An Asteroid Just Skimmed Past Earth And Scientists Discovered It Has 2 Moons

Asteroid Florence flew by Earth last week, skimming at a distance of 4.4 million miles (7 million kilometers). It’s the biggest asteroid to come this close in more than a century and it was dragging two moons with it.

Florence is so big that it has two little moons of its very own, according to radar images obtained by NASA when Florence was at its closest to the Earth on 31 August and 1 September. The asteroid flew by as predicted, but the fact that it has two moons came as a surprise. “While many known asteroids have passed by closer to Earth than Florence … all of those were estimated to be smaller,” said JPL NASA’s Paul Chodas, manager of the Center for Near-Earth Object Studies. “Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”

But just how big does the asteroid have to be in order to have two moons? Florence isn’t actually all that big. It measures just 2.7 miles or 4.4 kilometers across. The moons themselves truly are actually pretty small too by comparison to our moon. They measure between  300-1,000 yards (100-300 meters) across, with orbits of around eight hours for the inner moon and between 22 and 27 hours for the outer moon.

Scientists claim that is isn’t uncommon for asteroids, even the smaller ones, to have moons. Around 60 near-Earth asteroids of the roughly 16,400 known have at least one moon. But triple asteroids like Florence, however, are definitely rare. A triple asteroid has two moons.

Florence is only the third near-Earth triple asteroid found to date by scientists. The others are Asteroid 1994 CC, discovered to have moons in 2009, and Asteroid 2001 SN263, discovered to have moons in 2008. Neither of those flew as close to the Earth as Florence, however, which offered a rare opportunity to observe the celestial objects in closer detail before it continued on its journey around the sun taking it’s moons along for the ride.

Scientists didn’t only get a glimpse at Florence’s moons either.  hey were able to gather more information about the asteroid, which could come in handy when determining other near misses. But we won’t have to worry about Florence or its moons for quite some time. The next time the asteroid will narrowly miss the Earth will be in 2500.