What at first was thought by scientists to be a good-sized asteroid currently hurtling past Earth has turned out to be two giant rocks in tandem.
The setup, catalogued as 2008 BT18, was thought to be nearly a half-mile wide after its discovery by MIT's LINEAR search program in January. Nothing else was known about it.
Now seen as two objects orbiting each other, the pair will be closest to Earth on July 14, at about 1.4 million miles (2 million kilometers) away. That's nearly six times as far from us as the moon.
It will not strike the planet. But scientists want to learn more about binary asteroids because one day they might find one headed our way. Deflecting a binary off course could be considerably more challenging that altering the path of a single rock.
Radar observations from the Arecibo Observatory in Puerto Rico on July 6 and 7 "clearly show two objects," said Lance Benner of NASA's Jet Propulsion Laboratory.
The objects are estimated to be 1,970 feet (600 meters) and 650 feet (200 meters) in diameter. The larger one rotates upon its axis in 3 hours or less.
Additional observations from NASA's Goldstone radar in the Mojave Desert in California are expected to reveal more about the density, shapes and orbit of the pair.
Asteroids are often loose rubble piles rather than solid objects, and pairs are common. Scientists announced earlier this month that binaries can be created when energy from sunlight splits a loose asteroid in two.