DETECTION OF OCEAN GLINT AND OZONE ABSORPTION USING<i>LCROSS</i>EARTH OBSERVATIONS

Abstract

The Lunar CRater Observation and Sensing Satellite (LCROSS) observed the\ndistant Earth on three occasions in 2009. These data span a range of phase\nangles, including a rare crescent phase view. For each epoch, the satellite\nacquired near-infrared and mid-infrared full-disk images, and partial-disk\nspectra at 0.26-0.65 microns (R~500) and 1.17-2.48 microns (R~50). Spectra show\nstrong absorption features due to water vapor and ozone, which is a\nbiosignature gas. We perform a significant recalibration of the UV-visible\nspectra and provide the first comparison of high-resolution visible Earth\nspectra to the NASA Astrobiology Institute's Virtual Planetary Laboratory\nthree-dimensional spectral Earth model. We find good agreement with the\nobservations, reproducing the absolute brightness and dynamic range at all\nwavelengths for all observation epochs, thus validating the model to within the\n~10% data calibration uncertainty. Data-model comparisons reveal a strong ocean\nglint signature in the crescent phase dataset, which is well matched by our\nmodel predictions throughout the observed wavelength range. This provides the\nfirst observational test of a technique that could be used to determine\nexoplanet habitability from disk-integrated observations at visible and\nnear-infrared wavelengths, where the glint signal is strongest. We examine the\ndetection of the ozone 255 nm Hartley and 400-700 nm Chappuis bands. While the\nHartley band is the strongest ozone feature in Earth's spectrum, false\npositives for its detection could exist. Finally, we discuss the implications\nof these findings for future exoplanet characterization missions.\n