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Saturday, 6 December 2014

Comet dust found in Antarctica

Researchers have discovered comet dust preserved in the ice and snow of Antarctica, the first time such particles have been found on Earth’s surface. The discovery unlocks a promising new source of this material. The oldest astronomical particles available for study, comet dust can offer clues about how our solar system formed.


A single particle of comet dust collected from Antarctic ice, as seen through an electron microscope

“It’s very exciting for those of us who study these kinds of extraterrestrial materials, because it opens up a whole new way to get access to them,” says Larry Nittler, a planetary scientist in the Department of Terrestrial Magnetism at the Carnegie Institution for Science in Washington, D.C., who was not involved with the research. “They’ve found a new source for something that’s very interesting and very rare.”

Until recently, the only way scientists could collect “chondritic porous interplanetary dust particles,” or comet dust, without going to space has been by flying research planes high in the stratosphere. It’s painstaking work: Several hours of flying time typically yield one particle of dust. Working with such small samples significantly limits the kinds of tests and analysis scientists can perform on the material, says study co-author John Bradley, an astromaterials scientist at the Hawaii Institute of Geophysics and Planetology of the University of Hawaii, Manoa.

The researchers found a bigger haul of the particles in Antarctica, he notes. “Two to four more orders of magnitude mass of material is potentially collectible this way,” he says. “I think it could precipitate a paradigm shift in the way these kinds of materials are collected.”

The dust gathered in Antarctica is also cleaner. Right now, scientists gathering comet dust by plane use plates coated with silicon oil to trap the particles like flies in flypaper. That leaves them contaminated with both the oil and the organic compounds later used to clean them, making it especially difficult for scientists who want to study what organic material they might contain.

Comparing the particles found in Antarctica with the ones collected in the stratosphere will help scientists figure out which components of the dust are part of their natural chemical makeup and which come from contaminants, Nittler says.

In 2010, a team of French scientists reported that they had found dense, unusually carbon-rich comet particles in the Antarctic snow, but this is the first time more typical comet dust has been found and its identity confirmed. Scientists had thought the highly porous, extremely fragile particles couldn’t survive on Earth.

To find them, the researchers collected snow and ice from two different sites in Antarctica over several years, starting in 2000. By melting the ice and filtering the water, they collected more than 3000 micrometeorites, tiny particles from space that were 10 microns in diameter or larger. Analyzing the micrometeorites one by one under a stereomicroscope over a period of 5 years yielded more than 40 particles with the characteristics of comet dust. A closer analysis found they were indistinguishable from comet dust collected in the stratosphere, and they also matched samples collected from the coma of a comet by NASA’s Stardust mission in 2006, the researchers report online ahead of print in Earth and Planetary Science Letters.

“Our result shows that such fragile particles can be preserved not only in … snow, but also in ice,” says the study’s lead author, Takaaki Noguchi, a meteorite researcher at Kyushu University in Fukuoka, Japan.

A good next step would be to make a more detailed analysis of the organic material in the particles, says meteorite researcher Cécile Engrand of the Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse of Paris-Sud University in Orsay, a co-author of the earlier French research. “The study of these cometary particles will help shed more light on the material that served for planetary formation,” she says. “They are the best witnesses that we have of that period of time.”