NASA scientists hope to learn more about how comets work by blasting a hole in one.
By CURTIS KRUEGER, Times Staff Writer
Published January 9, 2005
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Deep Impact Nasa hopes to intercept and smash into a comet.
TITUSVILLE - Since the time of Aristotle, humans have searched the skies for comets and wondered at their mystical meanings. But this week will mark the first time scientists have tried to punch a hole in one.
NASA's unmanned Deep Impact spacecraft is scheduled to launch from Cape Canaveral on Wednesday and zoom up to a comet called Tempel 1. The ship eventually will unleash a smaller spacecraft, an 820-pound hunk of copper that will become a kind of high-tech cannonball, smashing into the comet's surface.
The impact will blow open a crater at least as big as a house and maybe the size of a football stadium. Meanwhile, the Hubble and two other space telescopes will be watching, and so will two more powerful telescopes on board the main Deep Impact spacecraft.
There's even a chance the impact - scheduled for July 4 - will be beamed to Earth so people can watch it on a Web site.
"We're really excited about this mission," Rick Grammier, NASA's Deep Impact project manager said during a recent media briefing. "We're actually going to go smash a big piece of copper into a comet's nucleus and see what happens, see what's inside."
NASA is not planning to destroy the comet, which was the plot of a 1998 movie also called Deep Impact, but to study it.
The mission has been in development for years, but for NASA, the launch is coming at an opportune time.
The space agency is now preparing for a May or June launch of the Space Shuttle Discovery, the first shuttle launch since the Columbia disaster. Last week NASA shipped Discovery's newly redesigned booster rocket via barge to the Kennedy Space Center.
As the shuttle program revs back up, the comet mission may serve as a reminder that NASA is charging ahead with interplanetary science projects that don't require astronauts. Deep Impact is among a series of missions to explore space by remote control. A past example was the 1997 Mars Pathfinder mission that sent the Sojourner rover to roll across the Martian surface. A future mission would launch a satellite called Kepler to search the heavens for Earth-sized planets that could be capable of supporting life.
The Deep Impact mission is designed to help scientists learn more about comets, partly by peeking inside of one.
Scientists already know something about the makeup of comets. They are speeding clods of ice, gas and dust, which is why they were nicknamed "dirty snowballs" by astronomer Fred L. Whipple. As comets speed through space, the sun melts the ice, and gas and dust spew out like jets spitting exhaust.
"What we don't know is what's buried inside," said Michael F. A'Hearn, an astronomy professor at the University of Maryland who is the top scientist for the Deep Impact mission.
The scientists say they hope to learn whether the inside layers of the comet are solid or porous, weak or strong, and whether ice inside the comet is frozen water or some other substance, such as frozen carbon dioxide.
One reason for their interest: Comets are thought to be cosmic leftovers from the early stages of the solar system, formed some 4.5-billion years ago.
If all goes according to plan, the Deep Impact spacecraft will launch atop a Delta II rocket on Wednesday from Cape Canaveral. The spacecraft will contain two parts, a large vehicle called the fly-by and a smaller one called the impactor.
The combined craft will aim toward the comet, with many tests and calibrations along the way.
To picture the final phase of Deep Impact, imagine a kid who walks to the edge of a race track and throws a pebble. A race car speeds around the track and smashes into the pebble, leaving a dent in the hood.
In the Deep Impact mission, the spacecraft is designed to approach the comet's orbit, like the kid walking to the edge of the track. Then the bigger spacecraft will release the smaller one, like the kid tossing the pebble.
Just as the race car speeds around the track, the comet Tempel 1 will speed around in its orbit, smashing into the slower-moving small spacecraft, the impactor. That force will blast open a crater on the comet's surface, if all goes according to plan.
Many eyes will be watching - through several professional and amateur telescopes on Earth, as well as the space telescopes.
The impactor will be outfitted with a sophisticated camera, so it can take pictures of the comet and transmit them right up to the final seconds before impact. Meanwhile, the bigger fly-by spacecraft will aim two more cameras at the comet, hoping to capture the precise moment of collision.
Watching how deep the copper impactor blasts into the comet, and seeing how much debris shoots up around it, will provide scientists new clues about comets.
Scientists say they aren't worried about breaking apart the comet. The impactor is about the size of a washing machine, and the comet is thought to be about 3.7 miles wide. One NASA scientist compares it to a Boeing 767 jet flying into a mosquito.
But they are worried about something going haywire. Grammier said he is confident of the mission, that the technology is not radical, and that the team has had ample time to test and retest.
Still, NASA lost contact in 2002 with CONTOUR, an attempt to fly a space craft nearby other comets. That sort of episode is difficult to forget.
"We've had some good results and we've had some not-so-good results with that sort of thing," said NASA spokesman Bruce Buckingham. Being aware of that possibility, "I think it makes people work a little harder and work a little later into the night," he said.
He said that's true not just of a comet-chasing mission like this one, but also of the upcoming space shuttle launch.
"We are very well aware of the fact that not only did we lose an orbiter, but we lost some lives."
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