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Gebauer S, Grenfell JL, Lammer H, de Vera JPP, Sproß L, Airapetian VS, Sinnhuber M, Rauer H. Atmospheric Nitrogen When Life Evolved on Earth. ASTROBIOLOGY 2020; 20:1413-1426. [PMID: 33121251 DOI: 10.1089/ast.2019.2212] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The amount of nitrogen (N2) present in the atmosphere when life evolved on our planet is central for understanding the production of prebiotic molecules and, hence, is a fundamental quantity to constrain. Estimates of atmospheric molecular nitrogen partial surface pressures during the Archean, however, widely vary in the literature. In this study, we apply a model that combines newly gained insights into atmospheric escape, magma ocean duration, and outgassing evolution. Results suggest <420 mbar surface molecular nitrogen at the time when life originated, which is much lower compared with estimates in previous works and hence could impact our understanding of the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments that simulate prebiotic chemistry on the early Earth. Our results that assume negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gyr ago, which suggest that the atmospheric pressure was probably less than half the present-day value. Our results contradict previous studies that assume N2 partial surface pressures during the Archean were higher than those observed today and suggest that, if the N2 partial pressure were low in the Archean, it would likely be low in the Hadean as well. Furthermore, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N2 per year (Tg N2/year), which is consistent with modern marine biofixation rates and, hence, indicate an oceanic origin of this fixation process.
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Affiliation(s)
- Stefanie Gebauer
- Institute for Planetary Research (PF), German Aerospace Centre (DLR), Berlin, Germany
| | - John Lee Grenfell
- Institute for Planetary Research (PF), German Aerospace Centre (DLR), Berlin, Germany
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
| | | | - Laurenz Sproß
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- Institute for Physics, University of Graz, Graz, Austria
| | - Vladimir S Airapetian
- NASA Goddard Space Flight Center (GSFC), Greenbelt, Maryland, USA
- American University, NW Washington, District of Columbia, USA
| | - Miriam Sinnhuber
- Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Heike Rauer
- Institute for Planetary Research (PF), German Aerospace Centre (DLR), Berlin, Germany
- Institute for Geological Sciences, Planetology and Remote Sensing, Freie Universität Berlin (FUB), Berlin, Germany
- Centre for Astronomy and Astrophysics, Technische Universität Berlin (TUB), Berlin, Germany
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Lammer H, Sproß L, Grenfell JL, Scherf M, Fossati L, Lendl M, Cubillos PE. The Role of N 2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats. ASTROBIOLOGY 2019; 19:927-950. [PMID: 31314591 DOI: 10.1089/ast.2018.1914] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Since the Archean, N2 has been a major atmospheric constituent in Earth's atmosphere. Nitrogen is an essential element in the building blocks of life; therefore, the geobiological nitrogen cycle is a fundamental factor in the long-term evolution of both Earth and Earth-like exoplanets. We discuss the development of Earth's N2 atmosphere since the planet's formation and its relation with the geobiological cycle. Then we suggest atmospheric evolution scenarios and their possible interaction with life-forms: first for a stagnant-lid anoxic world, second for a tectonically active anoxic world, and third for an oxidized tectonically active world. Furthermore, we discuss a possible demise of present Earth's biosphere and its effects on the atmosphere. Since life-forms are the most efficient means for recycling deposited nitrogen back into the atmosphere at present, they sustain its surface partial pressure at high levels. Also, the simultaneous presence of significant N2 and O2 is chemically incompatible in an atmosphere over geological timescales. Thus, we argue that an N2-dominated atmosphere in combination with O2 on Earth-like planets within circumstellar habitable zones can be considered as a geo-biosignature. Terrestrial planets with such atmospheres will have an operating tectonic regime connected with an aerobic biosphere, whereas other scenarios in most cases end up with a CO2-dominated atmosphere. We conclude with implications for the search for life on Earth-like exoplanets inside the habitable zones of M to K stars.
