A team of astronomers announced its first snow Thursday — not due to the approaching winter, but from a spacecraft that observed a peanut-shaped comet spitting fluffy ice balls into space.
The Deep Impact spacecraft flew within 435 miles of the comet known as Hartley 2 on Nov. 4, snapping images as it whizzed past about 27,000 mph. Images released that day revealed a nearly 1 1/2-mile-long body with a smooth middle and rough, bulbous edges that was spewing gas from its surface.
In the two weeks since, scientists noticed the white specks circling the comet, as if it were inside an invisible snow globe. When they analyzed the images, they were in for another surprise — the smooth, middle portion, which they expected to be relatively inactive, was emitting water vapor; while the ends released chunks of ice, some as large as basketballs.
The flurry of white specks surrounding the comet's body caused the astronomers' jaws to drop, Peter Schultz, a team scientist from Brown University, said in a news conference at NASA headquarters in Washington.
Based on past experience, the scientists hadn't expected any such snowy showing, University of Maryland astronomer Michael A'Hearn added in an interview. Five years ago, Deep Impact shot an 820-pound copper slug into the much larger comet Tempel 1. That kicked up tiny grains of ice, not large, solid chunks.
After that mission, NASA officials redirected the spacecraft — still intact with a little fuel — to Hartley 2.
Based on the results from the flyby, A'Hearn said he figures that 40% to 50% of the comet's ice was made of frozen carbon dioxide, with the rest made of frozen water. That is probably the highest proportion of dry ice relative to water ice of any comet studied thus far, he said.
The preponderance of dry ice in the comet's bulbous ends may be a sign that Hartley 2 was formed way out in the solar system, far from the sun's rays, he said. But the fact that the middle section appears to lack dry ice may mean this comet was the result of the mixing that occurred as the solar system was coalescing. If so, it could tell us something about how that early development happened.
Though the flyby has come and gone, the spacecraft is still sending about 3,000 new images back to Earth each day, A'Hearn said. By Thanksgiving, the team expects to collect about 125,000 images in total.
The mission appears to have whetted the researchers' appetite for comet exploration.
"I'd sure as heck like to get a little closer to [one of] these guys and land on them," team scientist Jessica Sunshine of the University of Maryland said.