Smashed comet provides clues to the solar system

Tempel 1 dust is revealing evidence of materials that formed it, scientists say

September 07, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Smashed by a NASA probe this summer, the Tempel 1 comet is yielding clues to the types of materials that formed the early solar system, scientists said yesterday.

Images of dust ejected from the comet show the same type of minerals seen in just-forming solar systems, such as sootlike hydrocarbons, the type of calcium carbonates found in limestone and crystalline silicates.

There is also evidence of aluminum sulfides and iron sulfides, major constituents of the Earth's crust, said Carey Lisse, a member of the Deep Impact team and a senior scientist at the Johns Hopkins Applied Physics Laboratory.

Mostly unchanged

Scientists think comets have remained mostly unchanged since they formed at the birth of the solar system in the Oort Cloud, a frozen region hundreds of thousands of times farther from the sun than Earth. That's why NASA was so eager to examine the insides of Tempel 1.

Lisse said comets such as Tempel 1 probably supplied key ingredients to the solar system in its formative years.

"It's a missing link between what we've seen around these younger, baby stars and solar systems and what we now see around our own," he said.

Lisse used images from the Spitzer Space Telescope, managed by the California-based Jet Propulsion Laboratory, to analyze the dust ejected from Tempel 1. Spectrographs identified specific minerals by measuring the amounts of light given off.

In all, scientists captured images of the impact from 80 telescopes and from the Deep Impact spacecraft.

Michael F. A'Hearn, the University of Maryland, College Park astronomer who is the Deep Impact mission's principal investigator, said it surprised him that Tempel 1 contained so much fine, grainy material that it could have an almost pillow-like surface.

"We learned that the outer layers of the comet, several tens of meters of material, is unbelievably fragile," he said.

Unlike the two other comets whose compositions have been closely studied by NASA - Wild 2 and Borelly - Tempel 1's surface is marked with craters, he said.

Initial findings

A'Hearn and other scientists discussed initial findings with reporters yesterday to coincide with reports they released yesterday and today at an astronomy conference in Cambridge, England. They also will publish studies online Thursday in the journal Science.

NASA launched Deep Impact in January, sending it on a 268 million-mile trajectory that allowed it to intercept Tempel 1's path July 4. The spacecraft released an 820-pound copper projectile about the size of a washing machine, known as an impactor, then moved into position to receive images from the impactor as it crashed into Tempel 1, which is about half the size of Manhattan.

The $330 million project is one of the most closely watched in NASA history.

The 80 observatories trained on the impact worldwide made at least one observation per minute over the 17 days after the impact, said Karen Meech, an astronomer at the University of Hawaii who coordinated the effort.

In addition to seeking clues about the formation of the solar system an estimated 4 billion years ago, the project is intended to shed light on whether ancient comets delivered water and other organic molecules to Earth and gave the planet a start as a home for life.

A'Hearn said dust ejected by the impact shows large amounts of molecules contain carbon, an essential building block for life.

Probe's force

The probe hit the comet with the force of five tons of TNT, forming a crater the size of a football field, A'Hearn said, as it plunged "tens of meters" down into the comet.

The impact spewed out millions of gallons of water in tiny droplets and up to 10 times that much dust.

Deep Impact, in small part, also was intended to better inform scientists about ways to destroy or deflect comets that may threaten to collide with Earth, A'Hearn said.

Knowing the composition of Tempel 1 might help design a missile or other comet-destroying system, he said.

Composition

"Certainly, knowing it's highly porous would help," he said.

The dust and water particles spewed out by impact were so tiny and bright that no images have captured the crater's location.

Researchers are still working on pinpointing the location by enhancing images, A'Hearn said.

He said he hopes NASA will approve a $30 million mission to use the Deep Impact spacecraft to probe the Comet Boethin in 2008. Boethin, discovered in 1975, orbits the sun every 11 years.

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