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Cohen O, Glocer A, Garraffo C, Drake JJ, Bell JM. Energy Dissipation in the Upper Atmospheres of Trappist-1 Planets. THE ASTROPHYSICAL JOURNAL. LETTERS 2018; 856:L11. [PMID: 32944211 PMCID: PMC7493050 DOI: 10.3847/2041-8213/aab5b5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present a method to quantify the upper-limit of the energy transmitted from the intense stellar wind to the upper atmospheres of three of the Trappist-1 planets (e, f, and g). We use a formalism that treats the system as two electromagnetic regions, where the efficiency of the energy transmission between one region (the stellar wind at the planetary orbits) to the other (the planetary ionospheres) depends on the relation between the conductances and impedances of the two regions. Since the energy flux of the stellar wind is very high at these planetary orbits, we find that for the case of high transmission efficiency (when the conductances and impedances are close in magnitude), the energy dissipation in the upper planetary atmospheres is also very large. On average, the Ohmic energy can reach 0.5 - 1 W/m 2, about 1% of the stellar irradiance and 5-15 times the EUV irradiance. Here, using constant values for the ionospheric conductance, we demonstrate that the stellar wind energy could potentially drive large atmospheric heating in terrestrial planets, as well as in hot jupiters. More detailed calculations are needed to assess the ionospheric conductance and to determine more accurately the amount of heating the stellar wind can drive in close-orbit planets.
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Affiliation(s)
- Ofer Cohen
- Lowell Center for Space Science and Technology, University of Massachusetts Lowell 600 Suffolk St., Lowell, MA 01854, USA
- Harvard-Smithsonian Center for Astrophysics,60 Garden St., Cambridge, MA 02138, USA
| | - Alex Glocer
- NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Cecilia Garraffo
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts, USA
| | - Jeremy J Drake
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts, USA
| | - Jared M Bell
- National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666, USA
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102
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The Influence of a Substellar Continent on the Climate of a Tidally Locked Exoplanet. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aaad0a] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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103
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Meadows VS, Arney GN, Schwieterman EW, Lustig-Yaeger J, Lincowski AP, Robinson T, Domagal-Goldman SD, Deitrick R, Barnes RK, Fleming DP, Luger R, Driscoll PE, Quinn TR, Crisp D. The Habitability of Proxima Centauri b: Environmental States and Observational Discriminants. ASTROBIOLOGY 2018; 18:133-189. [PMID: 29431479 PMCID: PMC5820795 DOI: 10.1089/ast.2016.1589] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 09/04/2017] [Indexed: 05/21/2023]
Abstract
Proxima Centauri b provides an unprecedented opportunity to understand the evolution and nature of terrestrial planets orbiting M dwarfs. Although Proxima Cen b orbits within its star's habitable zone, multiple plausible evolutionary paths could have generated different environments that may or may not be habitable. Here, we use 1-D coupled climate-photochemical models to generate self-consistent atmospheres for several evolutionary scenarios, including high-O2, high-CO2, and more Earth-like atmospheres, with both oxic and anoxic compositions. We show that these modeled environments can be habitable or uninhabitable at Proxima Cen b's position in the habitable zone. We use radiative transfer models to generate synthetic spectra and thermal phase curves for these simulated environments, and use instrument models to explore our ability to discriminate between possible planetary states. These results are applicable not only to Proxima Cen b but to other terrestrial planets orbiting M dwarfs. Thermal phase curves may provide the first constraint on the existence of an atmosphere. We find that James Webb Space Telescope (JWST) observations longward of 10 μm could characterize atmospheric heat transport and molecular composition. Detection of ocean glint is unlikely with JWST but may be within the reach of larger-aperture telescopes. Direct imaging spectra may detect O4 absorption, which is diagnostic of massive water loss and O2 retention, rather than a photosynthetic biosphere. Similarly, strong CO2 and CO bands at wavelengths shortward of 2.5 μm would indicate a CO2-dominated atmosphere. If the planet is habitable and volatile-rich, direct imaging will be the best means of detecting habitability. Earth-like planets with microbial biospheres may be identified by the presence of CH4-which has a longer atmospheric lifetime under Proxima Centauri's incident UV-and either photosynthetically produced O2 or a hydrocarbon haze layer. Key Words: Planetary habitability and biosignatures-Planetary atmospheres-Exoplanets-Spectroscopic biosignatures-Planetary science-Proxima Centauri b. Astrobiology 18, 133-189.
