New Carbon Compounds Found in Space

By William J. Cromie

Gazette Staff

Earthlings are a carbon-based form of life. No plant or animal can survive without it. So the recent discovery, by Harvard researchers, of strange forms of carbon in their laboratory and in nearby space is of more than passing interest.

"We're not finding strange science-fiction chemistry," notes Patrick Thaddeus, professor of astronomy and applied physics. "It's the same organic chemistry we know on Earth, but with some exotic variations and twists."

The fact that this kind of chemistry is smeared all over our galaxy must inevitably be connected to the origin of life on Earth and, perhaps, elsewhere.

"The nature of that connection is, at this point, purely speculative," Thaddeus cautions. "We don't have solid facts yet that tie specific carbon molecules in space to the start of life on Earth. But we do have the first chapter in the history of organic chemistry on the grand scale of the universe."

Cosmic Chemistry
Well-known and unfamiliar forms of carbon have become much easier to find thanks to an ultrasensitive instrument built by Michael McCarthy and Michael Travers, postdoctoral fellows at both the Harvard Smithsonian Center for Astrophysics and the Division of Applied Sciences. Their device is a spectrometer that accurately detects frequencies broadcast by electrically charged molecules spinning unseen in dark clouds of gas that occupy large areas of the Milky Way. These high-frequency radio waves serve as fingerprints to identify individual molecules, the way a radio station is identified by tuning to a specific number on a dial.

"Such radio fingerprints are so incredibly sharp and precise that no scientist would question the identify of the broadcaster," Thaddeus says.

Travers and McCarthy developed a way to simulate an interstellar molecular cloud in the laboratory, using gases such as acetylene and argon. They then use the spectrometer to tune in on various carbon molecules made in the gases. The technique can identity the source of broadcasts picked up by powerful radio antennae, or telescopes, in places like West Virginia, Spain, and Australia. Alternately, signals generated in a laboratory cloud may reveal the presence of previously unknown carbon compounds, whose actual existence in space can be verified with such telescopes.

About 12 years ago, Canadian skywatches detected what appeared to be the largest molecule ever found in space. It was identified as a long, straight chain of 11 carbon atoms with a hydrogen atom at one end and a nitrogen atom at the other. Recently, McCarthy and Travers used their spectrometer to try to detect this huge carbon in a laboratory cloud. They couldn't find it.

Suspecting that the Canadians had not actually found a new molecule at that frequency, the Harvard team scanned nearby frequencies. The spectrometer, sensitive enough to pick up a signal from one molecule through the static of dozens of others, finally tuned in a signal that apparently matches the big carbon. The Canadians agree that their original finding is spurious. Now they and others are searching the dark sky on the new frequency.

Thaddeus feels confident that the wayward molecule will be found at the new location on the celestial dial. He and his team have found seven other carbon chains in the laboratory this year, and they are certain that these new molecules also will be detected. One of them is a Brobdingnagian chain of 13 carbon atoms, which measures nearly a tenth of a millionth of an inch long. This giant would be, by far, the biggest known molecule in the heavens.

"The first of eight molecules found in the lab by our team was found in space just a few months ago," Thaddeus notes. "I have just received an e-mail message from our collaborators in Europe that a second one has just been detected by an antenna in Spain. I am confident that the others, including the biggest one to date, will be found within the next year or two."

His team includes research associate Carl Gottlieb and two undergraduate students, Attila Kovacs '97 and Peter Kalmus '97.

Precursors of Life?
The carbon finds would add to what Thaddeus calls a "stockroom of 110 familiar and unfamiliar chemicals" found in space by radio astronomers. They include water, alcohol, ammonia, carbon monoxide, carbon dioxide, and most recently, acetic acid, which gives vinegar its piquant flavor. Molecules such as ammonia and acetic acid, both of which contain carbon, can combine to produce amino acids, the basic building blocks of proteins. On Earth, the formation of amino acids in warm, shallow waters is considered one of the first steps on the evolutionary road to life.

Amino acids and other carbon compounds might have arrived on Earth aboard meteorites or comets. Scientists have discovered gigantic molecules, containing 60 carbon atoms arranged in the shape of soccer balls, in impact craters in Canada. This adds to speculation that blazing visitors from space carried the seeds that sparked our origins.

In the past two years, evidence of a half-dozen planets has been detected beyond our solar system. Carbon molecules might also have landed on such other worlds. If these planets boast the right conditions, some forms of Earthlike or unearthly life may have taken hold there.

"These sorts of connections are plausible," Thaddeus remarks, "but an enormous gulf exists between a dilute smog of carbon compounds in space and living cells capable of getting food and reproducing themselves on a planet. The origin of life is one of the most profound mysteries facing science, and we lack both the facts and understanding needed to solve it."

In the meantime, Thaddeus and his colleagues are trying to piece together the kind of chemistry that goes on beyond Earth and the rest of the solar system. In another project, he, Thomas Dame, a lecturer in astronomy, and Lambertus Hartmann, a visiting scholar from Holland, scan molecular clouds with a small radio telescope located on the roof of the Center for Astrophysics. These clouds are not static blotches of gas and dust, but dynamic celestial wombs where nature conceives and births new stars. One cloud, trillions of miles across and located in the constellation Orion, gave birth to several sunlike star less than 100,000 years ago, when humans were already spreading across Earth.

Inside the clouds, gravity pulls together atoms of hydrogen and dozens of other elements. When the pressure and heat become high enough, hydrogen atoms fuse together, creating a nuclear inferno known as a star.

Some of the stars, dubbed giants and supergiants, run out of hydrogen fuel and burn themselves out more quickly than those the size of the sun. They end their relatively short, bright lives in tremendous explosions called supernovae, scattering their ashes across trillions of miles. These ashes contain many elements including carbon, iron, nickel, and other atoms from arsenic to zinc.

"The carbon in your body comes from this source," Thaddeus notes. "It has floated around in space for billions of years, being recycled through star deaths and rebirths. Roughly 5 billion years ago, some of these ingredients participated in the formation of our solar system and the birth of life."

Thaddeus and Dame scan molecular clouds for the presence of carbon monoxide. "It's a marker molecule," Thaddeus explains. "When we detect its radio signal, we know other carbon molecules exist there. Not only do we find carbon monoxide spread throughout the Milky Way like thunderstorms in a summer sky, we find it in other nearby galaxies. We have detected some of the smaller carbon molecules in our closest neighbors, the Andromeda galaxy and the Large Magellanic Cloud. Colleagues elsewhere found them in more distant galaxies.

"Now that we can read chapter one, we will continue to piece together the story of cosmic chemistry," Thaddeus says. "Someday, that story may reveal how well-known and unfamiliar molecules evolved and what roles they played in the origin of life. We want to see how much of the grand scheme we can learn as passive observers standing on one edge of one of the billions of galaxies."