Distinguishing Multicellular Life On Exoplanets By Testing Earth As An Exoplanet

Our conceptual design of a distant observer monitoring Earth and the change in backscattering as it revolves around the sun. Θ is the azimuth angle, Ω i is the solar zenith angle, Ω v is the view angle, and Ψ is the phase angle.

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 Arial Vehicles (UAVs) 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 Earths 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 modeled and empirical results and suggest additional steps to determine whether this technique could distinguish upright multicellular life on exoplanets.

Christopher E. Doughty, Andrew Abraham, James Windsor, Michael Mommert, Michael Gowenlock, Tyler Robinson, David Trilling
(Submitted on 24 Feb 2020)
Comments: 7 pages, 8 figures, 1 table
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2002.10368 [astro-ph.EP] (or arXiv:2002.10368v1 [astro-ph.EP] for this version)
Submission history
From: Chris Doughty
[v1] Mon, 24 Feb 2020 16:54:15 UTC (5,025 KB)
Astrobiology, exobiology

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