CHAMPAIGN, Ill. - In their continuing quest for large interstellar molecules, radio astronomers at the University of Illinois have located dense clumps of formic acid -- the simplest organic acid -- inside the hot star-forming cores in three interstellar molecular clouds.
"On Earth, formic acid is the colorless, pungent liquid found in ant bites, bee stings and nettle bristles," said Lewis E. Snyder, a U. of I. professor of astronomy. "In space, formic acid is of great interest because it shares similar structural elements with the common interstellar molecule methyl formate and the biologically important molecules acetic acid and glycine."
Acetic acid was discovered in space in 1996 by a team of researchers led by U. of I. research scientist David Mehringer and Snyder. Glycine has not yet been confirmed in interstellar space.
Glycine is the simplest biologically important amino acid. "All that is needed to form glycine is to combine acetic acid and ammonia, which was discovered in space in 1969," Snyder said. "So it is plausible that simple amino acids do form in space."
Amino acids are the building blocks of proteins and DNA. Because of the connection between formic acid and glycine, detections of formic acid sources "will provide important constraints on future searches for glycine sources," Snyder said. "We can use formic acid as a Rosetta stone to help identify regions in space where more complex, biologically important molecules might be located."
In interstellar space, formic acid was first identified in 1970 and subsequently studied with single-element telescopes. For the recent measurements, however, graduate student Sheng-Yuan Liu, Mehringer and Snyder used the 10 telescopes of the Berkeley-Illinois-Maryland Association (BIMA) millimeter array near Hat Creek, Calif.
"Interferometric observations of this kind provide the sharpest possible pictures of these regions, revealing the spatial location and distribution of emission from the molecule," said Liu, who presented his team's findings at a meeting in Chicago of the American Astronomical Society on June 3. "We have detected formic acid toward the hot cores in three molecular clouds: Sagittarius B2, Orion and W51."
Hot cores are high-temperature, high-density compact regions in molecular clouds where stars and possibly planetary systems are forming. "These are regions where complex molecules are often found, so they provide a test bed for probing interstellar dust grain chemistry," Liu said.
Interstellar dust grains -- the seeds for the formation of planetary systems -- are thought to have played a crucial role in synthesizing complex molecular species like formic acid, acetic acid and glycine on the early Earth to help start prebiotic organic chemistry.
The formic acid observations were supported by the Laboratory for Astronomical Imaging in the U. of I. astronomy department and the National Science Foundation.
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