Only Mercury and Venus lack natural satellites. The other six planets in the Solar System have them, but the two gas giants — Jupiter and Saturn — have the most. While the exact number of Jupiter's moons is known today, the situation is a bit more complex. So how many moons do Jupiter and Saturn actually have, and which planet has the most? This is discussed by Live Science.
Europa is one of the four most famous and largest of Jupiter's moons, often referred to as the Galilean moons. These were first discovered in 1610 by the renowned scientist Galileo Galilei.
2In addition to Europa, the largest moons of Jupiter are Ganymede, Callisto, and Io. These worlds are named after characters from ancient Greek mythology associated with the chief god Zeus. The largest planet in the Solar System carries his name, although this name is derived from ancient Roman mythology, where Zeus became Jupiter.
3All four of Jupiter's main moons are either about the same size as the Moon or larger. Interestingly, the mass of this quartet accounts for approximately 99.97% of the mass of all objects orbiting the gas giant. Due to their size and the geological processes occurring on these worlds, the Galilean moons possess a thin atmosphere.
As of October 2024, 95 moons have been discovered around Jupiter. However, the situation regarding the number of moons of this planet is somewhat more complicated.
The remaining 91 moons, aside from the four mentioned above, have a diameter of over 1 km. Interestingly, only 57 of them have names. Furthermore, only 8 from this extensive list have proper circular orbits. Notably, it is known that none of these moons possess an atmosphere, as they are too small to retain one.
In addition to the officially recognized 95 moons, thousands of smaller "moons" also orbit Jupiter. Most of these are captured asteroids and their fragments due to the gravity of the gas giant.
Another planet in the Solar System with a vast number of moons is Saturn, the second-largest world orbiting the Sun. For decades, Jupiter and Saturn have competed for the title of the planet with the most moons. So far, Saturn has emerged victorious.
4The eight largest moons of Saturn were discovered between 1671 and 1848. For nearly 80 years, starting in the early 20th century, astronomers knew that Saturn had 8 moons while Jupiter had 12. However, everything changed in 1979 when NASA's two Voyager probes, "Voyager 1" and "Voyager 2," discovered 2 new moons around Jupiter and 3 around Saturn.
Based on this data, astronomers concluded that these planets likely have many more moons than currently known. Over the next 40 years, the hunt for unknown worlds orbiting the two gas giants continued. From 2018 to 2023, the title of the planet with the record number of moons shifted back and forth between Saturn and Jupiter.
As of October 2024, the current winner in this cosmic competition is Saturn, with 146 moons discovered.
5The largest moon of Saturn is called Titan, which is nearly twice the size of the Moon. This unique world features a thick atmosphere, as well as seas, rivers, and lakes on its surface. However, they are not made of water but are primarily composed of methane. Scientists believe that extraterrestrial life may also exist on Titan, similar to Europa.
Whether aliens, likely in the form of microorganisms, exist and whether the necessary ingredients for life are present on Europa and Titan will likely be revealed in the near future. The Europa Clipper spacecraft is set to study Jupiter's moon starting in 2030. If all goes according to plan, NASA will send the Dragonfly aircraft to Titan in 2028, which will begin studying Saturn's moon in 2034.