NASA/JPL-Caltech/T. Pyle

Primordial soup.
Astronomers are finding more protoplanetary disks, like the one in this artist's conception, that contain organic chemicals and water vapor.

A Solar System That Looks Like Home

A disk of gas and dust 450 light-years away bears a close resemblance to our early solar system, astronomers report. The region contains relatively large quantities of some of the most important basic building blocks of life, and these are concentrated at a potentially habitable distance away from the parent star. The finding should provide new insights into how life managed to arise in our own neighborhood.

Over the past couple of decades, astronomers have been able to detect hundreds of disks of dust and gas surrounding very young stars, which signify new planets in the making. The key to understanding the evolution of these protoplanets--and whether they might spawn life--lies in getting a closer look. "Until now, it has only been possible to see gas very near the star or very far from it," says astronomer Dan Watson of the University of Rochester in New York. But the enhanced instruments aboard NASA's Spitzer Space Telescope are breaching that barrier in a critical way: by detecting extremely subtle differences in wavelengths of infrared light, enough to isolate the nature and quantities of simple organic molecules.

Astronomers John Carr of the Naval Research Laboratory in Washington, D.C., and Joan Najita of the National Optical Astronomy Observatory in Tucson, Arizona, used Spitzer to tease out the signals revealing the molecular composition of the gas in the disk surrounding AA Tauri, a star less than a million years old located in the constellation Taurus. The spacecraft's sensitive spectrometer was able to register the chemical signatures not only of water vapor but also of hydrogen cyanide, carbon monoxide, and carbon dioxide--all precursors of the more complex molecules that scientists think eventually gave rise to life on Earth. Other astronomers have detected these molecules before in interstellar space, but the researchers report in tomorrow's issue of Science that they have pinpointed the location of these molecules in AA Tauri's disk, which means they might have been manufactured there. They are in a zone located about three times the distance from the star as Earth is from the sun--still close enough, theoretically, to coalesce into more complex molecules from which life could spring. This is the first time simple organic molecules and water have been found lurking around another star at Earth-like distances, the team reports.

"The abundance [of the molecules] we measured provide new clues to how molecules are created, destroyed, or transported in disks," Najita says. "These clues may ultimately help us answer questions such as whether the chemical precursors for life are commonly created in planet-forming disks." Carr adds that these are critical details for "understanding the details of how both Earth-like and Jupiter-like planets are formed."

The study represents "a major advance in our understanding of protoplanetary disks and their evolution," Watson says. And astronomer Zoltan Balog of the Steward Observatory in Tucson, Arizona, says he thinks the research "basically means that protoplanetary disks might be able to produce prebiotic molecules and ultimately the basic building blocks for life at the place where an Earth would form."

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