"These moons are the last remnants of the building blocks of the giant planets as all other material in the giant planet region likely fell into the planets to help form them", Sheppard said. This is in contrast to other Jupiter moons such as Ganymede - the biggest in the solar system with a diameter of 5,268km.
Over the weeks following full opposition, Jupiter will reach its highest point in the sky four minutes earlier each night, appearing as a bright, star-like object.
The inner moons take about a year to circle Jupiter, while the outer moons take twice as long.
The initial discovery of most of the new moons were made on the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile and operated by the National Optical Astronomical Observatory of the United States.
Sheppard did not set out to detect new moons.
Before Sheppard's team conducted their survey, there were 69 known Jovian moons, but there's always been reason to believe there are quite a few more.
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Due to their sizes-one to three kilometers-these moons are more influenced by surrounding gas and dust. The lost moons were initially sighted in 2003, but scientists could not define their exact orbits and lost track of them.
The chance find brings Jupiter's tally of moons to 79, 17 more than Saturn, the planet with the second most.
The team proposed naming that tiny moon Valetudo, after the goddess of health and hygiene.
"We think there were originally only three retrograde moons and they were each broken apart through collisions with other objects".
The oddball is thought to be Jupiter's smallest moon; it measures roughly 3,000 feet across. It moved in the prograde motion together with Jupiter and then collided with another object, causing the smaller retrograde-moving moons.
Jupiter's moons are arranged in a specific pattern that the giant planet has worked out over time.
Nine of the new moons are in a group of more distant moons in prograde orbits.
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Sheppard says Jupiter's prograde moons probably formed from the same spinning disc of stuff that eventually coalesced to form the planet. Even though a dozen new moons is a pretty good haul, Sheppard expects that more searching will turn up even more moons.
The 12th new moon is a bit of an oddball, Sheppard said, with "an orbit like no other known Jovian moon".
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. "Head-on collisions would quickly break apart and grind the objects down to dust".
Sheppard said these moons were probably objects that formed near Jupiter during the early days of the solar system and were "captured" by the planet's strong gravitational pull.
The remaining moon is less than a kilometer across, further out than the two conventional moons and has a 1.5-year orbit-and the orbit is inclined. We already have a classification for dwarf planets. Since they are still around, now, that means they formed after that gas and dust had been swept away by the solar wind.
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