Jupiter is the fifth planet from the Sun and the largest planet in the solar system. It is a gas giant composed mainly of hydrogen and helium, with no solid surface beneath its deep atmosphere. Its immense size, striped cloud bands, Great Red Spot and extensive system of moons make Jupiter one of the solar system’s most distinctive worlds.
Jupiter Quick Facts
- Planet type: Gas giant
- Position from the Sun: Fifth planet
- Equatorial diameter: 142,984 km (88,846 miles)
- Average distance from the Sun: 778 million km (484 million miles)
- Length of day: About 9 hours 56 minutes
- Length of year: 11.86 Earth years
- Average cloud-top temperature: About −110°C (−166°F)
- Known moons: 115
- Ring system: Four principal components
- Surface gravity: About 2.5 times Earth’s gravity
- Spacecraft currently orbiting Jupiter: Juno
The Largest Planet in the Solar System
Jupiter has an equatorial diameter of about 142,984 km (88,846 miles), making it roughly 11 times wider than Earth. More than 1,300 Earths could fit inside Jupiter by volume, although the often-quoted figure of 1,000 Earths allows for the gaps that would remain between spherical planets. Jupiter is also more than twice as massive as all the solar system’s other planets combined. Despite its enormous size, it is much less dense than Earth because it consists predominantly of hydrogen and helium.
A Gas Giant With No Solid Surface
Jupiter consists mainly of hydrogen and helium, the same two elements that dominate the Sun. Its atmosphere does not end at a distinct surface; instead, the gas becomes progressively hotter, denser and more compressed with depth.
Far below the visible clouds, the immense pressure is thought to transform hydrogen into a liquid and then into electrically conducting metallic hydrogen. Jupiter probably has a dense central core containing rock, metals and heavier compounds, although its exact structure remains uncertain. A spacecraft attempting to descend through the atmosphere would be destroyed by increasing pressure and temperature long before reaching the deep interior.
Cloud Bands, Powerful Winds and the Great Red Spot
Jupiter’s striped appearance is produced by alternating light-colored zones and darker belts moving around the planet in opposite directions. Powerful east–west winds separate these bands, while rising and sinking gases create constantly changing swirls, storms and smaller oval-shaped vortices.
The highest visible clouds contain ammonia ice, but the chemical processes responsible for Jupiter’s white, orange, brown and red colors are not fully understood. Compounds altered by ultraviolet sunlight may contribute to the different shades.
The Great Red Spot is a vast high-pressure storm that has been observed for centuries. It is currently slightly wider than Earth, although historical measurements show that it has been gradually shrinking since the 1800s. Winds around its outer edge exceed 400 km/h (250 mph).
Jupiter Has the Shortest Day of Any Planet
Jupiter rotates once in about 9 hours 56 minutes, giving it the shortest day of any planet in the solar system. Its rapid rotation produces powerful atmospheric currents and causes the planet to bulge around its equator. Because Jupiter is not a solid body, different parts of its atmosphere rotate at slightly different speeds. Astronomers therefore use the rotation of its magnetic field to define the planet’s standard day length. Jupiter takes 11.86 Earth years to complete one orbit around the Sun.
An Enormous Magnetic Field and Brilliant Auroras
Jupiter has the strongest magnetic field of any planet in the solar system. It is generated deep inside the planet by the movement of electrically conducting metallic hydrogen and creates an immense region of magnetic influence known as the magnetosphere.
Charged particles trapped within this magnetosphere produce intense radiation belts that can damage visiting spacecraft. They also create powerful auroras around Jupiter’s poles. Unlike Earth’s auroras, which are driven mainly by the solar wind, Jupiter’s are continuously supplied with particles from several sources—particularly volcanic material released by its moon Io.
Jupiter’s Moons and Faint Rings
Jupiter has 115 officially recognized moons, ranging from large spherical worlds to small, irregular bodies. Its four largest—Io, Europa, Ganymede and Callisto—are known as the Galilean moons because Galileo Galilei first observed them through a telescope in 1610.
Each is a distinctive world. Io is the most volcanically active body in the solar system, Europa probably contains a global ocean beneath its icy crust, Ganymede is the solar system’s largest moon, and Callisto has an ancient, heavily cratered surface.
Credit: NASA/JPL/DLR
Jupiter also has a faint ring system composed mainly of dust released when small objects strike its inner moons. Unlike Saturn’s bright icy rings, Jupiter’s dark rings are difficult to observe from Earth and were not discovered until Voyager 1 passed the planet in 1979.
How Jupiter’s Gravity Shapes the Solar System
Jupiter’s immense gravity has strongly influenced the arrangement of objects throughout the solar system. Orbital resonances with the planet help create gaps in the asteroid belt, while two large groups of Trojan asteroids travel around the Sun ahead of and behind Jupiter.
Jupiter is sometimes described as a shield that protects Earth by capturing or ejecting comets and asteroids. Its role is more complicated: the planet can remove potentially hazardous objects from the inner solar system, but it can also redirect some objects toward it. Jupiter is therefore better understood as a powerful gravitational influence than as Earth’s protector.
Spacecraft Exploration of Jupiter
Nine spacecraft have visited Jupiter. Pioneer 10 made the first flyby in 1973, followed by Pioneer 11, Voyager 1 and 2, Ulysses, Cassini and New Horizons. Most used the encounter to study Jupiter while receiving a gravitational boost toward another destination.
Galileo became the first spacecraft to orbit Jupiter in 1995 and released a probe into its atmosphere. NASA’s Juno entered orbit in 2016 and continues to investigate the planet’s interior, atmosphere, magnetic field and moons. Two further spacecraft are now traveling toward the Jupiter system. NASA’s Europa Clipper is due to arrive in April 2030 and repeatedly fly past Europa, while ESA’s Juice mission is expected to arrive in July 2031 and study Europa, Callisto and Ganymede.
How to Find and Observe Jupiter
Jupiter is one of the brightest objects in the night sky and is easily visible without optical aid when it is above the horizon. It appears as a steady, cream-colored point along the zodiac and generally twinkles less than nearby stars. The best time to observe it is around opposition, when Earth passes between Jupiter and the Sun and the planet is visible for most of the night.
Ordinary binoculars can reveal some or all of the four Galilean moons as tiny points arranged in a changing line beside the planet. Resting the binoculars on a firm support makes them much easier to see.
A small telescope will show Jupiter as a disk crossed by two dark equatorial belts. Larger apertures and steady atmospheric conditions may reveal additional bands, shadow transits by its moons and the Great Red Spot. The spot rotates in and out of view and often appears pale salmon rather than vivid red, so its predicted transit time should be checked before observing.
Who Discovered Jupiter?
No single person discovered Jupiter because the planet is bright enough to see without a telescope and has been known since ancient times. Babylonian astronomers recorded its movements thousands of years ago, while Greek and Roman observers recognized it as one of the wandering lights that moved against the background stars.
Galileo Galilei made the first detailed telescopic observations of Jupiter in January 1610. He discovered four objects changing position around the planet—Io, Europa, Ganymede and Callisto. Their movement provided powerful evidence that not everything in the heavens orbited Earth.
Why Jupiter Is Named After the King of the Roman Gods
The Romans named the planet after Jupiter, the chief god of their mythology and ruler of the sky and thunder. His Greek counterpart was Zeus. The name suited the brightest of the planets that could remain visible throughout the night and, by coincidence, the world we now know to be the largest in the solar system. Jupiter is also sometimes called Jove, while the adjective Jovian means “relating to Jupiter.” Astronomers consequently refer to its moons as the Jovian moons and to the surrounding planetary system as the Jovian system.