Distinguishing multicellular life on exoplanets by testing Earth as an exoplanet
arXiv:2002.10368 · doi:10.1017/S1473550420000270
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 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.
arXiv comment7 pages, 8 figures, 1 table. International Journal of Astrobiology 2020
References in corpus (11)
- A terrestrial planet candidate in a temperate orbit around Proxima Centauri
- Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
- Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
- Water vapour in the atmosphere of the habitable-zone eight Earth-mass planet K2-18 b
- Exoplanet Biosignatures: A Framework for Their Assessment
- Exoplanet Biosignatures: Observational Prospects
- Vegetation signature in the observed globally-integrated spectrum of Earth: Modeling the red edge strength using simultaneous cloud data and application for extrasolar planets
- Phase Functions and Light Curves of Wide Separation Extrasolar Giant Planets
- Enduring Quests-Daring Visions (NASA Astrophysics in the Next Three Decades)
- Proxima Centauri b is not a transiting exoplanet
- Detecting 3D vegetation structure with the Galileo space probe: Can a distant probe detect vegetation structure on Earth?