And one of them has a very odd trip around the planet, leading it to be dubbed an "oddball". Sheppard, who is broadly interested in the formation of solar systems and has been involved in the discovery of 48 of Jupiter's known moons, realized this was the ideal opportunity to advance two separate research goals with the same telescope data.
But why are scientists just now finding these moons? For greater detail, a spacecraft is needed. Telescopes in Chile, Hawaii and Arizona were used for the discovery and confirmation.
They first spotted the 12 new moons in the spring of 2017, but they had to conduct several more observations before they could confirm that the moons actually orbited Jupiter, according to Gareth Williams of the International Astronomical Union's Minor Planet Centre.
Over the lifetime of the solar system, a collision seems inevitable. While the team did discover 12 new moons, two were announced previous year. Where their observations had previously been akin to looking through a straw, their capability now is 10 times bigger. The solar system's ocean worlds might be the most promising place to look.
Because Jupiter is also a bright planet, astronomers have had to deal with the issue of glare and scattered light affecting the space where moons can exist.
"This is an unstable situation", said United States astronomer Dr Scott Sheppard from the Carnegie Institution for Science in Washington DC, who led the discovery team. While Jupiter, the fifth planet from the Sun, has large moons such as Ganymede - the biggest in the solar system with a diameter of 3,273 miles (5,268 km) - the new ones range in size from about six-tenths of a mile (1 km) to 2.5 miles (4 km).
They are thought to be the remnants of three once larger moons that broke apart during collisions with asteroids, comets or other moons.
Two new moons are closer in, go the right way, and take about an Earth year for one orbit.
It's further away than the prograde moons, taking around one and a half years to orbit around the planet.
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The researchers, from the Carnegie Institution for Science in Washington, DC, picked out one of the 12 moons as an "oddball". The second is that it "has an orbit like no other known Jovian moon", Sheppard says. Valetudo is the name of Jupiter's great-granddaughter and a Roman goddess of health and hygiene, so it fits the bill.
This oddball is a bit more distant than its prograde brothers, and it takes about a year and a half to orbit Jupiter.
The renegade moon has an inclined orbit that crosses those of others moving in the opposite direction, greatly increasing the possibility of a collision.
Scott Sheppard: "So it's basically going down the highway in the opposite direction, so it's like going against traffic". The best forecast, for now, is some time in the next billion years.
The giant planet region is where the largest planets in our solar system formed, and it's devoid of objects now because the planets gobbled up all of the material to form.
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.
Astronomers group Jupiter's moons by their distance from the planet as well as their orbital direction.
These building blocks of planets can provide a window into the early years of the solar system.