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Meteorite that landed on Earth 200 years ago upends previous theories of how Mars formed

A meteorite that hit Earth more than 200 years ago could fundamentally change our understanding of how Mars was formed.

Most of what we know about the Red Planet’s interior comes from three space rocks that landed on our planet after being blasted off Mars by impacts.

They include the Chassingy meteorite, which came down in north-eastern France in 1815, and two others known as Shergotty and Nakhla.

New analysis of Chassingy suggests that the interior chemical make-up of Mars largely came from meteorite collisions, rather than from a giant cloud of gas called the solar nebula as previously thought. 

It contradicts current thinking about how rocky planets like the Earth and Mars acquire volatile elements such as hydrogen, carbon, oxygen, nitrogen and noble gases as they form.

Mars is of special interest because it formed relatively quickly — solidifying in about 4 million years after the birth of the Solar System, while the Earth took 50 to 100 million years to form. 

Discovery: New analysis of the Chassingy meteorite (pictured) suggests that the interior chemical make-up of Mars largely came from meteorite collisions, rather than from a giant cloud of gas called the solar nebula as previously thought

MARS: THE BASICS

Mars is the fourth planet from the sun, with a ‘near-dead’ dusty, cold, desert world with a very thin atmosphere. 

Mars is also a dynamic planet with seasons, polar ice caps, canyons, extinct volcanoes, and evidence that it was even more active in the past. 

It is one of the most explored planets in the solar system and the only planet humans have sent rovers to explore.

One day on Mars takes a little over 24 hours and a year is 687 Earth days.

Facts and Figures 

Orbital period: 687 days

Surface area: 144.8 million km²

Distance from Sun: 227.9 million km

Gravity: 3.721 m/s²

Radius: 3,389.5 km

Moons: Phobos, Deimos

Scientists had thought that the newly-forming worlds first collected these volatiles from the nebula around a young star, before the elements initially dissolve into a magma ocean and then degass back into the atmosphere while the planet is still a ball of molten rock.

The theory assumes that later on, chondritic meteorites crashing into the young planet deliver more volatile materials.

It had been believed that the volatile elements in the interior of the planet should reflect the composition of the solar nebula, or a mixture of solar and meteoritic volatiles, while the volatiles in the atmosphere would come mostly from meteorites. 

This was supported by previous research into Chassingy which looked at isotopes of xenon, a chemically inert gas which can survive unchanged for millions of years.

The isotope ratios from the meteorite seemed to match those of both Mars’s atmosphere and the solar nebula, which led to the assumption that its volatile elements, such as hydrogen, carbon and oxygen, came from the solar nebula and that additional elements came from meteorites later. 

However, the new study by researchers at the University of California, Davis disputes this.

They analysed a sample from Chassigny but this time looked at isotopes of krypton — a different  inert gas which allows for more precise measurements. 

‘With xenon isotopes, it’s difficult to distinguish the precise source of volatiles, but that’s not the case with krypton,’ one of the study’s authors Sandrine Péron told the New Scientist. 

‘With krypton, you can better see the difference between potential sources like from solar or meteorites… but krypton isotopes are more difficult to measure than xenon isotopes, so that’s why it had not been previously done.’ 

The researchers found that the isotopes came from meteorites rather than from the solar nebula. 

That means that meteorites were delivering volatile elements to the forming planet much earlier than previously thought, and in the presence of the nebula, reversing conventional thinking.

Mars is of special interest because it formed relatively quickly — solidifying in about 4 million years after the birth of the Solar System, while the Earth took 50 to 100 million years to form

Mars is of special interest because it formed relatively quickly — solidifying in about 4 million years after the birth of the Solar System, while the Earth took 50 to 100 million years to form 

‘The Martian interior composition for krypton is nearly purely chondritic, but the atmosphere is solar,’ Péron said. ‘It’s very distinct.’

The results show that Mars’ atmosphere cannot have formed purely by outgassing from the mantle, as that would have given it a chondritic composition. 

The planet must have acquired atmosphere from the solar nebula, after the magma ocean cooled, to prevent substantial mixing between interior chondritic gases and atmospheric solar gases.

The new results suggest that Mars’ growth was completed before the solar nebula was dissipated by radiation from the sun. 

But the irradiation should also have blown off the nebular atmosphere on Mars, suggesting that atmospheric krypton must have somehow been preserved, possibly trapped underground or in polar ice caps.

‘However, that would require Mars to have been cold in the immediate aftermath of its accretion,’ Mukhopadhyay said. 

‘While our study clearly points to the chondritic gases in the Martian interior, it also raises some interesting questions about the origin and composition of Mars’ early atmosphere.’

The study has been published in the journal Science.

Explained: The difference between an asteroid, meteorite and other space rocks

An asteroid is a large chunk of rock left over from collisions or the early solar system. Most are located between Mars and Jupiter in the Main Belt.

A comet is a rock covered in ice, methane and other compounds. Their orbits take them much further out of the solar system.

A meteor is what astronomers call a flash of light in the atmosphere when debris burns up.

This debris itself is known as a meteoroid. Most are so small they are vapourised in the atmosphere.

If any of this meteoroid makes it to Earth, it is called a meteorite.

Meteors, meteoroids and meteorites normally originate from asteroids and comets.

For example, if Earth passes through the tail of a comet, much of the debris burns up in the atmosphere, forming a meteor shower.

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