- The Washington Times - Tuesday, December 21, 2004

BALTIMORE — The biggest firework of any Independence Day celebration next summer will be launched this winter.

A University of Maryland spacecraft is to be launched by NASA next month as part of the Deep Impact mission, and is expected to crash July 4 into the comet Tempel 1 with the force of more than four tons of TNT.

Although the two are to collide near the orbit of Mars, the crash may be visible with the naked eye in California, Hawaii, Australia, and parts of eastern Asia, said astronomer Lucy McFadden, a co-investigator in the College Park team leading the program.

Researchers hope the collision will excavate a stadium-size hole and reveal secrets contained in the comet since it was created.

“We’re doing celestial archaeology, digging up the past to see what the solar system was made of 4.5 billion years ago,” Mrs. McFadden said.

The spacecraft is actually two vessels. One, called the impactor, has a camera and will send back pictures until it is destroyed. A companion spacecraft will record the collision.

The Hubble Space Telescope, the Spitzer Space Telescope and the Chandra X-Ray Observatory are expected to observe the crash from space. Several ground-based observatories also are expected to record it.

Although other spacecraft have flown past comets and through the tails that boil off their icy cores, Deep Impact will be the first to make contact.

Mrs. McFadden said the collision is expected to dig up the “oldest and coldest” material from the beginning of the solar system and allow scientists to test theories that comets may have seeded life on Earth by providing the raw materials from which life evolved.

“Comets are treasure chests” from the farthest edges of the solar system, Mrs. McFadden said, containing “the starting materials that have been in a deep freeze since the beginning of the solar system.”

The $330 million mission is part of NASA’s Discovery program, which allows universities to manage spacecraft launched by the space agency. The Deep Impact mission is the first NASA program led by the university’s astronomy department, although Mrs. McFadden, principal investigator Michael A’Hearn and others in the department have participated in other space missions, she said.

Mr. A’Hearn said the collision will not noticeably change the orbit of the comet, but what exactly will happen to the comet is not known. A cone-shaped cloud of debris is expected to be ejected into space. Mr. A’Hearn said that even the shape of the plume of debris will provide clues to its composition.

“It is this uncertainty in the wide range of predictions which makes it important to do this conceptually very simple experiment,” Mr. A’Hearn said.

The researchers in College Park expect to collect 13 minutes of data, including thousands of images and infrared spectrographs, which will reveal information about the material ejected from the core.

After the collision, the data will be shared on the Internet, Mrs. McFadden said.

Mr. A’Hearn said the remaining craft might be steered to another comet after it leaves Tempel 1. But with the impactor destroyed, the second comet would just get a look from the surviving spacecraft.

Keith Noll, an astronomer at the Space Telescope Science Institute in Baltimore, which operates the Hubble Space Telescope, said the orbiting observatory already has been used once to observe the comet for the Deep Impact program.

The space telescope will be used again in late June to observe the comet as the probe approaches.

The June observation will be used to help the craft avoid geysers that erupt from the surface of the comet because of heating from the sun, Mr. Noll said.

“It doesn’t want to fly through one of those geysers if it can help it,” Mr. Noll said.

A geyser could damage the camera before the crash and cloud its view.

A number of proposals for using the Hubble to view the collision are expected, but have not been submitted, Mr. Noll said.

Exactly how far into the comet the impactor will go is not known.

The impactor is packed with ballast made of copper. The metal was used so researchers can distinguish between the remains of the spacecraft and the material from the comet’s core, said Emilia Reed, a spokeswoman for the company that made the spacecraft, Boulder, Colo.-based Ball Aerospace & Technologies Corp.

“It’s a pure metal and they can pull out that signature from the spectrometer readings,” Miss Reed said. “What’s important to the scientists is what comes out of the crater.”

“Knowing what they know about copper they can say, ‘All right, this is vaporized spacecraft and the rest is comet.’ And that little spacecraft will be vaporized; it will be traveling at 23,000 miles an hour at impact.”

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