Space.com - 13 May 2010
Colors of a Second Earth: Estimating the Fractional Areas of Ocean, Land, and Vegetation of Earth-like ExoplanetsA new way of comparing the color and intensity changes of light reflected off of Earth's surface to the flickers from exoplanets may help reveal the presence of oceans, continents and – possibly – life on alien worlds.
Researchers came up with a color scheme for how our uniquely life-filled, ocean-soaked planet would appear to observers tens of light-years away.
By comparing the changes in observed hues of an alien planet as it rotates to this distinct Earthly color palette, "we can infer the surface composition of the [exo]planet," said Yuka Fujii, a doctoral student at the University of Tokyo and lead author of a paper published in the May 4 issue of the Astrophysical Journal.
The method might let astronomers to soon hunt for soil, snow, seas or even plant life on exoplanets that for decades will otherwise remain too faint to directly visualize.
- The Astrophysical Journal, Volume 715, Number 2 (2010 May 4), doi: 10.1088/0004-637X/715/2/866
Characterizing the surfaces of rocky exoplanets via their scattered light will be an essential challenge in investigating their habitability and the possible existence of life on their surfaces. We present a reconstruction method for fractional areas of different surface types from the colors of an Earth-like exoplanet. We create mock light curves for Earth without clouds using empirical data. These light curves are fitted to an isotropic scattering model consisting of four surface types: ocean, soil, snow, and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. The results offer some hope for detection of vegetation via the distinct spectral feature of photosynthesis on Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere plays an important role, and for terrestrial exoplanets with an atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.