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Affiliation(s)
- Helmut Lammer
- 1Austrian Academy of Sciences, Space Research Institute, Graz, Austria
| | - Laurenz Sproß
- 1Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- 2Institute of Physics, University of Graz, Graz, Austria
| | - John Lee Grenfell
- 3Department of Extrasolar Planets and Atmospheres, German Aerospace Center, Institute of Planetary Research, Berlin, Germany
| | - Manuel Scherf
- 1Austrian Academy of Sciences, Space Research Institute, Graz, Austria
| | - Luca Fossati
- 1Austrian Academy of Sciences, Space Research Institute, Graz, Austria
| | - Monika Lendl
- 1Austrian Academy of Sciences, Space Research Institute, Graz, Austria
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3
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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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4
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Lehmer OR, Catling DC. Hydrodynamic Escape of Hot Protoatmospheres During a Star's X-ray and Extreme Ultraviolet Saturation May Limit Rocky Exoplanets to ~1.8 Earth Radii. THE ASTROPHYSICAL JOURNAL 2017; 845:130. [PMID: 33041344 PMCID: PMC7545495 DOI: 10.3847/1538-4357/aa8137] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Recent observations and analysis of low mass (<10 M ⊕ ), exoplanets have found that rocky planets only have radii up to 1.5-2 R ⊕ . Two general hypotheses exist for the cause of the dichotomy between rocky and gas-enveloped planets (or possible water worlds): either low mass planets do not necessarily form thick atmospheres of a few wt. %, or the thick atmospheres on these planets easily escape driven by x-ray and extreme ultraviolet (XUV) emissions from young parent stars. Here we show that a cutoff between rocky and gas-enveloped planets due to hydrodynamic escape is most likely to occur at a mean radius of 1.76±0.38 (2σ) R ⊕ around Sun-like stars. We examine the limit in rocky planet radii predicted by hydrodynamic escape across a wide range of possible model inputs using 10,000 parameter combinations drawn randomly from plausible parameter ranges. We find a cutoff between rocky and gas-enveloped planets that agrees with the observed cutoff. The large cross-section available for XUV absorption in the extremely distended primitive atmospheres of low mass planets results in complete loss of atmospheres during the ~100 Myr phase of stellar XUV saturation. In contrast, more massive planets have less distended atmospheres and less escape, and so retain thick atmospheres through XUV saturation and then indefinitely as the XUV and escape fluxes drop over time. The agreement between our model and exoplanet data leads us to conclude that hydrodynamic escape plausibly explains the observed upper limit on rocky planet size and few planets (a "valley") in the 1.5-2 R ⊕ range.
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Affiliation(s)
- Owen R Lehmer
- Dept. Earth and Space Sciences, Box 351310, University of Washington, Seattle, WA
- MS 239-4, Space Science Division, NASA Ames Research Center, Moffett Field, CA
| | - David C Catling
- Dept. Earth and Space Sciences, Box 351310, University of Washington, Seattle, WA
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Pascal R. Physicochemical Requirements Inferred for Chemical Self-Organization Hardly Support an Emergence of Life in the Deep Oceans of Icy Moons. ASTROBIOLOGY 2016; 16:328-334. [PMID: 27116590 DOI: 10.1089/ast.2015.1412] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
UNLABELLED An approach to the origin of life, focused on the property of entities capable of reproducing themselves far from equilibrium, has been developed recently. Independently, the possibility of the emergence of life in the hydrothermal systems possibly present in the deep oceans below the frozen crust of some of the moons of Jupiter and Saturn has been raised. The present report is aimed at investigating the mutual compatibility of these alternative views. In this approach, the habitability concept deduced from the limits of life on Earth is considered to be inappropriate with regard to emerging life due to the requirement for an energy source of sufficient potential (equivalent to the potential of visible light). For these icy moons, no driving force would have been present to assist the process of emergence, which would then have had to rely exclusively on highly improbable events, thereby making the presence of life unlikely on these Solar System bodies, that is, unless additional processes are introduced for feeding chemical systems undergoing a transition toward life and the early living organisms. KEY WORDS Icy moon-Bioenergetics-Chemical evolution-Habitability-Origin of life. Astrobiology 16, 328-334.
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Affiliation(s)
- Robert Pascal
- Institut des Biomolécules Max Mousseron (IBMM, UMR 5247, CNRS/Université de Montpellier/ENSCM), Montpellier, France
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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: 94] [Impact Index Per Article: 11.8] [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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Schwarz R, Funk B, Bazsó Á. On the Possibility of Habitable Trojan Planets in Binary Star Systems. ORIGINS LIFE EVOL B 2015; 45:469-77. [PMID: 26113154 DOI: 10.1007/s11084-015-9449-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 02/24/2015] [Indexed: 10/23/2022]
Abstract
Approximately 60% of all stars in the solar neighbourhood (up to 80% in our Milky Way) are members of binary or multiple star systems. This fact led to the speculations that many more planets may exist in binary systems than are currently known. To estimate the habitability of exoplanetary systems, we have to define the so-called habitable zone (HZ). The HZ is defined as a region around a star where a planet would receive enough radiation to maintain liquid water on its surface and to be able to build a stable atmosphere. We search for new dynamical configurations-where planets may stay in stable orbits-to increase the probability to find a planet like the Earth.
