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News Navigator: Where do meteorites come from and what can we learn from them?

This supplied photo shows fragments of a meteorite that were found in Narashino, Chiba Prefecture, east of Tokyo. (Photo courtesy of the National Museum of Nature and Science)

The Mainichi Shimbun answers some common questions readers may have concerning meteorites.

    Question: I heard that fragments of a meteorite were recently found in Chiba Prefecture, east of Tokyo, right?

    Answer: On July 2, a large fireball was seen crossing the sky in eastern Japan's Kanto region and the central Tokai region. Meteorite fragments were later discovered in the Chiba Prefecture cities of Narashino and Funabashi. It was the first case in Japan where a meteorite was actually found within an area estimated based on the fireball's route. The meteorite's discovery was the 53rd to be recorded in the country. Generally, it is difficult to distinguish between meteorites and regular rocks on Earth, so many meteorites are found in the snow- and ice-covered Antarctic, as well as sandy deserts. About 70% of some 64,000 meteorites registered with the Meteoritical Society were found in the Antarctic.

    Q: Where do meteorites come from?

    A: Many of them are thought to be pieces of asteroids broken off in collisions with other celestial bodies long, long ago. Although there are also rocks that appear to have come from the moon or Mars, they make up only a tiny portion of observed meteorites. Based on comparisons of the rocks' fiery tracks across the sky and asteroid orbits, three small asteroids orbiting close to Earth have been raised as the possible "birthplace" of the meteorite that landed in Chiba Prefecture.

    Q: Are there cases of meteorites hitting people on the ground?

    A: Although there have been cases in the United States and other places where people were hit directly and injured, there have been no clearly confirmed cases of fatalities, and injuries are also highly rare. Meteoroids plunge into the Earth's atmosphere at a speed surpassing 10 kilometers per second, but air resistance eventually slows them down to about the same speed as a stone dropped from a high building.

    Q: What can we learn from meteorites?

    A: Asteroids and meteorites are sometimes called "fossils of the Solar System," and can be used as clues to gain knowledge on how the Earth and other planets formed. The Japanese space probes Hayabusa and Hayabusa2 took on the challenge of collecting samples from asteroids, but if the asteroids from which meteorites break off can be determined, their makeup can be analyzed without sending probes into space.

    (Japanese original by Tomohiro Ikeda, Science & Environment News Department)

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