Outer-space nurseries
Chemistry that gave rise to life on Earth may have begun in outer space. An international research team recently reported the discovery of eight "biologically significant molecules" in two interstellar clouds.
Team leader Jan Hollis at the NASA Goddard Space Flight Center in Greenbelt, Md., says the discovery suggests "that a universal prebiotic chemistry is at work." His colleague Phil Jewell, at the National Radio Astronomy Observatory in Green Bank, W.Va., which made the observations, adds that "the first of many chemical processes that ultimately led to life on Earth probably took place even before our planet was formed."
Many astronomers would have laughed at such statements a few decades ago. They couldn't conceive of complex molecules surviving interstellar space. Then they learned how dust grains provide a base on which complex molecules can form. When molecules float freely, clouds of dust and gas provide protective cloaks. They have now identified 141 such molecules, including the newly discovered "biologically significant" eight, over the past 35 years. Some 90 percent of those 141 molecules are organic, meaning they contain carbon. That's the keystone element for organic life as we know it.
Detecting these molecules is tricky. The way a molecule absorbs or emits radiation creates a distinctive pattern, called its spectrum, in its light and radio emissions. Astronomers compare these spectrums, as seen from Earth, with molecule spectrums recorded in the laboratory. But, as seen from Earth, cosmic spectrums can be a muddle. The spectrum one wants can be lost in a jumble of other emissions. It often can be detected only by radio or infrared observation, since the protecting dust cloud also blocks visible light. Even when detected, the spectrum of the desired molecule may be missing some lines, making positive identification difficult. That is why Dr. Hollis called the unambiguous detection of those eight prebiotic chemicals in just two years "a feat unprecedented in the 35-year history of searching for complex molecules in space."
In its Aug. 7 announcement, NASA says five of the chemicals are in the interstellar cloud Sagittarius B2(N) some 26,000 light-years away, near our galaxy's center. The other three chemicals are in the Taurus Molecular Cloud 450 light-years away. While not part of living organisms, such prelife chemicals help build other molecules that do take part in life processes. For example: Acetamide, one of the eight, can help link up amino acids to form proteins.
Last December, another research team found DNA and protein-precursor chemicals in a young star's "terrestrial zone." That's a zone similar to Earth's distance from the sun, where conditions favor life. The star, IRS 46, is in the constellation Ophiuchus, 375 light-years away. Using NASA's Spitzer Space Telescope, the team found the infrared signatures of acetylene and hydrogen cyanide. Mixed with water and concentrated on a surface, these chemicals yield organic compounds, including building blocks of DNA and protein.
NASA says this is the first time acetylene and hydrogen cyanide have been found in a star's terrestrial zone other than that of the Sun. Team member Fred Lahuis, with the Leiden Observatory in the Netherlands, says that "this infant [star] might look a lot like ours did billions of years ago, before life arose on Earth."
