Washington, May 26 (ANI): Using instruments aboard the Deep Impact spacecraft, a team of astronomers and astrobiologists has devised a technique to tell whether an Earth-like exoplanet harbors 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, a University of Washington doctoral student in astronomy and lead author of a paper explaining the new technique.
As part of NASA's Extrasolar Planet Observation and Characterization mission, the 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.
Earth appears gray at most wavelengths because of cloud cover, but it appears blue at short wavelengths because of the same atmospheric phenomenon that makes the sky look blue to people on the surface.
The researchers studied small deviations from the average color caused by surface features like clouds and oceans rotating in and out of view.
They found two dominant colors, one reflective at long, or red, wavelengths and the other at short, or blue, wavelengths.
They interpreted the red as land masses and the blue as oceans.
According to Cowan, 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.
"You sum up the brightness into a single pixel in the telescope's camera, so it truly is a pale blue dot," he said.
Since Earth's colors changed throughout the 24-hour-long observations, the scientists made maps of the planet in the dominant red and blue colors and then compared their interpretations with the actual location of the planet's continents and oceans.
"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 having liquid water," he added.
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.
"It will be some years before the launch of space telescopes capable of making similar observations for Earth-sized exoplanets, but devising this technique now could guide the construction of those instruments," he explained. (ANI)