When Deep Impact’s probe crashed into Comet Tempel 1 on July 4, how big a crater did it leave?


Deep Impact produced a spectacular show on July 4 when its 370 kg (820 pound) copper probe crashed into the surface of comet Tempel 1 at about 10.2 km/second (22,000 miles per hour) relative velocity, but we may never know exactly how big a crater was left behind. The force of the impact was equivalent to approximately 4.8 tons of TNT exploding. The blast produced a bright flash as many thousand tons of the comet’s material was hurled into space. The cloud of debris hid the crater from Deep Impact’s cameras. The Deep Impact science team is still searching the images taken as the main spacecraft flew past the comet, but there may be no pictures good enough to resolve the crater. You can read more about this story in Lucy McFadden’s notes at http://deepimpact.umd.edu/mission/update-200509.html.

Meanwhile, a host of observations that were made of the impact are starting to piece together more about the comet. Here are some of the results:

The European Space Agency’s Rosetta mission compared the amount of water vapor seen in the plume with the dust content. The discovered far more dust than had been expected. The conventional model of comets as “dusty snowballs” seems in this case to be more like an “icy dirtball.”

The Swift mission, taking time away from watching gamma-ray bursts, studied the X-rays from the ejected material. This measurement is one way to tell the total amount of material that was blasted off the comet.

The Spitzer Space Telescope, along with a number of ground-based telescopes, looked for the composition of the comet material. Because comets are thought to be remnants of the earliest time in our Solar System, they should carry information about material from its formation era. Water and dust (silicates) were expected, but other unexpected materials were found, including clay and carbonates, which ordinarily only form in the presence of liquid water. Organic materials containing carbon and hydrogen were also seen.

Although Deep Impact (without its probe) has flown far past Comet Tempel 1, the many observations made during and after the impact on July 4 will continue to be studied for a long time.

Here are some Web sites with information about Deep Impact. Please note that some of these links are not NASA sites, and this listing does not constitute NASA endorsement.

http://www.nasa.gov/mission_pages/deepimpact/main/index.html
http://deepimpact.jpl.nasa.gov/home/index.html
http://deepimpact.umd.edu/home/index.html
http://www.universetoday.com/am/publish/cat_index_35.html

This week's question comes from Dr. Dave Thompson. Dr. Thompson is an astrophysicist who studies gamma rays in the Exploration of the Universe Division. He helped build, test, and analyze data from EGRET on the Compton Gamma Ray Observatory, and he is now helping build part of the Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2007. His particular scientific interest is gamma-ray pulsars.