The excellent Space News Blog is reporting that NASA’s Deep Impact spacecraft is scheduled to hit a comet called Tempel 1 on July 4th. Before you shed any tears, though, be aware that this crash is deliberate; the idea is to gouge a hole in the thing to see what comets are like on the inside. Tempel 1 is reportedly about half the size of Manhattan, and the crater made by the spacecraft’s “impactor” — which is a detachable projectile that will slam into the comet while the rest of the Deep Impact probe remains safely behind to observe — may range in size from a large house to a football stadium, and be up to 14 stories deep.

Comets are already known to be “dirty snowballs” composed mostly of dust and ice, but no one has any idea what their internal structure is like, and they are also believed to contain material that’s been relatively unchanged since the formation of our system. This should be interesting…