Comet mission loses some focus.

On July 4, the Deep Impact spacecraft is scheduled to fire a 1,800-kilogram projectile into the icy heart of comet Tempel-1. The craft remains on course for that encounter, but its main camera won't record the landmark event quite as sharply as astronomers had expected. Tests have revealed that the camera has only one-third to one-fourth the resolution it was designed to have, NASA announced March 25.

Mission scientists at first suspected that the problem was temporary, caused by condensation of water vapor in the barrel of the 11.8-inch telescope that houses the camera. But after heaters were turned on to bake out any water, the camera's focus improved only slightly. This suggests that the flaw originated during the telescope's construction, says mission scientist Lucy McFadden of the University of Maryland in College Park.

Even so, Deep Impact's pictures will be the sharpest ever taken of a comet, notes McFadden. By studying the material blasted into space when the projectile plows into Tempel-1, astronomers plan to learn about the composition of this comet and other frozen objects left over from the era of planet formation about 4, billion years ago.--R.C.