How many moons does Jupiter have?

Jupiter is the 5th planet in the Solar System and the 2nd largest celestial body, the Sun being the 1st. Although its size already makes it distinguishable, among the characteristics of Jupiter, it should be noted that it has numerous moons or satellites orbiting around it, which can be regular or irregular depending on their formation. So far, more than 70 moons have been identified orbiting this planet and, although this number is lower than the number of moons that Saturn has, it is believed that Jupiter may have hidden many others, which will be discovered over the years.

If you are curious to know how many there are and what they are called Jupiter’s moons, keep reading this curious article from EcologíaVerde about how many moons Jupiter has , where the four most important ones are also briefly described to learn about some of their characteristics.

How many moons does Jupiter have and what are they called?

Recent studies affirm that during 2020 a total of 79 moons or natural satellites orbiting around Jupiter were counted. Experts expect this figure to increase by 2021, since new moons have been discovered since the 17th century. If you want to get an idea of ​​how many moons Jupiter has since 2020 , you can read the study by Edward Ashton et al. entitled Six hundred 1-km retrograde jovian irregular moons. [1]

Among the satellites of Jupiter, the Galilean moons stand out. These 4 spherical moons were discovered by Galileo Galilei in 1610, who considered them to be one of the largest in the Solar System. Initially, Galileo called them Jupiter I, Jupiter II, Jupiter III and Jupiter IV, following an order of distance from the planet (from innermost to outermost). However, they are currently known by the names of Jupiter’s moons that Simon Marius later proposed, being: Io, Europa, Ganymede and Callisto , respectively.

These Galilean moons , described below, are regular moons, that is, they formed in orbit around the planet rather than being captured, as irregular moons are.


Europa, or Jupiter II is, despite it being the smallest Galilean Satellite. It has a diameter 3122 km and is the most interesting of Jupiter’s moons. Why is this moon so appealing? Because of the belief that there is a great ocean [2] beneath the 100km thick ice, scientists have been paying special attention to this moon. This ocean is where life could be possible due to the heat emitted by the nucleus of nickel and iron. NASA confirmed this in 2016. This has raised hopes of aquatic life developing on the satellite despite the lack of scientific evidence.

Concerning other aspects, it is worth noting that the satellite orbits at 671,100km makes a complete return from Jupiter in just 3.5 days. Its geological youth is evident by the more than 100m elevation it has. It is also important to note that the atmosphere of this surface is made up of oxygen of non-biological source. This is a result of the interaction of light and frozen surfaces.


Io , also coined Jupiter I by its discoverer, is one of the 4 Galilean satellites , the third largest and the closest to Jupiter (the innermost moon). Larger than the moon of planet Earth (if you are interested in learning more about the natural satellite of our planet, here we talk about what are the phases of the moon ), it has a diameter of about 3,643 km and goes around Jupiter in 1 .77 days at a distance of 421,800 km. This moon is characterized by several aspects:

  • In the first place, with more than 400 active volcanoes on the surface, it has a great geological activity, in fact, the highest in the entire Solar System. What is this about? Mainly due to tidal heating caused by the friction that derives from the attraction between Jupiter and other larger moons. The result is plumes of volcanoes capable of reaching and sometimes exceeding 500 km in height and the lack of visible craters on the surface.
  • Finally, it has fewer water molecules than other satellites.
  • Its orbit is influenced by Jupiter’s magnetic field and by Io’s proximity to the Galilean moons Europa and Ganymede.
  • It has a higher density than the rest of celestial objects in the Solar System.
  • Its atmosphere is composed of sulfur dioxide (SO2).
Io (moon) - Wikipedia


Ganymede, or Jupiter III, as Galileo called them, is the biggest Galilean moon. Ganymede, with a diameter 5,262 km, surpasses Mercury in size and completes its orbit about Jupiter in 7 days at 1,070,

It has many unique characteristics that make it stand out from the rest.

  • This silicate-ice moon is composed of a liquid iron core, and an inner ocean. Scientists believe that this may be more than the water on our planet.
  • It also has its own magnetic field that is different from the rest. This is thought to be due to the convection in its liquid core.
  • It is not only the largest satellite, but it also has the highest brightness Galilean satellite.


Callisto, or Jupiter IV, is another large satellite. However, it has a lower density. It measures 4,821km in diameter and orbits Jupiter 1,882,700 km in 17 days. This moon is outermost among the 4, which could explain why it is not as affected by Jupiter’s magnetic fields.

It is notable for its oldest surface geologically and for its thin atmosphere of carbon dioxide and oxygen. Callisto could be home to subterranean liquid water oceans, as it is believed.

Other moons of Jupiter

Of Jupiter’s 79 moons, only 8 are regular. In addition to the 4 Galilean moons, which we have already mentioned, being included in the group of regular moons, there are also 4 satellites of the Amalthea group (Tebe, Amalthea, Adrastea and Metis). They all have in common that they are the closest satellites to Jupiter, rotate in the same direction and have a low orbital inclination.

In contrast, irregular satellites have elliptical orbits and are at great distances from the planets. Among the irregular moons of Jupiter we find: the Himalia group, Themisto, Carpo and Valetudo.