Astronomers searching for signs of a large planet far beyond Pluto have stumbled across 12 previously undetected moons orbiting Jupiter, pushing the giant planet's total to a record 79, the Carnegie Institution reported Tuesday. Most likely to be pieces of a once larger moon that was broken up in orbit, they take almost a year to complete a lap around Jupiter.
Astronomers are still finding moons at Jupiter, 400 years after Galileo used his spyglass to spot the first ones. His team at Carnegie, along with collaborators at the University of Hawaii and Northern Arizona University, was hunting for objects far beyond Pluto. Precise calculations were also performed by scientists with the International Astronomical Union's Minor Planet Center, and NASA's Jet Propulsion Laboratory, using the initial observations, to not only confirm that these were not just asteroids passing through their field of view, but also to ensure that astronomers could keep track of these tiny moons and not lose them. "It took a year to figure out what these objects were". They are part of a larger group, all with similar distances and angles of inclination, taking little less than a year to orbit Jupiter.
This moon, now called Valetudo, moves in a prograde motion, though it is slightly inclined compared to the orbits of the other moons. "We think Jupiter captured them as these objects got too close to Jupiter in the past".
The oddball is thought to be Jupiter's smallest moon; it measures roughly 3,000 feet across.
The "oddball" moon, which has been named Valetudo after the Roman goddess of health and hygiene, has an orbit that is dissimilar to any other known moon around Jupiter. It's just 1 kilometer wide, which makes it Jupiter's smallest moon, and takes a year and a half to orbit the planet.
From Jupiter's entire collection of 79 moons, Sheppard has been involved in the discovery of 54 of them, including most of the known retrograde moons.
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. "Head-on collisions would quickly break apart and grind the objects down to dust". One of the moons, Valetudo (between orange markers), can be seen in these images.
This survivor could be the last remnant of a once-larger prograde moon that collided with an object to create the retrograde moons.
Elucidating the complex influences that shaped a moon's orbital history can teach scientists about our Solar System's early years. One moon is located in the outer group but orbits in the opposite direction.
A greater number of irregular moons because it tells us about a time during Jupiter's formation when the planet was still growing. Since they are still around, now, that means they formed after that gas and dust had been swept away by the solar wind.
The Blanco 4-meter telescope Sheppard was using is uniquely suited to spotting potential new moons both because the camera installed on it can photograph a huge area of sky at once and because it's particularly good at blocking stray light from bright objects nearby - say, Jupiter - that might wash out fainter ones. Nine of the new discoveries are found in this group. In their recent observations, Sheppard's team documented nine of these (along with two prograde, closer-in moons).