A serendipitous encounter has brought the total of Jupiter’s moons to 79, according to the International Astronomical Union, which confirmed the discovery of the moons earlier this week. The funny thing is astronomers weren’t even looking for the moons before they were found.
A team of astronomers was originally searching for a mysterious planet thought to be in our solar system. But at the last moment they decided to also search for moons in Jupiter’s immediate vicinity. So, with the help of the Víctor Blanco Telescope in Chile, the team looked around Jupiter—and to their surprise, they spotted 12 new moons.
Nine of the moons are said to be part of a cluster of moons that are in retrograde orbit. In other words, they’re orbiting Jupiter in the opposite direction Jupiter rotates.
“They didn’t form with Jupiter,” said Scott Sheppard of the Carnegie Institution for Science. “We think Jupiter captured them as these objects got too close to Jupiter in the past.”
There’s one moon in particular that the team thought was odd. It’s a prograde moon—it rotates the same direction Jupiter does—but its orbit takes it out as far as retrograde moons. Scientists have named it “oddball” because of its unusual behavior and size, coming in at just 1 kilometer across.
Although it’s less than a mile across, it’s being considered a moon. Sheppard believes oddball may be the result of a collision the moon had with a retrograde moon. That’s why you don’t drive the wrong way down the highway.
Check out the illustration above to see how the orbits of the new moons travel around Jupiter.