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NASA's approval today of the $279 million Deep Impact mission means humanity will no longer be only on the receiving end of comet impacts. Now we're going to go and slam into a comet ourselves. Or at least send a robot to do it.
With today's announcement, development will now proceed on the robotic mission to carry a camera-packing copper probe that will smash into Comet Tempel 1 on Independence Day 2005. The launch is targeted for January 2004.
Scientists will study the impact from ground-based telescopes. And, depending on how things go, the fireworks might even be visible to everyone on Earth.
Beating Europe to the punch
Deep Impact will launch one year after the European Space Agency's 2003 launch of
Rosetta -- a kinder, gentler mission that will rendezvous with Comet 46 P/Wirtanen rather than pummeling it. But Rosetta will take a circuitous route to its target, gaining gravity assists from Earth and Mars in an effort to save fuel on an eight-year journey. Like a low-budget Hollywood flick headed for video cassette, Deep Impact will take a more direct route, reaching its prey and making fireworks on July 4, 2005 -- six years before Rosetta catches up with its target.
Michael A'Hearn, a University of Maryland astronomer, will manage the mission.
Orbit-altering crash
A'Hearn said that while most NASA missions are passive in terms of how they explore an object, Deep Impact is "completely different, because it is a real experiment in which we do something to another body in the solar system and see how it reacts."
And how. The 770-pound (350-kilogram) probe will hit the comet at 22,300 miles (35, 885 kilometers) per hour and penetrate 16 to 32 feet (5 to 10 meters). Much, but not all of the probe will be vaporized.
Then a bunch of the comet's innards will spew outward at about half the speed that the projectile came in. Over the course of about 200 seconds, more material will be excavated, carving a hole as big as a football field and seven stories deep.
Before impact, the comet will be visible in a good amateur telescope. But the freshly ejected material will enlarge the halo of debris around the comet, off of which sunlight reflects, and it will brighten dramatically.
"It should be easily visible in good binoculars, and it might be easily visible with the naked eye," A'Hearn said in a telephone interview.
The impact will be strong enough to alter the comet's orbit, and there has been some public concern over whether humanity's impact of a comet might alter its orbit enough to cause it to threaten Earth.
No such retribution is possible, A'Hearn said. The comet's present orbit would never come within 50 million miles (80.5 million kilometers) or so of our planet, and the force of the probe's impact won't change that by more than 330 feet (100 meters).
Pristine target
The point of the impact, of course, is to learn about comets. But comets never sit still. At least not until they crash into a planet or something.
This propensity to threaten their neighbors -- which can make a planetary mess of things -- makes comets supremely interesting to scientists, who still know very little about what's inside the icy bodies with their long, wacky orbits around the Sun. Some comets travel a fifth of the way to the next nearest star.
And then there's the fact comets hoard a vault of pristine information about the formation of the very planets they like to smash into. The recent breakup of a comet provided researchers with an unprecedented view of its nucleus, and scientists were thrilled at
what they learned.Along with ground-based observations, a camera and an infrared spectrometer on the Deep Impact mother ship will watch the action. A'Hearn said that after the mother ship has transmitted all the data back to Earth, which will take about two days, the craft is slated to be abandoned to wander through the solar system.
"There are currently no plans" to utilize the mother ship for any further purpose, A'Hearn said.
Comet Tempel 1, the target, was discovered in 1867. It's what is called a short-period comet, orbiting the Sun every five and a half years.
Scientists are eager to learn whether comets exhaust their supply of gas and ice to space or seal it into their interiors. They would also like to learn how a comet's interior is different from its surface.
Creating a crater in a comet is also expected to teach researchers how craters form.
A side benefit of the mission is that it will teach researchers something about how to deflect a comet or asteroid, in the event that one ever is heading our way.
Pressure release
A'Hearn was relieved that the mission had been approved. He and his colleagues have spent the past three to four months scrambling, trimming expenses and pushing numbers around to make sure the mission would be under budget with sufficient reserves to cover unforeseen costs.
"One kind of pressure is now gone," he said, "and it's replaced by another kind of pressure." That would be getting the craft built and ready to launch on time.
Ball Aerospace Technology Corp will build the spacecraft, and the mission will be run out of NASA's Jet Propulsion Laboratory in Pasadena, California.
Sister missions
Deep Impact is the seventh mission in NASA's Discovery program, which seeks lower-cost, highly focused missions. The first of these was the 1997 Mars Pathfinder lander and rover. More recently, the Near Earth Asteroid Rendezvous (NEAR) spacecraft orbited Asteroid 433 Eros for a year, then in a late change of plans
landed on it on Feb. 12, 2001.The other Discovery missions:
- The Lunar Prospector orbiter mapped the Moon's composition and gravity field. It completed its highly successful mission in July 1999.
- The
Stardust mission to gather samples of comet dust and return them to Earth was launched in February 1999 and is on its way to Comet Wild 2. The Genesis mission to gather samples of the solar wind and return them to Earth is scheduled for launch on July 30, 2001. The Comet Nucleus Tour (CONTOUR) mission is planned to fly closely by three comets. It is scheduled for launch in June 2002.
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