From an even simpler beginning...tracing life's origins to space

Charles Darwin received ample tribute at the AAAS meeting in Chicago, which opened 200 years after the scientist's birth and 150 years after the publication of his watershed work On the Origin of Species. One speaker took the talk of origins back to a more primal stage, spotlighting the formation of the first organic molecules in the dusty neighborhoods of young stars.

In a 13 February symposium on "The Cosmic Cradle of Life," Anthony Remijan of the National Radio Astronomy Observatory (NRAO) unveiled a new resource that may help astrochemists trace the genesis of the ingredients for life on Earth -- and possibly life elsewhere in the universe.

"We know that complex chemicals exist in interstellar space before stars and planets form," Remijan said. "With the new research tools coming in the next few years, we're on the verge of learning how the chemistry of the interstellar clouds, the young stars and their environments, and the disks from which planets are formed are all linked together to provide the chemical basis for life on those planets."

In 2008, Remijan and his NRAO colleagues launched the Prebiotic Interstellar Molecule Survey (PRIMOS), a large-scale search for new organic molecules in the dilute gases spread between stars. Using the Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, participating scientists scan a star-forming region near the center of the Milky Way Galaxy for radio signals in the 300 MHz to 50 GHz range, which include the many of the telltale "radio fingerprints" of prebiotic compounds.

It's the same basic technique astronomers have used for decades, since NRAO observers first spotted the radio fingerprint of interstellar formaldehyde in 1969. The method exploits a natural property of most organic molecules: they can exist in many rotational conformations, and with a quick twist, they can switch from one form to another. Each transition releases a burst of electromagnetic radiation with a characteristic frequency. Scientists know those frequencies from terrestrial studies, so when a pattern shows up in telescopic data, it's easy to make the match.

In years past, astronomers have searched the skies for the radio signatures of one known molecule at a time. That method identified approximately 130 unique interstellar molecules, about half from signals originating in a star-forming region called Sagittarius B2(N).

The PRIMOS project, which is backed by the National Science Foundation's Center for the Chemistry of the Universe, presents a new strategy. Researchers capture as much radio data as possible from that region, then release the complete set of data for the astronomical community to mine. "This is a major change in how we search for molecules in space," Remijan explained.

The tactic seems to be working. Over the last two years, Remijan's team has identified eight new species, a feat, the group's website says, "that is unequaled in such a short time by any other telescope or observing team in the history of molecular spectral line astronomy."

As of early 2009, the PRIMOS investigators have conducted more than 45 individual GBT observations, producing more than nine gigabytes of data. From that pool, they have singled out 720 spectral lines, of which 240 represent still-unknown species. That means hundreds of fresh questions, and the PRIMOS project has also created a new opportunity for uncovering answers.

Four times a year, the PRIMOS team releases its spectrographic data on the project's website [http://www.cv.nrao.edu/~aremijan/PRIMOS/index.html], where it remains open to scientists and students across the world. The site incorporates a specialized search engine to aid would-be molecule identifiers, called the Spectral Line Search Engine. Users type in a desired frequency range, and the engine churns out a graph of the corresponding spectral data from PRIMOS. Lucky searchers might just recognize a distinguishable fingerprint in that output.

The survey is a major step in cataloguing the biological precursors in the cosmos, but Remijan has more expansive hopes for the future. Foremost on the horizon are the startup of the Atacama Large Millimeter Array and the Expanded Very Large Array, both projected to occur in 2012. The GBT also anticipates a series of upgrades, which the PRIMOS research may help to steer. All three developments will enhance our view of the radio universe, adding still more chemical pieces to the puzzle of life's origins.

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Rachel Carr is a native of Maryland, a recent resident of Michigan, and a current student at the University of Virginia. She will graduate in May with a bachelor's degree in physics and philosophy. She plans to continue writing about science in a fourth state, as yet undetermined. Reach her at rachelcarr@virginia.edu