A fireball that lit up the Japanese skies in 2017 was a part of a big one which might one day slam into Earth, scientists have worked out.
The asteroid that burned up in the atmosphere over Kyoto in April that year was smaller than a ping pong ball, but its parent 2003 YT1 is about 2km across - the length of Auckland's Queen St.
Astronomers in Japan wanted to know where the tiny asteroid of 2017 came from, so mapped its trajectory closely - and found it matched up with 2003 YT1.
- Space agencies gather to fight off fictional asteroid threat
- Earth's closest brush with an asteroid in 2019
- NASA issues 'near-Earth' warning as asteroids approach
The mother asteroid was discovered in 2003, and orbits the sun in the same region of space as Earth. It's classified as a potentially hazardous object, with a 6 percent chance of hitting the Earth sometime in the next 10 million years.
It's not clear how the baby split off 2003 YT1, but as the latter is a loose clump of rocks that spins around every couple of hours, astronomers say it's possible it was just flung into space.
2003 YT1 is so big it even has its own moon, which is wide enough to fit a couple of rugby fields.
It was deemed a minor planet in 2007, but is yet to be given a catchier name.
The astronomers' findings were detailed in a paper uploaded to arxiv.org last week.