the age of Martian meteorites
Scientists in Yale's Department of Geology and Geophysics have devised a method to date precisely the timing and temperature of a meteorite impact on Mars that led to ejection of a piece of the planet into space and its eventual impact on Earth.
Meteorites are the main source of mass exchange between planets and carry with them characteristic clues about the nature and history of the planets or planetesimals where they originated, the impacts that dislodged them and the time they spent in space.
Kyoungwon Kyle Min, postdoctoral fellow in geology, reported an innovation for determining the timing and temperatures of ancient impacts that liberated meteorites from extraterrestrial bodies such as Mars.
To measure both the age and thermal history of the piece of Martian rock, Min assayed the natural radioactive decay of uranium and thorium to the gas helium in these meteorites, and combined it with knowledge of how temperature affects helium loss over time. The researchers used this (U-Th)/He dating method on single grains of minerals in the so-called "Los Angeles" Martian meteorite in order to get a far more accurate picture than the conventional method of analyzing chunks of meteorite. The "helium age" of about three million years corresponds with the estimated cosmogenic space exposure age.
According to co-author Peter W. Reiners, assistant professor of geology and geophysics, "The three million-year age of this meteorite is also important because other meteorites we're working on, including some Martian ones, are several hundred million to billions of years older. These methods allow us to better understand both the timing and dynamics of ancient impacts on other planets, and how these events relate to interplanetary material transfer."
Scientists have long looked at meteorites to answer the question of whether there is now, or once was, life on Mars. They now can compare data from meteorites with the observations of space vehicles to learn more about past activities on the surface of Mars.
Stefan Nicolescu and James Greenwood from Yale co-authored the study, which was supported by a grant from the National Science Foundation.
-- By Janet Rettig Emanuel
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