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Affiliation(s)
- Victoria S. Meadows
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Giada N. Arney
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Edward W. Schwieterman
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland
- Department of Earth Sciences, University of California at Riverside, Riverside, California
| | - Jacob Lustig-Yaeger
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Andrew P. Lincowski
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Tyler Robinson
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, California
| | - Shawn D. Domagal-Goldman
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Russell Deitrick
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Rory K. Barnes
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - David P. Fleming
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Rodrigo Luger
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Peter E. Driscoll
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC
| | - Thomas R. Quinn
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - David Crisp
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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104
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Identifying Exoplanets with Deep Learning: A Five-planet Resonant Chain around Kepler-80 and an Eighth Planet around Kepler-90. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aa9e09] [Citation(s) in RCA: 180] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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105
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106
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Demarcating Circulation Regimes of Synchronously Rotating Terrestrial Planets within the Habitable Zone. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aa9f1f] [Citation(s) in RCA: 88] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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107
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Observational Techniques with Transiting Exoplanetary Atmospheres. ASTROPHYSICS AND SPACE SCIENCE LIBRARY 2018. [DOI: 10.1007/978-3-319-89701-1_1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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108
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Krissansen-Totton J, Olson S, Catling DC. Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life. SCIENCE ADVANCES 2018; 4:eaao5747. [PMID: 29387792 PMCID: PMC5787383 DOI: 10.1126/sciadv.aao5747] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 12/19/2017] [Indexed: 05/04/2023]
Abstract
Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. We omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. We find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the Proterozoic and Phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water, which, for an exoplanet twin, may be remotely detectable. On the basis of this disequilibrium, we argue that the simultaneous detection of abundant CH4 and CO2 in a habitable exoplanet's atmosphere is a potential biosignature. Specifically, we show that methane mixing ratios greater than 10-3 are potentially biogenic, whereas those exceeding 10-2 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario.
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Affiliation(s)
- Joshua Krissansen-Totton
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, WA 98195, USA
- Virtual Planetary Laboratory, University of Washington, Seattle, WA 98195, USA
| | - Stephanie Olson
- Department of Earth Sciences and NASA Astrobiology Institute, University of California, Riverside, Riverside, CA 92521, USA
| | - David C. Catling
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, WA 98195, USA
- Virtual Planetary Laboratory, University of Washington, Seattle, WA 98195, USA
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109
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Atmospheric escape from the TRAPPIST-1 planets and implications for habitability. Proc Natl Acad Sci U S A 2017; 115:260-265. [PMID: 29284746 DOI: 10.1073/pnas.1708010115] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question of whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all of the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution.
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110
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Szostak JW. The Origin of Life on Earth and the Design of Alternative Life Forms. MOLECULAR FRONTIERS JOURNAL 2017. [DOI: 10.1142/s2529732517400132] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
To understand the origin of life on Earth, and to evaluate the potential for life on exoplanets, we must understand the pathways that lead from chemistry to biology. Recent experiments suggest that a chemically rich environment that provides the building blocks of membranes, nucleic acids and peptides, along with sources of chemical energy, could result in the emergence of replicating, evolving cells. The broad scope of synthetic chemistry suggests that it may be possible to design and construct artificial life forms based upon a very different biochemistry than that of existing biology.
