Blasting Into the Core of a Comet to Learn Its Secrets

NY Times ^ | January 11, 2005 | WARREN E. LEARY

[neverdem]

WASHINGTON, Jan. 10 - Since the earliest days of the solar system, comets have periodically smashed into Earth, blasting holes in the surface and scattering cosmic debris. Now it is our turn to strike back.

On Wednesday, NASA is to launch a spacecraft called Deep Impact toward the comet Tempel 1. In six months, if all goes well, the craft will release an 820-pound copper-core "impactor" that will smash into the comet's nucleus at 23,000 miles per hour, excavating a crater that scientists say could be as large as a sports coliseum.

Launching of the spacecraft from the Cape Canaveral Air Force Station in Florida has twice been delayed because of software concerns and problems with the Boeing Delta 2 booster rocket. If the mission does not get off the ground by Jan. 28, the $330 million project will have to be delayed for months while a new target comet is selected.

The collision planned for July 4, expected to eject tons of comet material into space, will be more than a kind of celestial fireworks display for the nation's 229th birthday. Scientists say this first direct contact with the core of a comet should free some of its pristine inner material for their first true view of what makes up these icy bodies.

"The point of Deep Impact is to get down to the ice and material at depth in a comet and determine its properties and characteristics," said Dr. Michael A'Hearn of the University of Maryland, the principal investigator for the project. So little is known about the structure of comets that scientists are not sure exactly what will happen when Tempel 1 is hit, he said, although they expect a cone-shaped cloud of debris to be ejected into space.

If comets, which are bodies of ice, rocks and dust, are somewhat porous and not tightly packed, as Dr. A'Hearn suspects, Deep Impact should produce a crater about 100 feet deep and 300 feet in diameter. If the comet is like packed snow, the probe, striking with the force of 4.5 tons of dynamite, could penetrate 300 feet or more but create only a small surface crater, he said. There is even an extremely remote possibility that the comet could be so porous that the impactor goes right through it like a bullet.

"We're just going to hit it and see what happens," Dr. A'Hearn said.

Impact by the washing-machine-size probe will not affect the path of the comet, a mountain of an object some 9 miles long and 3.7 miles across, nor break it apart, scientists said.

Deep Impact, built for NASA by Ball Aerospace and Technologies Corporation, is a twin spacecraft made up of the impactor and a flyby vessel containing the most powerful telescopic camera ever put on a deep-space probe, as well as an infrared spectrometer for identifying materials from the comet. About 24 hours before intercepting Tempel 1 some 83 million miles from Earth, the flyby craft will release the impactor into the comet's path and veer away. When the comet literally runs into the impactor, the mother craft will observe the strike from hundreds of miles away. The impact probe, carrying 317 pounds of copper ballast to help it make a significant crater, also includes an imaging system that will take close-up pictures of the comet until just before the collision.

The strike will also be witnessed by scores of observatories on Earth and hundreds of amateur astronomers, who are expected to pool their telescopic observations on the Internet. In addition, NASA's fleet of powerful Earth-orbiting observatories, including the Hubble Space Telescope, the Chandra X-Ray Observatory and the Spitzer Infrared Space Telescope, will record the event.

Because of the distance, neither the comet nor the impact will be visible to the naked eye on Earth.

Comets are believed to be remnants of the materials that formed the solar system some 4.5 billion years ago. Astronomers think the interiors of comets have undergone little change since then and contain the pristine ice, gases, dust and other materials from which the rest of the solar system formed.

Another reason to study comets and their structure is that they, along with asteroids, pose the threat of striking Earth and causing cataclysmic damage. Potential planetary defense requires knowing more about these objects in hope of deflecting or destroying dangerous ones.

[neverdem]

Ball Aerospace/NASA
A drawing of Deep Impact, to be launched tomorrow toward Tempel 1.

3 Giant Stars May Point the Way to Our Sun's Destiny

[neverdem]

ping

[RightWhale]

Because of the distance, neither the comet nor the impact will be visible to the naked eye on Earth

Others say the impact may be visible to the naked eye. If not for this, the mission would be of no interest.

[billorites]

"We're just going to hit it and see what happens," Dr. A'Hearn said.

That was my dating strategy from 1972-1980.

[weenie]

Blasting Into the Core of a Comet to Learn Its Secrets...

OK, I've blasted inside...now what secrets am I looking for..?

[ProudVet77]

Heads up for the Cassini descent in 3 days.

http://www.esa.int/SPECIALS/Cassini-Huygens/index.html

[neverdem]

FReepmail me if you want on or off my health and science ping list.

[Verginius Rufus]

Events in space don't have to be visible to the naked eye to be interesting. The Mars rovers aren't visible to observers on earth, but they have sent back very interesting photos. When Comet Shoemaker-Levy 9 collided with Jupiter in 1994, it wasn't visible to the naked eye on earth, but we later saw photos of the impact.

[neverdem]

Thanks for the link.

[Kerfuffle]

"We're just going to hit it and see what happens," Dr. A'Hearn said.

I like the way this guy thinks.