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Biosignature Anisotropy Modeled on Temperate Tidally Locked M-Dwarf PlanetsA planet’s atmospheric constituents (e.g., O2, O3, H2Ov, CO2, CH4, and N2O) can provide clues to its surface habitability, and may offer biosignature targets for remote life detection efforts. The plethora of rocky exoplanets found by recent transit surveys (e.g., the Kepler mission) indicates that potentially habitable systems orbiting K- and M-dwarf stars may have very different orbital and atmospheric characteristics than Earth. To assess the physical distribution and observational prospects of various biosignatures and habitability indicators, it is important to understand how they may change under different astrophysical and geophysical configurations, and to simulate these changes with models that include feedbacks between different subsystems of a planet’s climate. Here we use a three-dimensional (3D) Chemistry–Climate model (CCM) to study the effects of changes in stellar spectral energy distribution (SED), stellar activity, and planetary rotation on Earth analogs and tidally locked planets. Our simulations show that, apart from shifts in stellar SEDs and UV radiation, changes in illumination geometry and rotation-induced circulation can influence the global distribution of atmospheric biosignatures. We find that the stratospheric day-to-nightside mixing ratio differences on tidally locked planets remain low (<20%) across the majority of the canonical biosignatures. Interestingly, however, secondary photosynthetic biosignatures (e.g., C2H6S) show much greater (∼67%) day-to-nightside differences, and point to regimes in which tidal locking could have observationally distinguishable effects on phase curve, transit, and secondary eclipse measurements. Overall, this work highlights the potential and promise for 3D CCMs to study the atmospheric properties and habitability of terrestrial worlds.
Document ID
20190001532
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Chen, Howard
(Northwestern University Evanston, IL, United States)
Wolf, Eric T.
(Weber State Univ. Ogden, UT, United States)
Kopparapu, Ravi
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Domagal-Goldman, Shawn
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Horton, Daniel E.
(Northwestern University Evanston, IL, United States)
Date Acquired
March 12, 2019
Publication Date
November 15, 2018
Publication Information
Publication: The Astrophysical Journal Letters
Publisher: The American Astronomical Society
Volume: 868
Issue: 1
ISSN: 2041-8205
e-ISSN: 2041-8213
Subject Category
Space Sciences (General)
Report/Patent Number
GSFC-E-DAA-TN63288
Funding Number(s)
CONTRACT_GRANT: NNX15AN37G
CONTRACT_GRANT: 80NSSC17K0257
Distribution Limits
Public
Copyright
Other

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