Near-Earth object 2017 YE5 was first spotted by astronomers at the Oukaïmeden Observatory in Morocco in December of last year, but virtually nothing about it, beyond its presence, was known. In June, the object made the closest approach it will make to Earth for the next 170 years, allowing scientists to take a closer look. What was initially assessed as a single asteroid turned out to be two objects in orbit around each other: a double asteroid.
Normally we’d say this is no biggie; around 15 percent of all known asteroids larger than 650 feet (200 meters) in diameter are binaries. But 2017 YE5 is special because it’s an “equal mass” binary, in which the two objects are roughly the same mass. The vast majority of binaries involve an unequal pair, in which one asteroid is significantly larger than the other. Astronomers have documented tens of thousands of asteroids in the Solar System, yet this is just the fourth known equal mass binary. The latest observations are now offering the most detailed images ever taken of this exceptionally rare phenomenon.