UCSD, Stanford Scientists Find Easier Way to Check Meteorites’ Content

A team of scientists at Stanford University and UC San Diego have found an easy way to detect minuscule amounts of organic chemicals inside meteorites, a technique that promises to shed new light on the origin of the solar system as well as to answer more down-to-Earth questions.

The two-minute laser technique could give researchers quick access for the first time to a comprehensive range of clues about how organic chemicals formed in the dusty cloud from which the planets condensed 4.5 billion years ago. It could bolster or debunk the notion that a cosmic rain of meteorites seeded the early Earth with organic compounds, ultimately making life possible here.

It also holds potential as an easy, non-destructive method of analyzing everything from fossils to Martian soil to computer chips.

“The problem with standard chemical techniques for doing organic analyses of meteorites and other rare materials is that they are laborious, destroy the sample and require one to 10 grams of the material to be tested,” said Jeffrey L. Bada, a geochemist at UCSD’s Scripps Institution of Oceanography.

In Fraction of Time

“Our method can reduce the analysis time from a month or more to just a few minutes, and we need only a microgram, or one-millionth of a gram, to do the test,” Bada said.

A report on the new way to analyze meteorites is being published in the journal Science today. Bada co-authored the paper with Richard N. Zare, a Stanford chemistry professor who developed the analytical process, and Stanford graduate students John Hoon Hahn and Renato Zenobi.

“I really believe that this technique might be a breakthrough in what one is able to do in cosmogeochemistry,” Zare said. “Because you are able to analyze such small amounts so sensitively in an almost non-destructive manner.”

Ronald J. Angione, astronomy professor at San Diego State University, said this attribute of such a process would open doors for scientists.

“A lot of meteorites are in private collections, and people simply aren’t willing to let anybody else have any of it. If you’re talking about a milligram, then I think people would be much more willing to allow their sample to be analyzed,” Angione said.

Preserved in Ice

In addition, it might provide an easy way to test the organic content of meteorites that have been preserved in Antarctic ice for millions of years and which researchers recently have begun collecting, said Roy Clarke, curator of the meteorite collection at the National Museum of Natural History in Washington, D.C.

Meteoritic composition is considered important because, when a rock plummets to Earth from space, it carries relatively unaltered information about conditions that existed when planets condensed out of the gas and dust cloud known as the solar nebula. The nature and amounts of organic compounds in meteorites might reflect, for instance, the temperature of the nebula at the time the rocks formed.

“Just the fact that we can detect them now in such a rapid way is going to give us a data base that we didn’t have a year ago” for studying the evolution of organic chemicals, Bada said.

In conventional mass spectrometry, a meteorite chunk as big as 100 grams must be ground up and put through months of processing and purification before the “mass spectrum” of its organic components can be taken, Bada said.

Electrical Charge

The mass spectrometer delivers an electrical charge to the gaseous sample and moves the resulting charged, or ionized, molecules through an electromagnetic field. A detector records their movement through the field, creating a mass spectrum of their molecular weights. These then can be compared to standard tables of molecular weights to identify the sample’s components.

Zare’s technique instead uses laser light to create the ions needed for a mass spectrum.

In the experiment reported on in Science, the surface molecules from about a milligram of ground meteorite--the equivalent of about two grains of sand--were vaporized with an infrared laser. The gas was hit with an ultraviolet laser that selectively ionized it. Again, an electrical field pushed the ions toward a detector to identify them via their molecular weights.

Start to finish, the process takes about two minutes. Further research also has shown it works with a meteorite sample as small as a microgram, a millionth of a gram, Zare said.

Next Step

Bada said the researchers’ next step is to try to test a variety of meteorites to see how their contents of a certain type of hydrocarbon, called polycyclic aromatic hydrocarbons, compare with those of the six samples tested for the Science article.

“We have got one meteorite, and it is loaded with these compounds, but the remarkable thing is this only has three of them, whereas other ones have 10 or 12,” Bada said.

Such patterns haven’t been apparent in the past because so few meteorites could be tested for their specific organic contents. As patterns emerge, they might lead to conclusions about how conditions in the solar nebula evolved as planets formed.

Bada said he is especially excited about the possibility of being able to analyze the hydrocarbon content of a meteorite that fell in 1860 in France. A piece of it has been stored in a partial vacuum since then to prevent contamination by Earthbound organics, Bada said. “They’ve never opened it because analyzing it would destroy it,” he said.

From a more practical standpoint, Zare said, using different lasers in his mass spectrometer would give it a wide range of applications in science and industry.

“The same technique can be applied to looking at fossils or various geological formations, or to prospect to see if rocks contain oil,” Zare added.

Because the laser method does not break the organic molecules apart, it also might be useful in helping biomedical researchers identify proteins and hormones in minute amounts, Zare said. This could be particularly valuable for companies that make genetically engineered products, “to know how pure what they make is.” Similarly, it might provide a way to test for impurities in computer chips.

Bada, a marine geochemist, and his research group at Scripps are building a system similar to the Stanford one to study organic compounds in ocean sediments and polar ice. They will be looking for extraterrestrial compounds brought to the Earth by meteorites over millions of years.

Some scientists suspect that meteorites brought organic chemicals to Earth necessary for life to begin.

The meteorite work was an exciting test of the new spectrometry technique, Bada said.

“There are very few experiments that you do in your life that come out so perfectly as this did,” he said. “We did the whole experiment in three days and wrote the paper in a week.”