What a difference five years makes. New portraits of Comet Tempel 1 reveal pitting, erosion and other surface features that weren’t there in July 2005, the last time the comet was photographed at close range.
The new images, recorded during a Valentine’s Day encounter with NASA’s Stardust spacecraft, mark the first time any comet has had two separate sets of close-ups. Tempel 1 has completed a full passage around the sun since its visit by Deep Impact, another NASA craft. Researchers unveiled the new images during a press briefing on February 15 at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
The Stardust portraits also show for the first time the crater that was gouged when Deep Impact shot a 372-kilogram copper slug into Tempel 1 in 2005 (SN: 7/9/05, p. 22). Dusty debris dredged up from that violent encounter had prevented the craft from seeing the hole it created.
“I make craters for a living but I’ve never had to wait five and a half years to see the results,” quipped Stardust scientist Peter Schultz of Brown University in Providence, R.I., who also worked on the Deep Impact mission. The crater is about 150 meters wide and has softened features with a central mound on the crater floor. The mound was probably formed when debris kicked up by the 2005 impact fell back down, Schultz said, partially burying the crater and attesting to the fragility of Tempel 1.
While passing Tempel 1, Stardust viewed parts of the comet never before seen up close, including extensive areas of layered deposits and a heavily pitted area. On the side that Deep Impact did closely examine, scientists found that what were three distinct pits on the comet’s surface five years ago have now eroded to become one continuous scar.
Like a World War II bomber flying through flak, the craft cruised through clods of disintegrating ice and dust that were shed by the comet when it neared the sun, said Stardust researcher Don Brownlee of the University of Washington in Seattle. The comet passed as close as it will get to the sun during its 5.5-year orbit only a month ago.
Twelve of the particles were large enough to puncture a shield about the thickness of a finger on the front of the craft. A dust detector recorded some 5,000 smaller hits in staccato bursts. Another detector revealed that some of the particles contained carbon bound to nitrogen, indicating the presence of organic compounds in the dust, Brownlee said.
The craft came within about 178 kilometers of Tempel 1 on February 14 and recorded 72 images. Stardust had previously flown past the comet Wild 2 and returned samples of that comet’s dusty shroud to Earth (SN: 1/10/04, p. 19).
“It’s great to use one’s spacecraft to go to multiple targets with the same instruments,” said Brownlee.