Distinguishing multicellular life on exoplanets by testing Earth as an exoplanet

Item Type Journal paper
Abstract

Can multicellular life be distinguished from single cellular life on an exoplanet? We hypothesize that abundant upright photosynthetic multicellular life (trees) will cast shadows at high sun angles that will distinguish them from single cellular life and test this using Earth as an exoplanet. We first test the concept using unmanned aerial vehicles at a replica moon-landing site near Flagstaff, Arizona and show trees have both a distinctive reflectance signature (red edge) and geometric signature (shadows at high sun angles) that can distinguish them from replica moon craters. Next, we calculate reflectance signatures for Earth at several phase angles with POLDER (Polarization and Directionality of Earth's reflectance) satellite directional reflectance measurements and then reduce Earth to a single pixel. We compare Earth to other planetary bodies (Mars, the Moon, Venus and Uranus) and hypothesize that Earth's directional reflectance will be between strongly backscattering rocky bodies with no weathering (like Mars and the Moon) and cloudy bodies with more isotropic scattering (like Venus and Uranus). Our modelling results put Earth in line with strongly backscattering Mars, while our empirical results put Earth in line with more isotropic scattering Venus. We identify potential weaknesses in both the modelled and empirical results and suggest additional steps to determine whether this technique could distinguish upright multicellular life on exoplanets.

Authors Doughty, Christopher E.; Abraham, Andrew J.; Windsor, James; Mommert, Michael; Gowanlock, Michael; Robinson, Tyler & Trilling, David E.
Journal or Publication Title International Journal of Astrobiology
Language English
Subjects other research area
HSG Classification contribution to scientific community
HSG Profile Area None
Refereed Yes
Date October 2020
Publisher Cambridge University Press
Publisher DOI 10.1017/S1473550420000270
Depositing User Dr. Michael Mommert
Date Deposited 23 Nov 2020 13:25
Last Modified 10 Dec 2020 07:57
URI: https://www.alexandria.unisg.ch/publications/261512

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Doughty, Christopher E.; Abraham, Andrew J.; Windsor, James; Mommert, Michael; Gowanlock, Michael; Robinson, Tyler & Trilling, David E. (2020) Distinguishing multicellular life on exoplanets by testing Earth as an exoplanet. International Journal of Astrobiology,

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https://www.alexandria.unisg.ch/id/eprint/261512
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