Kyoto fireball was caused by a chunk falling off potentially hazardous asteroid

At 1 a.m. local time on April 29, 2017, something strange appeared over Kyoto, Japan: A bright, relatively slow fireball streaking through the night sky. At the time, astronomers were baffled as it what it could have been. But now, researchers from the National Astronomical Observatory of Japan (NAOJ) have figured out what it was and where it came from.

“We uncovered the fireball’s true identity,” Toshihiro Kasuga, visiting scientist at NAOJ and Kyoto Sangyo University, said in a statement. “It has a similar orbit to that of the near-Earth asteroid 2003 YT1, which is likely its parent body.”

Images capturing the 2017 fireball from different angles and a map showing where the cameras were located.
Images capturing the 2017 fireball from different angles and a map showing where the cameras were located. NAOJ/Kasuga et al.

2003 YT1 is a bright asteroid approximately 1.2 miles across, in a highly eccentric orbit which occasionally passes very close to Earth. At its closest point, it is just a little further away than the moon is, so it is classified as a potentially hazardous asteroid. The researchers believe that this asteroid is shedding material and dust, some of which is what formed the 2017 fireball.

“The potential break-up of the rock could be dangerous to life on Earth,” Kasuga said. “The parent body 2003 YT1 could break up, and those resulting asteroids could hit the Earth in the next 10 million years or so, especially because 2003 YT1 has a dust production mechanism.”

This particular asteroid is releasing more dust and rocks than most asteroids do due to its rotational instability. As the asteroid is warmed by the sun, this produces a small amount of thrust, which is matched by a small recoil. This recoil twists the asteroid, sometimes against the forces of gravity, which can cause small pieces to break off.

“The released particles can enter Earth’s atmosphere and appear as fireballs, which is exactly what happened in 2017,” Kasuga explained.

The 2017 event may have been dramatic, but it wasn’t threatening to people on the ground due to its small size. However, we may not be so lucky in the future if larger pieces break off nearby asteroids.

“The 2017 fireball and its parent asteroid gave us a behind-the-scenes look at meteors,” Kasuga said. “Next, we plan to further research predictions for potentially hazardous objects approaching the Earth. Meteor science can be a powerful asset for taking advanced steps towards planetary defense.”

The findings are published in The Astronomical Journal.

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