What can we learn about the impactor?

Jubilation at NASA’s Jet Propulsion Labs in California, as the first picture of the collision comes in from the Deep Impact mother ship. Just before six o’clock GMT, the impactor, weighing a third of a ton, smashed into Comet Tempel I at a speed of thirty seven thousand kilometers an hour.
    Telescopes across the world, and in Earth orbit, will be watching the giant spray of debris thrown out by the impact. The brightened comet in the constellation Virgo may even be visible to the naked eye, allowing members of the public around the world to join in this historic moment in astronomy.