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March 18, 1997
Michael Lipschutz, professor of chemistry who has analyzed trace elements in 11 of the 12 known Martian meteorites, says the samples contain a different mix of volatile elements than do rock samples from Earth, indicating that the Red Planet was created from a different nebular womb.
"It looks like the cloud of gas and dust from which Mars was born contained more volatile elements such as thallium, bismuth and cadmium than did the cloud from which Earth was formed," Lipschutz says.
Prior studies of the oxygen isotopes in the Martian meteorites indicated that they all came from the same planet. But other studies, using nonvolatile chemical markers, had revealed differences in their composition, indicating that the samples had encountered different experiences as the planet formed and evolved.
"Our study is the first to show that the characteristics revealed by the nonvolatile elements are also present in the volatile elements," Lipschutz says. "That is to say that these meteorites share some common characteristics, but due to differences in their composition, they belong to the three separate categories that are commonly used to distinguish these meteorites."
He presented his findings today (3/18) at the 28th Lunar and Planetary Science Conference in Houston.
Lipschutz, who has studied the solar system and meteorites for more than 30 years, based his findings on studies of 15 trace elements in 11 of the 12 meteorites identified as originating from the planet Mars. He will complete studies of the 12th meteorite this spring.
His studies of the Martian meteorites focused on the volatile trace elements, the chemical elements that were most likely to condense last as the planet solidified from a cloud of dust and gas.
Trace elements and ultratrace elements -- especially volatile ones found in parts per million or parts per billion -- can yield important information about a meteorite because the composition levels are so low that even the smallest change induced by a physical or chemical transformation is magnified into a relatively large change.
In addition, the samples from Mars show that the planet has experienced at least two fractionation events -- events that separate the volatile trace elements from the non-volatile elements, Lipschutz says.
"The amazing thing is that whatever chemical fractionation events Mars experienced, all of the elements -- volatile or not -- were able to remain and record the events," he says. "This is unlike the situation in other extraterrestrial bodies where late heating, caused for example by the shock of an impact, can vaporize the volatile elements and destroy evidence of past events. In the case of some of the meteorites from the moon, chemical elements were introduced by events such as volcanism, which also clouded the historical record."
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