First radar images of asteroid 1998 QE2 were obtained when the asteroid was about 3.75 million miles (6 million kilometers) from Earth. (Photo credit: NASA/JPL-Caltech/GSSR)

First radar images of asteroid 1998 QE2 were obtained when the asteroid was about 3.75 million miles (6 million kilometers) from Earth. (Photo credit: NASA/JPL-Caltech/GSSR)

PASADENA (CBSLA.com) — A mile-long asteroid set to pass safely by Earth on Friday appears to be bringing along a companion.

Radar imagery showed that asteroid “1998 QE2” is a binary asteroid, according to researchers at Jet Propulsion Laboratory (JPL) in Pasadena.

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About 16 percent of asteroids that are about 655 feet or larger are binary or triple systems, according to JPL.

Data shows the main body of the asteroid is approximately 1.7 miles in diameter and has a rotation period of less than four hours. Radar imagery also shows the space rock has several dark surface features that suggest large concavities.

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The preliminary estimate for the size of the asteroid’s satellite, or moon, is approximately 2,000 feet wide, researchers said. The moon appears in JPL images as a small, bright object orbiting 1998 QE2.

The radar observations were led by JPL scientist Marina Brozovic using a sequence of radar images captured by the agency’s 230-foot Deep Space Network antenna in Goldstone, Calif.

1998 QE2 is expected to pass safely by Earth at its closest distance of more 3 million miles — about 15 times the distance between Earth and the moon — before heading back out to deep space, where it isn’t expected to pass this close for another 200 years.

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The fly-by comes just over three months after the football field-sized asteroid 2012 DA14 flew by just 17,000 miles past Earth.