One is the loneliest number, especially if you’re a moon circling the Earth (Earth is rather far away, after all). But just as you are about to lose hope and accept your solitary fate, NASA announces there could be a new ‘mini-moon’ come to keep you company.
Sure, it is smaller than you and goes around the Earth amazingly irregularly, but still, two of anything is (usually) always better than one.
It turns out that the second “moon” is asteroid 2016 HO3, and it is currently locked into “a little dance” with Earth, and it has been dancing for a century. The rock’s orbit is highly elliptical, causing it to go a wee bit off tangent—between 38 and 100 times the distance of our planet’s primary moon—and bob up and down across Earth’s orbital plane.
HO3 is tilted by about 8° and it circles the Sun for 365.93 days, which is slightly longer than Earth’s 365.24 day-long year.
Because of its tilted and elliptical orbit, sometimes it is a bit closer to the Sun and moving a slightly faster than Earth. Other times, it is a bit farther out and moving a bit more slowly, though it never gets closer than about 14 million kilometers from Earth or farther than about 40 million kilometers.
NASA says it’s larger than 120 feet (36.5 metres) across, but no more than 300 feet (91 metres) wide, and will orbit for many more centuries to come.
Astronomers first found out about 2016 HO3 on April 27 with the Pan-STARRS 1 asteroid survey telescope in Haleakala, Hawaii.