Twelve new moons discovered around Jupiter

And with that, Jupiter — at Saturn’s expense — enters the books as the planet with the most moons. But it is doubtful whether the gas giant can retain that title as well.

How many moons does Jupiter have? Until recently, the answer was 80. But thanks to new observations, astronomers can now add 12 more. This brings the counter to 92 (!) moons. And that’s enough to surpass Saturn, with 83 moons and until recently the planet with the most moons.

Two birds with one stone
Astronomers have observed new moons in 2021 and 2022, while simultaneously searching for planets beyond Pluto’s orbit. “We noticed that Jupiter was close to our search area in 2021 and 2022. And so, while looking for distant, slower-moving objects in the background and likely beyond Pluto and the Kuiper Belt, we decided to also search directly for objects that were moving around Jupiter in the foreground,” explains astronomer Scott Sheppard. Scientias.nl.

twelve moons
And successfully. Sheppard and his colleagues discovered several objects that appeared to orbit Jupiter at great distances. “Follow-up observations, which lasted about a year, then had to confirm that these objects are actually orbiting Jupiter and are therefore moons.” As mentioned, this eventually led to the discovery of 12 new moons.

These moons are currently still unnamed. “He Center of minor planets will number these moons,” Sheppard explains. “Each moon is given a number as soon as we know its orbit. This will probably happen in the next few months. And then we can also start giving them names. At least: some of those moons. “THE International Astronomical Union allows you to name the moons if they are greater than 1.5 miles (about 2.5 kilometers, editor’s note). About half of the new moons are larger than this and will be so named. »

A name for a moon
The names of new moons are determined by the International Astronomical Union. Astronomers who have discovered the moons are allowed to make suggestions (which the IAU can then adopt or reject). However, they should keep in mind that it is traditional to name the moons of Jupiter after the lovers and descendants of Zeus (or Jupiter). For example, Jupiter already has a moon called Io (named after a mistress of Zeus), but also a moon – also discovered by Sheppard’s research team – called Carpo (named after a daughter of Zeus).

New discoveries
The discovery of twelve new moons now brings Jupiter’s total moon count to 92. But it doesn’t stop there, Sheppard says. “We are currently tracking many more (candidate) moons around Jupiter, but we need to observe these moons for a year before we can officially announce them as moons.” So it’s only a matter of time before the number of moons around Jupiter has to be adjusted again. “Jupiter has over 100 moons over 1 kilometer long,” predicts Sheppard.

many small moons
So today Jupiter has many small moons. But this has not always been the case. Astronomers believe the gas giant originally had a few large moons that fragmented into several smaller pieces due to collisions. They deduce this from the fact that the orbits of some small moons have similarities. This suggests that they have the same origin or descend from the same “mother moon”. Based on these orbits, researchers have already been able to classify Jupiter’s moons into six groups or families. These six “families” would then descend from six large moons that originally revolved around Jupiter. Until recently, the three-kilometer large Carpo moon always fell by the wayside; with its strange orbit, the moon really didn’t belong to any family. But among the 12 moons that have now been discovered, researchers believe they have found a relative of Carpo. One of the 12 moons – S/2018 J4 – appears to follow an orbit similar to the orbit of the moon Carpo. Researchers therefore suspect that Carpo and S/2018 J4 (and possibly other undiscovered moons as well) together form a separate family. If so, there would originally have been seven major moons orbiting Jupiter.

Jupiter versus Saturn
For now, Jupiter proudly leads the list of planets with the most moons. And since it’s in line with expectations for more moons to be discovered around Jupiter in the long term, you can expect that to remain the case for quite some time. But it is certainly not acquired. Because Saturn – with 83 moons firmly in second place in the same ranking – also has some surprises in store for us. “We also track very many (candidate) moons around Saturn,” Sheppard says. “As Saturn is further away, it is more difficult to detect moons around Saturn.” While astronomers have discovered or at least believe they have spotted all moons larger than 1 kilometer around Jupiter, all moons larger than 3 kilometers have only been spotted on Saturn. Eventually, the researchers expect that Saturn – if all moons larger than 1 kilometer have also been detected there – will beat Jupiter.

Saturn could possibly have more moons; those of Jupiter are – at least for now – a bit more interesting. It is possible that we can closely observe one of the small moons orbiting Jupiter at some distance. And thanks to ESA’s JUICE space probe or NASA’s Europa Clipper space probe. Both will visit Jupiter in the near future and – hopefully – might catch a glimpse of one of the smaller moons. This should happen before space probes go into orbit around Jupiter. “Once orbiting Jupiter, they’re too close to Jupiter to observe these more distant moons up close,” Sheppard says. “The hope is that if we find enough of these small moons, there will be one that lies just along the path the spacecraft travels from the outer regions of the Jupiter system to the inner regions.” In such a scenario, space probes would be able to see and study such a small moon very closely. And it is precious. “It is important to better understand these outer moons, because they are the last vestiges of a population of objects originating from the vicinity of the gas giants; the rest is actually integrated into the planets. So if we could take a closer look at one of these moons, we might better understand the material the planets are made of.