杏吧原创

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鈥檚 formation caused two reservoirs of asteroids to gather in the solar system, one inside the giant planet鈥檚 orbit and聽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聽things such as water and carbon聽that were able to survive further from the sun鈥檚 heat.

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

Now, at the University of M眉nster in Germany and his colleagues have found some of the best evidence yet for聽mixing. It comes from a meteorite that appears to contain both carbonaceous and non-carbonaceous material. 鈥淭his implies it鈥檚 a mixture between these two reservoirs,鈥� says Spitzer.

This space rock, called the Nedagolla meteorite, fell in India in 1870. It was already unusual in聽that its chemical composition didn鈥檛 match any other meteorites analysed to date, suggesting it didn鈥檛 share a common origin with聽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鈥慶arbonaceous 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鈥檚 gravitational pull as it moved towards or away from the sun.

鈥淚t鈥檚 nice to find evidence that this actually happened,鈥� says Spitzer. If the team is correct, it聽would be some of the first meteoritic evidence that the mixing really took place.

鈥淚t鈥檚 exciting,鈥� says at Rowan University in New Jersey. 鈥淚t鈥檚 what we should be聽able to see if Jupiter was migrating and throwing material in and out of the solar system.鈥�

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

鈥淭hen there鈥檚 the massive diversity of material in the asteroid belt, which is really a jumble of super-ice-rich stuff and聽stuff that鈥檚 at [relatively] high聽temperature,鈥� says Russell. 鈥淵ou need to have something stirring the pot to mix things up.鈥�

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

鈥淭here鈥檚 so many parts of the聽collections that are really unexplored,鈥� says Russell. 鈥淚鈥檓聽sure there are loads and loads聽of secrets to find out.鈥�

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