Deep Impact Begins Search for Extrasolar Planets

Launched on January 12, 2005, the Deep Impact space probe has become one of its successes. When it made history in 2005 by directing an impact from the spacecraft in to the comet Tempel 1 on July 4, things were good. The mission has recently been extended as well, being redirected for a flyby of comet Hartley on October 11, 2010.

However in the meantime, its largest of five telescopes will be directed at a cluster of stars nearby (relatively speaking of course in the hopes of detecting exosolar planets. The stars are orbited by planets which were previously discovered to be like our own Jupiter, but orbiting much closer to their sun; thus they have garnered the nickname “Hot Jupiters.”

To be led by University of Maryland astronomer Michael A'Hearn, the new mission is entitled Epoxi; a combination of the names for the two extended mission components: the exosolar planet observations, called Extrasolar Planet Observations and Characterization (Epoch), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (Dixi).

Though we have already discovered planets in orbit around these stars, we hope to find more. "We're on the hunt for planets down to the size of Earth, orbiting some of our closest neighboring stars," said Epoxi Deputy Principal Investigator Drake Deming of NASA's Goddard Space Flight Center in Greenbelt, Md.

The majority of the exosolar planets – in excess of 200 now – have been detected indirectly, due to the gravitational pull they exert on their parent star. The problems with detecting exosolar planets is in that being so close to their sun they are reflecting light that is already in abundance; try picking out a floating light bulb next to the sun.

However unlike my imaginary light bulb, the planets in question are not translucent, and thus when they eclipse their sun when looked at from Earth, light from the planet can be seen directly.

"When the planet appears next to its star, your telescope captures their combined light. When the planet passes behind its star, your telescope only sees light from the star. By subtracting light from just the star from the combined light, you are left with light from the planet," said Deming, who is leading the search for exosolar worlds with Deep Impact. "We can analyze this light to discover what the atmospheres of these planets are like."

Posted by Josh Hill.

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