PROVIDENCE, R.I. — The surface of comet Tempel 1, hit by aNASA space probe during a spectacular July 4 experiment, bears evidenceof impact craters, suggesting that the comet has collided withasteroids or other space travelers in its journeys around the Sun.
Severaldozen circular features that appear to be impact craters, ranging from40 to 400 meters across, were spotted on Tempel 1 during the DeepImpact mission, according to first results from the mission teampublished by Science and released at the annual meeting of the Divisionof Planetary Sciences of the American Astronomical Society held at theUniversity of Cambridge.
Tempel 1 is the first comet to showevidence for impact craters. In fact, differences in the comet’stopography and shape compared with Borrelly and Wild 2 – the two othercomets studied in detail by scientists – “raises the question ofwhether any comet is typical when looked at closely,” the team writes.
“Thiscomet is a geologic wonder,” said Peter Schultz, a professor ofgeological sciences at Brown University and a co-investigator on themission team. “There are smooth surfaces, filled-in craters, ridges,cliffs. Tempel 1 also features an area marked by innumerable bumps andvalleys. This all suggests a long history of evolution.”
DeepImpact, managed by NASA’s Jet Propulsion Laboratory and the Universityof Maryland, aims to better understand how comets are built and whatthey’re made of. Some scientists believe that comets, which containwater ice and organic matter, may have carried ingredients necessaryfor life to Earth during a long-ago collision.
On Tempel 1, bothice and organic dust were initially seen in the plume that rapidly leftthe comet within the first few seconds after a copper-wrapped impactorhit. The team found that the comet’s surface consists of a powderylayer tens of meters deep.
“The most significant finding is thenature of the surface of the comet,” Schultz said. “We now know that itisn’t covered in a hard crust. It’s a fine-grained, loosely glued layerof organic powder and ice. You couldn’t make a snowball on Tempel 1.”
Twograduate students in the Department of Geological Sciences at Brown –Clara Eberhardy and Carolyn Ernst – were at the Jet PropulsionLaboratory in July to analyze data. Eberhardy assisted in spectralanalysis; Ernst examined the flash after the space probe hit. Both areco-authors on the Science paper.
Schultz said the science teamstill has years of work ahead to determine fully the structure andcomposition of the comet. For example, scientists were unable toidentify all the organic compounds that make up Tempel 1, informationthat could shed new light on formation of the solar system or how lifecame to Earth.
“Deep Impact lived up to its name and more,”Schultz said. “But there are undoubtedly more surprises to be pulledout of the treasure trove of data.”
NASA funded the work.
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