BALTIMORE -- A NASA spacecraft is speeding to overtake a comet Thursday morning, and should soon be sending back photos snapped just 435 miles from the comet's mysterious icy nucleus.
Comet 103P/Hartley 2 passed within 11 million miles of the Earth last month, with NASA's EPOXI spacecraft in hot pursuit. The flyby -- at a scorching 27,000 mph -- is set for 9:50 a.m. EDT, with live coverage on NASA TV.
Scientists with the University of Maryland-led mission say cameras aboard the spacecraft began running continuously 18 hours before EPOXI's close encounter with Hartley 2.
They should have the first close-up images of the comet downloaded from the spacecraft and posted on the EPOXI website (epoxi.umd.edu) within a few hours of the flyby. A live press briefing with more photos is set for 4 p.m. Thursday, also on NASA TV
University of Maryland, College Park astronomer Michael F. A'Hearn, the principal investigator on the mission, said everything the probe does within 50 minutes of the encounter has been pre-programmed. And everything it sees must be recorded for playback later, because EPOXI can't aim its telescopic cameras at the comet and point its high-gain antenna back at Earth at the same time.
"Thirty minutes later, we will start transferring images stored on board back to the ground," he said. More images should be released Friday.
The mission's goal is to capture imagery and data on the structure and composition of the comet and its halo of dust and gas. Scientists hope that a comparison of Hartley 2 data with information gathered from other comets will explain observed differences between them, and yield new clues to the conditions present during the formation of the solar system 4.5 billion years ago.
Discovered in 1986 by Australian astronomer Malcolm Hartley, the comet is the smallest of the five that have been visited by spacecraft from Earth. Its nucleus is believed to be only about three-quarters of a mile across.
"Despite that, it puts out more gas per minute," A'Hearn said. "It's a really active nucleus for its size."
Early images have revealed multiple jets of gas spewing from the comet as it spins in space.
"This is going to give us the most extensive view of a comet to date," said Tim Larson, the EPOXI project manager at NASA's Jet Propulsion Laboratory in California.
It's not easy. Mission planners had to steer EPOXI close enough to be able to see detail on the little comet, but not so close that it cannot swivel fast enough to keep the comet in its sights.
EPOXI scientists expect to collect 5,000 images. And no one will be more thrilled to see them than Malcolm Hartley.
"It's a very special time for me," he said. "I couldn't imagine, 24 years ago, that I could be seeing something like this."
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