An Asteroid Flew Exceptionally Close To The Earth Monday Night, And Brought A Surprise: Its Own Moon

An exceptionally large asteroid passed exceptionally close by the Earth Monday night, and it brought a rare treat to astronomers watching it: its own moon, CNN is reporting.

Asteroid 2004 BL86 is about 230 feet wide; as near-Earth asteroids go, that’s pretty big. And it got as close as 745,000 miles away; as asteroids go, that’s pretty close. In fact, it’s a little too close: as previously reported by the Inquisitr, scientists studying these things consider an asteroid close if it comes to within about 20 LD (Lunar Distance: the distance between the Earth and the Moon). Monday’s asteroid flew past at about 3 LD.

Still, the asteroid never posed any threat to Earth. It did, however, present a rare opportunity for scientists and backyard astronomers alike. Because it passed us by so close, and it was so large, it was visible to people with small telescopes and even binoculars. People who knew where to look, that is.

Scientists using much more sophisticated equipment than backyard telescopes trained their sights on the asteroid, and found something rather unexpected, according to NPR: its own moon. Thanks to the Deep Space Network antenna at Goldstone, California, we get to see a rather stunning peek into what’s going on in our celestial neighborhood.

Gif of Asteroid 2004 BL86 and its moon.

DC Agle of NASA’s Jet Propulsion Laboratory explains what’s happening above.

“The 20 individual images used in the movie were generated from data collected at Goldstone on Jan. 26, 2015. They show the primary body is approximately 1,100 feet (325 meters) across and has a small moon approximately 230 feet (70 meters) across… The resolution on the radar images is 13 feet (4 meters) per pixel.”

Agle explains further that asteroids with their own moons aren’t particularly rare.

“In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons).”

This week’s flyby marks the last anyone will see of asteroid 2004 BL86, and its moon, for about two hundred years. It’s also the only asteroid of this size expected to come near the Earth for a couple of decades – until 1999 AN10 heads this way in 2027.

The good news, according to the BBC, is that scientists are confident they’ve identified and tracked 90 percent of the asteroids and other Near-Earth Objects (NEO’s) in the Earth’s neck of the cosmic woods that are big enough to be a threat to the planet. The bad news is twofold. First, there’s that remaining 10 percent that could come out of nowhere at any moment (like what happened in Chelyabinsk, Russia; and second, even if science finds one that’s most-assuredly, absolutely positively going to hit the Earth, there’s not a thing anyone can do about it.

[Image courtesy of: NBC News]