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111
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112
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113
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Very Low-mass Stars and Brown Dwarfs in Upper Scorpius UsingGaiaDR1: Mass Function, Disks, and Kinematics. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-3881/aa9751] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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114
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Kilpua E, Koskinen HEJ, Pulkkinen TI. Coronal mass ejections and their sheath regions in interplanetary space. LIVING REVIEWS IN SOLAR PHYSICS 2017; 14:5. [PMID: 31997985 PMCID: PMC6956910 DOI: 10.1007/s41116-017-0009-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2017] [Accepted: 10/03/2017] [Indexed: 06/09/2023]
Abstract
Interplanetary coronal mass ejections (ICMEs) are large-scale heliospheric transients that originate from the Sun. When an ICME is sufficiently faster than the preceding solar wind, a shock wave develops ahead of the ICME. The turbulent region between the shock and the ICME is called the sheath region. ICMEs and their sheaths and shocks are all interesting structures from the fundamental plasma physics viewpoint. They are also key drivers of space weather disturbances in the heliosphere and planetary environments. ICME-driven shock waves can accelerate charged particles to high energies. Sheaths and ICMEs drive practically all intense geospace storms at the Earth, and they can also affect dramatically the planetary radiation environments and atmospheres. This review focuses on the current understanding of observational signatures and properties of ICMEs and the associated sheath regions based on five decades of studies. In addition, we discuss modelling of ICMEs and many fundamental outstanding questions on their origin, evolution and effects, largely due to the limitations of single spacecraft observations of these macro-scale structures. We also present current understanding of space weather consequences of these large-scale solar wind structures, including effects at the other Solar System planets and exoplanets. We specially emphasize the different origin, properties and consequences of the sheaths and ICMEs.
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Affiliation(s)
- Emilia Kilpua
- Department of Physics, University of Helsinki, Helsinki, Finland
| | - Hannu E. J. Koskinen
- Department of Physics, University of Helsinki, Helsinki, Finland
- Finnish Meteorological Institute, Espoo, Finland
| | - Tuija I. Pulkkinen
- Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland
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115
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116
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117
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Abstract
Oxygenic photosynthesis is Earth's dominant metabolism, having evolved to harvest the largest expected energy source at the surface of most terrestrial habitable zone planets. Using CO2 and H2O-molecules that are expected to be abundant and widespread on habitable terrestrial planets-oxygenic photosynthesis is plausible as a significant planetary process with a global impact. Photosynthetic O2 has long been considered particularly robust as a sign of life on a habitable exoplanet, due to the lack of known "false positives"-geological or photochemical processes that could also produce large quantities of stable O2. O2 has other advantages as a biosignature, including its high abundance and uniform distribution throughout the atmospheric column and its distinct, strong absorption in the visible and near-infrared. However, recent modeling work has shown that false positives for abundant oxygen or ozone could be produced by abiotic mechanisms, including photochemistry and atmospheric escape. Environmental factors for abiotic O2 have been identified and will improve our ability to choose optimal targets and measurements to guard against false positives. Most of these false-positive mechanisms are dependent on properties of the host star and are often strongest for planets orbiting M dwarfs. In particular, selecting planets found within the conservative habitable zone and those orbiting host stars more massive than 0.4 M⊙ (M3V and earlier) may help avoid planets with abundant abiotic O2 generated by water loss. Searching for O4 or CO in the planetary spectrum, or the lack of H2O or CH4, could help discriminate between abiotic and biological sources of O2 or O3. In advance of the next generation of telescopes, thorough evaluation of potential biosignatures-including likely environmental context and factors that could produce false positives-ultimately works to increase our confidence in life detection. Key Words: Biosignatures-Exoplanets-Oxygen-Photosynthesis-Planetary spectra. Astrobiology 17, 1022-1052.
