Common meteorites come from two debris fields: Study

The most common meteorites that fall to Earth -- known as L chondrites -- come from at least two different debris fields in the asteroid belt, a study has found. According to the study published in the journal Meteoritics and Planetary Science, the belt contains many debris fields created from former dwarf planets, or those in the making, that collided long ago. These fragments, called asteroids, continue to collide, producing the meteorites that fall to Earth today. "When meteorites fell near Creston, California on October 24, 2015, they initially seemed to be from the same debris field as those that fell three years earlier in Novato, 200 miles to the North," said Peter Jenniskens, a researcher at NASA's Ames Research Centre in the US.

"Both meteorites were classified as L chondrites of type L6 and shock stage S3," said Jenniskens.

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L chondrites are the most common type of meteorites, but they come in two varieties: meteorites like Novato that long ago, at the dawn of the solar system, experienced shocks so massive they are now dark in part, and those like Creston that just have some dark veins.

An international consortium of 33 scientists compared the meteorites and found that the meteorite that fell in Creston managed to avoid collisions for a much longer period of time than those that previously fell in Novato.

"Before it fell to Earth, Creston had been in space for about 45 million years, while the Novato meteorites came from a much more recent collision, about nine million years ago," said cosmochemist Kees Welten of University of California, Berkeley in the US.

Scientists are keen to find out where in the asteroid belt those collisions occurred, hoping to identify the asteroid family that spawns our most common meteorites.

When the rock, the size of a large grapefruit, entered Earth's atmosphere near Creston, travelling at a speed of 16 kilometers per second, the blinding light of the fireball was photographed by an all sky camera in Sunnyvale, US.

"To track which direction and from what distance meteorites approach Earth, we operate automated all sky cameras in California," said Jenniskens.

"The project is now part of a larger Global Fireball Observatory in collaboration with Curtin University in Australia. This was the first meteorite fall photographed by the new project at a time when we were still testing the cameras," Jenniskens said.

The meteor was also captured, serendipitously, from the pier in Goleta, California by photographer Christian M Rodriguez, providing its track from a different perspective.

Triangulation of the two tracks revealed that both the Creston and Novato meteorites approached on shallow inclined orbits relative to the plane of the planets, but Novato took three years to circle the Sun and Creston only 1.5 years.

That suggests Novato was delivered by a resonance further from the Sun and deeper into the asteroid belt. As soon as orbits resonate with that of Jupiter or Saturn, they can rapidly change into orbits that meet Earth.