The asteroid flying by Earth has its own baby moon

At 5 p.m. EST, a large asteroid 1.7 miles in diameter is set to whiz past Earth, giving NASA scientists their best chance to date to study an asteroid up close. And better still: The space rock is towing some teeny-tiny company.

1998 QE2, as scientists have dubbed it, is a binary asteroid that's being orbited by a satellite: Its own 2,000-foot-wide mini-moon. It was first spotted by Marina Brozovic, a scientist at NASA's Jet Propulsion Lab in Southern California. She used radar images taken from the Deep Space Network antenna when the asteroid was still 3.75 million miles away.

Which isn't to say scientists are all that surprised. According to NASA, 16 percent of asteroids bigger than 655 feet have binary or even ternary systems.

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Named for the year it was discovered, 1998 QE2's arrival represents a major notch in the belt of NASA's Near-Earth Object tracking program, which is charged with mapping the thousands of high-speed asteroids in our solar system in case one is headed our way. "It's one of the initial successes of our effort to find the big asteroids that could hit the Earth and cause global catastrophe," Paul Chodas, a scientist with the project, tells CNN. To date, NASA astronomers have identified only 10 percent of the 10,000 objects they believe will zoom by our planet in the coming decades.

1998 QE2 is a big one, too. (In the radar imagery above, one fuzzy pixel is calculated to represent 250 feet.) It's massive enough to easily wipe out a major metropolitan area.

Luckily, when the asteroid passes by Earth on Friday, it will still be about 3.6 million miles away — 15 times the distance to the moon — and we won't have to worry about it again for at least another 200 years.

However, "for an asteroid of this size," says Chodas, "it's a close shave."