Big asteroid that skimmed Earth has its own moon, NASA says

January 27, 2015
This animation, created from 20 individual radar images, clearly show the rough outline of 2004 BL86 and its newly-discovered moon. Credit: NASA/JPL-Caltech

An unusually large asteroid that just skimmed by Earth had its own moon, NASA said Tuesday as the US space agency released its first radar images of the flyby.

The asteroid known as 2004 BL86 made its closest approach late Monday at a distance about three times further than Earth's own Moon.

Radar images from NASA's Deep Space Network antenna in Goldstone, California show that the asteroid itself was about 500 feet (150 meters) smaller than expected, and measured about 1,100 feet (325 meters) across.

The asteroid's small moon was approximately 230 feet (70 meters) across.

Canadian astronaut Chris Hadfield called the discovery "strangely delightful," and wondered on Twitter: "Who gets to name it?"

The asteroid was already unusual because it was about 10 times bigger than most near-Earth objects, which range from 50 to 100 feet (15 to 30 meters) in diameter.

NASA said that about 16 percent of asteroids in 2004 BL86's size category—meaning those that are 655 feet (200 meters) or larger—are "binary," meaning there is a primary asteroid with a smaller asteroid moon orbiting it.

Some even have two moons.

The double asteroid (90) Antiope and its companion S/2000 (90) 1. The two objects are separated by 106 miles (171 km), and they perform their celestial dance in 16.5 hours. The adaptive optics observations couldn’t resolve the shape of the individual components as they are too small. Credit: ESO

The odd couple of 2004 BL86 and its moon will not come this way again for another two centuries, astronomers say.

The next big space rock known to be heading this way is asteroid 1999 AN10, which NASA said should fly past Earth in 2027.

The asteroid known as 2004 BL86 passed Earth late Monday at a distance about three times further than Earth's own Moon

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adam_russell_9615
not rated yet Jan 27, 2015
With that low of a gravity they must have an extremely long orbit.

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