Elektra was first discovered in 1873, orbiting in the asteroid belt between Mars and Jupiter. Oblong-shaped and 160 miles across on its longest side, it is a relatively large asteroid and completes an orbit of the sun every five years. In 2003, the first moon was discovered orbiting Elektra, and in 2014 a second. The discoveries were interesting, but not unusual — more than 150 asteroids are known to have one or two moons, in the same way planets can have moons that are gravitationally bound to them. “Multiple moons can be found around large asteroids,” said Bin Yang, an...