Scientists at Caltech have discovered an asteroid that is about a kilometer in size that has what they term the shortest “year” known for any asteroid. What they mean by “year” is the time it takes the asteroid to complete a full orbit around the sun. The asteroid, known as 2019 LF6, orbits the sun once every 151 days.
The asteroid’s orbit takes it beyond the orbit of Venus, and at times it comes closer to the sun than Mercury. Caltech researchers state that 2019 LF6 is only of only 20 known “Atira” asteroids that have an orbit that falls completely within that of the Earth.
Caltech researcher Quanzhi Ye says that finding kilometer-sized asteroids is rare. Most objects this large have been found already making the discovery of this sort of asteroid rare. The unique orbit of the asteroid is what allowed it to remain undiscovered for so long. 2019 LF6 was discovered using the Zwicky Transient Facility or ZTF.
ZTF is a state-of-the-art camera at the Palomar Observatory that scans the skies every night for transient objects like exploding and flashing stars and moving asteroids. The camera scans the skies rapidly making it well-suited for finding Atira asteroids with short observing windows. The program has discovered one other Atira asteroid so far.
The other asteroid is 2019 AQ3 boasting an orbit that takes 165-days to make a full revolution around the sun. Both of these asteroids orbit well outside of the plane of the solar system. The off-plane orbits suggest that they were flung out of the plane of the solar system by coming too close to Venus or Mercury at some time in the past. ZTF has discovered around 100 near-Earth asteroids and about 2,000 orbiting in the Main Belt between Mars and Jupiter.