Astronomers peering into the depths of the solar system in search of a presumed ninth planet far beyond Pluto happened to be looking past Jupiter during their observations and happened to discovery 12 new moons orbiting the giant planet.
“Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant solar system objects, 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,” said the Carnegie Institution’s Scott Sheppard.
A team led by Sheppard initially spotted the moons in 2017 while scanning the outer solar system in search of “Planet X,” a hypothesised world thought to be responsible for the observed orbits of several bodies in the remote Kuiper Belt. In 2014,
Sheppard, Dave Tholen of the University of Hawaii and Chad Trujillo of Northern Arizona University discovered the most distant known solar system body and were among the first to consider the possibility of a massive, undetected planet beyond Pluto, a claim shared by veteran planet hunder Mike Brown and his colleagues at the California Institute of Technology.
The newly discovered Jupiter moons, with diameters of one to three kilometres (0.62 to 1.9 miles), required multiple observations to verify.
Nine of the moons are part of an outer “swarm” that orbit in the opposite, or retrograde, direction of Jupiter’s spin, taking about two years to complete one trip around the planet. The moons orbit in three different groupings and are thought to be the remnants of three bodies that were broken apart in earlier collisions.
Two other new moons were found to be part of a closer group that orbits in the prograde, or same direction as Jupiter’s rotation. They also are thought to be the result of an earlier collision and take about a year to complete one orbit.
The 12th new moon is a bit of an oddball, Sheppard said, with “an orbit like no other known Jovian moon. It’s also likely Jupiter’s smallest known moon, being less than one kilometre in diameter.”
The moon orbits in the prograde direction, but at a greater distance from Jupiter with an orbital period of about a year and a half. As such, the orbit crosses those of the more distant retrograde moons, raising the possibility of a possible head-on collision at some point in the future.
“This is an unstable situation,” said Sheppard. “Head-on collisions would quickly break apart and grind the objects down to dust.”
Most of the discoveries were made with the Dark Energy Camera on the Blanco 4-metre telescope at Cerro Tololo Inter-American in Chile, operated by the National Optical Astronomical Observatory of the United States. Confirmation came with help from a variety of observatories, including the 6.5-metre Magellan telescope at Carnegie’s Las Campanas Observatory in Chile, the 4-metre Discovery Channel Telescope at Lowell Observatory in Arizona, the 2.2-metre University of Hawaii telescope and the 8-metre Subaru and Gemini Telescopes, also in Hawaii.