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Affiliation(s)
- Richard Schwarz
- Institute for Astronomy, University of Vienna, Vienna, Austria,
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8
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Luger R, Barnes R. Extreme water loss and abiotic O2 buildup on planets throughout the habitable zones of M dwarfs. ASTROBIOLOGY 2015; 15:119-43. [PMID: 25629240 PMCID: PMC4323125 DOI: 10.1089/ast.2014.1231] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
We show that terrestrial planets in the habitable zones of M dwarfs older than ∼1 Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ∼5 bar/Myr on Earth-mass planets and up to ∼25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars.
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Affiliation(s)
- R Luger
- 1 Astronomy Department, University of Washington , Seattle, Washington
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9
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Luger R, Barnes R, Lopez E, Fortney J, Jackson B, Meadows V. Habitable evaporated cores: transforming mini-Neptunes into super-Earths in the habitable zones of M dwarfs. ASTROBIOLOGY 2015; 15:57-88. [PMID: 25590532 DOI: 10.1089/ast.2014.1215] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ∼1 M⊕ solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars.
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Affiliation(s)
- R Luger
- 1 Astronomy Department, University of Washington , Seattle, Washington
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10
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Lammer H, Schiefer SC, Juvan I, Odert P, Erkaev NV, Weber C, Kislyakova KG, Güdel M, Kirchengast G, Hanslmeier A. Origin and stability of exomoon atmospheres: implications for habitability. ORIGINS LIFE EVOL B 2014; 44:239-60. [PMID: 25515344 PMCID: PMC4669541 DOI: 10.1007/s11084-014-9377-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Accepted: 11/18/2014] [Indexed: 11/30/2022]
Abstract
We study the origin and escape of catastrophically outgassed volatiles (H2O, CO2) from exomoons with Earth-like densities and masses of 0.1, 0.5 and 1 M⊕ orbiting an extra-solar gas giant inside the habitable zone of a young active solar-like star. We apply a radiation absorption and hydrodynamic upper atmosphere model to the three studied exomoon cases. We model the escape of hydrogen and dragged dissociation products O and C during the activity saturation phase of the young host star. Because the soft X-ray and EUV radiation of the young host star may be up to ~100 times higher compared to today’s solar value during the first 100 Myr after the system’s origin, an exomoon with a mass < 0.25 M⊕ located in the HZ may not be able to keep an atmosphere because of its low gravity. Depending on the spectral type and XUV activity evolution of the host star, exomoons with masses between ~0.25 and 0.5 M⊕ may evolve to Mars-like habitats. More massive bodies with masses >0.5 M⊕, however, may evolve to habitats that are a mixture of Mars-like and Earth-analogue habitats, so that life may originate and evolve at the exomoon’s surface.
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Affiliation(s)
- Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria,
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11
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Erkaev N, Lammer H, Elkins-Tanton L, Stökl A, Odert P, Marcq E, Dorfi E, Kislyakova K, Kulikov Y, Leitzinger M, Güdel M. Escape of the martian protoatmosphere and initial water inventory. PLANETARY AND SPACE SCIENCE 2014; 98:106-119. [PMID: 25843981 PMCID: PMC4375622 DOI: 10.1016/j.pss.2013.09.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 07/20/2013] [Accepted: 09/06/2013] [Indexed: 05/15/2023]
Abstract
Latest research in planet formation indicates that Mars formed within a few million years (Myr) and remained as a planetary embryo that never grew to a more massive planet. It can also be expected from dynamical models that most of Mars' building blocks consisted of material that formed in orbital locations just beyond the ice line which could have contained [Formula: see text] of H2O. By using these constraints, we estimate the nebula-captured and catastrophically outgassed volatile contents during the solidification of Mars' magma ocean and apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere during the early active epoch of the young Sun. The amount of gas that has been captured from the protoplanetary disk into the planetary atmosphere is calculated by solving the hydrostatic structure equations in the protoplanetary nebula. Depending on nebular properties such as the dust grain depletion factor, planetesimal accretion rates and luminosities, hydrogen envelopes with masses [Formula: see text] to [Formula: see text] could have been captured from the nebula around early Mars. Depending on the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was [Formula: see text] times stronger compared to the present value, our results indicate that early Mars would have lost its nebular captured hydrogen envelope after the nebula gas evaporated, during a fast period of [Formula: see text]. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of [Formula: see text] H2O and [Formula: see text] CO2 could have been lost during [Formula: see text], if the impact related energy flux of large planetesimals and small embryos to the planet's surface lasted long enough, that the steam atmosphere could have been prevented from condensing. If this was not the case, then our results suggest that the timescales for H2O condensation and ocean formation may have been shorter compared to the atmosphere evaporation timescale, so that one can speculate that sporadically periods, where some amount of liquid water may have been present on the planet's surface. However, depending on the amount of the outgassed volatiles, because of impacts and the high XUV-driven atmospheric escape rates, such sporadically wet surface conditions may have also not lasted much longer than [Formula: see text]. After the loss of the captured hydrogen envelope and outgassed volatiles during the first 100 Myr period of the young Sun, a warmer and probably wetter period may have evolved by a combination of volcanic outgassing and impact delivered volatiles [Formula: see text] ago, when the solar XUV flux decreased to values that have been [Formula: see text] times that of today's Sun.
