Correction to This Article
The headline in earlier versions of this article, including in Wednesday's print edition of The Post, misspelled the name of the Tempel 1 comet. This version has been corrected.

Tempel 1 comet surface may be much more fragile than thought

From left, Ed Weiler, Tim Larson, Joe Veverka, Don Brownleeand and Pete Schultz discuss the Stardust mission at the California Institute of Technology's Jet Propulsion Laboratory in Pasadena, Calif.
From left, Ed Weiler, Tim Larson, Joe Veverka, Don Brownleeand and Pete Schultz discuss the Stardust mission at the California Institute of Technology's Jet Propulsion Laboratory in Pasadena, Calif. (Damian Dovarganes)

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By Amina Khan
Wednesday, February 16, 2011

LOS ANGELES - Close-up images of comet Tempel 1 taken by the Stardust spacecraft during its close encounter on Monday night suggest that the comet's surface is much more fragile than astronomers had anticipated, with major changes occurring during its five-year orbit of the sun, researchers said Tuesday.

The pictures also showed an unexpected layering of the comet's interior, a feature that researchers had not been able to detect in 2005, when an earlier mission shot an 820-pound impactor into the comet's side.

From the images and other data Stardust has sent back, scientists hope to learn more about the comet's surface, interior, the dust particles it gives off and about how a comet changes over time, mission principal investigator Joe Veverka said Tuesday at an afternoon news conference.

"It was 1,000 percent successful," he said of the encounter.

The Valentine's Day rendezvous brought Stardust, a repurposed spacecraft that has already taken images of the asteroid Annefrank as well as the dust of another comet, Wild 2, within 110 miles of Tempel 1 just before 11:40 p.m. Eastern time Monday. Stardust snapped photos every six seconds and sent them to Earth at a rate of one image every 15 minutes.

This second look at the comet, which will use up the last cup of Stardust's hydrazine fuel, offers scientists a chance they largely missed in 2005 when the Deep Impact spacecraft shot the impactor into the comet's surface. The resulting explosion of ice and dust held lessons about what Tempel 1 was made of, but the cloud of debris obscured their view of the crater at the time.

From the images, scientists can see that the manmade crater is about 150 meters across and "subdued," meaning it is not as well-defined as had been expected, said co-investigator Peter Schultz, a planetary geologist at Brown University. The images also showed that material that had been tossed up by Deep Impact had fallen down to form a small mound in the center of the crater.

NASA researchers were looking for any changes in Tempel 1's landscape since 2005. Since that time, the comet has completed one full revolution around the sun. Veverka noted that a depression in the comet's surface had visibly changed shape and lost a substantial amount of material.

That's probably because the comet's orbit takes it as far from the sun as Jupiter and as close to the sun as Mars - and when it's close to the sun, the accumulated ice on its surface would sublimate: turn straight from a solid into a gas without first becoming a liquid. The sublimated ice would then escape the comet's surface and take dust particles with it.

The researchers were able to get a glimpse of other sides of the comet they had not seen, finding areas where the rocky surface appeared thickly layered (with each layer a few meters thick), and other regions that looked heavily pocked and pitted. This, Veverka said, was "geology we did not see on the other face of Tempel."

- Los Angeles Times


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