Astronomers' understanding of stellar evolution takes a step forward with Jason Cardelli's 1994 publication showing the abundances of the heaviest elements, including thallium and lead, yet detected in interstellar dust.
To make a planet, start with an interstellar cloud of ice-covered dust and gas. Then add random turbulent processes to create structure within that cloud. A portion of the mixture can become dense enough to collapse under its own weight and begin star formation. The material that doesn’t collapse forms a disk that rotates around the protostar. Eventually, the dust and gas in the disk start to aggregate, forming planets, as well as asteroids and comets.
The dust grains have carbonaceous or silicate cores encased by ices composed of frozen compounds such as water and carbon dioxide, and the chemistry that occurs on their surfaces is key to understanding the chemistry of newborn planets. But “it’s only recently that the astronomy and astrochemistry communities have embraced the role of grain surfaces,” said Thomas Orlando, a chemistry professor at Georgia Institute of Technology and co-organizer of a symposium on astrochemistry at the American Chemical Society national meeting in San Francisco last month. “There’s now a full realization that the grain surface is very important in the formation of even the simplest molecules and could be at the heart of the formation of bigger molecules,” such as polyaromatic hydrocarbons (PAHs), Orlando said.
The molecular species that astrochemists look at tend to be simple—H2, CO, HCN, CH4, C2H2, and NH3, for example—but groups are also working to identify and understand more complex compounds. Much chemistry on interstellar dust particles is driven by radiation, in particular ultraviolet light and X-rays from protostars and cosmic-ray particles. Astrophysicists and astrochemists both observe the compounds present in space—principally through ground-based and satellite telescope observations—and try to emulate astronomical conditions in laboratory experiments.
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Excerpted with permission, Chemical & Engineering News
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