Early in the morning of April 28, 2017, a small fireball crawled across the sky over Kyoto, Japan. With the data from the SonotaCo meteor survey, researchers have now discovered that the fiery space rock was a sliver of a much larger asteroid that could threaten Earth (far away).
The meteor that burned over Japan was tiny. Based on the SonotaCo data, the researchers found that the object, with a mass of about 1 ounce (29 grams) and a diameter of only 1 inch (2.7 centimeters), entered the atmosphere. It threatened nobody. But small meteors like these are interesting because they can provide data about the larger objects they produce. In this case, the researchers traced the small stone back to its parent: an object known as the 2003 YT1
The binary file was not released from Earth in 2017, so there is no immediate obvious link between the Meteor and its parents. The researchers, however, studied how the fireball moved across the sky and was able to rebuild the object's orbit through space, setting it at 2003 YT1 with a high degree of certainty.
The researchers said they were not sure how small they are The rock split off from 2003 YT1, but is thought to be part of a larger stream of dust thrown off the asteroid. And they provided some possible explanations for the genesis of this stream: perhaps tiny micrometeorites routinely hit the larger asteroid in the binary file and splinter it like bullets hitting a cliff face. Or maybe heat changes have cracked one of the asteroid's surfaces and spewed small pieces into the dark.
One scenario offered by the authors is that the shards are the result of the process that made the YT1 system in 2003 in the first place.  Related: Space-y Tales: The 5 Strangest Meteorites
Most people imagine asteroids to be large rocks, magnified versions of the rocks they would find here on Earth. But 2003 YT1, the authors wrote, is more likely to be a "heap of rubble", a jumble of things loosely interconnected by gravity, eventually merging into two orbiting bodies over the last 10,000 years. The forces that hold the masses together as single asteroids are likely to be weak, and since the two stacks are spinning chaotically every few hours, they could hurl more of themselves into space.
There are other, more exotic ways, the authors wrote. Water ice may be sublimated from one of the asteroid surfaces (from solid to gaseous) and form small ice balls in free space. But that and other models are unlikely, the researchers wrote.
Currently we know that a small piece of a large asteroid has visited Earth. And this little piece is probably part of a stream of other small pieces that sometimes go unnoticed into the earth's atmosphere. And sometime way down the road, this big asteroid could follow its young children and strike the earth. This fireball would be much, much bigger.
The article describing these results has not yet been peer-reviewed. A draft was published in the Preprint journal arXiv on 16 October.
Originally published on Live Science .