"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 Deep Impact principal investigator Michael A'Hearn, a professor of astronomy at the University of Maryland, College Park, MD. "Our analysis of data produced by Deep Impact is revealing a great deal, much of it rather surprising."
Scientists found comet Tempel 1 has a very fluffy structure that is weaker than a bank of powder snow. The fine dust of the comet is held together by gravity. However, that gravity is so weak, if you could stand on the bank and jump, you would launch yourself into space.
Another surprise for A'Hearn and his colleagues was the evidence of what appears to be impact craters on the surface of the comet. Previously two other comets had their nuclei closely observed, and neither showed evidence of impact craters.
"The nucleus of Tempel 1 has distinct layers shown in topographic relief ranging from very smooth areas to areas with features that satisfy all the criteria for impact craters, including varying size," A'Hearn said. "The problem in stating with certainty that these are impact craters is
that we don't know of a mechanism by which some comets would collide with the flotsam and jetsam in our solar system, while others would not," he added.
According to A'Hearn, one of the more interesting findings may be the huge increase in carbon-containing molecules detected in spectral analysis of the ejection plume. This finding indicates comets contain a substantial amount of organic material, so they could have brought such material to Earth early in the planet's history when strikes by asteroids and meteors were common.
Another finding is the comet interior is well shielded from the solar heating experienced by the surface of the comet nucleus. Mission data indicates 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 many scientists had suggested.
