The Hubble Space Telescope's Near-UV And Optical Transmission Spectrum Of Earth As An Exoplanet

We have combined the transmission spectra of Figure 7 and 8 into one plot (left panel) and compared to the model transmission spectra from Garc´ıa Mu˜noz & Pall´e (2011) (right panel). The dashed lines represent the model that includes O3, O2, and Rayleigh scattering, and the dotted lines represent the model that excludes O3. Spectral features have been labeled.

We observed the 2019 January total lunar eclipse with the Hubble Space Telescope's STIS spectrograph to obtain the first near-UV (1700-3200 Å) 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 characterizing 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 photochemically 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. We describe the observations and methods used to extract a transmission spectrum from Hubble lunar eclipse spectra, and identify spectral features of O3 and Rayleigh scattering in the 3000-5500 Å region in Earth's transmission spectrum by comparing to Earth models that include refraction effects in the terrestrial atmosphere during a lunar eclipse.

Our near-UV spectra are featureless, a consequence of missing the narrow time span during the eclipse when near-UV sunlight is not completely attenuated through Earth's atmosphere due to extremely strong O3 absorption and when sunlight is transmitted to the lunar surface at altitudes where it passes through the O3 layer rather than above it.

Allison Youngblood, Giada N. Arney, Antonio García Muñoz, John T. Stocke, Kevin France, Aki Roberge

Comments: 27 pages, 14 figures, 1 table, published in the Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
DOI: 10.3847/1538-3881/aba0b4
Cite as: arXiv:2008.01837 [astro-ph.EP] (or arXiv:2008.01837v1 [astro-ph.EP] for this version)
Submission history
From: Allison Youngblood
[v1] Tue, 4 Aug 2020 21:20:41 UTC (4,124 KB)

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