Posted on 06/26/2005 12:27:21 AM PDT by Cincinatus' Wife
The game plan for a first-of-its-kind space mission called Deep Impact unfolds like a cosmic billiards match.
Early July 4, the NASA spacecraft will attempt to smack into the heart of a distant comet, Tempel 1.
Scientists think the blow could open a crater as large as a football stadium and as deep as a 14-story building. With the observations by a companion spacecraft of the crater and the debris that is tossed out, astronomers expect to learn more about how the solar system formed 4.6 billion years ago.
About half the size of New York City's Manhattan Island, Tempel 1 is one of the millions of comets that swirl through the distant reaches of the solar system. Occasionally visible in the night sky of the Earth, comets are collections of the ancient ice and dust particles that provided brick and mortar for the assembly of the sun and planets, theorists think.
What's more, the bombardment of the Earth by comets for hundreds of millions of years after the construction drew to a close may have delivered the abundant water that filled the oceans as well as the chemical precursors for life, some say.
Building blocks
If the $333 million mission is successful, the collision will allow scientists to observe and characterize the chemical makeup of the primordial building blocks that have been preserved inside comets for billions of years.
"This is a tremendously exciting, daring first-of-its-kind mission," said Rick Grammier, the Deep Impact project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"What makes it new and exciting also makes it extremely difficult and challenging from a technical viewpoint," Grammier told a pre-impact news briefing. "It's a bullet trying to hit a second bullet, with a third bullet in the right place at the right time watching the first two bullets."
Deep Impact was launched from Cape Canaveral, Fla., on Jan. 12, hurtling the spacecraft on a course that will intersect Tempel 1 about 83 million miles from Earth.
Deep Impact is actually a pair of spacecraft, a smaller 39-inch wide impactor and a larger, more capable flyby spacecraft. Both are equipped with cameras that will transmit images of the encounter back to Earth. The flyby also carries spectral instruments that will pioneer the chemical analysis.
After separating early July 3 (12:52 a.m. CDT), the impactor will rely on an internal guidance system to maneuver out in front of the speeding comet.
High-speed collision
Those maneuvers will enable Tempel 1 to overrun the 800-pound impactor July 4 at 12:52 a.m., colliding with a velocity of 23,000 mph.
After the July 3 release, the flyby spacecraft will steer out of the comet's path on a new course that should sweep it 5,300 miles away from Tempel 1 at the time of impact.
Within 14 minutes of the collision, the flyby companion will pass within 310 miles of Tempel 1 to gather photographs of the crater and freshly exposed dust and ice tossed from the crater.
Tempel 1 will be visible from Earth before and after the explosive encounter to observers with small telescopes or powerful binoculars.
However, at the impact time, the comet will be visible in the United States only to observers on the West Coast.
Scientists think the impact could make Tempel 1 glow brightly enough to be visible to naked-eye observers in the days that follow the collision.
Close observations
The United States is among several nations that have launched missions that swooped close to comets for observations.
Stardust, another NASA mission, snatched a sample of the dust and ice streaming off the comet Wild 2 in January of last year. Those fragments are on their way back to Earth and should descend by parachute into the Utah desert in January.
At their advanced age, comets have developed a thick outer crust, a weathering of the original building blocks by their many orbital journeys from the outer solar system to the sun and out again, said Michael A'Hearn, the University of Maryland astronomer who serves as Deep Impact's principal investigator.
Each time a comet advances toward the sun and retreats, it heats and cools, altering the outer layer. Tempel 1's crust could be as shallow as a few inches or as thick as 50 yards, scientists say.
"The whole purpose of Deep Impact is to go back and understand the differences between the surface layer and the interior," A'Hearn said."What we don't have any control over, is what will happen when we do the impact. We know so little about comets that it's very hard to predict."
Those uncertainties make it difficult to guess how large of a dent Deep Impact will make in Tempel 1, and whether the debris will fly off into space or slump back and encircle the crater.
The Earth's most powerful ground-based telescopes as well as the orbiting Hubble Space Telescope, the Chandra X-ray Observatory and the Spitzer Infrared Telescope will join Deep Impact's flyby companion in recording the collision that should reveal Tempel 1's chemical composition.
Flaw corrected
Although Deep Impact's journey has proceeded smoothly since liftoff, the spacecraft team discovered a flaw in one of two telescopes that will be used by the camera aboard the flyby spacecraft.
During pre-launch testing, the 12-inch mirror in the telescope apparently flexed, slightly creating a blur in the camera imagery. However, the flaw was detected early enough after the launch that scientists were able to develop a computer software correction technique.
Laugh!
I read this earlier, but I didn't make the connection.
Don't feel too bad, Flyer.
You would have made the connection, too, if you, like me, had a superior female brain.
BWAHAHAHAHAHAHAHAHAAAHAHAAAAHAHA!!!!!
Thempact will probaboy knock the comet off course such that it collides with and unites with another larger comet thus changing course again such that it collides with Chicago and we're all gonna die.
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