Michael Schirber at Space.com:
Now that the fireworks are over, scientists are sorting through what was learned from the Deep Impact collision with Comet Tempel 1 on July 4.
“It looks like we got a pretty good pop,” Pete Schultz from Brown University told SPACE.com yesterday.
Although Deep Impact’s 820-pound impactor struck the comet’s surface at approximately a 25-degree angle, it was still able to kick up an impressive plume of dust.
The preliminary images and data indicate the comet has a cratered surface that is too soft to be made of ice, once thought to be the main component of comets. The impactor-induced crater was not visible directly due to the thick cloud of dust, but researchers estimate it to be at least 330 feet (100 meters) wide.
“The major surprise was the opacity of the plume the impactor created and the light it gave off,” said Michael A’Hearn of the University of Maryland. “That suggests the dust excavated from the comet’s surface was extremely fine, more like talcum powder than beach sand.”
More here.