A NASA probe smashed into its comet target Sunday, at the climax of a suicide mission that scientists hoped would provide new insights into the origins of the solar system.

The 820-pound (373-kilogram) copper probe intercepted Tempel 1, a pickle-shaped comet half the size of Manhattan as scheduled at 10:52 PM PT Sunday (1:52 AM ET Monday).

The Deep Impact mission's "Impactor" probe separated from its "Flyby" mothership almost exactly 24 hours before the crash, on its way to smash a hole in Tempel 1 so that scientists could get their first peek at the heart of one of the icy celestial bodies.

The mothership, meanwhile, fired its thrusters to slightly change course and stake out a front-row seat 5,000 miles (8,000 kilometers) from the high-speed collision, 83 million miles (133 million kilometers) from Earth.

Sampling the solar system's leftovers

Comets are leftover building blocks of the solar system, which formed when a giant cloud of gas and dust collapsed to create the sun and planets. Because comets were born in the system's outer fringes, their cores still possess some of the primordial ingredients, and studying them could yield clues to how the solar system formed 4.5 billion years ago.

The probe was to designed to shoot close-up pictures at a relative speed of 23,000 mph (37,000 kilometers per hour) until hitting the comet. After that, the mothership was to take over recording the scene through its high-resolution telescope.

Among the challenges workers in mission control were facing at NASA's Jet Propulsion Laboratory in Pasadena was the probe's switch to autopilot two hours before the encounter, relying on computer software and thrusters to steer itself into the path of the comet. After the switch, software engineer Anne Elson said ground controllers had to make only minor corrections to the automated flight paths.

"This is terrific," she said on NASA Television.

Engineers reported intermittent problems with telemetry, but they said that such glitches were expected and should have no impact on the mission's success.

About 15 minutes after the probe's impact, the 1,325-pound (600-kilogram) mothership was to make its closest flyby of the comet nucleus, approaching within 310 miles (500 kilometers). Scientists expected it would be bombarded with flying debris and will stop taking pictures, turning on its dust shields for protection.

Telescopes watching

NASA's brigade of space-based observatories, including the Hubble Space Telescope, Chandra X-ray Observatory and Spitzer Space Telescope, were pointing toward the comet to record the impact — as were telescopes on Earth. The probe's anticipated impact could cause the comet to shine brighter than normal, and stargazers may be able to see celestial fireworks with a telescope in parts of the Western United States and Latin America.

Little is known about comet anatomy, so it wasn't clear exactly what would happen. Scientists expected the collision to spray a cone-shaped plume of debris into space with a resulting crater ranging anywhere from the size of a large house to a football stadium and be between two and 14 stories deep.

Deep Impact blasted off in January from Cape Canaveral, Fla., for its six-month, 268 million-mile (429 million-kilometer) journey. In what scientists say is a coincidence, the spacecraft shares the same name as the 1998 movie about a comet that hurtles toward Earth. In a case of science imitating fiction, the mission's findings on comet composition could conceivably help researchers draw up strategies for diverting celestial objects that might threaten Earth.

Scientists emphasized that there was no chance that the mission's Impactor could destroy Comet Tempel 1 or put it into a hazardous orbit.

Discovered in 1867, Tempel 1 moves around the sun in an elliptical orbit between Mars and Jupiter every six or so years.

In April, the Deep Impact spacecraft took its first picture of Tempel 1 from 40 million miles (64 million kilometers) away, revealing what amounts to a celestial snowball. Last month, still 20 million miles (32 million kilometers) away, scientists saw the solid core of Tempel 1 for the first time.

(Chinadaily.com via agencies July 4, 2005)