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The Last Asteroid That Passed the Earth Has a Moon

The Last Asteroid That Passed the Earth Has a Moon

An asteroid passed 745,000 miles from the Earth this past Monday, but the most interesting thing about its passing was its tiny moon.

The passing asteroid is called 2004 BL86, and we knew it was coming. Astronomers have been tracking its trajectory and knew that this pass would be its closest to the Earth for the next two centuries. So astronomers working at NASA’s Deep Space Network antenna at Goldstone, California, were ready.

What they found in radar images is that BL86, which is only about 1,100 feet across, has a very small moon about 230 feet across that’s been traveling through space with it. The pair were captured in 20 individual images that NASA stitched together into a movie.

AsteroidMoonThis GIF shows asteroid 2004 BL86, which safely flew past Earth on Jan. 26, 2015.

It’s actually not that rare for asteroids to have companion bodies. In the population of known near-Earth asteroids, about 16 percent are like BL86 — larger than 655 feet across and part of a pair or binary system. Some are even known to have two moons.

For the moment, this recent pass by BL86 is the closest an asteroid will come to the Earth until the asteroid1999 AN10 flies past us in 2027. But there are more asteroids out there that we don’t know about that we should want to find. If one looks like it’s going to come uncomfortably close to our planet, we’re going to need time to Armageddon that thing.

There are a few ways to deflect an asteroid so it doesn’t hit the Earth and wipe out humanity, though nuking it and turning it into more rocks isn’t the best one. A solar sail could use concentrated solar energy to nudge an asteroid’s path just enough for it to miss hitting the Earth. Spacecraft with mirrors aiming light onto the asteroid, and also painting one white are two other possible ways to use solar energy to deflect an asteroid. Some scientists have considered attaching ballast to an asteroid, changing its center of gravity and thus its orbit. Zapping an asteroid with lasers could break pieces off of it, changing its trajectory just enough to make it miss the Earth.

There are a lot of interesting ways to deflect asteroids out there. Because while it’s fascinating to find an asteroid with a moon, it’s better to find an asteroid with a moon knowing it’s not going to impact the Earth.


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  1. Jason Frazier says:

    Here’s an idea. Instead of blasting or redirecting NEOs, why don’t we come up with ways to capture the darn things, put them in a stable Earth orbit, and mine them for resources? I mean they’re potential gold mines of mineral wealth whether they’re carboniferous or metallic based.
    *BTW your sign-in with Facebook button doesn’t work. Says the page cannot be accessed directly.

  2. Stephen says:

    Asteroids with moons are trying to kill us. Seems about right for a Monday.

  3. jm5150 says:

    Why is the asteroid spinning horizontally but the moon rotating vertically?