Biosignature

Astronomers have long analyzed the light spectrum of heavenly objects to determine the chemical compositions of stars and planetary atmospheres. With the discovery of extrasolar planets-- by the hundreds, so far, but soon, no doubt, by the thousands-- they are looking at more ways to squeeze information out of light. Specifically, astronomers want to develop ways to identify Earth-like planets that also support life. They want a biosignature.

A new study suggests, reasonably enough, that a technique used by satellites that look back at Earth be adapted to studying exoplanets. The basic principle of the technique is that light reflects better off things like trees than it does off rock. Therefore, Earth-like worlds that are brighter are more likely to harbor life than those that are dimmer. Similarly, worlds covered by water will be brighter because water is a good reflector of light. Liquid water, of course, is essential to life as we know it.

Coupled with a spectroscopic analysis of the light bouncing off the atmosphere of an Earth-like exoplanet, such insights and techniques could build a solid case for life elsewhere in the galaxy.