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A research project at the NSLS has turned to dust – star dust, that is. After months of studying particles collected from a comet passing inside Jupiter’s orbit, a group of NSLS users and scientists has finished its preliminary examination on the dust, revealing details that might help explain the beginning of the solar system.

As part of an international team of more than 175 members, NSLS users and scientists used x-ray, infrared, and ultraviolet light to study the chemical composition and properties of the extremely small dust particles, most less than 15 micrometers in diameter. The diameter of a human hair, in comparison, is about 50 micrometers. Locked within the particles, which were collected from the comet Wild 2 by the NASA Stardust spacecraft, is unique chemical and physical information that provides a record of the formation of the planets and the materials from which they were made.

“Comets represent what’s left over from the primitive solar nebula,” said University of Chicago geochemist Tony Lanzirotti, who worked on multiple aspects of the analysis. “If you want to figure out what the solar system is made out of, that’s where you want to go.”

Working with about a picogram, one trillionth of a gram, of dust, the scientists studied the elemental composition, organic materials, and mineralogy and petrology of the particles at four NSLS beamlines – X26A, X1A1, U10A, and U10B. Their findings, combined with those from other synchrotrons and institutions, were published in three of the seven Stardust papers published in the December 15, 2006 issue of Science Express, the online edition of the journal Science.

The first samples from Stardust arrived at the NSLS in February 2006, suspended within “aerogel,” a silicon-based substance used to capture the particles in space. This sponge-like material is 99.8 percent air and was fit to a tennis racket-shaped collector on the spacecraft. To study the aerogel-encased particles, scientists used extremely tiny and bright infrared and x-ray beams to extract chemical and mineralogical information. Once the particles were extracted from the gel, a powerful x-ray imaging device was used to collect detailed images of some of the smallest particles as well as to determine their elemental makeup. In particular, the scientists looked for the element carbon, which can indicate that the particles contain organic compounds — compounds that may have formed at the birth of our solar system.

Infrared light was used to identify specific minerals within the particles, as well as identify any organic compounds that were detected. Unlike x-ray methods, the information collected using these infrared techniques can be compared with the astronomical observations of distant interstellar dust clouds, including those involved with the formation of planetary systems like ours, said Stony Brook University physicist Sue Wirick, who has worked extensively on the composition of meteorites and interplanetary dust particles.

“To get to look at a comet and compare it to these other things is really exciting,” she said.

One of the main findings of the study is that the materials from which our solar system formed must have undergone a considerable amount of mixing while the sun and planets were forming. “The common perception is that comets come from these really cold regions of the solar system with lots of ice,” Lanzirotti said. “But we found minerals like olivine, high-temperature minerals that on Earth are formed in magma. It really says a lot about the violent early history of the solar system, where you have high-temperature phases being mixed with cold regions of outer space in a very rapid manner.”

The comet dust was found to contain a wide variety of minerals, as well as organic materials. Some of these minerals and organics look similar to those seen in primitive types of meteorites, but both the minerals and the organics show the presence of some new materials not previously seen in meteorites.

One of the biggest challenges was accounting for the deterioration of the dust particles as they crash-landed into the aerogel at 14,000 miles per hour.

“They’re looking at all the little components that were left behind after the particle hit the aerogel, and in the end, they want to get the composition of the original particle,” said NSLS physicist Larry Carr. “The particles are a composite with parts getting ripped off and left behind in the form of a debris trail. It would be like finding a dead body in the woods, along with footprints, pieces of cloth, and hair, and trying to figure out who the victim was.”

“And the body has been torched,” added Wirick.

Another challenge came with the aerogel itself, which contained organic materials that could have been confused during the analyses with the organics in the particles. “To mix this stuff with who knows how many compounds and then try to make sense of it is not optimum,” Wirick said.

Now that the preliminary examination is completed, the samples will be made available to the general scientific community for more detailed study, possibly at the NSLS, where this small amount of dust has caused a great deal of attention.

“To think that we have the capability to go out hundreds of millions of miles away, collect these particles, and then land this thing back in an isolated desert in Utah is just incredible,” Carr said. “It’s just really cool to have a personal connection to a project like this instead of just hearing about it in a newspaper.”

-Kendra Snyder

 

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Last Modified: January 31, 2008