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Affiliation(s)
- Victoria S Meadows
- 1 Department of Astronomy and Astrobiology Program, University of Washington , Seattle, Washington
- 2 NASA Astrobiology Institute-Virtual Planetary Laboratory , USA
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118
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The Solar Neighborhood. XXXX. Parallax Results from the CTIOPI 0.9 m Program: New Young Stars Near the Sun. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-3881/aa8457] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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119
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A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100-hrSpitzerCampaign. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-3881/aa855b] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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120
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121
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122
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Affiliation(s)
- Petra Schwille
- Abteilung für Zelluläre und Molekulare Biophysik; MPI für Biochemie; Am Klopferspitz 18 82152 Martinsried Deutschland
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123
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Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-3881/aa859c] [Citation(s) in RCA: 94] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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124
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125
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Takizawa K, Minagawa J, Tamura M, Kusakabe N, Narita N. Red-edge position of habitable exoplanets around M-dwarfs. Sci Rep 2017; 7:7561. [PMID: 28790357 PMCID: PMC5548919 DOI: 10.1038/s41598-017-07948-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 07/07/2017] [Indexed: 11/09/2022] Open
Abstract
One of the possible signs of life on distant habitable exoplanets is the red-edge, which is a rise in the reflectivity of planets between visible and near-infrared (NIR) wavelengths. Previous studies suggested the possibility that the red-edge position for habitable exoplanets around M-dwarfs may be shifted to a longer wavelength than that for Earth. We investigated plausible red-edge position in terms of the light environment during the course of the evolution of phototrophs. We show that phototrophs on M-dwarf habitable exoplanets may use visible light when they first evolve in the ocean and when they first colonize the land. The adaptive evolution of oxygenic photosynthesis may eventually also use NIR radiation, by one of two photochemical reaction centers, with the other center continuing to use visible light. These “two-color” reaction centers can absorb more photons, but they will encounter difficulty in adapting to drastically changing light conditions at the boundary between land and water. NIR photosynthesis can be more productive on land, though its evolution would be preceded by the Earth-type vegetation. Thus, the red-edge position caused by photosynthetic organisms on habitable M-dwarf exoplanets could initially be similar to that on Earth and later move to a longer wavelength.
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Affiliation(s)
- Kenji Takizawa
- Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan.,National Institute for Basic Biology, National Institutes of Natural Sciences, 38 Nishigonaka, Myodaiji, Okazaki, Aichi, 444-8585, Japan
| | - Jun Minagawa
- National Institute for Basic Biology, National Institutes of Natural Sciences, 38 Nishigonaka, Myodaiji, Okazaki, Aichi, 444-8585, Japan
| | - Motohide Tamura
- Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan.,Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.,National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan
| | - Nobuhiko Kusakabe
- Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan.,National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan
| | - Norio Narita
- Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan. .,Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. .,National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan.
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126
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Habitable Moist Atmospheres on Terrestrial Planets near the Inner Edge of the Habitable Zone around M Dwarfs. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/aa7cf9] [Citation(s) in RCA: 115] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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127
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Multiple Climate States of Habitable Exoplanets: The Role of Obliquity and Irradiance. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/aa7a03] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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128
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Garcia-Lopez E, Cid C. Glaciers and Ice Sheets As Analog Environments of Potentially Habitable Icy Worlds. Front Microbiol 2017; 8:1407. [PMID: 28804477 PMCID: PMC5532398 DOI: 10.3389/fmicb.2017.01407] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 07/11/2017] [Indexed: 01/09/2023] Open
Abstract
Icy worlds in the solar system and beyond have attracted a remarkable attention as possible habitats for life. The current consideration about whether life exists beyond Earth is based on our knowledge of life in terrestrial cold environments. On Earth, glaciers and ice sheets have been considered uninhabited for a long time as they seemed too hostile to harbor life. However, these environments are unique biomes dominated by microbial communities which maintain active biochemical routes. Thanks to techniques such as microscopy and more recently DNA sequencing methods, a great biodiversity of prokaryote and eukaryote microorganisms have been discovered. These microorganisms are adapted to a harsh environment, in which the most extreme features are the lack of liquid water, extremely cold temperatures, high solar radiation and nutrient shortage. Here we compare the environmental characteristics of icy worlds, and the environmental characteristics of terrestrial glaciers and ice sheets in order to address some interesting questions: (i) which are the characteristics of habitability known for the frozen worlds, and which could be compatible with life, (ii) what are the environmental characteristics of terrestrial glaciers and ice sheets that can be life-limiting, (iii) What are the microbial communities of prokaryotic and eukaryotic microorganisms that can live in them, and (iv) taking into account these observations, could any of these planets or satellites meet the conditions of habitability? In this review, the icy worlds are considered from the point of view of astrobiological exploration. With the aim of determining whether icy worlds could be potentially habitable, they have been compared with the environmental features of glaciers and ice sheets on Earth. We also reviewed some field and laboratory investigations about microorganisms that live in analog environments of icy worlds, where they are not only viable but also metabolically active.
