Radar images taken by the JPL’s Goldstone radar antenna were stacked to create this video of 1998 QE2 and its new moon
Radar images made on May 29, 2013, when the Earth-approaching asteroid 1998 QE2 was about 3.75 million miles (6 million km) from Earth show a bright moon circling papa. The pictures also reveal several large, crater-like concavities in the main asteroid.
Binary asteroids are somewhat uncommon but not rare. To date we know of 230 with companions, nine of which are triple systems. About 16% of asteroids 655 feet (200 m) or larger are binary. One of the most famous is the pair of Ida and Dactyl discovered in images taken during Galileo space probe flyby in August 1993. Ida’s about 34 miles (54 km) across and its wee follower Dactyl only 4,600 feet wide (1.4 km).
The preliminary estimate for the size of the asteroid’s satellite, or moon, is
about 2,000 feet (600 meters) wide. It’s “papa” is 1.7 miles (2.7 km) end to end.