* Astronomy

The origin of the microscopic meteorites that make up cosmic dust has been revealed for the first time in new research out today (1 September 2008).
The research, published in the journal Geology, shows that some of the cosmic dust falling to Earth comes from an ancient asteroid belt between Jupiter and Mars. This research improves our knowledge of the solar system, and could provide a new and inexpensive method for understanding space.
Cosmic dust particles, originally from asteroids and comets, are minute pieces of pulverised rock. They measure up to a tenth of a millimetre in size and shroud the solar system in a thin cloud. Studying them is important because their mineral content records the conditions under which asteroids and comets were formed over four and a half billion years ago and provides an insight into the earliest history of our solar system.

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Each year nearly 40,000 tons of cosmic dust fall to Earth from outer space. Now, the first successful chronological study of extraterrestrial dust in Antarctic ice has shown that this amount has remained largely constant over the past 30,000 years, a finding that could help refine efforts to understand the timing and effects of changes in the Earth's past climate.

The same study also used an improved analytical technique to show that dust carried to Antarctica from continental sources changed depending on climate.
The study, which appears in the July 28 issue of the journal Science, involved researchers from the Lamont-Doherty Earth Observatory, a part of The Earth Institute, and the Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven, Germany. The depth of the core they examined corresponded to the period between 6,800 and 29,000 years before the present day — a span that includes the height of the last glacial period, and the transition to warm conditions similar to today.
The scientists collected particulate matter from the EPICA (European Project for Ice Coring in Antarctica) ice core and measured the concentration of helium-3 (3He), a rare isotope that is plentiful in the sun's solar wind and is carried to Earth imbedded in cosmic dust particles measuring just a few thousandths of a millimetre in diameter. These dust particles carry their exotic helium load to the Earth’s surface where they are preserved in the snow and ice of the polar ice caps, among other places.
Because ice cores from the polar caps provide a high-resolution temporal record of the past, the researchers were able to measure fine variations in the rate of cosmic dust accumulation between glacial and interglacial periods as well as the helium isotope characteristics of these rare particles. They found that the accumulation of cosmic dust did not change appreciably as the Earth emerged from the last great Ice Age and entered the current warm period, a fact that is likely to bolster the use of cosmic dust measuring techniques in future climate studies.
In addition, this was the first study to examine both cosmic and terrestrial dust using the same helium-isotope technique. As a result, they also found that the composition of mineral dust particles carried by wind from the southern continents to Antarctica changed considerably as the Earth's climate changed.

"The terrestrial dust coming down on Antarctica during the Ice Age obviously is not the same as that during warm periods. This may be due to the mineral dust originating from different regional sources or to changes in the process responsible for producing the dust" - Gisela Winckler, a Doherty associate research scientist at Lamont-Doherty and lead author on the study.

The project was supported by the Comer Science and Education Foundation.

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