Scientists eagerly study comet, its debris

Mission to blast Tempel 1 hailed as a great success

July 05, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Smashed by a NASA probe, the comet Tempel 1 spewed jets of gas yesterday as scientists continued to study an impact designed to deepen understanding of the origin of the solar system.

The Deep Impact spacecraft flawlessly launched a probe early yesterday that smashed into the comet at 23,000 mph in one of the most widely watched projects in NASA history.

The impact, just before 2 a.m., created a bright flash, a steady plume of gas jets and an emotional outburst from NASA scientists supervising the mission.

"We had grown men in here crying because they had been thinking of this moment for so long. I certainly cried," said Lucy McFadden, a University of Maryland astronomer and a member of NASA's science team.

The Deep Impact spacecraft released an 820-pound copper projectile about the size of a washing machine, known as an impactor, and then moved into a position to receive images from the impactor as it crashed into the comet 83 million miles from Earth.

The spacecraft, about the size of a car, also relayed images with medium- and high-resolution cameras as it passed within about 300 miles of the comet.

The impactor scored a direct hit - which hadn't been guaranteed - sending out the best images ever recorded of a comet's surface.

McFadden, who had been working on the project since 1998, was one of about 50 scientists and technicians who watched from a control room at the Jet Propulsion Lab in Pasadena, Calif., Sunday night and early yesterday. She said the images beamed from the impact exceeded the expectations of everyone in the room.

"There was this big bright flash and we couldn't believe it. And then there was more and more and more," she said.

McFadden said she had been concerned that the impactor, designed to hit the comet at its brightest spot, might strike only a glancing blow and fail to create the crater, dust and gas debris that were the object of the mission.

The spacecraft was launched Jan. 12 and traveled 268 million miles, keeping the comet in its cross hairs with cameras that used celestial navigation. Two years ago, cost overruns had threatened to kill the $330 million project.

Worth the effort

But NASA scientists and other experts say the project was a success and that the information gathered makes it worth the effort.

"It's hard to imagine what could have gone better," said John C. "Jack" Brandt, a comet expert and retired astronomer from the NASA Goddard Space Flight Center.

Astronomers say that comets hold clues about the formation and evolution of the solar system.

Scientists believe comets have remained largely unchanged since they formed billions of years ago in the Oort Cloud, a region in the distant reaches of the solar system.

Better understanding of the ice, gas and dust that make up a comet could shed light on how the planets formed and how the solar system evolved 4.5 billion years ago.

Earth and other planets offer fewer clues to the origin of the solar system because the heat generated during their formation transformed their composition.

Since 1985, scientists have sent spacecraft past several comets for close inspections, including Halley, Giacobini-Zinner, Borely and Wild2.

While other comets have been observed and imaged with powerful cameras, Deep Impact is the first space mission to pierce a comet's interior.

"It's by far the best look at a comet ever," said Clark Chapman, a planetary scientist at the Southwest Research Institute who was responsible for imaging the Shoemaker Levy comet when it smashed into Jupiter in 1994.

`We touched a comet'

The impact blast was equivalent to the ignition of almost 5 tons of TNT on a comet the size of Manhattan.

"We touched a comet and we touched it hard," said Peter H. Schultz, a Brown University astronomer and a member of the NASA team.

Schultz estimated the crater formed by the impact to be "about the size of a house," but he said he's unsure because the comet is still obscured by the dusty emissions.

Astronomers will spend months studying the flash of the impact, the crater formed, the gases emitted by Tempel 1 and any changes in its heat, brightness and chemistry.

More than 100 space- and ground-based telescopes are trained on Tempel 1, including the Hubble, Spitzer and Chandra X-Ray Observatory.

"This is going to be one of the most closely studied events you could imagine," said Chapman.

NASA scientists told reporters yesterday that how long the comet continues to emit gases depends on what's under the comet's surface. Carbon dioxide and other gases could spew out for a long time, they said, providing an extensive opportunity to study the comet's composition.

"If there's a lot of volatile gases, it could go on for weeks," said Michael A'Hearn, a University of Maryland scientist and the project's principal investigator.

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