Arxiv:2008.01837V1 [Astro-Ph.EP] 4 Aug 2020 Sunlight Is Transmitted to the Lunar Surface at Altitudes Where It Passes Through the O3 Layer Rather Than Above It
Draft version August 6, 2020 Typeset using LATEX preprint style in AASTeX62 The Hubble Space Telescope's near-UV and optical transmission spectrum of Earth as an exoplanet Allison Youngblood,1, 2 Giada N. Arney,2, 3, 4 Antonio Garc´ıa Munoz,~ 5 John T. Stocke,6 Kevin France,1, 6 and Aki Roberge2 1Laboratory for Atmospheric and Space Physics, 1234 Innovation Dr, Boulder, CO 80303, USA 2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 3NASA NExSS Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA 4Sellers Exoplanet Environments Collaboration, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 5Zentrum f¨urAstronomie und Astrophysik, Technische Universit¨atBerlin, Hardenbergstrasse 36, D-10623, Berlin, Germany 6Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389, Boulder, CO 80309, USA ABSTRACT We observed the 2019 January total lunar eclipse with the Hubble Space Telescope's STIS spectrograph to obtain the first near-UV (1700-3200 A)˚ observation of Earth as a transiting exoplanet. The observatories and instruments that will be able to perform transmission spectroscopy of exo-Earths are beginning to be planned, and characteriz- ing the transmission spectrum of Earth is vital to ensuring that key spectral features (e.g., ozone, or O3) are appropriately captured in mission concept studies. O3 is photo- chemically produced from O2, a product of the dominant metabolism on Earth today, and it will be sought in future observations as critical evidence for life on exoplanets. Ground-based observations of lunar eclipses have provided the Earth's transmission spectrum at optical and near-IR wavelengths, but the strongest O3 signatures are in the near-UV.
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