Latest images of comet Tempel 1 reveal a fragile surface
Images of comet Tempel 1 taken by the Stardust spacecraft during its Monday night close encounter suggest that the comet’s surface is much more fragile than astronomers had anticipated, with major changes occurring during its 5 1/2-year orbit of the sun, researchers said Tuesday.
The close-up 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 probe into Tempel 1’s side.
From the images and other scientific data Stardust has sent back, scientists hope to learn more about the comet’s surface, interior, the dust particles it gives off and how a comet changes over time, mission principal investigator Joe Veverka said at a news conference Tuesday.
“It was a thousand percent successful,” Veverka, of Cornell University, said of the encounter.
The Valentine’s Day rendezvous brought Stardust, a repurposed NASA spacecraft that has taken images of the asteroid Annefrank and collected dust from another comet, Wild 2, within 110 miles of Tempel 1 just before 8:40 p.m. Pacific time on 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 six years ago when the Deep Impact spacecraft shot the probe 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 the view of the crater at the time.
From the latest images, scientists can see that the man-made crater is about 500 feet 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 kicked up by Deep Impact’s projectile had fallen back to the comet surface to form a small mound in the center of the crater.
NASA researchers also 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 as Mars. When it’s closer 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 at other sides of the comet they had not seen before, 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.”
In the Stardust spacecraft’s primary mission, it collected dust from the coma of Wild 2 in 2004 and brought it back to Earth two years later, the first time comet dust has ever been retrieved. The cost of its Tempel 1 mission, its last, is estimated to be $29 million, less than one-tenth of other NASA “new discovery” missions, said Ed Weiler, the associate administrator of the agency’s Science Mission Directorate.
With barely any hydrazine left in its tank, Stardust will eventually float off into space.
