordinated infrastructure and funding system.
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Affiliation(s)
- Gerda Horneck
- European Astrobiology Network Association
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Köln, Germany
| | | | - Frances Westall
- Centre National de la Recherche Scientifique–Centre de Biophysique Moléculaire, Orleans, France
| | - John Lee Grenfell
- Institute for Planetary Research, German Aerospace Center (DLR), Berlin, Germany
| | - William F. Martin
- Institute of Molecular Evolution, Heinrich-Heine University of Düsseldorf, Düsseldorf, Germany
| | - Felipe Gomez
- INTA Centre for Astrobiology, Torrejón de Ardoz, Madrid, Spain
| | - Stefan Leuko
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Köln, Germany
| | - Natuschka Lee
- Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden
- Department of Microbiology, Technical University München, München, Germany
| | - Silvano Onofri
- Department of Ecological and Biological Sciences, University of Tuscia, Viterbo, Italy
| | - Kleomenis Tsiganis
- Department of Physics, Section of Astrophysics, Astronomy and Mechanics, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Raffaele Saladino
- Department of Agrobiology and Agrochemistry, University of Tuscia, Viterbo, Italy
| | | | - Ernesto Palomba
- INAF–Institute for Space Astrophysics and Planetology, Rome, Italy
| | - Jesse Harrison
- Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria
| | - Fernando Rull
- Department of Condensed Matter Physics, Crystallography and Mineralogy, Valladolid University, Valladolid, Spain
| | | | | | | | - Petra Rettberg
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Köln, Germany
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Cockell CS, Bush T, Bryce C, Direito S, Fox-Powell M, Harrison JP, Lammer H, Landenmark H, Martin-Torres J, Nicholson N, Noack L, O'Malley-James J, Payler SJ, Rushby A, Samuels T, Schwendner P, Wadsworth J, Zorzano MP. Habitability: A Review. ASTROBIOLOGY 2016; 16:89-117. [PMID: 26741054 DOI: 10.1089/ast.2015.1295] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Habitability is a widely used word in the geoscience, planetary science, and astrobiology literature, but what does it mean? In this review on habitability, we define it as the ability of an environment to support the activity of at least one known organism. We adopt a binary definition of "habitability" and a "habitable environment." An environment either can or cannot sustain a given organism. However, environments such as entire planets might be capable of supporting more or less species diversity or biomass compared with that of Earth. A clarity in understanding habitability can be obtained by defining instantaneous habitability as the conditions at any given time in a given environment required to sustain the activity of at least one known organism, and continuous planetary habitability as the capacity of a planetary body to sustain habitable conditions on some areas of its surface or within its interior over geological timescales. We also distinguish between surface liquid water worlds (such as Earth) that can sustain liquid water on their surfaces and interior liquid water worlds, such as icy moons and terrestrial-type rocky planets with liquid water only in their interiors. This distinction is important since, while the former can potentially sustain habitable conditions for oxygenic photosynthesis that leads to the rise of atmospheric oxygen and potentially complex multicellularity and intelligence over geological timescales, the latter are unlikely to. Habitable environments do not need to contain life. Although the decoupling of habitability and the presence of life may be rare on Earth, it may be important for understanding the habitability of other planetary bodies.
