On July 4, well before all the fireworks, NASA’s Deep Impact probe slammed into Comet Tempel 1 at 10 kilometers per second. Designed to lay bare the comet’s innards as a way of studying the composition of the early solar system, the collision caused a glow that revealed the comet’s surface features, including possible impact craters. It also kicked up a fan-shaped plume of fine dust, gas and organic compounds moving at twice the speed of a commercial jet. Initial analysis of the ejecta suggests that the surface is highly porous and held together weakly by gravity, possibly indicating that the comet formed slowly. The mission team is still working to determine how much ice escaped the comet as gas. “We will have years of continuing analysis,” says principal investigator Michael F. A’Hearn of the University of Maryland, “and we should have new results on a regular basis.”