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Affiliation(s)
| | - Cristina Cid
- Microbial Evolution Laboratory, Centro de Astrobiología (Consejo Superior de Investigaciones Cientificas-Instituto Nacional de Técnica Aeroespacial)Madrid, Spain
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129
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The Cosmic Shoreline: The Evidence that Escape Determines which Planets Have Atmospheres, and what this May Mean for Proxima Centauri B. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/aa7846] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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130
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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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131
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Cantine MD, Fournier GP. Environmental Adaptation from the Origin of Life to the Last Universal Common Ancestor. ORIGINS LIFE EVOL B 2017; 48:35-54. [PMID: 28685374 DOI: 10.1007/s11084-017-9542-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 06/15/2017] [Indexed: 01/03/2023]
Abstract
Extensive fundamental molecular and biological evolution took place between the prebiotic origins of life and the state of the Last Universal Common Ancestor (LUCA). Considering the evolutionary innovations between these two endpoints from the perspective of environmental adaptation, we explore the hypothesis that LUCA was temporally, spatially, and environmentally distinct from life's earliest origins in an RNA world. Using this lens, we interpret several molecular biological features as indicating an environmental transition between a cold, radiation-shielded origin of life and a mesophilic, surface-dwelling LUCA. Cellularity provides motility and permits Darwinian evolution by connecting genetic material and its products, and thus establishing heredity and lineage. Considering the importance of compartmentalization and motility, we propose that the early emergence of cellularity is required for environmental dispersal and diversification during these transitions. Early diversification and the emergence of ecology before LUCA could be an important pre-adaptation for life's persistence on a changing planet.
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Affiliation(s)
- Marjorie D Cantine
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Gregory P Fournier
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
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Abstract
Will we be ever able to produce living matter artificially? Despite our increasingly precise understanding of the details of life, its fundamental principles still lie in the dark. Armed with today's technology and knowledge about living systems, it is high time for us to re-address this persistent challenge in understanding nature. Graphics: Monika Krause, MPIB.
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Affiliation(s)
- Petra Schwille
- Department of Cellular and Molecular Biophysics, MPI of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
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133
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Inner Workings: All eyes on Proxima Centauri b. Proc Natl Acad Sci U S A 2017; 114:6646-6648. [PMID: 28655828 DOI: 10.1073/pnas.1706680114] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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134
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Abstract
We present a simple model for estimating the probability of interplanetary panspermia in the recently discovered system of seven planets orbiting the ultracool dwarf star TRAPPIST-1 and find that panspermia is potentially orders of magnitude more likely to occur in the TRAPPIST-1 system compared with the Earth-to-Mars case. As a consequence, we argue that the probability of abiogenesis is enhanced on the TRAPPIST-1 planets compared with the solar system. By adopting models from theoretical ecology, we show that the number of species transferred and the number of life-bearing planets are also likely to be higher because of the increased rates of immigration. We propose observational metrics for evaluating whether life was initiated by panspermia on multiple planets in the TRAPPIST-1 system. These results are also applicable to habitable exoplanets and exomoons in other planetary systems.
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135
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A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host. Nature 2017; 546:514-518. [PMID: 28582774 DOI: 10.1038/nature22392] [Citation(s) in RCA: 171] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Accepted: 04/19/2017] [Indexed: 11/08/2022]
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136
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A Statistical Comparative Planetology Approach to the Hunt for Habitable Exoplanets and Life Beyond the Solar System. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/2041-8213/aa738a] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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137
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Affiliation(s)
- Roy D Sleator
- a Department of Biological Sciences , Cork Institute of Technology , Bishopstown , Cork , Ireland
| | - Niall Smith
- b Blackrock Castle Observatory, Cork Institute of Technology , Cork , Ireland
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138
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139
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A temperate rocky super-Earth transiting a nearby cool star. Nature 2017; 544:333-336. [DOI: 10.1038/nature22055] [Citation(s) in RCA: 241] [Impact Index Per Article: 34.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 03/09/2017] [Indexed: 11/08/2022]
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141
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142
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O’Malley-James JT, Kaltenegger L. UV surface habitability of the TRAPPIST-1 system. ACTA ACUST UNITED AC 2017. [DOI: 10.1093/mnrasl/slx047] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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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: 1] [Impact Index Per Article: 0.1] [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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These seven alien worlds could help explain how planets form. Nature 2017. [DOI: 10.1038/nature.2017.21512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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