How many moons does Jupiter have? The 2026 count, the four big ones and how to see them

Jupiter has 115 moons that are officially recognised by the International Astronomical Union, NASA says (NASA's Jupiter pages, updated in autumn 2026). Most are small. Four are big enough to be worlds of their own: Io, Europa, Ganymede and Callisto, the Galilean moons.

Widths are twice the mean radius, distances the average orbit size (semi-major axis), from NASA JPL Horizons. You can see these four moons yourself. Jupiter is well placed around its opposition on 11 February 2027 at 00:17 UT (7:17 p.m. EST on 10 February), and our animation below shows where the moons are predicted to be, night by night.

How many moons does Jupiter have in 2026?

NASA's Jupiter moons page (updated 21 September 2026) says: "Jupiter has 115 moons that have been officially recognized by the International Astronomical Union." The number keeps growing as astronomers find and confirm more small moons, so you may see lower numbers, such as 79 or 95, in older articles. For an up-to-date count, check NASA's page.

For comparison, NASA says "Saturn has 293 confirmed moons in its orbit as of August 2026, far more than any other planet in our solar system". So Jupiter is not the planet with the most moons, but it does have the biggest one.

Io, Europa, Ganymede and Callisto: the four Galilean moons

The four big moons were "first observed by the astronomer Galileo Galilei in 1610 using an early version of the telescope", NASA writes, which is why they are called the Galilean moons. They are very different worlds:

• Io, the closest, is "the most volcanically active body in the solar system", according to NASA. It goes around Jupiter in less than two days.
• Europa is covered in ice, and NASA thinks a liquid-water ocean may lie beneath it.
• Ganymede is the largest moon in the solar system, NASA says, "even bigger than Mercury, and Pluto".
• Callisto, the farthest of the four, is Jupiter's second-largest moon. It takes almost 17 days to go around Jupiter once.

Which is Jupiter's largest moon?

Ganymede. Ranked by size, using the widths in NASA JPL Horizons:

NASA also describes Europa as about 90% the size of Earth's Moon. Ganymede is wider than the planet Mercury, but much less dense: Horizons gives it a density of 1.94 grams per cubic centimetre, against 5.43 for Mercury.

Could there be life on Jupiter's moons?

Nobody knows yet. Europa is a target for investigating whether conditions suitable for life exist. NASA writes: "A liquid-water ocean with the ingredients for life may lie beneath the frozen crust of Europa." Note the word "may": no life has been found. Water alone is not enough: NASA's Europa Clipper team lists water, chemical building blocks and a source of energy as the "ingredients" needed for life as we know it.

NASA's Europa Clipper spacecraft "launched Oct. 14, 2024" and is due "to reach Jupiter in April 2030", NASA says. One of its objectives, NASA says: "Determine if Europa has conditions suitable to support life." In other words, it will not look for living things directly, but for places where life could survive.

How to see Jupiter's moons yourself

You do not need much. NASA's Night Sky Network says "Most binoculars will show at least one or two moons orbiting the planet", and "Small telescopes will show all four of the Galilean moons if they are all visible". On 11 February 2027 their brightness ranges from magnitude +4.8 (Ganymede) to +5.8 (Callisto) in NASA JPL Horizons (lower numbers mean brighter). The problem is that they sit right next to Jupiter, which is about 840 times as bright as Ganymede at 00:00 UT on 11 February, in our calculation.

They also move fast. The animation below shows their predicted positions from NASA JPL Horizons every 30 minutes (25.6 seconds of motion, then a 2-second pause). You can see them change sides from night to night, pass in front of Jupiter and disappear behind it or into its shadow; short events can fall between two frames. This rotated chart puts celestial east on the left; the moons' line may be tilted in binoculars, and telescope views may be inverted or mirrored. Callisto gets up to about 10 arcminutes from Jupiter in this period (an arcminute is 1/60 of a degree; 10 arcminutes is about a third of the full Moon's width); Io reaches about 2.2 arcminutes from Jupiter's centre.

Where the moons are at 05:00 UT each night (midnight in New York), from NASA JPL Horizons. Moons are listed in the order you see them from left (east) to right (west):

Tips: rest your binoculars on something steady, look again an hour or two later to see the moons move, and expect to see fewer than four sometimes: a moon can be in front of Jupiter, behind it or in its shadow.