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Affiliation(s)
- C S Cockell
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - T Bush
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - C Bryce
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - S Direito
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - M Fox-Powell
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - J P Harrison
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - H Lammer
- 2 Austrian Academy of Sciences, Space Research Institute , Graz, Austria
| | - H Landenmark
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - J Martin-Torres
- 3 Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology , Kiruna, Sweden; and Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla, Granada, Spain
| | - N Nicholson
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - L Noack
- 4 Department of Reference Systems and Planetology, Royal Observatory of Belgium , Brussels, Belgium
| | - J O'Malley-James
- 5 School of Physics and Astronomy, University of St Andrews , St Andrews, UK; now at the Carl Sagan Institute, Cornell University, Ithaca, NY, USA
| | - S J Payler
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - A Rushby
- 6 Centre for Ocean and Atmospheric Science (COAS), School of Environmental Sciences, University of East Anglia , Norwich, UK
| | - T Samuels
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - P Schwendner
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - J Wadsworth
- 1 UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh , Edinburgh, UK
| | - M P Zorzano
- 3 Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology , Kiruna, Sweden; and Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla, Granada, Spain
- 7 Centro de Astrobiología (CSIC-INTA) , Torrejón de Ardoz, Madrid, Spain
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Rowe JF, Coughlin JL, Antoci V, Barclay T, Batalha NM, Borucki WJ, Burke CJ, Bryson ST, Caldwell DA, Campbell JR, Catanzarite JH, Christiansen JL, Cochran W, Gilliland RL, Girouard FR, Haas MR, Hełminiak KG, Henze CE, Hoffman KL, Howell SB, Huber D, Hunter RC, Jang-Condell H, Jenkins JM, Klaus TC, Latham DW, Li J, Lissauer JJ, McCauliff SD, Morris RL, Mullally F, Ofir A, Quarles B, Quintana E, Sabale A, Seader S, Shporer A, Smith JC, Steffen JH, Still M, Tenenbaum P, Thompson SE, Twicken JD, Laerhoven CV, Wolfgang A, Zamudio KA. PLANETARY CANDIDATES OBSERVED BY
KEPLER
. V. PLANET SAMPLE FROM Q1–Q12 (36 MONTHS). ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0067-0049/217/1/16] [Citation(s) in RCA: 150] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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31
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Davison CL, White RJ, Henry TJ, Riedel AR, Jao WC, Bailey III JI, Quinn SN, Cantrell JR, Subasavage JP, Winters JG. A 3D SEARCH FOR COMPANIONS TO 12 NEARBY M DWARFS. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0004-6256/149/3/106] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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32
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Quintana EV, Barclay T, Raymond SN, Rowe JF, Bolmont E, Caldwell DA, Howell SB, Kane SR, Huber D, Crepp JR, Lissauer JJ, Ciardi DR, Coughlin JL, Everett ME, Henze CE, Horch E, Isaacson H, Ford EB, Adams FC, Still M, Hunter RC, Quarles B, Selsis F. An Earth-sized planet in the habitable zone of a cool star. Science 2014; 344:277-80. [PMID: 24744370 DOI: 10.1126/science.1249403] [Citation(s) in RCA: 227] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
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.
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Affiliation(s)
- Elisa V Quintana
- SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043, USA
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33
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Atri D, Hariharan B, Grießmeier JM. Galactic cosmic ray-induced radiation dose on terrestrial exoplanets. ASTROBIOLOGY 2013; 13:910-919. [PMID: 24143867 DOI: 10.1089/ast.2013.1052] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This past decade has seen tremendous advancements in the study of extrasolar planets. Observations are now made with increasing sophistication from both ground- and space-based instruments, and exoplanets are characterized with increasing precision. There is a class of particularly interesting exoplanets that reside in the habitable zone, which is defined as the area around a star where the planet is capable of supporting liquid water on its surface. Planetary systems around M dwarfs are considered to be prime candidates to search for life beyond the Solar System. Such planets are likely to be tidally locked and have close-in habitable zones. Theoretical calculations also suggest that close-in exoplanets are more likely to have weaker planetary magnetic fields, especially in the case of super-Earths. Such exoplanets are subjected to a high flux of galactic cosmic rays (GCRs) due to their weak magnetic moments. GCRs are energetic particles of astrophysical origin that strike the planetary atmosphere and produce secondary particles, including muons, which are highly penetrating. Some of these particles reach the planetary surface and contribute to the radiation dose. Along with the magnetic field, another factor governing the radiation dose is the depth of the planetary atmosphere. The higher the depth of the planetary atmosphere, the lower the flux of secondary particles will be on the surface. If the secondary particles are energetic enough, and their flux is sufficiently high, the radiation from muons can also impact the subsurface regions, such as in the case of Mars. If the radiation dose is too high, the chances of sustaining a long-term biosphere on the planet are very low. We have examined the dependence of the GCR-induced radiation dose on the strength of the planetary magnetic field and its atmospheric depth, and found that the latter is the decisive factor for the protection of a planetary biosphere.
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Affiliation(s)
- Dimitra Atri
- 1 Blue Marble Space Institute of Science , Seattle, Washington
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34
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Rushby AJ, Claire MW, Osborn H, Watson AJ. Habitable zone lifetimes of exoplanets around main sequence stars. ASTROBIOLOGY 2013; 13:833-849. [PMID: 24047111 DOI: 10.1089/ast.2012.0938] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
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 7.79×10⁹ 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.
