Locked in the core of comet Tempel 1 are mystery ingredients that may explain the creation of planets, and the conditions of the early solar system. After six years of preparation and 268 million miles of travel, NASA's Deep Impact spacecraft will finally unleash these secrets by placing its impactor spacecraft in the path of the hurtling comet, which is zooming along at a relative speed of 23,000 miles per hour. This collision will create a plume of cosmic dust and a large crater on the face of the comet. Watching from the sideline will be Deep Impact's flyby spacecraft and, farther away, the Spitzer Space Telescope.
Spitzer will offer astronomers spectral images of the cosmic particles at infrared wavelengths undetectable to telescopes on Earth. This contribution will allow astronomers to identify molecules with emission features in the 5 to 8.87 micron range, providing valuable insights into the molecular components of the early solar system.
According to Dr. Carl Grillmair, staff scientist at the Spitzer Science Center at the California Institute of Technology, astronomers have some suspicions that molecules like carbon dioxide and water will be ejected from Tempel 1. But they are not absolutely certain of everything they will see because the inside of a comet has never been observed.
"Spitzer has a crucial role in this mission," says Dr. Grillmair. "Data from Spitzer will be able to tell us exactly what comes out of the comet, in a wavelength region that no one else can explore."
For roughly an hour around impact, Spitzer will taking in data every two seconds. This quick response will give astronomers a continuous view of the event. After that, Spitzer will slow down its data collection rate and broaden its wavelength coverage, allowing astronomers to identify cosmic particles with longer wavelength emission.
Spitzer will continue to collect data on the comet until August 17, 2005.
According to Dr. Grillmair, by tracking the crater, astronomers hope to verify the theory that sunlight changes the chemical composition of a comet's surface over time. This hardening process is believed to create a thick black shell that seals in dust and gas particles of the early solar system. If this theory is correct, then the newly formed crater can be thought of as an open wound, and Spitzer can be regarded as documenting the crater's one-and-a-half month-long "healing process."
Spitzer began its crucial role in the Deep Impact mission in early 2004, when, together with the Hubble Space Telescope, it helped to pin down Tempel 1's size, rotation rate and reflectivity. Previous observations of the comet using ground-based telescopes portrayed the object as dark and oblong with a width of a few kilometers. Spitzer refined this image by using infrared technology to determine that the comet was 8.7 by 2.5 miles or roughly half the size of Manhattan. The two telescopes ascertained that Tempel 1 rotates approximately once every two days and reflects only four percent of the sunlight that falls on it.