PASADENA, Calif. – The Deep Impact spacecraft slammed into a comet right on schedule last Sunday night, a historic collision that sprayed brilliant particles into space and sent the NASA control room into a huge celebration.
“The impact was bigger than I expected and bigger than most of us expected,” said Donald Yeomans, a co-investigator for the mission at NASA’s Jet Propulsion Laboratory.
Jubilant NASA controllers cheered and pumped their fists about 11 p.m. PDT as a spectacular image confirmed that the comet spilled its guts of gas, dust and rock that had been locked inside since the birth of the solar system some 4.6 billion years ago.
With less than 15 minutes before the collision, high-resolution images from the impactor showed it heading toward a bright area toward the lower right side of the comet’s nucleus, rather than toward the center.
Yeomans said the controllers had decided to target this area because it was on the side of the comet that the flyby craft would pass as it came in to get a close-up.
“It’s a pretty gutsy maneuver,” Yeomans said, “but it looks like it played out pretty well.”
Photos from the doomed impactor showed the comet approaching – first a bright blob of light, then a craggy, pear-shaped rock with a dark spot on one side.
“The spacecraft is doing remarkably well for something that’s about to vaporize,” said Yeomans, a co-investigator for the mission who provided a running commentary on the event.
The final images showed circular features, just tens of meters across, and then some degradation of the picture – the probable result, Yeomans said, of dust particles sandblasting the telescope.
Minutes later, back at NASA, a voice in the control room said: “Gang, we’ve got confirmation.”
On Saturday, the flyby spacecraft successfully released its impactor – an 820-pound, copper-reinforced probe, shaped vaguely like a lug nut and about the size of a washing machine – into the path of the comet, which is tumbling through space.
Then the main spacecraft slowed, moving out of the way and preparing to record the crash from a safe distance. From that point on the impactor was programmed to navigate itself.
Based on what they know about comets and on previous observations, researchers believe Tempel 1 is a “jet-black, pickle-shaped, icy dirt ball about the size of Washington, D.C.,” Yeomans said.
But they had never seen it as anything more than a bright speck of light. After a journey of 268 million miles, controllers on the ground would not only have to steer the impactor into the path of the speeding comet, but also direct the flyby spacecraft to aim its cameras at exactly the location where the probe hit, giving scientists their first-ever view of a crater being formed in a heavenly body.
To complicate matters, the comet has produced four violent burps of gas and dust over the past two weeks, causing it to temporarily glow up to 50 percent brighter.
Michael A’Hearn of the University of Maryland, principal scientist for the mission, said it looks like these outbursts happen at fairly regular intervals, at a certain point in the rotation of the comet’s nucleus as it tumbles through space, indicating that they may come from the same point on the surface.
There was also some danger that particles thrown off by the comet – or by the impact – could damage the flyby spacecraft. The spacecraft was programmed to hide behind protective shields during the most hazardous parts of its flyby, which would take it within 310 miles of the comet in the minutes after the impact.
“A lot of scientists think most of the water and organic material on Earth came from comets roughly 4 billion years ago,” A’Hearn said. “We really want to know what those materials were, because the conditions the planets formed under are not well understood yet. We want to understand how the inside of a comet is different from what we see on the ground.”
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AP-NY-07-04-05 1444EDT
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