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Affiliation(s)
- Andrew J Rushby
- 1 School of Environmental Sciences, University of East Anglia , Norwich, UK
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35
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Shields AL, Meadows VS, Bitz CM, Pierrehumbert RT, Joshi MM, Robinson TD. The effect of host star spectral energy distribution and ice-albedo feedback on the climate of extrasolar planets. ASTROBIOLOGY 2013; 13:715-39. [PMID: 23855332 PMCID: PMC3746291 DOI: 10.1089/ast.2012.0961] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO(2) (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO(2) in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global ice coverage. The surface ice-albedo feedback effect becomes less important at the outer edge of the habitable zone, where atmospheric CO(2) could be expected to be high such that it maintains clement conditions for surface liquid water. We showed that ∼3-10 bar of CO(2) will entirely mask the climatic effect of ice and snow, leaving the outer limits of the habitable zone unaffected by the spectral dependence of water ice and snow albedo. However, less CO(2) is needed to maintain open water for a planet orbiting an M-dwarf star than would be the case for hotter main-sequence stars.
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Affiliation(s)
- Aomawa L Shields
- Department of Astronomy, University of Washington, Seattle, WA 98195-1580, USA.
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36
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Sozzetti A, Bernagozzi A, Bertolini E, Calcidese P, Carbognani A, Cenadelli D, Christille JM, Damasso M, Giacobbe P, Lanteri L, Lattanzi M, Smart R. The APACHE Project. EPJ WEB OF CONFERENCES 2013. [DOI: 10.1051/epjconf/20134703006] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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37
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Barnes R, Mullins K, Goldblatt C, Meadows VS, Kasting JF, Heller R. Tidal Venuses: triggering a climate catastrophe via tidal heating. ASTROBIOLOGY 2013; 13:225-50. [PMID: 23537135 PMCID: PMC3612283 DOI: 10.1089/ast.2012.0851] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 11/28/2012] [Indexed: 05/04/2023]
Abstract
Traditionally, stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here, we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets "Tidal Venuses" and the phenomenon a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e., with negligible tidal heating) in the habitable zone (HZ). However, these planets are not habitable, as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. We simulated the evolution of hypothetical planetary systems in a quasi-continuous parameter distribution and found that we could constrain the history of the system by statistical arguments. Planets orbiting stars with masses<0.3 MSun may be in danger of desiccation via tidal heating. We have applied these concepts to Gl 667C c, a ∼4.5 MEarth planet orbiting a 0.3 MSun star at 0.12 AU. We found that it probably did not lose its water via tidal heating, as orbital stability is unlikely for the high eccentricities required for the tidal greenhouse. As the inner edge of the HZ is defined by the onset of a runaway or moist greenhouse powered by radiation, our results represent a fundamental revision to the HZ for noncircular orbits. In the appendices we review (a) the moist and runaway greenhouses, (b) hydrogen escape, (c) stellar mass-radius and mass-luminosity relations, (d) terrestrial planet mass-radius relations, and (e) linear tidal theories.
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Affiliation(s)
- Rory Barnes
- Astronomy Department, University of Washington, Seattle, Washington 98195, USA.
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38
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Forecasting Life: A Study of Activity Cycles in Low-Mass Stars. ORIGINS LIFE EVOL B 2012; 42:143-52. [DOI: 10.1007/s11084-012-9283-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Accepted: 01/08/2012] [Indexed: 10/27/2022]
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39
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O'Malley-James JT, Raven JA, Cockell CS, Greaves JS. Life and light: exotic photosynthesis in binary and multiple-star systems. ASTROBIOLOGY 2012; 12:115-124. [PMID: 22283409 DOI: 10.1089/ast.2011.0678] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The potential for Earth-like planets within binary/multiple-star systems to host photosynthetic life was evaluated by modeling the levels of photosynthetically active radiation (PAR) such planets receive. Combinations of M and G stars in (i) close-binary systems; (ii) wide-binary systems, and (iii) three-star systems were investigated, and a range of stable radiation environments were found to be possible. These environmental conditions allow for the possibility of familiar, but also more exotic, forms of photosynthetic life, such as IR photosynthesizers and organisms that are specialized for specific spectral niches.
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Affiliation(s)
- J T O'Malley-James
- School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, UK.
