Seeing the crater produced by the Deep Impact mission鈥檚 violent encounter with Comet Tempel 1 on Monday 鈥� one of the mission鈥檚 key goals 鈥� could now be impossible.
The plume of gas and dust kicked up by the impact was much bigger, brighter and less transparent than expected. As a result, the crater itself, hidden behind the plume, will be very difficult to detect in the images taken by the flyby spacecraft.
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But the science team has already figured out some indirect ways of determining the crater鈥檚 dimensions, if the optical images cannot provide enough information. In any case, any problem with getting data on the crater challenge is far outweighed by the wealth of information returned from the first-ever deliberate comet impact.
And the show may go on for a while yet. Measurements by the Hubble space telescope and other observatories show the comet continued to brighten 鈥� and its new plume of ejected material continued to expand 鈥� for at least several hours after the impact.
And if the impact exposed a lot of fresh, volatile material at the bottom of the crater, the growing plume 鈥渃ould go on for weeks鈥�, according to the mission鈥檚 chief scientist, Mike A鈥橦earn, at mission control at NASA鈥檚 Jet Propulsion Laboratory in Pasedena, California, US
NASA has produced a series of videos showing:
聲 The flash when the comet ran over the probe, .
聲 The flash, .
聲 The , right up to seconds before impact.
Clearly, the science team has plenty to work on. Analysis of infrared images should soon reveal the precise temperatures of every part of the comet鈥檚 surface. This, in turn, will reveal how solid or porous the surface is, by showing how quickly it heats in response to changes in the amount of sunlight it receives.
As for the crater, it should be cooler than the surface, meaning it could be revealed by the infrared images.
And because the ejected plume casts a very clear shadow on the comet鈥檚 nucleus in optical images, it should be possible to determine the size of the plume鈥檚 base 鈥� and that should correspond exactly to the size of the crater.
Impact depth
Analysis of the exact shape of the plume as it developed could also show just how deeply the impactor penetrated into the nucleus, and even the consistency of the materials, and whether it has a layered structure.
The plume will be crucial in revealing the composition of material in the comet鈥檚 hidden interior, via spectroscopic analysis which is still being processed.
There are also the spectacularly detailed images of the comet鈥檚 mountain-sized nucleus, taken before impact, which reveal a highly varied surface. The science team will try to interpret crater-like rings, dark linear scarp-like features, flat areas, and scattered bright patches.
Until that analysis is completed the science team is sticking to food analogies. A鈥橦earn said the nucleus 鈥渄oes not look like a pickle or a cucumber, it鈥檚 closer to a loaf of bread or a muffin鈥�. And Jay Melosh, another Deep Impact team member, said that its internal porosity may make it 鈥渨eaker than the weakest souffl茅鈥�.
