7 May 2010

Carbon-rich comet fragments found in Antarctic snow

By
Cosmos Online
Two tiny meteorites recently recovered from Antarctic snow contain comet material dating back to the birth of our Solar System, and may provide clues about the delivery of organic matter to Earth.
Collecting snow in Antarctica

One of the researchers collects clean snow from a trench near the CONCORDIA Antarctic
station. Credit: J Duprat/CSNSM-CNRS

SYDNEY: Two tiny meteorites recently recovered from Antarctic snow contain material dating back to the birth of our Solar System, and may provide clues about the delivery of organic matter to Earth.

Researchers believe that these micrometeorites likely came from the cold, comet-forming outer regions of the gas and dust cloud that comprised the early Solar System, and sample its composition.

Discovered in 2006, the particles measure less than 0.25 mm across and survived their journey through Earth’s atmosphere relatively unscathed. More importantly, scientists found that they contain unusually high amounts of organic matter.

New family of interplanetary objects

“We don’t know so much about the cold regions of the protoplanetary disk where the icy objects of the Solar System formed,” said Jean Duprat of the Centre for Nuclear Spectrometry and Mass Spectrometry at the University of Paris, lead author of the study published in the journal Science.

“These micrometeorites represent a new family of interplanetary objects because they have a very high carbon content,” he said.

Many scientists believe that the organic compounds necessary for life on Earth could be delivered by cometary material, and this study supports how it is possible.

Much of what we know about the formation of our Solar System comes from asteroids, which fall to the Earth in larger, more easily obtained chunks. But scientists recognise that fragments such as comet dust preserve the Solar System’s history better since they formed in a region cold enough to incorporate more of the volatile components of the protosolar disk.

Comet dust hard to come by

Comet dust, however, is much harder to come by. NASA’s Stardust mission in 2004 was the first to collect comet dust, returning ancient particles from comet 81P/Wild2 to Earth for study. Finding comet remnants on the Earth’s surface is difficult.

“If you want to understand what happened in the outer part of the disk of gas and dust that once surrounded the young sun, you first need to have samples that have not changed too much for the last 4.5 billion years [when our Solar System formed],” said Duprat.

Yet his team found material of comparable chemical composition to the comet dust in fragments that are much larger and easier to analyse.

Meteorite hunters flock to Antarctica where ice transports and concentrates larger meteorites at the margins of flows. This dynamic environment pulverises fragile micrometeorites, however.

To find these sub-millimetre-scale particles, Duprat and colleagues melted and sieved untainted snow that fell near the French-Italian CONCORDIA station in central Antarctica between 1955 and 1970.

High concentrations of organic matter

Using electron microscopy, the French team found that the two micrometeorites in the study contain extremely high amounts of carbon. Scientists typically see such high concentrations of organic matter in material of interstellar origins.

However, the structure of silicate minerals contained in the micrometeorites suggests that they formed within the Solar System. “Such materials help us to draw the difficult conceptual line between our Solar System and what predates it,” said Duprat.

Seeds of life

The high carbon content of the particles may provide more evidence for comets as the initial source of organic material on an early, sterile Earth. The discovery of these micrometeorites show how bits of organic material can be delivered to Earth with minimal alteration.

Duprat and others say that the process that generated the organic material within the micrometeorites is yet to be explained. “It definitely opens more questions that it answers,” said Trevor Ireland, planetary scientist at the Australian National University in Canberra, who was not involved with the study.

“It’s an interesting result,” he added. “Organic matter from [such] cometary material could’ve been the seeds of life.”

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