Near-Earth asteroid has its own moon
Asteroid 2020 BX12 is hurtling through the cold emptiness of space, but it’s not going alone.
The rock, recently spotted during a Nasa survey of nearby and potentially hazardous asteroids, has a moon. Neither of them are a threat to Earth.
‘‘It was really exciting to find out it was a binary,’’ meaning an asteroid-moon pair, said Luisa Fernanda Zambrano-Marin, a doctoral student from Spain’s University of Granada.
In early February, ZambranoMarin and her colleagues took radar images of the space rocks from the Arecibo Observatory in Puerto Rico.
The asteroid is 165 metres in diameter. It spins on an axis, as does Earth, though it completes its rotation in under three hours.
Its moon is less than half its size, at just 70m wide. It spins much more slowly, completing a rotation every 50 hours or so.
The orbiting moon was ‘‘tidally locked’’ to the large asteroid, Zambrano-Marin said. If you were to stand on the surface of 2020 BX12, you would always see the same face of its moon.
Astronomers detected 2020 BX12 from Hawaii’s Mauna Loa Observatory as part of the Nasafunded asteroid warning system called ATLAS. Further inspection using the Puerto Rico telescope revealed that what appeared to be one space rock was actually two.
The binary asteroid travelled as close as 300,000 kilometres to Earth’s trajectory.
‘‘2020 BX12 poses no danger at this time and is currently receding from Earth,’’ said the National Astronomy and Ionosphere Centre, which operates the Arecibo station. The duo will return close to our planet in 2101.