“The impact on comet Tempel 1, the flyby of comet Hartley 2, and the remote sensing of comet Garradd have led to so many surprising results that there is a complete rethinking of our understanding of the formation of comets and of how they work. These small, icy remnants of the formation of our solar system are much more varied, both one from another and even from one part to another of a single comet, than we had ever anticipated,” said
“Deep Impact has been a principal focus of my astronomy work for more than a decade and I’m saddened by its functional loss. But, I am very proud of the many contributions to our evolving understanding of comets that it has made possible,” A’Hearn said.
First Look Inside a Comet
Deep Impact first made history and world-wide headlines on
A comet is composed of dust and ices and that form its body (nucleus) and tail (coma). The tail is created when heat from the Sun causes the body of the comet to give off dust and ice, forming a cloud that surrounds and extends out from the nucleus. According to A’Hearn, the key goal of the Deep Impact’s mission to Tempel 1 was to look for differences between the composition of the sun-heated surface of a comet’s nucleus and its colder, more primordial interior. “Much to our surprise, and contrary to most theoretical models, the different ices [of water, carbon dioxide and carbon monoxide] that were excavated from as deep as 20 meters had the same relative abundances as the ones that were evaporating just below the surface,” he said.
A’Hearn noted that science results of this mission also showed comets could be surprisingly fluffy. “We found that the nucleus of Tempel 1 as a whole is at least 50 percent empty space and the surface layer at the impact site at least 75 percent empty space. This finding confirmed the correctness of some previous indirect observations suggesting comets could be more porous than expected.”
And he said the wide variety of craters and other surface features, and particularly the prominent layering of the nucleus found on this comet imply that the nuclei of short-period comets (those which orbit the Sun every 20 years or less) are not fragments of larger bodies as had been argued by many scientists.
After the original mission was complete, the
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