A rare Martian meteorite could rewrite our theory of how planets form

A rare Martian meteorite could rewrite our theory of how planets form

It was 8 a.m. on October 3, 1815 when a space stone was seen falling mercilessly from the sky in Chassigny, north-eastern France, accompanied by loud bangs that shook the ground. The meteorite, from Mars, was called Chassigny and turned out to be no ordinary rock.

A recent analysis of the meteorite led by Sandrine Péron, a postdoctoral researcher at ETH Zürich, Switzerland, revealed results that suggest how rocky planets like Earth and Mars acquired volatile (life-forming) elements, including hydrogen, carbon, oxygen and nitrogen. , and the noble gases.

But these results contradict our fundamental understanding of how our planets form, according to a recent study published in the journal Science.

In other words, it could change much of what we know about planetary science.

It turns out that Mars formed faster than Earth

Mars is of particular interest to those studying early planetary formation. “Earth formation took about 50 to 100 million years,” said Professor Sujoy Mukhopadhyay of the Department of Earth and Planetary Sciences at the University of California, Davis. THAT’S TO SAY in an interview. “Mars, on the other hand, formed more rapidly, within a few million years. Mars may therefore provide us with a window into volatile delivery and accretion in the inner Solar System during the early stages of the formation of the planet. planet.”

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“We can piece together the history of volatile delivery over the first million years of the solar system,” Sandrine Péron, working with Mukhopadhyay, said in a statement.

Older models and their observations on planet formation

According to current models, planets are born from the debris of a star. The dust that accumulates contains carbon and iron, essential for the formation of planetary systems. Around a new star, clumps of matter smash and collapse into each other in the swirling disk of gas and dust called a solar nebula.

Within the disk, dust and gas clump together in a process that develops into a proto-planet. However, not all of these objects become planets – some clusters remain small and inactive like asteroids and comets.

The models indicated that “as a planet grows and reaches the size of Mars, or a little larger, the growing planet can capture the nebular gases from the swirling gas cloud in which the planets grow and dissolve those gases into a ocean of magma,” Mukhopadhyay said. .

Current hypotheses indicate that rocky planets contain elements with the same chemical characteristics both in the interior of the planet and in the atmosphere. Some of the volatile elements later degas back into the atmosphere.

When the ocean of magma – which covers the planet – cools, the “nebular signature” is imprinted inside the planet. Additional volatiles are also released into the atmosphere when meteorites crash into the young planet.

“After the nebula dissipates, the chondrite volatiles (including water, carbon, nitrogen) are delivered to the planets,” Mukhopadhyay said.

These birds are essential – on Earth they helped develop and sustain life.

Among the planets, Jupiter and Saturn are said to have a head start among their “peers”. They formed rapidly – during the first few million years or so of the solar system’s existence.

After the formation of the gas giant planets, there was not much gas left for planets like Mercury, Venus, Earth and Mars. Most of them then took tens of millions more years to form. However, Mars is of particular interest because it is believed to have solidified about 4 million years after the birth of the solar system, about 50 to 100 million years before the formation of Earth.

New study of an ancient space rock

For their study, Péron and Mukhopadhyay compared two Martian sources of krypton, a noble gas, because its isotopes contain information about the sources of volatile substances.

One was from Chassigny, a native of the Martian interior. The other krypton isotopes used were taken from Mars’ atmosphere by NASA’s Curiosity Rover.

“This particular meteorite, Chassigny, is the only one from a noble gas perspective that can provide access to the Martian interior composition,” Péron said. Vice. “All of the other Martian meteorites we currently have in the collection are totally or heavily influenced by Martian atmospheric composition. If we want those pure interior components, this is the only meteorite we have so far.”

However, because of its low abundance, krypton is quite delicate to measure and difficult to separate from argon and xenon. However, Péron and Mukhopadhyay used a new technique, which uses a cryogenic method to “cleanly” separate the gas. “Additionally, we used the latest generation of a mass spectrometer to accurately measure krypton isotopes,” Mukhopadhyay revealed.

To their surprise, the krypton signatures didn’t match.

“Because atmospheric krypton looks like [that also found in] the Sun, we certainly did not expect to find krypton from chondritic meteorites inside Mars. It seemed a bit retrograde to us to have meteoritic gases inside and solar (nebular) gases in the atmosphere,” Mukhopadhyay said.

(A chondritic meteorite is a meteorite that has been formed when dust and small grains at the beginning of the solar system accumulated and did not melt.)

The team’s observations of the meteorite challenged the sequences of events for volatile delivery and accretion “by indicating that chondritic volatiles are not added only at the later stages of planet formation”, said said Mukhopadhyay.

Surprising details revealed at the heart of the rocky planets

The results indicated that Mars’ atmosphere could not have formed solely by “mantle outgassing, as that would have given the atmosphere a chondritic composition,” Mukhopadhyay explained.

Researchers suspect the planet must have acquired its early atmosphere from the solar nebula after the ocean of magma cooled and at least partially solidified.

“We have suggested that the accretion of the nebula’s solar gases occurred after the solidification of the magma ocean, to prevent substantial mixing between the interior chondrite gases and the solar gases in the atmosphere, since the solidification of the magma ocean causes substantial outgassing If Mars were to capture nebular gases to form its early atmosphere after the magma ocean partially solidified, this indicates that Mars’ growth was complete before the nebula had collapsed dissipated due to irradiation from an early energetic sun,” Mukhopadhyay explained.

The order of events would then be, accordingly, that Mars acquired an atmosphere from the solar nebula after its global magma ocean cooled. Otherwise, the nebulous and chondritic gases would be more mixed than what the team discovered.

Mukhopadhyay then added: “Our observations mean that the meteorites delivered volatile elements to Mars much earlier than previously thought and in the presence of the nebula. Our observations also suggest that the formation of Mars was completed before the nebula has dissipated (the nebula is dissipating due to radiation from the early energetic Sun).”

But that raises another mystery.

Irradiation from the Sun would have had to blow through Mars’ nebular atmosphere, “requiring atmospheric krypton to have been somehow preserved, possibly trapped underground or in polar ice caps. However, this would require that Mars was quite cold immediately after its rise,” he added.

Breaking down the planet formation theory

The study highlights that there is so much more to learn about planetary formation.

“Our study raises interesting questions about the origin of Mars’ early atmosphere, its composition, and whether surface environments on Mars might have been suitable for early habitability,” Mukhopadhyay said.

Finding out how volatile elements are acquired and distributed is also key to understanding a planet’s chemical makeup, said Chris Ballentine of the University of Oxford. new scientist. “The timing and source of volatiles controls the state of oxidation, which in turn controls the structure and distribution of elements on the planet, which for our own Earth is why we can live.”

Scientists hope to make further observations of other Martian meteorites to get a detailed picture of their interior composition.

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