Deep Impact’s bold mission plan was formulated to answer one seemingly innocuous question: What’s a comet made of? In order to find out, NASA’s Jet Propulsion Laboratory (JPL) and the University of Maryland broadsided the nucleus of Comet Tempel 1 with a probe July 4, 2005.
The most significant finding gleaned from the collision is that the comet is geologically active. There’s water ice on its surface. “We have known for a long time that water ice exists in comets, but this is the first evidence of water ice on comets,” says Jessica Sunshine, Deep Impact coinvestigator and chief scientist with Science Applications International Corporation (SAIC).
Tempel 1’s surface area is about 45 square miles (117 square kilometers). Ice covers about 300,000 square feet (27,871 square meters) of area, and pure water ice covers about 18,000 square feet (1,672 square meters), or about 6 percent. Three ice-rich regions were found in areas with temperatures of about 53° Fahrenheit (12° Celsius), 62° F (17° C), and 71° F (22° C). Temperatures on the comet’s surface range from 8° F (-13° C) to 130° F (54° C), depending on whether the area is in shadow or direct sunlight.
Spectral data also revealed jets spewing dust and vapor, presumably bringing materials from the interior of Tempel 1 to its surface. Jets may also relocate surface and interior ice to the comet’s tail or coma — the envelope of dust and vapor that surrounds the comet.
The final conclusion? Brown University professor Peter Schultz says, “We’re looking at a geologically active body whose surface is changing over time.”
Sunshine is lead author of an article published online in Science February 2, 2006, that reports the team’s findings.