In the early morning of April 28, 2017, a small fireball crawled across the sky over Kyoto, Japan. And now, thanks to data collected from a SonotaCo meteor survey, researchers have determined that the space rock fire was a particle of a much larger asteroid that could (far down the road) endanger Earth.
The meteor burning over Japan was a tiny one. Studying SonotaCo's data, the researchers found that the object entered the atmosphere at a mass of about 1 ounce (29 grams) and was only 1 inch (2.7 centimeters) long. That didn't threaten anyone. But small meteors like this are interesting because they can offer data on larger objects that spawn them. And in this case, the researchers traced the small rock back to its parent: an object known as YT1
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2003 YT1 is a binary asteroid, composed of a large rock about 1.2 miles (2 kilometers) in orbit from a smaller asteroid 690 feet (210 meters) long. Founded in 2003, the binary system has a 6% chance of hitting Earth at some point in the next 10 million years. This makes the site what researchers call a "potentially dangerous site", although it is unlikely to hurt anyone in their lifetime.
The binary did not cross Earth in 2017, so there was no immediate apparent link between the meteor and its parent. But the researchers studied how the ball of fire moved through the sky and managed to re-engineer the orbit through space, attaching it to the 2003 YT1 with high security.
Researchers have said they are not sure how the rock has split since 2003 YT1, but believe it is part of a larger stream of dust that is rejected by the asteroid. And they offered several potential explanations for how this stream was formed: Perhaps the tiny micrometeorites routinely hit the larger asteroid in the binary, fragmenting it into bullets hitting a rock wall. Or maybe the changes in heat are cracking any of the surfaces of the asteroid, spitting small pieces in the dark.
One of the scenarios the authors propose is that the pieces are the result of the process that first formed the YT1 system since 2003.  Related: Space Tales: The 5 Weirdest Meteorites
Most people probably imagine asteroids as large, large rocks, scaled versions of the stones they would find here on Earth. But 2003 YT1, the authors wrote, is more likely a "pile of rubble", a bundle of gravity-free things that have merged into two orbiting bodies at some point in the last 10,000 years. The forces that hold the masses together as separate asteroids are probably weak, and as the two piles rotate randomly around each other every few hours, they could throw more of themselves into space.
There are other, more exotic possibilities, the authors wrote, Water ice can be sublimated (converted from solid to gas) from one of the surfaces of asteroids and reformed as small pellets of ice in open space. But this and other models are unlikely, the researchers wrote.
We know for now that the Earth is visited by a small piece of a large asteroid. And this small piece is probably part of a stream of other small pieces that sometimes enter the Earth's atmosphere unnoticed. And at some point along the way this large asteroid could follow its young children and hit the Earth. This fireball would be much, much bigger.
The document describing these findings has not yet been verified. The project was published on October 16 in the journal arXiv.
Originally published by Live Science .