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Affiliation(s)
- N.V. Erkaev
- Institute for Computational Modelling, 660041 Krasnoyarsk 36, Russian Academy of Sciences, Russian Federation
- Siberian Federal University, 660041 Krasnoyarsk, Russian Federation
| | - H. Lammer
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
- Corresponding author. Tel.: +43 31 6412 0641; fax: +43 31 6412 0690.
| | - L.T. Elkins-Tanton
- Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington DC 20015, USA
| | - A. Stökl
- Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
| | - P. Odert
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
- Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria
| | - E. Marcq
- LATMOS, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, France
| | - E.A. Dorfi
- Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
| | - K.G. Kislyakova
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
| | - Yu.N. Kulikov
- Polar Geophysical Institute, Russian Academy of Sciences, Khalturina 15, 183010 Murmansk, Russian Federation
| | - M. Leitzinger
- Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria
| | - M. Güdel
- Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
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12
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Forget F, Leconte J. Possible climates on terrestrial exoplanets. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130084. [PMID: 24664919 DOI: 10.1098/rsta.2013.0084] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance, to optimize future telescopic observations or to assess the probability of habitable worlds. To begin with, climate primarily depends on (i) the atmospheric composition and the volatile inventory; (ii) the incident stellar flux; and (iii) the tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes, which are difficult to model: origins of volatiles, atmospheric escape, geochemistry, photochemistry, etc. We discuss physical constraints, which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using global climate models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components, such as a 'dynamical core', a radiative transfer solver, a parametrization of subgrid-scale turbulence and convection, a thermal ground model and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive feedbacks. They can drive planets with very similar forcing and volatile inventory to completely different states. For instance, the coupling among temperature, volatile phase changes and radiative properties results in instabilities, such as runaway glaciations and runaway greenhouse effect.
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Affiliation(s)
- F Forget
- Laboratoire de Météorologie Dynamique, IPSL, Paris, France
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13
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Erkaev NV, Lammer H, Odert P, Kulikov YN, Kislyakova KG, Khodachenko ML, Güdel M, Hanslmeier A, Biernat H. XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: atmospheric expansion and thermal escape. ASTROBIOLOGY 2013; 13:1011-29. [PMID: 24251443 PMCID: PMC3865622 DOI: 10.1089/ast.2012.0957] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 09/07/2013] [Indexed: 05/15/2023]
Abstract
The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H₂O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R(Earth) and a mass of 10 M(Earth). We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general.
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Affiliation(s)
- Nikolai V. Erkaev
- Institute of Computational Modelling, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
- Siberian Federal University, Krasnoyarsk, Russian Federation
| | - Helmut Lammer
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
| | - Petra Odert
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Yuri N. Kulikov
- Polar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russian Federation
| | - Kristina G. Kislyakova
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Maxim L. Khodachenko
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Nuclear Physics, Moscow State University, Moscow, Russian Federation
| | - Manuel Güdel
- Institute of Astrophysics, University of Vienna, Austria
| | | | - Helfried Biernat
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
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14
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Kislyakova KG, Lammer H, Holmström M, Panchenko M, Odert P, Erkaev NV, Leitzinger M, Khodachenko ML, Kulikov YN, Güdel M, Hanslmeier A. XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part II: hydrogen coronae and ion escape. ASTROBIOLOGY 2013; 13:1030-48. [PMID: 24283926 PMCID: PMC3865724 DOI: 10.1089/ast.2012.0958] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a "super-Earth" with a radius of 2 R(Earth) and a mass of 10 M(Earth), located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×10²⁵ s⁻¹ to ∼5.3×10³⁰ s⁻¹, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EO(H)) to <3 EO(H) and usually is several times smaller in comparison to the thermal atmospheric escape rates.
