NASA’s Deep Impact gives clues how to discover water on distant planets

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Greenbelt (MD) – NASA’s search for extrasolar, earth-like planets is one of the most fascinating scientific projects of our time. 300 “alien worlds” have been found so far, but it remains difficult to determine whether there is water present on those planets in order to support life as we know it. Scientists now have found a way to discover water using NASA’s over a distance of tens of millions of miles.

It seems that there is now enough technology that allows astronomers to explore millions of planets throughout our galaxy. NASA recently launch the Kepler space telescope which will survey more than 100,000 planets in the Cygnus-Lyra region over the course of the next three years in the hope to discover planets that could sustain life.

This particular mission aims to identify at least a handful of such planets, but they clearly will be too far away to say for sure how the conditions on these planets really are. Scientists from the University of Washington claim to have now found a new method that could provide astronomers with clues whether these planets have oceans of water or not.

"A 'pale blue dot' is the best picture we will get of an earth-like extrasolar world using even the most advanced telescopes planned for the next couple decades," said Nicolas Cowan, of the University of Washington. "So how do we find out if it is capable of supporting life? If we can determine that the planet has oceans of liquid water, it greatly increases the likelihood that it supports life. We used the High Resolution Imager telescope on Deep Impact to look at earth from tens of millions of miles away - an 'alien' point of view - and developed a method to indicate the presence of oceans by analyzing how earth's light changes as the planet rotates. This method can be used to identify extrasolar ocean-bearing earths."

Deep Impact was used by NASA to release a probe into the Tempel 1 comet back in July 2005 and has since then been cruising through space, waiting for new missions.

The project group explained that earth “looks blue all the time because of Rayleigh scattering of sunlight by the atmosphere,” the same reason that the sky appears blue to us down on the surface. "What we studied in this paper was how that blue color changes in time: oceans are bluer than continents, which appear red or orange because land is most reflective at red and near-infrared wavelengths of light. Oceans only reflect much at blue (short) wavelengths," said Cowan.

"A spectrum of the planet's light that reveals the presence of water is necessary to confirm the existence of oceans," said Drake Deming, a co-author of the paper at NASA's Goddard Space Flight Center in Greenbelt. Instruments that produce a spectrum are attached to telescopes and spread out light into its component colors, like a prism separates white light into a rainbow. Every element and molecule emits and absorbs light at specific colors. These colors can be used like a fingerprint to identify them.

"Finding the water molecule in the spectrum of an extrasolar planet would indicate that there is water vapor in its atmosphere, making it likely that the blue patches we were seeing as it rotates were indeed oceans of liquid water. However, it will take future large space telescopes to get a precise spectrum of such distant planets, while our technique can be used now as an indication that they could have oceans," said Deming.

The project team said that the technique only requires relatively crude spectra to get the intensity of light over broad color ranges.

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