430 km long field filled with meteorites

Asteroid more than 200 tons crashed to Earth with a special flight path, creating a series of meteorite fragments scattered in a large area.

The largest piece of the Aletai meteorite, weighing 28 tons, was found by a farmer in 1898.

A long time ago, the asteroid Aletai plunged into the atmosphere above the Altay region of present-day Xinjiang, the heat shock ripping it into pieces and creating one of the world's largest iron meteor showers.

The fragments - some weighing 20 tons, others weighing several tens of kilograms - were scattered over a large area stretching about 430 km, making it the longest meteorite field the world has ever recorded. This place is unlike any meteorite field scientists have ever seen: Meteorite fragments from the same parent are usually located no more than 30-40 km apart.

Using numerical modeling, an international team of scientists from China, the US and Europe found that Aletai may have entered the atmosphere at a low angle and had a flight path similar to that of a rock sliding across a lake. The new findings were published in the journal Science Advances at the end of June.

"This is the first time such a unique orbit has been identified. This orbit explains why the asteroid Aletai has the longest meteorite field ever recorded. The meteorite field is an elliptical region with meteorites from a single crash," said Thomas Smith, an expert at the Institute of Geology and Geophysics at the Chinese Academy of Sciences, who was not involved in the study.

The new study also helps explain why meteorites do not create craters when they collide with the ground. That's because energy was expended during the long flight, Smith added.

The research results will help scientists more accurately assess the impact and risk of asteroids based on their orbits, and point out where more debris can be found. from Aletai.

In the new study, the international team of experts used different combinations of initial mass, speed and angle of impact to simulate the asteroid's orbit. They found that Aletai was 2.1 to 4.7 meters wide and weighed more than 200 tons. It moves at a speed of 43,200 - 54,000 km / h, entering the atmosphere at an angle of 6.5 - 7.3 degrees.

"The angle of impact is important. If it were steeper or flatter, the asteroid would either create a much shorter meteorite field, or bounce back into space," said Hsu Weibiao, an expert at the Purple Mountain Observatory. co-author of the study, explained.

To date, more than 74 tons of meteorite fragments from Aletai have been recovered. The largest piece discovered by a farmer in a ditch in 1898 weighed 28 tons. Many iron meteorites have been found in the area since 2004, but scientists initially did not realize they originated from the same asteroid. By 2015, Hsu and colleagues compared the mineral and trace element compositions of the three largest fragments. They found them to have similar characteristics and named them Aletai.

Aletai still has a lot to study, such as when the meteor shower occurs. "The 'ground age' of the Aletai meteorites can be relatively short and difficult to quantify in the laboratory," Smith said. The team also said that their model may change as more Aletai meteorite fragments are collected in the future.