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Monday, 4 October 2021

Weird hybrid meteorite may be evidence of a chaotic early solar system


A meteorite that fell on Earth more than a century ago may contain some of the first concrete evidence for a cosmic mash-up in the early solar system.

Following the birth of our sun 4.5 billion years ago, it is thought that Jupiter’s formation caused two reservoirs of asteroids to gather in the solar system, one inside the giant planet’s orbit and one outside. The former are known as non-carbonaceous asteroids, because they are traditionally low in carbon, whereas the latter are carbonaceous asteroids, richer in things such as water and carbon that were able to survive further from the sun’s heat.

There had been some evidence that dust from these two reservoirs had mixed, possibly as a result of Jupiter and the other outer planets migrating slightly in their orbits towards and away from the sun as the solar system settled.

Now, Fridolin Spitzer at the University of Münster in Germany and his colleagues have found some of the best evidence yet for mixing. It comes from a meteorite that appears to contain both carbonaceous and non-carbonaceous material. “This implies it’s a mixture between these two reservoirs,” says Spitzer.

This space rock, called the Nedagolla meteorite, fell in India in 1870. It was already unusual in that its chemical composition didn’t match any other meteorites analysed to date, suggesting it didn’t share a common origin with any meteorites on Earth.

When Spitzer and his team studied the meteorite to learn more about its origins, they were surprised to find pockets of the element molybdenum with different concentrations, some corresponding to carbonaceous meteorites and others to non‑carbonaceous ones.

Measurements of the radioactive decay of the meteorite suggest that it formed at least 7 million years after the birth of our solar system. Two asteroids from the inner and outer reservoirs appear to have smashed together to form the meteorite, possibly as a result of Jupiter’s gravitational pull as it moved towards or away from the sun.

“It’s nice to find evidence that this actually happened,” says Spitzer. If the team is correct, it would be some of the first meteoritic evidence that the mixing really took place.

“It’s exciting,” says Harold Connolly at Rowan University in New Jersey. “It’s what we should be able to see if Jupiter was migrating and throwing material in and out of the solar system.”

Other indirect evidence for this migration does exist, says Sara Russell at the Natural History Museum in London, such as the small size of the planet Mars – possibly the result of Jupiter being closer to Mars than it is today and sweeping up material, preventing Mars from growing larger.

“Then there’s the massive diversity of material in the asteroid belt, which is really a jumble of super-ice-rich stuff and stuff that’s at [relatively] high temperature,” says Russell. “You need to have something stirring the pot to mix things up.”

The Nedagolla meteorite would be the first physical evidence of a collision between a pair of asteroids from the two reservoirs, though. Meteorites already in collections on Earth may also contain similar evidence.

“There’s so many parts of the collections that are really unexplored,” says Russell. “I’m sure there are loads and loads of secrets to find out.”

Reference: 

Collisional mixing between inner and outer solar system planetesimals inferred from the Nedagolla iron meteorite by Fridolin Spitzer, Christoph Burkhardt, Jonas Pape, Thorsten Kleine

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