The dust particles, collected in the upper atmosphere by NASA aircraft, contain remnants of materials that existed during the formation of the solar system 4.5 billion years ago. By studying these complex particles, scientists hope to gain insight into the history --and the prehistory --of the solar system.
Scott Messenger, Ph.D., senior research scientist in physics at the University's McDonnell Center for Space Sciences, suggests that the high D/H ratios are due to the presence of material surviving from the molecular cloud that gave birth to our solar system. The high ratios result from a process called isotopic fractionation, which takes place during chemical reactions at low temperatures, where the difference in mass between deuterium and hydrogen becomes important.
From the D/H ratios, Messenger infers that an environment with "extremely low temperatures must have been present during the formation of this material, and not many places in the universe have such conditions," he said. "This must take place in vast molecular clouds, light years across, the birthplace of stars."
Messenger's preliminary results appeared in the journal Nature, and he presented an update at the American Chemical Society's August annual meeting in Washington, D.C.
One of the goals for this work is to use these particles as probes of interstellar material --to study molecular cloud chemistry in the laboratory. Such materials must have survived the violent processes of solar system formation, and remained unaltered for billions of years on their parent body (comet or asteroid).
Determining how pristine this material is remains a more difficult question. But the isotopic differences provide an important clue. "Isotopic evidence and understanding the chemical form of the deuterium-rich materials is crucial," Messenger said. "You have to know that before determining where things come from.
"If you find material that hasn't changed or been compromised isotopically in some way, you'd have material from all over the galaxy," he explained.
Unfortunately, the dust particles collected are on the order of nanograms in size, and determining the individual chemical composition of material that small still remains an unsolved challenge for modern technology. When complete chemical analysis becomes possible, scientists will be able to make inferences about the composition of interstellar clouds as well.
Currently, IDPs are the only source of cometary materials, but the Jet Propulsion Laboratory's Stardust spacecraft is now en route to collect material from comet Wild-2. The spacecraft will catch dust particles from the tail of the comet in January 2004 and parachute them in a re-entry capsule back to Earth in 2006.