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November 3, 2008
Seeking clues to life in stardust

By carol clark

It is now widely theorized that meteorites and comets brought water and basic biological materials to the early Earth, creating a primordial soup from which more advanced life emerged. But how did these biological materials form? And what are the chemical processes and ingredients needed to wind up with DNA?

Emory is one of a handful of universities in the country probing space for the answers to these questions, through an astrochemistry program launched by Susanna Widicus Weaver.

“We know that meteorites contain amino acids and sugars, the basic building blocks of life,” says Weaver, assistant professor of physical chemistry. “These small molecules are out there, and somehow we ended up with life. But at what point did the chemistry cross over into the more biologically important molecules, and why did that happen? Was Earth just a coincidence, with all the conditions right to form DNA?”

A Hubble Space Telescope photo of the Orion Nebula, a breathtaking swirl of dust and gases, hangs in her office. “I don’t get pretty pictures like that. I get a spectrum,” she says, pointing to a radiograph. “Each line in the graph represents a specific frequency, which corresponds to the rotational transition of a molecule.”

The results may not look spectacular, but when Weaver aims a radio telescope at the stardust in the Orion Nebula, she is seeking the ingredients of life. “It’s fascinating to go back to the beginning and try to look at the very first molecule that formed, and then try to figure out how life evolves, using the interstellar medium as a model for what could have happened on Earth,” she says.

Astrochemistry draws on astronomy, laboratory spectroscopy and chemical modeling to study chemical mechanisms in space. Weaver, who received her Ph.D. from Caltech and joined Emory this fall, is skilled in all three of these specialized areas.

“She is developing the technology to look at things we’ve never been able to look at before, within the largely unexplored terahertz range,” says David Lynn, chair of chemistry. Lynn is also co-leader of The Origins Project — a joint effort by Emory and Georgia Tech to understand what molecules were present on pre-biotic Earth. The astrochemistry program extends the reach of The Origins Project into deep space, billions of years beyond the Earth’s formation.

Weaver is interested in certain transient molecules — bridges to the formation of simple molecules of sugars and amino acids. She theorizes that the transient molecules

are present in deep space. On Earth, however, they are unstable, existing only for the blink of an eye.
Weaver is developing methods to make the molecules and keep them stable in a laboratory environment. She is also developing a high-sensitivity spectrometer that works in the terahertz range — the transmission frequency of the transient molecules. Recording the spectral “fingerprints” of the molecules in the lab will provide a guide to search for them in space.

Weaver is a frequent visitor to the Mauna Kea Observatory on the Big Island of Hawaii, where she acquires terahertz spectra with a 10.4-meter radio astronomy dish. When the Herschel Space Observatory is launched next year, providing the first terahertz instrument in space, she will have more chances to seek matches to her lab data.

She hired four undergraduates to join her three graduate student researchers. The students are now setting up the astrochemistry lab in the basement of Atwood. Three one-ton tables with pneumatic legs have been installed. On one of them rests a length of PVC pipe that the students helped outfit to do spectroscopy. It will serve as a test model, until the arrival of equipment needed to build the terahertz prototype.

“We’re actually helping make things,” says Mary Radhuber, a freshman majoring in physics and chemistry. Radhuber had never heard of astrochemistry until she met Weaver, but she was eager to join the lab. “I always wanted to be on the forefront of something new, and now I am,” she says.