Signs of life on Earth live in Earthshine — the sunlight that passes through Earth’s atmosphere, bounces off the moon and returns to observers on the ground. Now, a team of scientists reports in the March 1 Nature that Earthshine (visible as the dimmer portion of the moon above the bright crescent) not only carries the signatures of molecules such as oxygen, ozone and water, but reveals details like the percentage of cloud and vegetation cover for a given planetscape. Similar observations might one day be key to discerning properties of distant worlds: Starlight passing through a planet’s atmosphere is polarized by things like aerosols, cloud particles and reflections from land or water. In April and June 2011, scientists using the Very Large Telescope in Chile decoded the signatures of terrestrial life in Earth’s own reflection. Researchers then compared the results with images of Earth from the moon, setting a benchmark for future exoplanet measurements.
