The First Quadruple Asteroid: Astronomers Spot a Space Rock With 3 Moons

Astronomers had already spotted two other rocks orbiting the asteroid known as 130 Elektra, and think more quadruple systems are out there.

We already knew the asteroid 130 Elektra was special. Astronomers previously discovered it had two moons, making it a rare triple asteroid system. Now a third moon may have been found, making it even more uncommon — the first-known quadruple asteroid in the solar system.

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 astronomer from the European Southern Observatory in Chile who discovered Elektra’s second moon. A NASA mission, DART, is on target to collide with one such asteroid’s moon later in the year.