But it has more than size going for it Ganymede is also quite rocky, icy, and most likely has a liquid-iron core, making it even more planet-like than most moons.Īll that rock and iron provide it with its own magnetic field, further helping it impersonate a planet. Truly, if it had not been sucked into Jupiter’s orbit, Ganymede could easily have been a planet. Even more impressive is the fact that it is larger than the planet Mercury. Measuring 2270 km across, Ganymede is the largest of Jupiter’s moons and it’s also the largest moon in the entire solar system. Ganymede Ganymede, or Jupiter III, is the only moon in the Solar System with a magnetic field. But the gas giant Jupiter’s mass is so great that it draws planet-sized objects into its orbit. It should be noted that even though Galileo needed a telescope to see them, all of these moons would be visible to the naked eye if the light from Jupiter weren’t drowning them out.Īll four of these moons are planet-sized and would be considered such if they revolved around the Sun instead of another planet. To this day, those four moons of Jupiter are known as the Galilean moons and, if you wanted to, you could spot them with a telescope of your own.Īll four of the Galilean moons are massive. The following week, he noticed a fourth one and documented them all. It was definitive scientific proof that not everything in the universe revolved around the Earth, a groundbreaking discovery at the time. As the stars moved, Galileo realized he was looking at objects that were orbiting Jupiter, otherwise known as moons. While looking through his legendary telescope, he noticed 3 stars on either side of Jupiter that couldn’t be seen with the naked eye. The first discovery of the moons of Jupiter was by none other than Galileo way back in 1610. Let’s take a look at the moons of Jupiter. Nevertheless, Jupiter, the largest planet in the solar system, has claimed another crown. These numbers include moons within the orbit of the planets and do not count the various moonlets located within Saturn’s rings, or the hundreds of pieces of debris found within the space immediately around either planet. As it currently stands at the time of this article’s publication, Saturn has 83 moons, whereas Jupiter has about 95. However, it was recently discovered that Jupiter may actually have more moons than Saturn. Interestingly enough, Saturn held that record for a long time. Sorry, the comment form is closed at this time.How many moons does Jupiter have? More importantly, does it have the most moons of any planet in our solar system? Well, seeing as how it is the largest planet by a wide margin, it stands to reason that it should. Most of Io’s surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. Unlike most satellites in the outer Solar System, which are mostly composed of water-ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Some of these peaks are taller than Earth’s Mount Everest.

Io’s surface is dotted with, besides volcanoes and lava flows, more than 100 mountains. Ions escaping from this torus inflate Jupiter’s magnetosphere to over twice the size we would expect. Io’s volcanic ejecta also produce a large doughnut-shaped cloud of intense radiation referred to as a plasma torus. The materials produced by this volcanism provide material for Io’s extremely thin, patchy atmosphere. Numerous extensive lava flows, several more than 500 km in length, also mark the surface. Recent analysis of data reveals a subsurface ocean of molten or partially molten magma beneath the surface. A global magma ocean lying beneath about 30 to 50 km of Io’s crust helps explain the moon’s activity. Io’s volcanoes, distributed all over its surface, are the only known active magma volcanoes in the solar system other than those on Earth. Several volcanoes produce plumes of sulfur and sulfur dioxide (SO2) that climb as high as 500 km above the surface. This extreme geologic activity is the result of tidal heating from friction generated within Io’s interior as it is pulled between Jupiter and the other Galilean satellites-Europa, Ganymede and Callisto.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System. It has no water to speak of and no magnetic field. It has a young surface with no obvious impact craters. Io is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, the fourth-largest moon in the Solar System. Image Credit: NASA/JPL/University of Arizona

Io moon diameter in km