"We're asking, do all comets have this, do they do all these things, or is this a weirdness we should ignore?" A'Hearn said.
A'Hearn has been studying the origin, composition, and behavior of comets since he arrived at Maryland to teach astronomy in 1966.
"I got into them because nobody else was studying comets at the time, and I thought, here was an area where I could make a contribution," he said.
At 67, A'Hearn has no intention of retiring when the EPOXI mission is completed in 2010. He's on a team designing instruments that will help NASA and the European Space Agency land a probe on another comet in 2014.
He selected the comet Hartley 2 for the EPOXI mission because it's one of the few comets that will pass near enough for a detailed look in the next two years. "If you're going to study a comet, the first thing you have to make sure of is that you're close enough," he said.
Most of what astronomers know about comets is based on images from ground-based telescopes, A'Hearn said. But they're worth studying because they hold clues to mysteries of the solar system's formation 4.5 billion years ago, A'Hearn said.
As interstellar dust and other material drew together to form Earth and our neighboring planets, the process generated heat and changed each planet's chemistry, A'Hearn said. But that heat was never generated on the smaller, icy bodies we call comets and so their internal chemistry is still intact, he said.
"With a comet, you find preserved the molecular composition of everything that existed back then that could make anything solid," he said.
A'Hearn and researchers at the NASA Goddard Space Flight Center began the first part of the mission last week studying the first images in EPOXI's search for Earth-like planets.
As part of that search, EPOXI's telescope will spend the next five months collecting imagery and data from five stars orbited by planets much larger than the Earth, said Drake Deming, an astronomer at NASA Goddard Space Flight Center and deputy principal investigator on EPOXI.
Between star scans, the spacecraft will turn and take high- and medium resolution images of the Earth.
EPOXI's best hope for finding a habitable, Earth-sized planet lies in its scan of the heavens around Gliese 436, a star 33 light years away. Unlike the others, it is known to have an orbiting, Neptune-sized planet with hydrogen and helium in its atmosphere, Deming said. That means it might also have a smaller, Earth-sized body orbiting nearby.
But don't hold your breath.
"It's conceivable we could find a habitable Earth-like planet," Deming said. "But it is kind of a long shot."
dennis.obrien@baltsun.com
