Morocco’s Oukaimeden Sky Survey first spotted the near-Earth asteroid 2017 YE5 on December 2017. Not much detail about the asteroid’s physical properties was known until June this year when 2017 YE5 made its closest approach to Earth for at least the next 170 years. The asteroid came close to within six million kilometers of Earth, or about 16 times the distance between Earth and the Moon, allowing scientists to have a closer look at the object.
NASA’s Goldstone Solar System Radar (GSSR) closely observed the asteroid’s flyby on 21 and 22 June and came to the conclusion that 2017 YE5 could be a binary system. The astronomers used bistatic radar, which is a technique in which the transmitter and receiver are placed in two separate locations, to scan the asteroid, finding they had two asteroids in their hands. The observations were later confirmed by a team of astronomers at the Green Bank Observatory (GBO) in West Virginia.
Finally, the US space agency announced on July 12, that 2017 YE5, which was initially assessed as a single asteroid, is actually two asteroids, a pair of objects orbiting each other. They rotate around a common center.
Notably, around 15 percent of the tens of thousands of known asteroids in the solar system are binary asteroids. The majority of binaries involve an unequal pair, in which one asteroid is significantly larger than the other. But in the case of 2017 YE5, it is an equal mass binary in which the two objects are roughly of the same mass. It is just the fourth known equal mass binary ever found in the solar system.
It has been found that the two asteroids orbit each other once every 20 to 24 hours or so. Radar scans revealed that each of the asteroids measures about 3,000 feet (900 meters) in length. The two asteroids feature radically different densities and compositions near the surface.