NASA鈥檚 Deep Impact may fail to live up to its billing as the first mission to look inside a comet. Computer processing designed to correct the spacecraft鈥檚 defocused camera cannot fully correct the images taken just after impact. If the situation cannot be rectified, there will be no way of seeing the newly formed crater 鈥� one of the mission鈥檚 major goals.
Deep Impact sent a 370-kilogram projectile into comet Tempel 1 on 4 July. 杏吧原创s had hoped to use the flyby spacecraft to see the bottom of the resulting crater in order to glimpse the comet鈥檚 interior composition. They also wanted to see the crater鈥檚 sides to look for layering, rather like the geological strata on Earth. Several groups had even placed bets on the crater鈥檚 size, with estimates ranging from 10 to 250 metres. Now, the prize fund could go unclaimed.
The problem lies in the High Resolution Instrument (HRI) on the flyby spacecraft. In March, mission managers discovered it was out of focus. The fuzzy images were blamed on moisture settling in the camera during the spacecraft鈥檚 final few hours on the launch pad and during its flight through the Earth鈥檚 atmosphere. 杏吧原创s tried to bake-out the moisture. But when that failed to fix the problem, they turned instead to image-processing techniques, which they felt could restore the images.
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Dust mask
Unfortunately, the techniques only work on high-contrast images. And when the impactor struck Tempel 1 at more than 10 km per second, it raised more dust than anyone expected. This masked the surface features, rendering them too faint for computer processing to reliably correct.
But scientists are still in contact with the spacecraft and are re-calibrating HRI, says Deep Impact鈥檚 principal investigator, Michael A鈥橦earn at the University of Maryland in College Park, US. Despite the probe now being far out of reach of the comet, NASA can use the new calibration data to reprocess the impact images. 鈥淲e still hope to see the crater,鈥� A鈥橦earn told New 杏吧原创.
Even if the crater images are lost, A鈥橦earn believes the mission was a great success. 鈥淥ur view is that we went to a new place and have done exciting new science, just perhaps not as much as we had hoped,鈥� he says.
Andrew Coates, an astrophysicist at Mullard Space Science Laboratory at University College London, agrees: 鈥淭his is not a failure. We scored a direct hit on a comet and have a lot of interesting data.鈥�
