Alien Maps of an Ocean-Bearing World
N.B. Cowan, E. Agol, V.S. Meadows, T. Robinson (University of, Washington), T.A. Livengood, D. Deming (NASA Goddard), C.M. Lisse (Johns, Hopkins), M.F. A'Hearn, D.D. Wellnitz (University of Maryland), S. Seager, (MIT), D. Charbonneau (Harvard)

TL;DR
This study demonstrates that analyzing multi-band light curves of Earth as an exoplanet can reveal the presence of oceans and continents, using principal component analysis and spectral mapping techniques.
Contribution
The paper introduces a method to detect oceans and continents on exoplanets by analyzing diurnal light curve variations and eigencolor maps derived from multi-band observations.
Findings
Diurnal albedo variations of 15-30% observed.
Two dominant eigencolors explain 98% of color changes.
Near-infrared bands effectively distinguish land from water.
Abstract
[Abridged] To simulate the kinds of observations that will eventually be obtained for exoplanets, the Deep Impact spacecraft obtained light curves of Earth at seven wavebands spanning 300-1000 nm as part of the EPOXI mission of opportunity. In this paper we analyze disc-integrated light curves, treating Earth as if it were an exoplanet, to determine if we can detect the presence of oceans and continents. We present two observations each spanning one day, taken at gibbous phases. The rotation of the planet leads to diurnal albedo variations of 15-30%, with the largest relative changes occuring at the reddest wavelengths. To characterize these variations in an unbiased manner we carry out a principal component analysis of the multi-band light curves; this analysis reveals that 98% of the diurnal color changes of Earth are due to only 2 dominant eigencolors. We use the time-variations of…
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