FIVE THINGS ABOUT JUPITER’S MOONS

1 WHAT’S THE UPDATE?

Astronomers have just announced the discovery of a dozen more moons around Jupiter. The International Astronomical Union’s Minor Planet Center published the orbits for 12 new-found moons — bringing Jupiter’s total to 79, said Scott Sheppard, a scientist at the Carnegie Institution for Science in D.C.

2 HOW WERE THEY FOUND?

Sheppard and his team at Carnegie, along with collaborators at the University of Hawaii and Northern Arizona University, were hunting for objects beyond Pluto. In March 2017, the astronomers realized that Jupiter had moved into their field of view. “We were able to go a little bit fainter than anyone has been able to go in the past,” Sheppard said, “and that’s why we were able to find these new moons.”

3 HOW BIG ARE THEY?

Galileo discovered the first four of its moons, all huge, in 1610. The largest moon, Ganymede, is bigger than the planet Mercury. The moons Sheppard spied are farther-flung and tiny, each no more than three kilometres in diameter. One is the smallest Jovian moon discovered. They named it Valetudo, after a daughter of Jupiter.

4 IS 79 THE FINAL TALLY?

Gareth Williams, an astronomer at the Harvard-Smithsonian Center for Astrophysics, predicted that “there aren’t any bigger objects undiscovered out there” around Jupiter. But he expects astronomers will discover more tiny moons.

5 WHAT’S WEIRD ABOUT VALETUDO?

Valetudo has a prograde orbit — it orbits in the same direction as the planet rotates. This means moon-moon collisions could be possible.