When scientists were developing the Deep Impact mission, they set forth the following objectives:
- Observe how the crater forms
- Measure the crater's depth and diameter
- Measure the composition of the interior of the crater and the material that is ejected upon its creation
- Determine the changes in natural outgassing produced by the impact
They hope that the information they gather from these objectives will help them answer three primary questions about comets:
- Where is the pristine material in comets?
- Do comets lose their ice or seal it in?
- What do we know about crater formation?
Scientists believe the nucleus of a comet consists of two layers: an external layer called the mantle and an internal layer considered to be pristine. As a comet moves through the solar system, its mantle changes. As it approaches the sun, some of the external ice sublimates and is dispelled. It may also encounter and pick up additional debris. The protected, pristine interior of the comet, however, is thought to be unaffected by the comet's travels and could be as it was when the comet was formed. Scientists believe that a study of the differences between the two layers will tell them a great deal about the nature of the solar system, both its formation and its evolution through the years.
Another major question scientists have about comets is whether or not they go dormant or extinct due to the heat of the sun. A dormant comet is one in which the mantle has sealed off the pristine interior layer, and no gases pass from this interior layer to the exterior layer and out of the comet. An extinct comet has no more gases in its nucleus at all, and as such will never change. Results from the Deep Impact mission will give scientists a better view of the nature of the mantle and enable them to determine if Tempel 1 is active, dormant or extinct.
The results of the impactor's collision will provide lots of information about the nature of comets. The formation of the crater, how fast it formed and its final dimensions tell scientists how porous the mantle and the pristine layers are. A study of how the material ejected from the crater site will show both its porosity and density and potentially the mass of the comet as well. Information from the entire cratering process may give some indication of what kind of material actually makes up the comet, which will help scientists understand how the comet formed and how it has evolved over time.