Radar plot of the asteroid and its companion
Photo: Arecibo Observatory/NASA/NSF

An asteroid that whizzed within 3 million miles of Earth last week turned out to be two objects in a binary system, according to new observations.

The automated Asteroid Terrestrial-impact Last Alert System (ATLAS) on Mauna Loa in Hawaii discovered 2020 BX12 on January 27. It immediately determined that the asteroid was a potentially hazardous one. Now, that doesn’t mean that it was truly hazardous to life on Earth, just that it’s relatively large and its orbit will one day take it especially close to Earth. But when scientists followed up by pointing the Arecibo Observatory’s radar telescope at the rock, they realized it had a small companion orbiting it.

Just days after coming back online after a month-long shutdown due to the Puerto Rican earthquakes, Arecibo captured images of 2020 BX12 on February 4 and 5. The main asteroid is at least 165 meters across, rotating once every 2.8 hours. Its companion is 70 meters across and appears t

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