New technique will detect water on earth-like planets

May 26th, 2009 - 4:16 pm ICT by IANS  

Washington, May 26 (IANS) Since the early 1990s, astronomers have discovered more than 300 planets orbiting far away stars, nearly all of them being gas giants like Jupiter. Now, powerful telescopes, similar to NASA’s recently launched Kepler Mission, will help spot much smaller rocky extrasolar planets, or exoplanets with water, more similar to earth.
Seen from dozens of light years away, an exoplanet will appear a little more than a “pale blue dot,” the term coined by late astronomer Carl Sagan to describe how earth appeared in a 1990 photograph taken by the Voyager spacecraft from near the edge of the solar system.

Using instruments aboard the Deep Impact spacecraft, a team of astronomers and astrobiologists has devised a technique to tell whether such a planet harbours liquid water, which in turn could tell whether it might be able to support life.

“Liquid water on the surface of a planet is the gold standard that people are looking for,” said Nicolas Cowan, University of Washington (UW) doctoral astronomy student who led the study.

As part of NASA’s Extrasolar Planet Observation and Characterisation mission, scientists obtained two separate 24-hour observations of light intensity from earth in seven bands of visible light, from shorter wavelengths near ultraviolet to longer wavelengths near infrared.

The analysis was undertaken “as if we were aliens looking at earth with the tools we might have in 10 years” and did not already know earth’s composition, Cowan said. “You sum up the brightness into a single pixel in the telescope’s camera, so it truly is a pale blue dot.”

“You could tell that there were liquid oceans on the planet,” Cowan said. “The idea is that to have liquid water the planet would have to be in its system’s habitable zone, but being in the habitable zone doesn’t guarantee it having liquid water.”

The observations on March 18 and June 4, 2008 were made when the spacecraft was between 17 million and 33 million miles from Earth, and while it was directly above the equator.

Observations from above a polar region likely would show up as white, Cowan said, according to an UW release.

These findings will be published in Astrophysical Journal.

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