An asteroid that hissed within 3 million miles of Last week's Earth turned out to be two objects in a binary system .
The automated asteroid land alarm last alert system (A TLAS) on Mauna Loa in Hawaii discovered 2020 BX12 on January 27th. It immediately determined that the asteroid was a potentially more dangerous . This does not mean that it was really life-threatening for Earth only that it is relatively large and one day its orbit will bring it particularly close to Earth. When the scientists then pointed the radar telescope of the Arecibo Observatory onto the rock they discovered that a small companion was circling it.
Just days after being shut down for a month after a [ earthquake in Puerto Rico, Arecibo captured images of 2020 BX12 on February 4-5. The main asteroid has a diameter of at least 165 meters and rotates every 2.8 hours. His companion is 70 meters in diameter and appears to circle the larger rock approximately every 45 to 50 hours (although this could possibly be much faster), according to a post on the Arecibo Planetary Radar Science Group website .
Arecibo is a radio telescope, but uses radar to detect asteroids, radiate microwave and radio waves at targets, and generate images from the reflected light. Asteroids spin and cause Doppler shifts to the radar signal. The images (above) of 2020 BX12 show the smaller asteroid as lighter because it rotates more slowly . Further information on asteroids with radar imaging can be found here .
Binary asteroids are not that rare ; An estimate found that up to 16 percent of asteroids that are larger than 200 meters could have a companion. But it is an exciting find, especially for an asteroid that will now live on the NASA Near Earth Object Center database .