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40
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Seager S, Schrenk M, Bains W. An astrophysical view of Earth-based metabolic biosignature gases. ASTROBIOLOGY 2012; 12:61-82. [PMID: 22269061 DOI: 10.1089/ast.2010.0489] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Microbial life on Earth uses a wide range of chemical and energetic resources from diverse habitats. An outcome of this microbial diversity is an extensive and varied list of metabolic byproducts. We review key points of Earth-based microbial metabolism that are useful to the astrophysical search for biosignature gases on exoplanets, including a list of primary and secondary metabolism gas byproducts. Beyond the canonical, unique-to-life biosignature gases on Earth (O(2), O(3), and N(2)O), the list of metabolic byproducts includes gases that might be associated with biosignature gases in appropriate exoplanetary environments. This review aims to serve as a starting point for future astrophysical biosignature gas research.
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Affiliation(s)
- Sara Seager
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA.
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41
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Joshi MM, Haberle RM. Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone. ASTROBIOLOGY 2012; 12:3-8. [PMID: 22181553 DOI: 10.1089/ast.2011.0668] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
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 μm, 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.
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42
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Gowanlock MG, Patton DR, McConnell SM. A model of habitability within the Milky Way galaxy. ASTROBIOLOGY 2011; 11:855-873. [PMID: 22059554 DOI: 10.1089/ast.2010.0555] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
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.
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Affiliation(s)
- M G Gowanlock
- Department of Physics & Astronomy, Trent University, Peterborough, Ontario, Canada.
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Abstract
The Cassini-Huygens mission discovered an active "hydrologic cycle" on Saturn's giant moon Titan, in which methane takes the place of water. Shrouded by a dense nitrogen-methane atmosphere, Titan's surface is blanketed in the equatorial regions by dunes composed of solid organics, sculpted by wind and fluvial erosion, and dotted at the poles with lakes and seas of liquid methane and ethane. The underlying crust is almost certainly water ice, possibly in the form of gas hydrates (clathrate hydrates) dominated by methane as the included species. The processes that work the surface of Titan resemble in their overall balance no other moon in the solar system; instead, they are most like that of the Earth. The presence of methane in place of water, however, means that in any particular planetary system, a body like Titan will always be outside the orbit of an Earth-type planet. Around M-dwarfs, planets with a Titan-like climate will sit at 1 AU--a far more stable environment than the approximately 0.1 AU where Earth-like planets sit. However, an observable Titan-like exoplanet might have to be much larger than Titan itself to be observable, increasing the ratio of heat contributed to the surface atmosphere system from internal (geologic) processes versus photons from the parent star.
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Affiliation(s)
- Jonathan I Lunine
- Dipartimento di Fisica, University of Rome "Tor Vergata", Rome, Italy 00133.
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Segura A, Walkowicz LM, Meadows V, Kasting J, Hawley S. The effect of a strong stellar flare on the atmospheric chemistry of an earth-like planet orbiting an M dwarf. ASTROBIOLOGY 2010; 10:751-71. [PMID: 20879863 PMCID: PMC3103837 DOI: 10.1089/ast.2009.0376] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high-energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect, we estimated a proton flux associated with the flare of 5.9 × 10⁸ protons cm⁻² sr⁻¹ s⁻¹ for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the Carrington event. The simulations were performed with a 1-D photochemical model coupled to a 1-D radiative/convective model. Our results indicate that the UV radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reaches a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 s. Therefore, flares may not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity.
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Affiliation(s)
- Antígona Segura
- Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, México.
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45
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46
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Whitmire DP, Matese JJ. The distribution of stars most likely to harbor intelligent life. ASTROBIOLOGY 2009; 9:617-621. [PMID: 19778273 DOI: 10.1089/ast.2008.0272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Simple heuristic models and recent numerical simulations show that the probability of habitable planet formation increases with stellar mass. We combine those results with the distribution of main-sequence stellar masses to obtain the distribution of stars most likely to possess habitable planets as a function of stellar lifetime. We then impose the self-selection condition that intelligent observers can only find themselves around a star with a lifetime greater than the time required for that observer to have evolved, T(i). This allows us to obtain the stellar timescale number distribution for a given value of T(i). Our results show that for habitable planets with a civilization that evolved at time T(i) = 4.5 Gyr the median stellar lifetime is 13 Gyr, corresponding approximately to a stellar type of G5, with two-thirds of the stars having lifetimes between 7 and 30 Gyr, corresponding approximately to spectral types G0-K5. For other values of T(i) the median stellar lifetime changes by less than 50%.
