Carbon Found To Be Older Than The Solar System

Contact: Tony Fitzpatrick

314-935-5272
Washington University in St. Louis

Carbon found to be older than the Solar System

For the first time, researchers have identified organic material in
interplanetary dust particles (IDPs), gathered from the Earth's
stratosphere, that was made before the birth of our Solar System.

The material was identified on the basis of its carbon isotopic composition,
which is different from the carbon found on Earth and in other parts of the
Solar System. Isotopes are variations of elements that differ from each
other in the number of neutrons they have, making them similar chemically
but different physically.

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.

"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."

The finding helps in understanding the Solar System's formation and the
origin of organic matter on Earth. The work was published in the Feb. 27,
2004 issue of Science, and was supported by NASA grants.

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.

"The question has always been: Why don't we see any unusual carbon isotopic
compositions?" Floss said. "The thinking was if the nitrogen and hydrogen
isotopic anomalies are formed in the same regions of space, it was logical
to expect unusual carbon isotopic compositions as well. One school of
thought was that there were different fractionation processes with carbon in
opposite directions, that cancelled out any anomalies produced. Another
possibility was that the nitrogen and hydrogen might have been produced in
phases that weren't originally organic - that the organic material itself
was formed in the solar system and basically inherited the hydrogen and
nitrogen isotopic compositions from some precursor material. But our
isotopic analysis shows that the organic material was formed before the
Solar System existed and was later incorporated into the IDP."

Floss and Frank Stadermann, Ph.D., Washington University senior research
scientist in Physics, worked with colleagues at Lawrence Livermore National
Laboratory in drawing their conclusions.

"A lot of IDPs come from comets," Floss said. "It makes sense that organic
material would be preserved in a very cold environment, such as where comets
form at the edge of the Solar System. For something to stay this pristine
and primitive, one can assume that it came from that kind of environment."

Floss said it's estimated that, over a million years, about a centimeter of
carbonaceous material comes in the form of such cosmic dust and a
significant amount of that material may be presolar in origin.

Floss said that her work builds on the pioneering work of the late Robert
Walker, Ph.D., professor of Physics at Washington University. Walker was
instrumental in the acquisition of the NanoSIMS and in the 1980s made
landmark studies verifying the extraterrestrial origin of such stratospheric
dust particles.

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