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Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres

1
Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2
Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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School of Physics & Astronomy, Cardiff University, 4 The Parade, Cardiff CF24 3AA, UK
5
Department of Astronomy, University of Maryland at College Park, College Park, MD 20742, USA
*
Author to whom correspondence should be addressed.
Juan Carlos Torres Fellow.
Academic Editor: Apurva V. Oza
Universe 2021, 7(6), 172; https://doi.org/10.3390/universe7060172
Received: 19 February 2021 / Revised: 19 May 2021 / Accepted: 24 May 2021 / Published: 31 May 2021
(This article belongs to the Section Planetary Sciences)
The search for signs of life through the detection of exoplanet atmosphere biosignature gases is gaining momentum. Yet, only a handful of rocky exoplanet atmospheres are suitable for observation with planned next-generation telescopes. To broaden prospects, we describe the possibilities for an aerial, liquid water cloud-based biosphere in the atmospheres of sub Neptune-sized temperate exoplanets, those receiving Earth-like irradiation from their host stars. One such planet is known (K2-18b) and other candidates are being followed up. Sub Neptunes are common and easier to study observationally than rocky exoplanets because of their larger sizes, lower densities, and extended atmospheres or envelopes. Yet, sub Neptunes lack any solid surface as we know it, so it is worthwhile considering whether their atmospheres can support an aerial biosphere. We review, synthesize, and build upon existing research. Passive microbial-like life particles must persist aloft in a region with liquid water clouds for long enough to metabolize, reproduce, and spread before downward transport to lower altitudes that may be too hot for life of any kind to survive. Dynamical studies are needed to flesh out quantitative details of life particle residence times. A sub Neptune would need to be a part of a planetary system with an unstable asteroid belt in order for meteoritic material to provide nutrients, though life would also need to efficiently reuse and recycle metals. The origin of life may be the most severe limiting challenge. Regardless of the uncertainties, we can keep an open mind to the search for biosignature gases as a part of general observational studies of sub Neptune exoplanets. View Full-Text
Keywords: exoplanets; exoplanet atmospheres; biosignature gases exoplanets; exoplanet atmospheres; biosignature gases
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MDPI and ACS Style

Seager, S.; Petkowski, J.J.; Günther, M.N.; Bains, W.; Mikal-Evans, T.; Deming, D. Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres. Universe 2021, 7, 172. https://doi.org/10.3390/universe7060172

AMA Style

Seager S, Petkowski JJ, Günther MN, Bains W, Mikal-Evans T, Deming D. Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres. Universe. 2021; 7(6):172. https://doi.org/10.3390/universe7060172

Chicago/Turabian Style

Seager, Sara, Janusz J. Petkowski, Maximilian N. Günther, William Bains, Thomas Mikal-Evans, and Drake Deming. 2021. "Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres" Universe 7, no. 6: 172. https://doi.org/10.3390/universe7060172

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