Scientists compare
comet blast to sand

HILO » The material blasted out of Comet Tempel 1 Sunday night by the Deep Impact spacecraft looks like beach sand except the particles are much smaller, Gemini North Observatory announced.

"We are possibly seeing crystalline silicates which might even be similar to the beach sand here in Hawaii," said astronomer Chick Woodward of the University of Minnesota, one of the team members who used the Gemini telescope on Mauna Kea.

The comparison to sand was one of the first statements interpreting data from the impact, and scientists warned that their interpretation could change.

COURTESY GEMINI These images of Comet Tempel 1 were taken by the Gemini North telescope on Mauna Kea. At left is the comet 10 minutes before impact. At center is the comet three hours after impact. At right is the comet 24 hours after impact. Scale and orientation are the same for all images. Note: The middle image represents a physical expanse about that of the Big Island of Hawaii.

For one thing, the material is really more like dust than like grains of sand, said Gemini spokesman Peter Michaud.

But there was no doubt that the dust from the impact, seen in infrared light, was different from the dust around the comet before impact.

"The properties of the mid-infrared light were completely transformed after impact," said team member David Harker of the University of San Diego.

"In addition to brightening by a factor of four, the characteristics of the mid-infrared light was like a chameleon and within five minutes of the collision it looked like an entirely new object," he said.

Although the impact created a blast of dust, the comet may have been solid rock before it was hit, with the rock being crushed to dust, Michaud said.

On the night of the impact, University of Hawaii astronomer David Jewitt commented that the surface of the comet was really blacker than coal and looked bright only because light from it was electronically amplified.

Black rock doesn't look like silica-based beach sand.

Gemini Associate Director Jean-Rene Roy said the surface of the comet was black because of its long-term evolution under conditions in space. The studies by Woodward, Harker and others will tell more about the conditions underneath the black surface.

Gemini is continuing to observe the comet night after night, measuring the amount of dust kicked into space. That will allow the team to estimate the size of the crater created by the impact, Roy said.

The team also has to take into account that the comet's core is rotating every 41 hours, so it will look different on subsequent nights. "A lot of material keeps popping out," Roy said.