Astronomers Discover 12 New Moons Around Jupiter

Until the announcement this morning by the International Astronomical Union of the discovery of an additional 10 moons about the gas-giant planet.

They were first spotted past year by a team of astronomers originally on the hunt for the elusive Planet Nine, a hypothetical body speculated to exist beyond Neptune. The scientists embarked on a yearlong process that involved several observations to confirm the moons' existence, according to a Carnegie Institution for Science press release.

As part of that search, Sheppard was using the 4-meter Víctor Blanco Telescope in Chile in March of previous year and realized that Jupiter was right near the part of the sky he wanted to search. Jupiter happened to be in the same field of view, so they also looked for any as yet unknown moons. Of the 12 latest moons to join Jupiter's family, it's a maverick whose odd orbit may give astronomers crucial insights to understanding how the moons of Jupiter came to be.

Outside the orbits of the prograde moons is the largest group, the retrograde moons, which orbit around Jupiter in the opposite direction to the planet's spin.

The discovery brings Jupiter's total number of known moons to a whopping 79 - the most of any planet in our Solar System. Bob Jacobson and Marina Brozovic at NASA's Jet Propulsion Laboratory confirmed the calculated orbit of the unusual oddball moon in 2017 in order to double check its location prediction during the 2018 recovery observations in order to make sure the new interesting moon was not lost. Because of that small moon's orbit, it may be eventually be destined for an crash. The name Valetudo has been proposed for it, after the Roman god Jupiter's great-granddaughter, the goddess of health and hygiene.

The orbit of "oddball" Valetudo, shown in green, compared to the retrograde moons.

"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". Not yet, anyway. "Right now the only definition of a moon is something that orbits the planet", Sheppard said, as long as it isn't human-made.

As a result, head on collisions are much more likely to occur between this "oddball" prograde moon and its retrograde cousins moving in opposite directions. These regular satellites consist of an inner group of four moons that orbit very closely to the planet and a main group of four Galilean moons that are Jupiter's largest moons.

With the moon's orbit set at an angle to the rest, this means that Valetudo doesn't take the riskiest path around Jupiter, but it does dive through the orbits of the retrograde moons, inviting a collision at some point.

These are images of one of the new moons, named Valetudo.

The team suspect the "oddball" is the last-remaining remnant of a once-larger prograde moon that formed some of the retrogrades during past head-on collisions.

These new moons probably formed in a place in our solar system known as the giant planet region, which is between the asteroid belt, dominated by rocky asteroids, and the Kuiper belt, dominated by icy comets.

Elucidating the complex influences that shaped a moon's orbital history can teach scientists about our Solar System's early years. "Head-on collisions would quickly break apart and grind the objects down to dust". At the same time, they watched for Planet Nine or smaller, distant dwarf planets in the background. Only the two innermost planets in the solar system, Mercury and Venus, have none.

This was at a time when the Sun was still surrounded by a rotating disc of gas and dust from which the planets were born. The smallest moon is just over a half-mile across, while the largest is about three miles in diameter. So they were likely formed after they had dissipated.