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[31.13] Seasonal Variation in the Optical Appearance of Earth-like Planets

D.M. Williams (Penn State Erie, The Behrend College), E. Gaidos (University of Hawaii)

The brightness of Earth at optical wavelengths has been observed to vary seasonally by as much as 10% by Earth-orbiting spacecraft and through the analysis of Earthshine. Earth is brightest in the Northern hemisphere spring, which suggests that the bulk of the variation results from changes to snow and ice cover and the associated preponderance of cloud cover over snow-laden areas. Thus, the existence of an active hydrologic cycle on the Earth is measurable from space, and might be used to determine whether similar cycles exist on the surfaces of distant Earth-like planets. Here we model the optical light curves of hypothetical Earth-like planets in an attempt to contrast and de-convolve the effects of orbital and viewing angles, cloud cover, and geographic distribution of ice and snow. This is yet another way for the futuristic Terrestrial-Planet-Finder (NASA) or Darwin (ESA) spacecraft to detect water on the surface of a remote planet.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.