Carnegie Science researchers first spotted the newly discovered moons in the spring of 2017 as they searched for objects at the edge of the solar system, far beyond Pluto.
“Jupiter just happened to be in the sky near the search fields … so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our solar system,” Carnegie team leader Scott S. Sheppard said.
Jupiter has at least 79 moons orbiting it — the most of any planet in the solar system.
Scientists said the group of moons includes one “oddball” moon that is more distant than the others and has an orbit that crosses nine other, outer retrograde moons.
Retrograde moons orbit in the opposite direction of their parent planets. Prograde moons orbit in the same direction.
Sheppard said retrograde moons are “captured moons,” captured by Jupiter’s gravity as they approached it from the opposite direction and became retrograde in their orbits. If an object approaches Jupiter from behind, it is captured as a prograde and will orbit Jupiter in the same direction as it rotates.
The fact that the smallest moons in Jupiter’s orbital groups are abundant suggests the collisions that created them occurred after the era of planet formation, when a rotating disc of gas and dust surrounded the Sun.
This is important research, Sheppard said, because the influences that shape a moon’s orbital history provide information about our solar system’s early years.
He said a moon’s retrograde orbital direction means it’s likely to have a head-on collision with nearby prograde moons.
“This is an unstable situation,” Sheppard said. “Collisions would quickly break apart and grind the objects down to dust.”
This tendency to collide may be what caused orbital moon groupings that were formed eons years ago, Sheppard said.
Jupiter’s distant retrograde moons could be the remnants of three parent systems that broke apart during collisions with asteroids, comets or other moons, Sheppard said. The newly discovered retrograde moons take about two years to orbit Jupiter.
The name “Valetudo” has been proposed for the new oddball moon, Sheppard said. Valetudo was the Roman god Jupiter’s great-granddaughter, who was the goddess of health and hygiene.
Valetudo is a small moon, less than 1 kilometer in diameter.
Sheppard’s team in 2014 discovered Planet X — the object that is the farthest away in our solar system, even beyond Pluto.
Carnegie Science teams used the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile — one of the largest telescopes in the world — in their work to find the 11 new moons of Jupiter.
The discovery took “a lot of hard work,” Sheppard said. “It took over one year of constant observations to determine that these 12 objects were moons of Jupiter.”