Where is Jupiter in the sky? Opposition on 11 February 2027

Jupiter is at its best at opposition, when Earth passes roughly between the Sun and Jupiter. The next opposition is on 11 February 2027 at 00:17 UT, in our calculation with Astronomy Engine. That is 7:17 p.m. EST on 10 February in New York. Jupiter is then 652 million km from Earth, shines at magnitude −2.6 and looks 45 arcseconds wide, or about three-quarters of an arcminute (NASA JPL Horizons), in the constellation Leo. Mars is close by: about 12.5° away, about nine days before Mars' own opposition on 19 February (see our Mars article).

On the night of opposition (local time: EST in New York, GMT in London, AEDT in Sydney; city centres, sea level, flat horizon; our calculation):

Right now, in October 2026, Jupiter is a morning planet: from New York it rises at 01:53 local time on 18 October. Our Tonight page shows when it is up where you are. Jupiter's oppositions come about every 13 months: the February 2027 and March 2028 oppositions (12 March 2028) are about 396 days apart.

Jupiter's moons FAQ

How many moons does Jupiter have in 2026? 115 that are officially recognised by the International Astronomical Union, according to NASA's Jupiter pages (updated in autumn 2026).

Does Jupiter have 79 or 95 moons? Neither: NASA's current page gives 115, and the number can still grow. Lower numbers come from older articles.

What are Jupiter's four largest moons called? Io, Europa, Ganymede and Callisto, together called the Galilean moons. For the full list of Jupiter's moons, see NASA's Jupiter moons page.

Are Jupiter's moons tidally locked? The big ones are. NASA says "All the solar system's large moons are tidally locked with their planets", so the four Galilean moons keep roughly the same side facing Jupiter.

What are the largest moons of Jupiter, ranked by size? Ganymede, Callisto, Io and Europa (see the table above).

Which planet has the most moons? Saturn: NASA says it has 293 confirmed moons as of August 2026.

Could life exist on Jupiter's moons? It is possible but unknown. NASA says an ocean with the ingredients for life may lie under Europa's ice, and Europa Clipper is due at Jupiter in April 2030 to study whether Europa has conditions suitable for life.

How often does Jupiter go into opposition? About every 13 months: 11 February 2027, then 12 March 2028 and 12 April 2029, in our calculation.

Will Jupiter go retrograde in 2027? Yes, in the astronomical sense. Around opposition Jupiter seems to drift backwards (westward) against the stars for a few months, because Earth overtakes it. In NASA JPL Horizons data this backward drift runs from about 13 December 2026 to 13 April 2027.

How far away is Jupiter? At opposition on 11 February 2027 about 652 million km. NASA says Jupiter is 5.2 astronomical units from the Sun; see our Sun distance article for what an astronomical unit is.

How we checked

The number of moons and the facts about Io, Europa, Ganymede, Callisto and Galileo come from NASA's Jupiter moons page (updated 21 September 2026) and Jupiter facts (updated 15 October 2026); Saturn's count from NASA's Saturn moons page (updated 22 September 2026); Europa Clipper from NASA's mission page (updated 10 September 2026). The widths, orbit sizes, orbit times and densities come from the physical data in NASA JPL Horizons.

The animation uses NASA JPL Horizons' apparent positions of the four moons relative to Jupiter, every 30 minutes from 4 to 20 February 2027, and its codes for when a moon is in front of, behind or in the shadow of Jupiter. We turned the view by 21° so that the moons' track is level; events shorter than 30 minutes can fall between frames. Jupiter's distance, brightness and size and the moons' brightness also come from Horizons. The opposition dates, rise and set times (city-centre coordinates, sea level, flat horizon) and the Mars-Jupiter separation come from Astronomy Engine 2.1.19; the retrograde dates from the daily positions in Horizons. The sky view was made in Stellarium 26.3 and checked against Astronomy Engine.

The photos are NASA images; NASA says its images are generally not subject to copyright in the United States, and we credit each one. The animation, charts and diagrams are our own. None of the images or videos is AI-generated.