Using Light To Identify Earths

Ever since Newton showed light was made up of components that could be separated, as using a prism does, scientists have been trying to discover new ways to gain information from light. A basic tool of astronomers has long been the spectrograph, for example, which lays out light from a target across the visible light spectrum, allowing scientists to identify elements in that target by studying markers in that spectrum.

Simple light may also help us to find extrasolar Earths. Light from a home star glinting off the surface of a planetary ocean, for instance, could tell us that world may be Earthlike. That technique-- which has been tested by using ESA probes orbiting Mars and Venus to look at Earth-- works best when the target planet is in crescent phase, so the light will be coming from a dark background. Studying the"light curve"-- the nature of the light that is reflected away from a body-- can also tell us whether the light bounced off water, ice, or dry land, and perhaps give an indication of the planet's rate of rotation on its axis.

The planet finder probes scheduled for launch in the next decade could give us some wonderful surprises.