NASA's Deep Impact mission, which slammed an impactor spacecraft into the icy heart of comet Tempel 1 last July, has produced reams of data that reveals surprising characters of the comet, scientists reported on Wednesday.

Comets contain relatively pristine ice, dust, and other remnants from the earliest days of the solar system. Until the Deep Impact experiment, scientists' ideas about the interiors of these objects came primarily from theoretical models.

"Prior to our Deep Impact experiment, scientists had a lot of questions and untested ideas about the structure and composition of the nucleus, or solid body of a comet, but we had almost no real knowledge," said mission principal investigator Michael A'Hearn.

"Our analysis of data produced by Deep Impact is revealing a great deal, much of it rather surprising."

Three papers describing the mission results will appear in Sep. 8 online issue of the journal Science. The researchers also reported their findings at an astrophysical meeting in Britain Wednesday.

In an overview paper that presents results collected by the instruments aboard the impactor and the flyby spacecraft that launched it, A'Hearn and colleagues described some of Tempel 1's most distinctive features.

Overall, they said that Tempel 1 is a typical Jupiter-family comet, although its shape and surface features are quite different from the two other comets whose nuclei have been studied, Wild 2 and Borelly.

The authors reported that the comet undergoes frequent outbursts of dust, probably triggered by sunlight. It's also dotted with round depressions that appear to be impact craters, which have not been seen before on comets.

The comet's surface seems to heat up quickly in response to sunlight, suggesting that the heat doesn't penetrate very deeply into the comet's interior, said the scientists.

Mission data indicated the nucleus of Tempel 1 is extremely porous. Its porosity allows the surface of the nucleus to heat up and cool down almost instantly in response to sunlight.

This suggests heat is not easily conducted to the interior, and the ice and other material deep inside the nucleus may be pristine and unchanged from the early days of the solar system, just as scientists had suggested.

The comet consists largely of extremely fine particles that seem to be very loosely bound together, more like a pile of powder than a solid rock. It also contains a relatively high concentration of organic compounds; these were more abundant during and after the outburst than water and carbon dioxide, the scientists reported.

In the second paper, a group of scientists reported their observation of the collision and its aftermath with at least 70 different telescopes around the world.

This coordinated international effort, the largest such astronomical campaign ever, provided important information about the effects of the impact and earlier, natural cometary outbursts as well.

Observers reported that the material ejected from the comet after the impact had a different composition than the material that was bursting out in small, natural eruptions before the impact.

The new activity, which suggested differences between the comet 's interior and surface materials, only lasted a few days. Researchers on Earth also recorded early changes in the brightness of the comet, which they hope will provide information about the formation and evolution of the new crater created by the impact.

In the third paper, scientists described the data collected by the European Space Agency's Rosetta spacecraft on the gas and dust components of the impact cloud. The Rosetta had trained its cameras on Tempel 1 for 17 days from a distance of roughly 80 million km away.

The fastest particles moved with speeds of around 400 meters per second, though larger particles moved more slowly. According to preliminary estimates, the total mass of dust that left the comet nucleus was at least as large as that of water, said the researchers.

Source: Xinhua