I subscribe to Sky and Telescope Magazine, which is a magazine for amateur astronomers and those who enjoy astronomy. The cover article of the current issue (December, 2005) is about the good work that the European orbiter Mars Express is doing at the Red Planet; the photographs are just spectacular.
There’s also a report on the Deep Impact probe that slammed into the comet Tempel 1. According to the spectroscopic analysis, the comet is made up of water, carbon dioxide, hydrogen cyanide, methyl cyanide, and other organic molecules. There are also minerals like olivine, calcite, and aluminum oxide.
Based on the nature of the explosion from the impact and the way the dust looked and acted, the concensus at the moment is that the mass of Tempel 1 is 72 trillion kilograms. Its density is about 0.6 gram per cubic centimeter. That value, along with the gravity dominated nature of the nucleus, has led team members of the Deep Impact mission to conclude that Comet Tempel 1 is a porous rubble pile–a loose body that is weakly held together by gravity.
The crater created by the Deep Impact probe’s colision is thought to be about 100 meters (330 feet) across and about 30 meters deep.
They got some neat photos, too, one of which was in the article in this current issue of Sky and Telescope.