Enlarge Image ZTF/Caltech Optical Observatories

Astronomers have discovered an usual asteroid that sets a record for the shortest year among space rocks smaller than a planet.

The asteroid cataloged as "2019 LF6" orbits the sun in just 151 days.

It whips around space in a very unusual elliptical loop that sees it sometimes coming closer to the sun than Mercury on one end and then traveling out past Venus on the other. This makes it just one of 20 so-called "Atira" asteroids known that orbit the sun entirely inside Earth's own orbit.

But 2019 LF6 is doubly rare because it is also relatively big, measuring around a kilometer across.

"You don't find kilometer-size asteroids very often these days," Caltech's Quanzhi Ye, the asteroid's discoverer, said in a statement. "Now that most of (the larger objects) have been found, the bigger ones are rare birds... Its unique orbit explains why such a large asteroid eluded several decades of careful searches."

The asteroid was spotted using the Zwicky Transient Facility at the Palomar Observatory, which also found another Atira asteroid earlier this year. Both of the objects orbit basically perpendicular to the essentially flat plane of the solar system that the planets inhabit.

NASA/JPL-Caltech

"This suggests that sometime in the past they were flung out of the plane of the solar system because they came too close to Venus or Mercury," said Tom Prince, a Caltech physics professor and scientist at NASA's Jet Propulsion Lab.

Most asteroids are found deeper in space, particularly beyond Mars in the main asteroid belt, but there could be many more hidden objects lurking between our planet and the sun.

One proposed NASA mission named NEOCam (for Near-Earth Object Camera) would launch a spacecraft equipped to look specifically for Atira asteroids.

More eyes in the sky is always a good idea when you consider that asteroids have a nasty habit of sneaking up on us.