A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone. (arXiv:2301.13836v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hall_C/0/1/0/all/0/1">C. Hall</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stancil_P/0/1/0/all/0/1">P. C. Stancil</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Terry_J/0/1/0/all/0/1">J. P. Terry</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ellison_C/0/1/0/all/0/1">C. K. Ellison</a>
It may be possible to detect biosignatures of photosynthesis in an
exoplanet’s atmosphere. However, such a detection would likely require a
dedicated study, occupying a large amount of telescope time. It is therefore
prudent, while searching for signs of life that we may recognise, to pick the
best target possible. In this work, we present a new region, the
“photosynthetic habitable zone” – the distance from a star where both liquid
water and oxygenic photosynthesis can occur. It is therefore the region where
detectable biosignatures of oxygenic photosynthesis are most likely to occur.
Our analysis indicates that in the most ideal conditions for life and no
atmospheric and greenhouse effects, the photosynthetic habitable zone is almost
as broad as the habitable zone. On the other hand, if conditions for life are
anything less than excellent and atmospheric attenuation and greenhouse effects
are even moderate, the photosynthetic habitable zone is concentrated at larger
separations around more massive stars. Such cases are also not tidally locked
to their host star, which could result in planetary rotation periods similar to
the Earth’s. We identify five planets, Kepler-452 b, Kepler-1638 b, Kepler-1544
b and Kepler-62 e and Kepler-62 f, that are consistently in the photosynthetic
habitable zone for a variety of conditions, and we predict their day lengths to
be between 9 and 11 hours. We conclude that the parameter space in which we
should search for signs of life is much narrower than the standard habitable
zone.
It may be possible to detect biosignatures of photosynthesis in an
exoplanet’s atmosphere. However, such a detection would likely require a
dedicated study, occupying a large amount of telescope time. It is therefore
prudent, while searching for signs of life that we may recognise, to pick the
best target possible. In this work, we present a new region, the
“photosynthetic habitable zone” – the distance from a star where both liquid
water and oxygenic photosynthesis can occur. It is therefore the region where
detectable biosignatures of oxygenic photosynthesis are most likely to occur.
Our analysis indicates that in the most ideal conditions for life and no
atmospheric and greenhouse effects, the photosynthetic habitable zone is almost
as broad as the habitable zone. On the other hand, if conditions for life are
anything less than excellent and atmospheric attenuation and greenhouse effects
are even moderate, the photosynthetic habitable zone is concentrated at larger
separations around more massive stars. Such cases are also not tidally locked
to their host star, which could result in planetary rotation periods similar to
the Earth’s. We identify five planets, Kepler-452 b, Kepler-1638 b, Kepler-1544
b and Kepler-62 e and Kepler-62 f, that are consistently in the photosynthetic
habitable zone for a variety of conditions, and we predict their day lengths to
be between 9 and 11 hours. We conclude that the parameter space in which we
should search for signs of life is much narrower than the standard habitable
zone.
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