By Roland Piquepaille
While looking at interplanetary dust particles (IDPs) found in the Earth's stratosphere, researchers from the Washington University in St. Louis have found carbon older than the Solar System. They identified the organic material by its carbon isotopic composition, different from the one of carbon found on Earth. [Isotopes are variations of elements that differ from each other in the number of neutrons they have, making them similar chemically but different physically.]Here is an image of a sample's isotopic structure at a sub-micrometer scale (Credit: Washington University in St. Louis).
Christine Floss, Ph.D., senior research scientist in Earth and Planetary Sciences and Physics at Washington University in St. Louis, said that the organic material in the IDP she and her colleagues analyzed probably was formed in molecular clouds in the interstellar medium before the formation of the Solar System. The isotopic anomalies are produced by chemical fractionation at the very low temperatures found in these molecular clouds.
Here is an image of such a molecular cloud (Credit: Unknown).
"Our findings are proof that there is presolar organic material coming into the Solar System yet today," Floss said. "This material has been preserved for more than 4.5 billion years, which is the age of the Solar System. It's amazing that it has survived for so long."
How did they find this?
Over the past 20 years, researchers have found isotopic anomalies in nitrogen and hydrogen from IDPs but never before in carbon. Floss said one of the reasons for this was the limitations of earlier instruments. She and her colleagues used a new type of ion microprobe called the NanoSIMS, which enables researchers to analyze particles at much greater spatial resolution and higher sensitivity than before. Until recently, ion probes could only measure the average properties of an IDP. In 2000, with help from NASA and the National Science Foundation, the University bought the first commercially available NanoSIMS. Made by Cameca in Paris, the NanoSIMS can resolve particles as small as 100 nanometers in diameter. A hundred thousand such particles side-by-side would make a centimeter. Typical sub-grains in IDPs range from 100 nanometers to 500 nanometers.
For more information about IDPs, please read this page written in plain English. But for much more technical details, read this scientific report (PDF format, 2 pages, very interesting illustrations, 283 KB).
Finally, this research work is published today by Science Magazine. Here is the abstract of the paper called "Carbon and Nitrogen Isotopic Anomalies in an Anhydrous Interplanetary Dust Particle."
Because hydrogen and nitrogen isotopic anomalies in interplanetary dust particles have been associated with carbonaceous material, the lack of similar anomalies in carbon has been a major conundrum. We report here the presence of a 13 depletion associated with a 15N enrichment in an anhydrous interplanetary dust particle. Our observations suggest that the anomalies are carried by heteroatomic organic compounds. Theoretical models indicate that low-temperature formation of organic compounds in cold interstellar molecular clouds can produce carbon and nitrogen fractionations, but it remains to be seen whether the specific effects observed here can be reproduced.
Sources: Washington University in St. Louis news release, February 26, 2004; Science Magazine, Volume 303, Number 5662, February 27, 2004, pp. 1355-1358
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