By Sid Perkins, Science News
TORONTO — New analyses of a meteorite that fell on Tagish Lake in Canada nearly a decade ago suggest that such extraterrestrial bodies may hold much higher concentrations of formic acid, a chemical precursor to life, than previously recognized.
Many simple organic chemicals, including formic acid, have been detected in clouds of dust and gas in interstellar space (SN: 5/1/04, p. 280). But scientists have typically found little if any formic acid in meteorites that formed within similar clouds that coalesced to form the solar system. Robert Hilts, a chemist at Grant MacEwan College in Edmonton, Canada, said it’s probably because the chemical is volatile and evaporates easily at temperatures found at Earth’s surface. Using a technique designed to squelch the evaporation of formic acid during chemical analyses, he and his colleagues have now detected substantial concentrations of the volatile chemical in a meteorite — the highest ever reported, Hilts announced May 24 at a meeting of the American Geophysical Union.
Many pieces of the Tagish Lake meteorite landed on the 3-meter-thick frozen surface of its namesake in January 2000 (SN: 5/19/01, p. 317). Although the body probably weighed about 60 tons when it entered the atmosphere, most of it burned up as it blazed through, Hilts said. Of the hundreds of pieces that have been recovered, typical fragments measure about 1 centimeter across and weigh just a few grams. What makes this meteorite special, however, is that several large pieces were recovered only a week after they fell to Earth, and they’ve never been exposed to temperatures above freezing. In fact, Hilts says, many of the fragments “spent a few years in a Ziploc bag in the freezer of the fellow who discovered them” before Hilts’ team acquired them for analysis.
Bulk analyses of Tagish Lake fragments reveal that the material is about 6 percent carbon, record content for meteorites, says Hilts. Slightly less than half of that carbon is locked in organic chemicals. After extracting those substances with solvents, Hilts and his colleagues increased the pH of the resulting solution and converted the organic chemicals, including formic acid, into less-volatile salts. This process minimized the opportunity for volatile components to evaporate before being detected and measured. Then the team evaporated much of the solvent, converted the salts back into their original form and isolated the chemicals by dipping an adsorbent fiber into the concentrated remnants of the solution.
Subsequent steps in the analyses revealed a number of organic chemicals, including formic acid and related substances such as acetic acid and capric acid, Hilts said. Formic acid concentrations in the fragments average about 200 parts per million by weight, about four times the levels found in the previous record-holder, a meteorite recovered from Antarctica.
Some of the organic substances detected during analyses of the Tagish Lake samples — including plasticizers that probably leached from the Ziploc bag that held the meteorite fragments — were obviously Earthly contaminants, Hilts said. But the ratio of deuterium to hydrogen in the formic acid, a key precursor to the organic chemicals that make up cell membranes, indicates that that chemical had an extraterrestrial origin. The findings bolster the notion that many of the raw ingredients for life on Earth could have been delivered by extraterrestrial bodies, Hilts said.
The team’s results “are very exciting,” says Conel Alexander, a geochemist at Carnegie Institution for Science in Washington, D.C. The new technique used by Hilts and his colleagues offers hope that scientists can now more fully account for all of the organic substances present in a meteorite — chemicals that many previous studies probably haven’t been able to detect because of evaporation during the analyses, Alexander notes.