A grand slam: in a winning move, NASA probe burrows into a comet.

The first fireworks this July 4 came from space. At 1:52 a.m. Eastern time, a 372-kilogram copper projectile released from NASA's Deep Impact spacecraft slammed into Comet Tempel 1, producing an incandescent flash. After a second flash a second or so later, the comet belched debris moving at 180 kilometers per hour in a fan-shaped pattern.

Scientists are now analyzing the images and other data collected from the explosion to learn about the interiors of comets, which are pristine relics from the formation of the solar system.

The short delay between the initial flash and the rest of the outburst suggests that the probe encountered fluffy material on the comet's surface, says Deep Impact investigator Pete Schultz of Brown University in Providence, R.I. Heated to high temperatures, this material generated the first flash.

The probe next burrowed into the comet and exploded. Then, a high-speed plume of gas blew back out the path created by the probe, creating the second flash, speculates team member Casey Lisse of the University of Maryland, College Park. A slower shock wave then reached the surface, releasing the cloud of debris.

The images show "all the components of a classic explosion," says investigator Lucy McFadden of the University of Maryland. The impact closely matches that predicted in simulations, she adds.

At press time, research leader Michael A'Hearn of the University of Maryland said that his team might have identified the crater gouged by the explosion. Images of the crater would reveal the composition and structure of the comet's interior.

For now, "we're in this confusing stage of trying to figure everything out, and it's a lot of fun," says McFadden, speaking from NASA's Jet Propulsion Laboratory in Pasadena, Calif. She then had to run. She didn't want to miss the next part of the celebration--a concert by a band called Bill Haley and the Comets.