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Geology professor maps multimillion-year journey of Mars meteorites

It is unclear where exactly on Mars the samples came from, Lapen said. | Isabel Pen/ The Cougar

A million years after a celestial object smashed into Mars, splintering part of the planet and launching debris into deep space, professor of geology Thomas Lapen is examining the rock samples born from the collision that found their way 30 million miles to Earth.

Using isotope geochemistry, Lapen was able to piece together formation, composition and a probable timeline of these rocks that managed to escape their birthplace on Mars in a recent publication in the journal Science Advances.

“We’re getting a pretty significant chunk of information about how the planet works over a long period of time and about what the mantle is like that partially melted to produce the lavas that eventually make it to the surface to form the largest volcanoes in the solar system,” Lapen said.

While Lapen and his team used the minute physical details and textures of the Martian meteorites, also called shergottites, to learn about the formation of the rock itself, the key to Lapen’s remote exploration of the largest volcanoes in the solar system lay in some of the smallest bits of nature: isotopes.

By analyzing quantities and specific types of these elements with differing numbers of neutrons, Lapen was able to deduce countless invaluable sets of information.

Details about the meteorites, such as the timeframe in which the samples were formed, how long they were in space and how long ago they landed on Earth, were all determined by examining the isotopes present in the rock samples.

After analyzing the isotope data, Lapen found there was a group of shergottites — a type of igneous rock that has fallen to earth as a meteorite — that, despite having different individual ages, were ejected from the surface of Mars together around 1.1 million years ago.

Lapen and his team concluded one of the samples he was analyzing, NWA 7635, was 2.4 billion years old — far older than the other rocks from the same ejection event.

“It seems like NWA 7635 came from one location on Mars with 10 other shergottites that share a similar chemical composition,” said UH lab supervisor and paper co-author Minako Righter. “These meteorites provide information about a single location on Mars suggesting that there was at least two billion years of volcanic activity on Mars.”

Researchers may know that these rocks came from the same volcanic area of Mars, but they have no way of knowing to which specific volcano the meteorites belong.

“We know that the samples that we studied as meteorites are Martian because they contain trapped Martian atmosphere and gasses,” said Anthony Irving, a collaborator on the project and affiliate professor at the University of Washington. “But until we go to Mars and bring a sample back, we won’t know exactly where they come from.”

Craters, which can often show a record of a planet’s bombardment, are not as useful in this instance, Lapen said. Because recent lava flows can overwrite existing craters, a characteristic smooth topography is common among Martian locations that experience igneous activity.

Though taking a core sample of the Martian surface is not logistically feasible at the moment, Lapen and his team plan to continue to study other shergottites in order to extrapolate more of the unsolved history of the planet.

“It’s a way of sampling the layered crust without drilling, without going out there and then being able to evaluate the geochemistry of that volcanic center that was active for billions of years,” Lapen said.

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        • “Lapen and his team plan to continue to study other shergottites in order to extrapolate more of the unsolved history of the planet.”

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