Biosignatures -Rainbows May Reveal
Biosignatures such as rainbows may be the key to identifying habitable planets around nearby star (rare "fiery rainbow" above).
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."
Darwin will use a flotilla of three space telescopes, each at least 3 metres in diameter, and a fourth spacecraft to server as communications hub. The telescopes will operate together to scan the nearby universe, looking for signs of life on Earth-like planets.
Jeremy Bailey of the Australian Center for Astrobiology at Macquarie University in Sydney said in the current issue of astrobiology taht light scattering in a planet's atmosphere would be a sensitive indicator of liquid water in its clouds.
Polarization, the same property of light that produces rainbows, could be a prime signal to look for liquid water.
"A rainbow is caused by light that is reflected in a water droplet that is scattered at a particular angle," Bailey 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."
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