Scientists find 'ultra-primitive' particles in comet dust
3 Nov
2009, 1415 Hrs
Washington, November 3 In a new study, samples of comet dust collected by high-flying aircraft in the upper atmosphere have yielded an unexpectedly rich trove of relicts from the ancient cosmos.
The stratospheric dust includes minute grains that likely formed inside stars that lived and died long before the birth of our sun, as well as material from molecular clouds in interstellar space.
This "ultra-primitive" material likely wafted into the atmosphere after the Earth passed through the trail of an Earth-crossing comet in 2003, giving scientists a rare opportunity to study cometary dust in the laboratory.
At high altitudes, most dust in the atmosphere comes from space, rather than the Earth's surface. Thousands of tons of interplanetary dust particles (IDPs) enter the atmosphere each year.
"We've known that many IDPs come from comets, but we've never been able to definitively tie a single IDP to a particular comet," said study coauthor Larry Nittler, of Carnegie's Department of Terrestrial Magnetism.
"The only known cometary samples we've studied in the laboratory are those that were returned from comet 81P/Wild 2 by the Stardust mission," he added.
The Stardust mission used a NASA-launched spacecraft to collect samples of comet dust, returning to Earth in 2006.
Comets are thought to be repositories of primitive, unaltered matter left over from the formation of the solar system.
Material held for eons in cometary ice has largely escaped the heating and chemical processing that has affected other bodies, such as the planets.
However, the Wild 2 dust returned by the Stardust mission included more altered material than expected, indicating that not all cometary material is highly primitive.
The IDPs used in the current study were collected by NASA aircraft in April 2003, after the Earth passed through the dust trail of comet Gregg-Skjellerup.
The research team analyzed a sub-sample of the dust to determine the chemical, isotopic and microstructural composition of its grains.
"What we found is that they are very different from typical IDPs," said Nittler. "They are more primitive, with higher abundances of material whose origin predates the formation of the solar system," he added.
The distinctiveness of the particles, plus the timing of their collection after the Earth's passing through the comet trail, point to their source being the Gregg-Skjellerup comet.
"This is exciting because it allows us to compare on a microscopic scale in the laboratory dust particles from different comets," said Nittler.
"We can use them as tracers for different processes that occurred in the solar system four-and-a-half billion years ago," he added. (ANI)
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