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Affiliation(s)
- Kristina G. Kislyakova
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
| | | | | | - Petra Odert
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Nikolai V. Erkaev
- Institute of Computational Modelling, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
| | | | - Maxim L. Khodachenko
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- SINP, Moscow State University, Moscow, Russian Federation
| | - Yuri N. Kulikov
- Polar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russian Federation
| | - Manuel Güdel
- Institute of Astrophysics, University of Vienna, Austria
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15
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Lammer H, Blanc M, Benz W, Fridlund M, Foresto VCD, Güdel M, Rauer H, Udry S, Bonnet RM, Falanga M, Charbonneau D, Helled R, Kley W, Linsky J, Elkins-Tanton LT, Alibert Y, Chassefière E, Encrenaz T, Hatzes AP, Lin D, Liseau R, Lorenzen W, Raymond SN. The science of exoplanets and their systems. ASTROBIOLOGY 2013; 13:793-813. [PMID: 24015759 DOI: 10.1089/ast.2013.0997] [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
A scientific forum on "The Future Science of Exoplanets and Their Systems," sponsored by Europlanet and the International Space Science Institute (ISSI) and co-organized by the Center for Space and Habitability (CSH) of the University of Bern, was held during December 5 and 6, 2012, in Bern, Switzerland. It gathered 24 well-known specialists in exoplanetary, Solar System, and stellar science to discuss the future of the fast-expanding field of exoplanetary research, which now has nearly 1000 objects to analyze and compare and will develop even more quickly over the coming years. The forum discussions included a review of current observational knowledge, efforts for exoplanetary atmosphere characterization and their formation, water formation, atmospheric evolution, habitability aspects, and our understanding of how exoplanets interact with their stellar and galactic environment throughout their history. Several important and timely research areas of focus for further research efforts in the field were identified by the forum participants. These scientific topics are related to the origin and formation of water and its delivery to planetary bodies and the role of the disk in relation to planet formation, including constraints from observations as well as star-planet interaction processes and their consequences for atmosphere-magnetosphere environments, evolution, and habitability. The relevance of these research areas is outlined in this report, and possible themes for future ISSI workshops are identified that may be proposed by the international research community over the coming 2-3 years.
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Affiliation(s)
- Helmut Lammer
- 1 Space Research Institute , Austrian Academy of Sciences, Graz, Austria
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16
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Abstract
Life is evolutionarily the most complex of the emergent symmetry-breaking, macroscopically organized dynamic structures in the Universe. Members of this cascading series of disequilibria-converting systems, or engines in Cottrell's terminology, become ever more complicated-more chemical and less physical-as each engine extracts, exploits and generates ever lower grades of energy and resources in the service of entropy generation. Each one of these engines emerges spontaneously from order created by a particular mother engine or engines, as the disequilibrated potential daughter is driven beyond a critical point. Exothermic serpentinization of ocean crust is life's mother engine. It drives alkaline hydrothermal convection and thereby the spontaneous production of precipitated submarine hydrothermal mounds. Here, the two chemical disequilibria directly causative in the emergence of life spontaneously arose across the mineral precipitate membranes separating the acidulous, nitrate-bearing CO2-rich, Hadean sea from the alkaline and CH4/H2-rich serpentinization-generated effluents. Essential redox gradients-involving hydrothermal CH4 and H2 as electron donors, CO2 and nitrate, nitrite, and ferric iron from the ambient ocean as acceptors-were imposed which functioned as the original 'carbon-fixing engine'. At the same time, a post-critical-point (milli)voltage pH potential (proton concentration gradient) drove the condensation of orthophosphate to produce a high energy currency: 'the pyrophosphatase engine'.
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Affiliation(s)
- Michael J Russell
- Planetary Science Section 3225, MS:183-301, Jet Propulsion Laboratory, California Institute of Technology, , 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA.
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