A top-down overhead view of the orbits of Jupiter's 92 moons. Credit: Scott Sheppard.
The moon hunter strikes again.
A team of astronomers led by Scott Sheppard of the Carnegie Institution has found and confirmed 12 new moons orbiting Jupiter, bringing the total of moons at the giant planet to 92. The new moons were quietly announced on the International Astronomical Union’s Minor Planet Center website last week, and the new discoveries puts Jupiter in the lead in a recent back-and-forth moon battle with Saturn.
Jupiter was solidly in the lead with Sheppard and team’s announcement of 12 new moons back in 2018, but then in 2019, Sheppard and colleagues found a whopping 20 new moons orbiting Saturn, bringing the ringed planet’s total number of moons to 82. But now this latest addition moves Jupiter back in the lead.
With Sheppard around, we may never know the final count.
A collage of Saturn (bottom left) and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. Credit: NASA/JPL/Space Science Institute
The reign of Jupiter, named after the father of the Olympian gods, has been long and sweet. Aside from being the largest planet in the Solar System, it was this gas giant that demonstrated in the 17th century that planets other than Earth can support a system of moons. Between its size, powerful magnetic field, and system of 79 moons, Jupiter looked set to remain the king of the planets indefinitely.
But it looks like Saturn, named after the father of Jupiter in Greco-Roman mythology, might have just knocked Jupiter off that pedestal. Thanks to a team led by famed astronomer Scott S. Sheppard 20 new moons have been discovered orbiting Saturn. That brings the total number of Saturnian (or Cronian) satellites to 82, putting it ahead of Jupiter’s 79. And the best part? You can help name them!
Above are the the discovery images for one of Jupiter's newest moons S/2011 J2. This object is faint so it doesn't have much visual information, but the moon was discovered by the optical telescope Magellan telescope on Sept. 27, 2011. You can see the motion of the satellite over 40 minutes between the two exposures while the background stars and galaxies do not move. Jupiter is about 0.5 degrees away from the bottom of these images. Images courtesy of Scott Sheppard
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Advances in technology have lead to the discovery of new planets outside of our Solar System, and now even new moons in our own backyard.
Last September, two satellites – the smallest ever discovered – were found orbiting Jupiter.
That brings the number of Jovian moons to a whopping 66. The moons – each about 1 km in size – are very distant from Jupiter. It takes the tiny satellites 580 and 726 days to orbit the gas giant.
The discovery could lead us one step closer to understanding the formation and evolution of our solar system. At least that’s the hope of Scott Sheppard, who works at the the Department of Terrestrial Magnetism at the Carnegie Institution of Science in Washington, D.C. It was Sheppard who, with the help of the massive Magellan telescope at Las Campanas, Chile, initially observed the moons.
“The new satellites are part of the outer retrograde swarm of objects around Jupiter. It is likely there are about 100 satellites of this size around Jupiter,” Sheppard said, explaining that Magellan has made it easier to detect objects further away from Earth. “Up until the last decade, the technology wasn’t there to discover these things because they are very small and very faint.”
The two tiny, irregular moons are called S/2011 J1 and S/2011 J2. Thankfully, those names aren’t expected to stick. Once officially confirmed (Sheppard expects it to happen this year), he will have the opportunity to name each. But, Sheppard can’t pick just any moniker. The names, according to the International Astronomical Union, must be related to Jupiter or Zeus, the Roman and Greek mythological figures who served as king of the gods.
Credit: NASA/ESA/E. Karkoschka (U. Arizona)
Maybe that’s why Sheppard hasn’t yet thought of any names for the soon-to-be members of the Jovian moon list. Are there any names that haven’t already been chosen? Europa, Thebe, Io, Callisto, Sinope, Ganymede …
Naming requirements will definitely need to change because, as Sheppard explains, there are a lot more moons to discover around some of our other gas – and ice – giants.
“There are a similar amount of objects orbiting Saturn and Neptune, which are more distant from the Sun,” Sheppard said, citing a survey of the sky conducted by the Carnegie Institution of Washington in the early 2000s. “If larger telescopes are built in the future, we’ll be able to discover more of these objects and find out what the objects are like,” Sheppard said.
And finding more of these smaller, distant, irregular satellites is a key to understanding our past.
Here’s why: Irregular satellites are believed to have been captured by their respective planets because the moons typically orbit in the opposite direction of the planet’s rotation, and, they also have eccentric and highly inclined orbits.
Those types of moons differ from regular satellites, which are believed to have formed from the same materials that comprise the planet. That’s because the moons tend to have nearly circular orbits, and, they orbit their respective planets in the same direction that the planet rotates.
A planet can temporarily capture an object, i.e. Shoemaker-Levy 9, but in the present time, “a planet has no known efficient mechanism to permanently capture satellites. Thus, outer satellite capture must have occurred near the time of planet formation when the Solar System was not as organized as it is now,” Sheppard said.
“The orbital history of a satellite can be very complex … but understanding where a satellite came from can tell us about the formation and evolution of our Solar System.”
Click here to learn more about the Carnegie Institution’s Department of Terrestrial Magnetism. For more information about Jovian moons, go to Scott Sheppard’s Jupiter Satellite Page.
