Purdue News

September 17, 1993 Noblesville Meteorite Beats The Odds WEST LAFAYETTE, IND. — A meteorite that beat one-in-a-million odds of being seen as it hit Earth has proven to have even rarer characteristics. The Noblesville meteorite, named for the Indiana location where it fell in 1991, is unusual in its age, type and size, says a Purdue University researcher who analyzed the fragment. "This meteorite has beaten the odds in a number of ways," says Michael Lipschutz, professor of chemistry. "Chemical and physical analyses of the specimen indicate that it took a turn off the beaten path long before reaching Earth." Details of the findings are outlined in the September issue of the journal Meteoritics, which is published by the Meteoritical Society. Studies of the radioactive and stable elements in the specimen indicate it came from a larger rock fragment — an asteroid — that dates back 4.5 billion to 4.6 billion years, around the time that the solar system was formed. In addition, analyses of the meteorite's cosmic-ray exposure indicate that the piece that fell to Earth broke away from the asteroid almost 45 million years ago. "Forty-five million years is an usually long time for a small fragment to exist in space," Lipschutz says, noting that such fragments often are broken apart by collisions with other objects in space. "Only three percent of all meteorites of this type, known as H chondrites, are that old." Though the Noblesville rock resembles H chondrites in chemical makeup, it shows low levels of radiation damage, indicating that its cosmic orbit took the meteorite through an unusually close passage to the sun, Lipschutz says. "The sun tends to 'bake-out' radiation damage caused by cosmic rays and other sources," he explains. "This heating process causes atoms in the meteorite to return to the state they were in before the radiation damage occurred." In addition, the prompt retrieval and analyses of the meteorite make it the "freshest" specimen to date, giving scientists a rare glimpse of a meteorite as it exists in space. "There's always a concern that by the time a meteorite is found, it will have absorbed water and oxygen on Earth, thus changing the chemical makeup of the specimen," Lipschutz says. "Because this specimen was retrieved immediately, it is, chemically speaking, as fresh as you can get without going to space to retrieve one." The meteorite was recovered by two boys who were standing in a yard in Noblesville on Aug. 31, 1991, heard a whistling sound and saw the meteorite land about 11 feet from where they stood. They called Purdue to have the rock analyzed. Lipschutz sent it to the Meteorite Processing Laboratory at NASA's Johnson Space Center, where it was described and photographed. Small pieces of the rock then were sent to Purdue and other institutions for further studies. The bulk of the meteorite was returned to Brodie Spaulding, who had retrieved the meteorite from his front yard. Lipschutz conducted a chemical analysis of the sample in several Purdue laboratories, including the Purdue Rare Isotope Measurement Laboratory. Such studies can provide information about a meteorite's age and history. The meteorite also may provide clues to the formation of our solar system, Lipschutz says. Studies of the specimen suggest that it originally existed as a layer of fine dust on the surface of an asteroid, and later compacted to form a rock-like exterior. Research under way in Zurich, Switzerland, aims to trace the fragment's history as a dust to look for clues to gases and particles present at the time the solar system was formed. Purdue News Service: (765) 494-2096; purduenews@purdue.edu