Jupiter

Jupiter is the largest planet in the Solar System, a gas giant made mostly of hydrogen and helium. It's home to the Great Red Spot, a storm bigger than Earth, and has more than 90 moons.

What kind of planet is it?

Jupiter is the fifth planet from the Sun, circling at an average distance of about 5.2 AU roughly once every 11.9 years. Its equatorial diameter is about 142,984 km, more than 11 times Earth's, and by volume over 1,300 Earths could fit inside. Its mass is more than twice that of all the other planets combined.

Jupiter is a gas giant with no solid ground. It's made mostly of hydrogen and helium, so in composition it resembles the Sun. Pressure rises enormously with depth, and deep inside, hydrogen is thought to exist in a metallic state that conducts electricity. This layer of metallic hydrogen, spinning rapidly, generates the strongest magnetic field of any planet in the Solar System. At the center there's thought to be a core of heavy elements, though observations from the Juno spacecraft suggest the core may be fuzzy and spread out, with no sharp boundary.

Jupiter spins faster than any other planet, so a day lasts only about 9 hours 56 minutes. All that spinning makes its equator visibly bulge. Gravity measured at the cloud tops is about 2.5 times Earth's.

Atmosphere and weather

Look at Jupiter through a telescope and you'll see horizontal stripes. The bright bands are called zones and the dark ones belts. They form as powerful jet streams blowing in opposite directions stretch the clouds into long bands. The clouds are thought to form several layers made of ammonia ice, ammonium hydrosulfide, water and more, and the average temperature at the cloud tops is about -110°C (-166°F).

Jupiter's most famous feature is the Great Red Spot, a giant reddish swirl south of the equator. It's a high-pressure storm larger than Earth. It has lasted so long that it's been observed continuously since at least the 1800s, but over recent decades it has been seen shrinking steadily.

Around Jupiter's poles, the Juno spacecraft spotted clusters of cyclones arranged in polygon-like patterns, and auroras and lightning far more powerful than Earth's have also been observed. Jupiter gives off more heat from its interior than it receives from the Sun, and this inner heat also helps drive its weather.

Moons and rings

As of 2025, Jupiter has more than 90 known moons. Most are small bodies just a few kilometers across, but the four large moons that Galileo Galilei discovered with his telescope in 1610 are each as impressive as a small planet. They're called the Galilean moons.

• Io: The most volcanically active body in the Solar System. Gravity from Jupiter and its neighboring moons kneads Io, producing heat that powers hundreds of volcanoes spewing sulfur and lava.
• Europa: A salty ocean is thought to be hidden beneath its smooth icy shell. It's one of the first places named when searching for environments beyond Earth where life could exist.
• Ganymede: About 5,268 km across, the largest moon in the Solar System. It's bigger than the planet Mercury and the only moon with its own magnetic field.
• Callisto: A moon with a very ancient face, its surface densely packed with craters.

Jupiter has rings too. Discovered by Voyager 1 in 1979, they're made mostly of fine dust knocked off small moons, so rather than being bright like Saturn's, they're very faint.

Exploration

• Pioneer 10 and 11 (USA, flybys in 1973 and 1974): Crossed the asteroid belt to become the first spacecraft to approach Jupiter, confirming that the radiation around it is extremely intense.
• Voyager 1 and 2 (USA, flybys in 1979): Discovered Jupiter's rings and Io's volcanic activity, and showed the Great Red Spot and the moons in vivid images.
• Galileo (USA, 1995–2003): The first spacecraft to orbit Jupiter. It dropped a probe into the atmosphere to take direct measurements and found evidence hinting at an ocean beneath Europa's surface. At the end of its mission it plunged into Jupiter's atmosphere to avoid contaminating the moons.
• Juno (USA, entered orbit 2016): Travels on an elongated orbit that passes over the poles, studying Jupiter's interior structure, magnetic field, polar cyclones and auroras in detail.

Cassini on its way to Saturn (2000) and New Horizons on its way to Pluto (2007) also observed Jupiter as they flew by. In 1994, fragments of Comet Shoemaker–Levy 9 were seen crashing into Jupiter one after another, making headlines around the world. Europe's JUICE launched in 2023 and NASA's Europa Clipper in 2024, and both are now on their way to Jupiter's icy moons.

Fun facts

• Jupiter has the shortest day of any planet in the Solar System, spinning once in under 10 hours.
• The center of mass shared by Jupiter and the Sun lies slightly outside the Sun's surface. Strictly speaking, the Sun and Jupiter both orbit that point together.
• Most of the time, Jupiter is the brightest planet after Venus, so it's easy to spot with the naked eye. Through binoculars you can see some of the Galilean moons as tiny dots.
• Jupiter's magnetosphere is so huge that if we could see it with our eyes, it would look bigger than the full Moon in the night sky.

See it in Planetica

In Solar System view, Jupiter appears on the fifth orbit, beyond Mars. Its position is its real location for today's date, calculated from J2000 orbital elements, but since it takes about 12 years to go around once, it barely seems to move over a few days. Check back every few months and you'll see it has shifted a little.

Pick Jupiter and fly in close to feel its overwhelming size. Moons approximating the real ones circle around it, drawn larger than their true proportions so they're easy to see. Size, gravity, day length, axial tilt, average temperature and orbital period are based on real values.

The surface patterns are created by Planetica's planet generator to suit the planet type. They don't show Jupiter's actual cloud map or the exact location of the Great Red Spot.

Other planets

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• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune