Ancient meteorite upends our ideas of how Mars formed

 

Ancient meteorite upends our ideas of how Mars formed
Mars as captured by the Mars Global Surveyor probe's camera NASA/JPL/MSSS

Early Mars may have obtained essential volatile components like hydrogen and oxygen from meteorite collisions rather than a cloud of gases, according to a meteorite study.

Our understanding of how Mars arose is being challenged by a meteorite that crashed on Earth more than 200 years ago. In contrast to what was previously believed, a new analysis of it shows that the Red Planet's inner chemical composition was mostly derived from meteorite strikes. As a result, the early creation of Mars is comparable to that of Earth.


Shergotty, Nakhla, and Chassigny are three Martian meteorites that fell to Earth after being blasted off Mars by impacts. They provide the majority of the information we have on Mars' mantle, the region of rock outside the planet's core.

The Chassigny, which arrived in France in 1815, has already been examined using isotopes of xenon, a chemically inert gas that can last unmodified for millions of years. These isotopes, which are atoms that differ by how many neutrons they have, exist in particular ratios that are linked to a location and a period.


The solar nebula, a massive cloud of gas from which the early solar system emerged, and Mars' atmosphere both appear to have isotope ratios that are similar to those of the meteorite. This gave rise to the theory that the solar nebula provided the volatile elements of the Red Planet, such as hydrogen, carbon, and oxygen, and that later meteorites provided other elements.

Now, using a high-resolution mass spectrometer, Sandrine Péron at the ETH Zurich in Switzerland and Sujoy Mukhopadhyay at the University of California, Davis, have examined a sample from Chassigny to look at isotopes of krypton, another inert gas, which enables more accurate measurements.


The precise source of volatiles can be identified with xenon isotopes, but not with krypton, according to Péron. "With krypton, you can more clearly distinguish between potential sources like meteorites and the sun... It had not been done before because krypton isotopes are more challenging to analyze than xenon isotopes.

The isotopes were discovered by the researchers to have originated from meteorites rather than the solar nebula. According to Péron, this suggests that the Martian atmosphere, which primarily consists of isotopes from solar nebulae, wasn't formed by gases ejecting from the solar-derived mantle as previously believed. So, from where did those gases enter the atmosphere? If the young Mars expanded swiftly and is being gradually freed by impacts, it may be that they were imprisoned in the earth closer to the surface or in the chilly polar caps.

The Natural History Museum in Vienna houses a fragment of the Chassigny meteorite from Mars. Wikipedia, Valugi, CC BY-SA 4.0
The Natural History Museum in Vienna houses a fragment of the Chassigny meteorite from Mars. Wikipedia, Valugi, CC BY-SA 4.0


The research could significantly alter our understanding of how Mars developed and support the idea of planetary formation in our solar system, in which Mars appeared to be an anomaly.

According to Chris Ballentine from the University of Oxford, "It's a major alteration in our understanding of the genesis of volatiles on Mars." The overall result is that Mars appears to have originated and acquired volatile components much more similar to how the Earth did, which provides a more consistent understanding of how planets acquire volatile elements.


Ballentine asserts that comprehending a planet's chemical composition also requires understanding the acquisition and distribution of volatile elements. "The timing and source of the volatiles regulate the oxidation state, which, in turn, controls the structure and distribution of elements in the globe, which is why we can survive on our own Earth," says the author.

Reference: Science, DOI: 10.1126/science.abk1175

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