Michael Lipschutz, professor of chemistry who headed the team that discovered the first evidence for a meteoroid stream in 1993, has found a second stream by analyzing a series of meteorites that have crashed to Earth between 1812 and 1992.
"This new stream appears to have deposited meteorites on Earth over two different intervals," Lipschutz says. "Apparently, the Earth intersected the stream's orbit at these points in time, and some of the meteoroids that were traveling in the stream landed on Earth."
He reported his findings in the April issue of the Journal of Geophysical Research-Planets.
Meteorites are the fragments of small objects called meteoroids that survive passage through the atmosphere and fall on the Earth's surface. Theoretically, a meteoroid stream is made up of a group of rocky fragments that are derived from the breakup of a near-Earth object and then travel in space in the same general orbit, Lipschutz says.
"Meteoroids traveling together would likely represent fragments of the same asteroid, thus they would have a similar chemical makeup," he says.
Using this knowledge, Lipschutz was able to link 17 meteorites that fell to Earth in two separate arrays by analyzing the trace elements in the meteorites. Trace elements are chemical markers that are found in very tiny amounts, such as parts per million or parts per billion.
He then compared the contents of the samples with a set of 33 meteorites of similar composition that fell to Earth at random between 1773 and 1970. The 17 meteorites proved to have a chemical makeup that was similar to each other and significantly different from the meteorites in the random falls.
"Only meteorites from a single source could account for these differences," Lipschutz says.
The 17 meteorites fell to Earth in over a period of time in two separate arrays, indicating that the Earth may have intersected two different parts of the stream, Lipschutz says. The first group of meteorites landed from 1812 through 1831, and a second group of meteorites landed from 1843 and 1992. The falls all occurred during the months of September and October.
In addition, several samples from the stream have interesting histories, Lipschutz says.
"The first meteorite fall, called Borodino, fell two days before the famous 1812 battle there, the ultimate result of which was the devastating retreat of Napoleon's army from Russia," he says, "although no mention appears in history treatises of the Napoleonic era."
The most recent fall, which occurred on Oct. 9, 1992, in Peekskill, N.Y., hit a car and was observed and videotaped over a five-state area, Lipschutz says.
The existence of meteoroid streams was first proposed by Lipschutz and colleagues in 1986 to explain chemical differences, such as concentrations of trace elements, between Antarctic and non-Antarctic meteorites.
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