PALOMAR MOUNTAIN —— Astronomers using the Hale telescope at Palomar Observatory have taken extra-sharp pictures of the comet Tempel 1 after its spectacular collision with a man-made probe in July.

Their preliminary results, obtained using a special mirror that can subtly change its shape, show what could be a plume of dust and gas extending hundreds of miles from the center of the seven-mile-long comet, scientists at the California Institute of Technology and NASA said recently.

NASA scientists designed a motorcycle-sized probe, part of the Deep Impact spacecraft, to smash into the comet at a speed of more than 20,000 miles per hour and make a crater. Their purpose was to examine the inside of a comet, which astronomers describe as being leftovers from the time that the solar system formed.

Immediately after impact on July 4, the rest of the Deep Impact spacecraft was able to take close-up pictures as it quickly flew by the comet, but Earth-bound astronomers all across the globe were watching the impact, as well.

"We had an advantage over the spacecraft, because we could watch Tempel 1 over several nights," said Bidushi Bhattacharya, an astronomer at the California Institute of Technology, which runs Palomar Observatory.

The comet rotates every 41 hours, so two days after initial impact, the Palomar astronomers could observe the plume a second time, she said.

The probe or "impactor's" impact seems to have removed a small part of the comet's outer surface, according to James Bauer, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena.

"The idea is that the outer layers protect the underlying ice," Bauer said. "If something scratches off the protective material, you may see the outgassing of freshly exposed ice."

So far, astronomers have had a tough time taking pictures of the crater itself because of the volume of dust thrown out by the impact.

"The major surprise was the opacity of the plume the impactor created and the light it gave off," said Michael A'Hearn at the University of Maryland, College Park, which managed the Deep Impact mission's science. "That suggests the dust excavated from the comet's surface was extremely fine, more like talcum powder than beach sand."

Along with many other scientists, Bauer and Bhattacharya are now studying exactly what the protective material and the inside of the comet are made of. Bhattacharya said her team is looking forward to presenting its results at a planetary sciences conference in Cambridge, England, next month.

The team members are trying to determine the size of the dust and how much it scatters light, Bauer said. Their data can be combined with that of other scientists who are gathering information on the comet's chemical composition, he said.

The Palomar team took pictures that were sharper than many ground-based telescopes' because it used a technique called adaptive optics. The extra resolution it provides helps Palomar's Hale, the world's largest telescope until 1992, keep up with newer orbiting instruments such as the Hubble Space Telescope.

Adaptive optics can remove a star's twinkle by correcting for the distortions in an image that come from the Earth's atmosphere.

Adaptive optics has a computer adjust the shape of a secondary mirror —— placed between a digital camera and the main 200-inch mirror —— thousands of times per second, usually using a bright star nearby the object being studied as a reference.

Several world-class telescopes are equipped with adaptive optics, including the Keck Observatory in Hawaii and the Lick Observatory in Northern California.

The images that Bauer and Bhattacharya took measured near-infrared light, a wavelength longer than what the human eye can see. Adaptive optics works better with longer wavelengths, making near-infrared ideal for looking at the scattered light from the comet dust, Bauer said.

Eventually, Caltech astronomers say they hope to expand the system to operate with visual light. A team from Caltech, Jet Propulsion Laboratory and Cornell University designed the adaptive optics camera and installed it on the Hale telescope in 1999.

Contact staff writer Quinn Eastman at (760) 740-5412 or qeastman@nctimes.com.