May 22, 2007 — Rainbows may be the key to identifying habitable planets around nearby stars, according to a researcher who says light scattering could indicate the presence of liquid water.
Jeremy Bailey of the Australian Center for Astrobiology at Macquarie University said looking at the way light bounces off droplets in a planet's atmosphere would be a sensitive indicator of liquid water in its clouds.
Bailey presented his case for using polarization, the same property of light that produces rainbows, to look for liquid water in the latest issue of the journal Astrobiology.
"A rainbow is caused by light that is reflected in a water droplet that is scattered at a particular angle," he said.
"That angle depends on the refractive index of the liquid that is scattering the light, so you can get rainbows at different angles depending on the types of liquids that might exist in clouds of other planets.
"That's how we determined that the clouds of Venus were droplets of concentrated sulfuric acid."
As liquid water gives its own characteristic scattering pattern, Bailey said astronomers would be able to use this to detect liquid water clouds in a planet's atmosphere.
NASA's Terrestrial Planet Finder missions and the European Space Agency's Darwin mission will use a number of telescopes orbiting in formation to detect extrasolar terrestrial planets and search for "biosignatures."
