DISCOVERY MISSION: DEEP IMPACT

The Deep Impact mission was the first experiment to probe beneath the surface of a comet, attempting to reveal never before seen materials that would provide clues to the internal composition and structure of a comet. A variety of instruments, both onboard the spacecraft and at ground-based and space-based observatories around the world, observed the impact with the comet and examined the resulting debris and interior material.

SCIENCE OBJECTIVES

The Deep Impact plan was to excavate a deep crater in a comet nucleus and:

• Observe how the crater forms
• Measure the crater's depth and diameter
• Measure the composition of the interior of the crater and its ejecta
• Determine the changes in natural outgassing produced by the crater

Mission scientists believed that observing the released gases and the crater formation would provide important information about the composition and structure of the comet.

MISSION PROFILE

Work on the Deep Impact mission began in January 2000. The spacecraft launched from Cape Canaveral on January 12, 2005, beginning its 268-million-mile journey to Comet Tempel 1. The two-part spacecraft consisted of a larger "flyby" spacecraft carrying a smaller "impactor" spacecraft.

On July 2, 2005, at 11:07 PDT, the impactor was successfully released at a distance of about 547,000 miles from the comet. The battery-powered, 770-lb impactor was designed to operate independently for just one day, taking over its own navigation and maneuvering into the path of the comet.

Nearly 24 hours later, at 10:52 pm PDT on July 3, traveling at a speed of 23,000 miles per hour, the impactor successfully placed itself into the path of comet Tempel 1. A camera on the impactor captured and relayed images of the comet nucleus as it approached and just before it collided with the comet.

Comet Tempel 1 90 seconds before impact, taken by the Impactor Targeting Sensor.  The impactor hit in the area between the two craters.

From 300 miles away, the flyby spacecraft observed and recorded the impact and the ejected material blasted from the crater. The collision sent a huge, bright cloud of debris upward and outward from the comet. Scientists were surprised to learn that the cloud was not composed of water, ice, and dirt. Instead, Deep Impact's instruments indicated that the huge cloud was made up of very fine, powdery material. Due to the massive amounts of dust, science team members can only estimate the size crater's size to be about 325 to 825 feet in diameter.

Comet Tempel 1 67 seconds after it collided with the impactor, taken by the high-resolution camera on the flyby spacecraft. The image reveals ridges, scalloped edges and possibly impact craters formed long ago.

The flyby spacecraft collected and returned data for 14 minutes before it entered a defensive posture called shield mode to protect vital components. It then sped away from the comet. It is now in a solar orbit with the possibility of being used again for a future mission.

SCIENCE RESULTS

Deep Impact has yielded unexpected results about the structure and composition of comets. Mission scientists found the first definitive evidence of water ice on the surface of a comet. The analysis of data also revealed that Tempel 1 has a very fluffy structure that is weaker than a bank of powder snow. The fine dust of the comet is held together by gravity. The science team was surprised to find evidence of what appear to be impact craters on the surface of the comet. Another interesting finding is the huge increase in carbon-containing molecules detected in spectral analysis of the ejection plume, indicating that comets contain a substantial amount of organic material and thus could have brought such material to Earth early in the planet's history.

Scientists learned the comet interior is well shielded from the solar heating experienced by the surface of the comet nucleus. Mission data indicate the nucleus is extremely porous, allowing the surface to heat up and cool down almost instantly in response to sunlight. This suggests heat is not easily conducted to the interior, and the ice and other material deep inside the nucleus may be pristine and unchanged from the early days of the solar system, just as many scientists had suggested.

The analyses of the vast amount of data gleaned from Comet Tempel 1 will be ongoing well into the future.

MISSION MANAGEMENT

The Deep Impact mission was managed for NASA by the Jet Propulsion Laboratory, Pasadena, CA. The Principal Investigator was Dr. Michael A'Hearn of the University of Maryland. Ball Aerospace and Technologies Corporation, Boulder, CO, was responsible for all flight hardware.

For more complete information on the mission, visit the Deep Impact home page.