NASA Succeeds In Crashing Craft Into Comet
Tuesday, July 5, 2005
PASADENA, Calif., July 4 -- NASA's Deep Impact spacecraft completed a flawless journey to oblivion early Monday, slamming into an onrushing comet to vaporize itself in an Independence Day blaze of glory.
Scientists and engineers here at NASA's Jet Propulsion Laboratory cheered as spectacular images taken by a second flyby spacecraft positioned nearby confirmed that the "impactor" had scored a perfect bull's-eye, smacking into comet Tempel 1 at its lower edge at 1:52 a.m. Eastern time, spewing a column of debris that lighted up the heavens.
"Oh, my God, look at that!" JPL astronomer Donald Yeomans shouted as the first images were posted. "There's considerably more material [debris] than I thought. It looks enormous."
By assessing the shape and size of the crater and chemically analyzing the debris that belched from it, scientists hope to gain new insights into the composition of the solar system at the time of its formation 4.5 billion years ago.
The flyby spacecraft, stationed 5,350 miles from the comet at impact, used two cameras and an infrared spectrometer to record the event and its aftermath for 13 minutes, then turned away in "shield mode" as the comet passed it only 310 miles away, traveling at a relative speed of 23,000 mph.
In addition, the impactor itself carried a camera that sent back crystal-clear pictures of ridgelike features, apparent craters and sinkholes, and other pockmarks that grew to dominate its field of vision as the spacecraft closed on the comet at 6.4 miles per second. The last image was sent only three seconds before the crash.
"It was just phenomenal. We didn't have to exercise one contingency plan," said the project manager, Rick Grammier of JPL. "We're minus one spacecraft: The impactor has been totally vaporized." But the flyby spacecraft emerged 40 minutes after impact none the worse for its close encounter with the comet.
Twelve hours after the explosion, the comet continued to spew a plume of debris thousands of miles into space. University of Maryland astronomer Michael A'Hearn, the project's lead scientist, said "the outgassing could last for weeks," as carbon dioxide and carbon monoxide ices within the comet vaporize in the sun.
Brown University crater specialist Peter Schultz said early analysis of the collision suggested an effect much like an armor-piercing artillery shell, with the impactor piercing a hard crust or thick sheet of surface dust and then diving into the comet, throwing up an almost vertical plume of debris.
Heat and pressure built as the impactor plunged deeper into the comet, finally causing the 820-pound projectile to explode, tossing an additional, much larger fan of debris into space. Project scientists have speculated about what the crater will look like once photo technicians subtract the debris from the images, but Schultz said final results will not be known for a week.
"I think it's big," Schultz said. "I think it's bigger than house-sized." But he would not guess about the prediction of many scientists: that it could reach the size of the Rose Bowl, the stadium only a few miles up the road from JPL.
Besides the spacecraft images, a network of about 60 Earth- and space-based telescopes and thousands of amateur astronomers were standing by to participate in the first-ever globally coordinated effort to watch an object dig a crater in a comet. Early results showed that the impact had caused the comet to brighten fivefold.