The newly discovered "oddball" moon has a prograde orbit, but it orbits farther from Jupiter than the other moons in the larger prograde group and it takes about one and a half Earth years to complete an orbit. 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.
That seems to be what happened to astronomers working at the Cerro Tololo Inter-American Observatory in Chile, where a planned survey of trans-neptunian objects was interrupted by Jupiter.
"It's also likely Jupiter's smallest known moon, being less than one kilometre in diameter".
They all turned out to be moons of Jupiter.
Nine of the new moons are part of a distant outer swarm of moons that orbit in the opposite direction of Jupiter's spin. Two of them go round in a prograde motion, in the same direction to Jupiter's spin.
"Our other discovery is a real oddball and has an orbit like no other known Jovian moon", Sheppard explained.
But what's particularly wild about these newly discovered moons is that researchers weren't even looking for them.
Astronomers looking for Planet Nine-a celestial body predicted to orbit in the outer reaches of our solar system-stumbled upon 12 new moons orbiting Jupiter. 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. So a telescope isn't able to capture much more than the moons' orbits.
Valetudo, as the team calls this oddball moon, is named after the Roman goddess of health, cleanliness and hygiene.
The team's results are not yet available in a peer-reviewed journal, as Sheppard's team is now running supercomputer simulations to try and figure out how often Valetudo might collide with a retrograde moon. "Essentially, it's going to be like a bug in the windshield", says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C. "It probably has collided with them over time", Sheppard said.
Because Valetudo's orbit crosses the orbits of some of the outer retrograde moons, it's possible that it suffered a head-on collision in the past.
The moon travels in the same direction as the prograde moons, but is located as far from Jupiter as the retrograde moons that travel in the opposite direction. "Head-on collisions would quickly break apart and grind the objects down to dust". The fresh haul of natural satellites brings the total number of Jovian moons to 79, more than are known to circle any other planet in our cosmic neighbourhood.
Elucidating the complex influences that shaped a moon's orbital history can teach scientists about our Solar System's early years.
"If we do find this planet in the next few years, it would be a pretty unbelievable discovery for astronomy". But then there was one more, a moon the researchers term the "oddball" of the bunch. They also include a cluster of moons beyond Callisto, shown in blue in the image above.
Finding a moon that tiny, he noted, means it must have formed after all the gas and dust had cleared.