"It's also likely Jupiter's smallest known moon, being less than one kilometre in diameter". Scott Sheppard of the Carnegie Institution for Science says he and his colleagues had been trying to track down a giant planet they think may be lurking at the outer reaches of our solar system. Yet it's orbiting in the same direction as the planet, against the swarm's traffic.
At less than two miles (3.2km) wide, the moons are all very small, which is why they have only now been identified thanks to the team's modern, sensitive telescopes. Observations were partly obtained at CTIO, NOAO, which are operated by the Association of Universities for Research in Astronomy, under contract with the NSF.
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. Jupiter is not in the frame, but off to the upper left.
They discovered the 12 moons, but the observation and confirmation process, using multiple telescopes, took about a year. And now, 12 new moons of Jupiter including the weirdest one yet.
A team of astronomers has been working since spring 2017 to confirm the dozen new outer moons, bringing Jupiter's total number of satellites to 79. These satellites are part of a large group of moons that orbit in retrograde far from Jupiter. These all travel in retrograde, or the opposite of Jupiter's rotation, while two more, also though to be moon remnants, travel in prograde. The irregular satellites didn't form around Jupiter in the same way that the planets formed around the Sun, or the regular satellites around Jupiter, from a flat disc in a prograde orbit.
Based on the team's observations, Gareth Williams at the International Astronomical Union's Minor Planet Center was able to calculate the orbits of the moons.
The other nine moons, grouped in clusters of three, have retrograde orbits. Because the planet is so big and bright, researchers surmised that unrecorded moons could be faint, or even obscured, or quite far from the gas giant. One moon detected by Sheppard and his colleagues is the smallest Jovian moon ever discovered. Because it is inclined, every so often it crosses the moons that are in retrograde. It's out where the outer, retrograde moons are, but it's orbiting Jupiter in the prograde direction, driving into the oncoming traffic. For the other 11 moons, Sheppard said they might let the public help out. The new ones were found because technology has gotten better and better over the years. The astronomers are now running computer simulations to determine how the ancient moons fragmented.
"Over a human lifetime, it doesn't happen".
Interestingly, the astronomers believe that this is what happened in the past.
Sheppard and his colleagues speculate that Valetudo was probably once much larger, but was ground down, over the course of billions of years, as a result of collisions.
These two groups of prograde and retrograde moons consist of "irregular" satellites, or moons whose orbits have irregular, or noncircular, shapes.
The findings are another piece of the puzzle of the formation of our solar system. They knew that the solar system's largest planet was going to be bright and hanging in the sky all night.
If they had formed earlier, the influence of gas and dust would have created drag and caused them to spiral inward to the planet, lost forever.
The moons are too small to see with the average telescope - measuring only a few kilometers in size.