Exoplanet Biosignatures: Future Directions

Walker, Sara Imari; Bains, William; Cronin, Leroy; DasSarma, Shiladitya; Danielache, Sebastian O.; Domagal-Goldman, Shawn; Kaçar, Betül; Kiang, Nancy Y.; Lenardic, Adrian; Reinhard, Christopher T.; Moore, W. B.; Schwieterman, Edward W.; Shkolnik, Evgenya L.; Smith, Harrison B.

doi:10.1089/ast.2017.1738

Cited by 96 publications

(111 citation statements)

References 253 publications

(413 reference statements)

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“…Experiments like the James Webb Space Telescope [17] are expected to directly characterize the atmospheres of several Earth-sized planets [18], the disequilibrium of which will make it possible to infer the presence or absence of biospheres [19]. In addition, further afield, when the next generation of telescopes such as TMT, PLATO, HabEx, and LUVOIR will be able to deliver a large enough population to do meaningful statistics on atmospheric properties [20], we will be able to characterize the ubiquity of microbial life, as well as which environmental factors its presence correlates with [21].…”

Section: Introductionmentioning

confidence: 99%

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Sandora

2019

Universe

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In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario.

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Section: Introductionmentioning

confidence: 99%

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Sandora

2019

Universe

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“…Berdyugina et al, 2016). An excellent summary of recent advances in exoplanetary biosignature science can be found in a series of review papers from the NASA Nexus for Exoplanet System Science (NExSS) and Astrobiology Program, namely: Schwieterman et al (2018) who provide an all-round review of the topic; Meadows et al (2018) who focus on oxygen; Catling et al (2018) who discuss a Bayesian approach; Walker et al (2018) who propose future methods for biosignature assessment and Fujii et al (2018) who summarize future relevant missions. A review of atmospheric biosignatures with a focus on photochemical responses in an exoplanetary context is provided by Grenfell (2017).…”

Section: Earth-like Exoplanetsmentioning

confidence: 99%

Geoscience for Understanding Habitability in the Solar System and Beyond

et al. 2019

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This paper reviews habitability conditions for a terrestrial planet from the point of view of geosciences. It addresses how interactions between the interior of a planet or a moon and its atmosphere and surface (including hydrosphere and biosphere) can affect habitability of the celestial body. It does not consider in detail the role of the central star but focusses more on surface conditions capable of sustaining life. We deal with fundamental issues of planetary habitability, i.e. the environmental conditions capable of sustaining life, and the above-mentioned interactions can affect the habitability of the celestial body.We address some hotly debated questions including:-How do core and mantle affect the evolution and habitability of planets? -What are the consequences of mantle overturn on the evolution of the interior and atmosphere? -What is the role of the global carbon and water cycles? -What influence do comet and asteroid impacts exert on the evolution of the planet? -How does life interact with the evolution of the Earth's geosphere and atmosphere?-How can knowledge of the solar system geophysics and habitability be applied to exoplanets?In addition, we address the identification of preserved life tracers in the context of the interaction of life with planetary evolution.

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“…This brings in layers of potentiality associated with evolution and historical contingency (to be clear, a contingent process is not the same as a random process [e.g., Bohm, 1957]). The approach to planetary life research would, as a result, need to move toward one that is more statistical/probabilistic than it is at present [Walker et al, 2018].…”

Section: Different Is Morementioning

confidence: 99%

Different Is More: The Value of Finding an Inhabited Planet That Is Far from Earth2.0

Lenardic

Seales

2019

Astrobiology

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The search for an inhabited planet, other than our own, is a driver of planetary exploration in our solar system and beyond. Using information from our own planet to inform search strategies allows for a targeted search. It is, however, worth considering some span in the strategy and in a priori expectation. An inhabited, Earth-like planet is one that would be similar to Earth in ways that extend beyond having biota. To facilitate analysis, we employ a metric akin to the Earth-similarity index of Schulze-Makuch et al. [2011]. The metric extends from zero, for an inhabited planet that is like Earth in all other regards (i.e., zero differences), toward end-member values for planets that differ from Earth but maintain life potential. The analysis shows how finding inhabited planets that do not share all other Earth characteristics could improve our ability to assess galactic life potential without a large increase in time-commitment costs. Search strategies that acknowledge the possibility of such planets can also minimize the potential of exploration losses (e.g., searching for long durations to reach conclusions that are search strategy biased). Discovering such planets could additionally provide a test of the Gaia hypothesis -a test that has proved difficult using only the Earth as a laboratory. Lastly, we discuss how an Earth2.0 narrative that has been presented to the public as a search strategy comes with nostalgia-laden philosophical baggage that does not best serve exploration.

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Exoplanet Biosignatures: Future Directions

Cited by 96 publications

References 253 publications

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Geoscience for Understanding Habitability in the Solar System and Beyond

Different Is More: The Value of Finding an Inhabited Planet That Is Far from Earth2.0

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