Life's ingredients in space
Posted: Monday, August 07, 2006 8:07 PM by Alan Boyle
The Green Bank Telescope in West Virginia hasn't yet found radio signals from alien life, but it has picked up other kinds of unexpected signals from space: the chemical signatures of biologically significant molecules, swirling around in the clouds from which stars and planets are made. The discovery of more and more organic compounds in interstellar space has led researchers to suspect that if life were to develop somewhere else in the universe, it wouldn't have to start from scratch.
The growing list of naturally occurring ingredients for biology "suggests that a universal prebiotic chemistry is at work," the leader for the Green Bank research team, Jan M. Hollis of NASA's Goddard Space Flight Center, said in today's news release from the National Radio Astronomy Observatory.
The NRAO says that the recipe book for interstellar chemistry is known to have 141 different molecular species - with 90 percent of those molecular types containing carbon, and therefore considered part of organic chemistry's repertoire.
Green Bank's 328-foot (100-meter) radio telescope is sensitive enough to detect the molecules by watching how they absorb and emit radiation at specific frequencies as they tumble through space. The latest discoveries are detailed in separate studies appearing in the Astrophysical Journal.
Among those discoveries are acetamide, cyclopropenone, propenal, propanol and ketenimine - all found in a cloud called Sagittarius B2 (N), which is 26,000 light-years away in the galactic center. Acetamide is of particular interest because it contains a chemical bond that can link amino acids together to form proteins.
Another three ingredients - methyl-cyano-diacetylene, methyl-triacetylene and cyanoallene - were detected just 450 light-years away from us in the Taurus Molecular Cloud, or TMC-1. Current observations indicate that the temperature there is on the order of 10 degrees above absolute zero, but the cloud could well condense and heat up to become a star-forming region.
The newly detected molecules contain six to 11 atoms each - certainly not as complex as the long chains that make up DNA molecules, but more complex than scientists would have expected in cold clouds of gas and dust.
"The discovery of these large organic molecules in the coldest regions of the interstellar medium has certainly changed the belief that large organic molecules would only have their origins in hot molecular cores," the NRAO's Anthony Remijan said. "It has forced us to rethink the paradigms of interstellar chemistry."
Scientists have come around to the view that larger molecules can build themselves up from smaller ones in the interstellar clouds. Gravitational attraction can cause the clouds to congeal, potentially cooking up even more complex molecules. This "chemical cycle" may well have been at work in our own solar system.
NRAO |
This graphic shows the "chemical cycle" for molecular clouds: At
upper left, a diffuse cloud of gas and dust becomes denser, and
eventually develops into a protoplanetary dust disk. The disk gives
birth to a star and its planets. At the end of its life, the star sheds
mass - by puffing away layers of material or blowing up in a
supernova - and the cycle begins again with a diffuse cloud.
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"The first of the many chemical processes that ultimately led to life on Earth probably took place even before our planet was formed," the NRAO's Phil Jewell said. "The GBT has taken the leading role in exploring the origin of biomolecules in interstellar clouds."
If that's so, it fits right in with Green Bank's history: Forty-five years ago, the Green Bank Conference was something of a coming-out party for astronomers interested in the search for extraterrestrial intelligence - following up on SETI pioneer Frank Drake's Project Ozma experiments at Green Bank. The NRAO site in the hills of West Virginia was the home of SETI research as recently as 1998, when the SETI Institute switched over to the Arecibo Observatory in Puerto Rico.
So even if E.T. never ended up placing a phone call to Green Bank, the telescope and the scientists who use it nevertheless have made a big contribution to the study of life's origins, here on Earth and perhaps elsewhere in the universe. For more on the subject, check out NASA's Origins Web site, this archived Web exhibit on astrochemistry, and Astrobiology magazine's report on "Building Life From Star-Stuff."
