Return to Heritage Home Page Current Image Gallery Archive Information Center Hubble Art Search
Return to Heritage Home Page Current Release Home Page Caption Fast Facts Biographies Supplemental Material Original Images


Click Here For More Information:

All Information From Deep Impact Web Site

What's deep inside a comet?
Comets are time capsules that hold clues about the formation and evolution of the solar system. They are composed of ice, gas and dust, which is the primitive debris from the solar system's earliest and coldest formation period, roughly 4.5 billion years ago. Deep Impact, a NASA Discovery Mission, is the first space mission to try to probe beneath the surface of a comet and reveal the secrets of its interior.

On July 4, 2005, the Deep Impact spacecraft targeted Comet Tempel 1 with its 370-kg (~820-lbs) copper impactor. Upon impact, scientists predicted a crater ranging in size from that of a house to that of a football stadium. Scientists hoped ice and dust debris would be ejected from the crater revealing fresh material beneath. Sunlight reflecting off ejected material was measured by the instruments onboard the spacecraft, and by other space- and ground-based observatories watching the event. Images from the Deep Impact cameras and spectrometer were sent to Earth covering the approach, the impact and its aftermath. The effects of the collision with the comet were also observable from certain locations on Earth. The data will be analyzed and combined with that of other NASA and international comet missions. Results from these missions will lead to a better understanding of both the solar system's formation and implications of comets colliding with Earth.

The Mission
Planning and design for the Deep impact mission started in November 1999. In January 2005, a Delta II rocket launched the Deep Impact spacecraft toward the comet. The spacecraft consists of two main parts- the impactor and the larger flyby vehicle. The combined spacecraft approached Tempel 1 and collected images of the comet before the impact. In early July 2005, 24 hours before impact, the flyby spacecraft pointed high-precision tracking telescopes at the comet and releaseed the impactor on a course to hit the comet's sunlit side.

Deep Impact's Orbital Path to Encounter Comet Tempel 1
(Diagram courtesy of JPL)

The impactor is a battery-powered spacecraft that operated independently of the flyby spacecraft for just one day. The impactor is more than a cannonball. After its release, it takes over its own navigation and maneuvers into the path of the comet. A camera on the impactor captured and relayed images of the comet's nucleus just seconds before collision. The impact was not forceful enough to make an appreciable change in the comet's orbital path around the Sun.

After release of the impactor, the flyby spacecraft maneuvered to a new path that, at closest approach passed 500 km (300 miles) from the comet. The flyby spacecraft observed and recorded data about the impact, the ejected material blasted from the crater, and the structure and composition of the crater's interior. The flyby spacecraft took additional data from the other side of the nucleus to look for changes in the comet's activity.

Comet Tempel 1
Comet Tempel 1 was discovered in 1867 by Ernst Tempel. The comet has made many passages through the inner solar system orbiting the Sun every 5.5 years. This makes Tempel 1 a good target to study evolutionary change in the mantle, or upper crust. Comets are visible for two reasons. First, dust driven from a comet's nucleus reflects sunlight as it travels through space. Second, certain gases in the comet's coma, stimulated by the Sun, give off light like a fluorescent bulb. Over time, a comet may become less active or even dormant. Scientists are eager to learn whether comets exhaust their supply of gas and dust to space or seal it into their interiors. They would also like to learn about the structure of a comet's interior and how it is different from its surface. The controlled cratering experiment of this mission is an attempt to answer these questions.

Technical Implementation
The flyby spacecraft carried a set of instruments and the impactor. Two instruments on the flyby spacecraft were designed to observe the impact, crater and debris with optical imaging and infrared spectral mapping. The flyby spacecraft used an X-band radio antenna (transmission at about eight gigahertz) to communicate with Earth as it also communicated with the impactor on a different frequency. For most of the mission, the flyby spacecraft communicated through the 34-meter antennae of NASA's Deep Space Network.

The image was taken July 9 2005, 4:01 UT at the
KPNO 4-m telescope, using the MOSAIC detector.
(Tony Farnham)