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A Space Probe's Problem: One Missing Comet

Irene Klotz, Discovery News

Photos

Deep Impact

Dec. 19, 2007 -- A NASA comet probe heading back to Earth for a gravity boost will be redirected after the disappearance of its intended target.

Deep Impact, which won funding for an extended mission after its successful close-up studies of Comet Tempel 1 in 2005, was expected to use its Dec. 31 flyby of Earth for a slingshot maneuver to rendezvous with a comet known as 85P/Boethin in 2008.

Scientists spent the summer and early fall searching for the target so Deep Impact could be dispatched on the right path. A hunt by the most sophisticated telescopes on the planet, however, turned up nothing.

"We couldn't find it," University of Maryland astronomer Michael A'Hearn, who heads the Deep Impact science team, told Discovery News.

The comet had only been seen twice before, but was expected to reappear last summer. A'Hearn believes the comet escaped detection because its orbit differs from predictions. But it could have fragmented into smaller pieces or even dissipated completely during its last pass around the sun.

"Comet Linear did that in 2000, but it's quite rare. If that is the right explanation, that's really fascinating," A'Hearn said.

Scientists had a backup target, Comet Hartley 2, but reaching it would take Deep Impact an extra two years and cost another $8 million.

"That's why we were trying so hard to find Comet Boethin," A'Hearn said.

With budgets tight, it was far from assured that NASA would pick up the extra expense, but last week the U.S. space agency agreed to do so.