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What is the true age of pieces of Mars that landed on Earth?

true-age-of-martian-meteorites

This question was a long-standing puzzle in Martian science which is now answered by a team of well-equipped geologists. They directed energy beams at tiny crystals found in Martian meteorite and discovered that the most common group of meteorites from Mars is almost 4 billion years younger than many scientists had believed. The discovery also showed a much clearer picture of the Red Planet's evolution that can now be compared to that of Earth. 

In a paper published yesterday in the journal Nature, lead author Desmond Moser, an Earth Sciences professor, Kim Tait, curator at Royal Ontario Museum, and a team of Canadian, U.S., and British collaborators show that a representative meteorite from the Royal Ontario Museum (ROM)'s growing Martian meteorite collection, started as a 200 million-year-old lava flow on Mars, and contains an ancient chemical signature indicating a hidden layer deep beneath the surface that is almost as old as the solar system

The team  also discovered crystals that grew while the meteorite was launched from Mars towards Earth, allowing them to narrow down the timing to less than 20 million years ago while also identifying possible launch locations on the flanks of the supervolcanoes at the Martian equator.

Moser and his group at Western's Zircon & Accessory Phase Laboratory (ZAPLab), one of the few electron nanobeam dating facilities in the world, determined the growth history of crystals on a polished surface of the meteorite. The researchers combined a long-established dating method (measuring radioactive uranium/lead isotopes) with a recently developed gently-destructive, mineral grain-scale technique at UCLA that liberates atoms from the crystal surface using a focused beam of oxygen ions.

Moser estimates that there are roughly 60 Mars rocks dislodged by meteorite impacts that are now on Earth and available for study, and that his group's approach can be used on these and a much wider range of heavenly bodies. 

"Basically, the inner solar system is our oyster. We have hundreds of meteorites that we can apply this technique to, including asteroids from beyond Mars to samples from the Moon," says Moser, who credits the generosity of the collectors that identify this material and make it available for public research.

But how do pieces of Mars end up on Earth? The only natural process capable of launching Martian rocks to Earth is meteorite impact. Mars’ surface has numerous impact craters of various sizes and ages. To be ejected from Mars, a rock must reach the escape velocity of 5.4 km/sec, which is more than five times the muzzle velocity of a hunting rifle. An impact capable of ejecting the Martian meteorites would have left a crater 10-100 km across. The fragments of Mars spent several million years in space before landing at various sites on Earth.

Sources: Western University, NASA

Featured image: Science @ NASA

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