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Affiliation(s)
- Daniel P Whitmire
- Department of Physics, University of Louisiana at Lafayette , Lafayette, Louisiana, USA.
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47
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Smith DS, Scalo JM. Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass. ASTROBIOLOGY 2009; 9:673-681. [PMID: 19778278 DOI: 10.1089/ast.2009.0337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
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.
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Affiliation(s)
- David S Smith
- Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA.
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Cockell CS, Léger A, Fridlund M, Herbst TM, Kaltenegger L, Absil O, Beichman C, Benz W, Blanc M, Brack A, Chelli A, Colangeli L, Cottin H, Coudé du Foresto F, Danchi WC, Defrère D, den Herder JW, Eiroa C, Greaves J, Henning T, Johnston KJ, Jones H, Labadie L, Lammer H, Launhardt R, Lawson P, Lay OP, LeDuigou JM, Liseau R, Malbet F, Martin SR, Mawet D, Mourard D, Moutou C, Mugnier LM, Ollivier M, Paresce F, Quirrenbach A, Rabbia YD, Raven JA, Rottgering HJA, Rouan D, Santos NC, Selsis F, Serabyn E, Shibai H, Tamura M, Thiébaut E, Westall F, White GJ. Darwin--a mission to detect and search for life on extrasolar planets. ASTROBIOLOGY 2009; 9:1-22. [PMID: 19203238 DOI: 10.1089/ast.2007.0227] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The discovery of extrasolar planets is one of the greatest achievements of modern astronomy. The detection of planets that vary widely in mass demonstrates that extrasolar planets of low mass exist. In this paper, we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines, including astrophysics, planetary sciences, chemistry, and microbiology. Darwin is designed to detect rocky planets similar to Earth and perform spectroscopic analysis at mid-infrared wavelengths (6-20 mum), where an advantageous contrast ratio between star and planet occurs. The baseline mission is projected to last 5 years and consists of approximately 200 individual target stars. Among these, 25-50 planetary systems can be studied spectroscopically, which will include the search for gases such as CO(2), H(2)O, CH(4), and O(3). Many of the key technologies required for the construction of Darwin have already been demonstrated, and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.
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Affiliation(s)
- C S Cockell
- CEPSAR, The Open University, Milton Keynes, UK.
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Abstract
'Replaying the tape' is an intriguing 'would it happen again?' exercise. With respect to broad evolutionary innovations, such as photosynthesis, the answers are central to our search for life elsewhere. Photosynthesis permits a large planetary biomass on Earth. Specifically, oxygenic photosynthesis has allowed an oxygenated atmosphere and the evolution of large metabolically demanding creatures, including ourselves. There are at least six prerequisites for the evolution of biological carbon fixation: a carbon-based life form; the presence of inorganic carbon; the availability of reductants; the presence of light; a light-harvesting mechanism to convert the light energy into chemical energy; and carboxylating enzymes. All were present on the early Earth. To provide the evolutionary pressure, organic carbon must be a scarce resource in contrast to inorganic carbon. The probability of evolving a carboxylase is approached by creating an inventory of carbon-fixation enzymes and comparing them, leading to the conclusion that carbon fixation in general is basic to life and has arisen multiple times. Certainly, the evolutionary pressure to evolve new pathways for carbon fixation would have been present early in evolution. From knowledge about planetary systems and extraterrestrial chemistry, if organic carbon-based life occurs elsewhere, photosynthesis -- although perhaps not oxygenic photosynthesis -- would also have evolved.
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Barnes R, Raymond SN, Jackson B, Greenberg R. Tides and the evolution of planetary habitability. ASTROBIOLOGY 2008; 8:557-568. [PMID: 18598142 DOI: 10.1089/ast.2007.0204] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Tides raised on a planet by the gravity of its host star can reduce the 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 ( less or similar to 0.35 M(circle)). Such migration may have important implications for the evolution of the atmosphere, internal heating, and the Gaia hypothesis. Similarly, a planet that is detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently discovered, approximately 5 M(circle) 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 constraints derived from the additional companions are included, most parameter choices that indicate 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.
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Affiliation(s)
- Rory Barnes
- Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA.
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