March 19, 2026
Jupiter Facts: Everything You Need to Know About the Giant Planet
Jupiter is the fifth planet from the Sun and the largest world in our solar system — a gas giant so immense that all other planets could fit inside it with room to spare. Named after the king of the Roman gods, Jupiter has fascinated astronomers since antiquity as the brightest "wandering star" in the night sky. From Galileo's first telescopic observations of its four great moons in 1610 to NASA's Juno spacecraft orbiting just 4,200 km above its cloud tops today, Jupiter continues to reveal secrets about planetary formation, atmospheric physics, and the conditions needed for life. This complete guide covers everything we know about Jupiter: its staggering size, the Great Red Spot, its 95 known moons, its role as the solar system's gravitational guardian, and the missions that have explored it — all drawn from NASA's Planetary Fact Sheets and decades of spacecraft data.
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Jupiter Fact File
How Big Is Jupiter?
Jupiter is the undisputed giant of our solar system. Its equatorial diameter is 142,984 km (88,846 miles) — more than 11.2 times the width of Earth. If Earth were the size of a grape, Jupiter would be the size of a basketball. The planet's polar diameter is noticeably smaller at 133,708 km because Jupiter's rapid rotation — the fastest of any planet — causes it to bulge significantly at the equator. This equatorial bulge is visible even through a small telescope.
Jupiter's volume is so enormous that approximately 1,321 Earths could fit inside it. Its mass is 1.898 × 10²&sup7; kg — 318 times Earth's mass and roughly 2.5 times the combined mass of every other planet in the solar system. Yet because Jupiter is composed primarily of hydrogen and helium gas, its average density is only 1.326 g/cm³ — barely denser than water. Its surface gravity is 24.79 m/s² (2.53 times Earth's), meaning a 70 kg person would weigh about 177 kg on Jupiter — if there were a surface to stand on.
Jupiter by the Numbers
Jupiter orbits the Sun at an average distance of 778.5 million km (5.2 AU), taking 11.86 Earth years to complete one orbit. At this distance, sunlight takes approximately 43 minutes to reach Jupiter, compared to about 8 minutes to reach Earth. Jupiter's orbital speed averages 13.1 km/s — relatively slow compared to the inner planets, a consequence of Kepler's laws applied to its vast orbital radius.
Despite its massive size, Jupiter has the shortest day of any planet: just 9 hours and 56 minutes. This breakneck rotation drives powerful atmospheric dynamics and gives Jupiter its characteristic flattened shape. The equatorial cloud tops move at about 45,300 km/h relative to the planet's interior. Jupiter's axial tilt is only 3.13 degrees — far less than Earth's 23.44 degrees — which means Jupiter has virtually no seasons. Whether it's January or July on Earth, Jupiter looks essentially the same.
The Great Red Spot and Atmospheric Bands
Jupiter's most iconic feature is the Great Red Spot — a colossal anticyclonic storm that has been raging for at least 350 years. First reliably observed in the 1830s (and possibly as early as 1665 by Giovanni Cassini), the storm is currently about 16,350 km wide, large enough to swallow Earth entirely. Although the spot has been shrinking over the past century — it was once three Earths wide — it shows no signs of dissipating. Wind speeds within the storm reach up to 680 km/h (432 mph), and NASA's Juno mission has revealed that the storm extends at least 300–500 km deep into Jupiter's atmosphere.
The reddish color is thought to come from complex organic molecules — possibly chromophores created when ultraviolet sunlight breaks apart ammonium hydrosulfide or other compounds in the upper atmosphere. The exact chemistry remains one of Jupiter's enduring mysteries.
Jupiter's atmosphere is organized into alternating bands (belts and zones) that run parallel to the equator. The lighter-colored zones are regions of rising gas and high-altitude ammonia ice clouds, while the darker belts are regions of sinking gas that expose deeper, warmer layers. These bands are driven by powerful jet streams with speeds exceeding 600 km/h. Smaller storms, white ovals, and cyclonic vortices constantly form, merge, and dissipate throughout Jupiter's turbulent atmosphere. In 2000, three white ovals merged to form Oval BA — nicknamed "Red Spot Jr." — a storm roughly half the size of the Great Red Spot.
Physical Features: Interior and Magnetic Field
Unlike the rocky terrestrial planets, Jupiter has no solid surface. Its visible "surface" is simply the top of a deep atmosphere that gradually transitions from gas to liquid with increasing depth and pressure. The atmosphere is primarily hydrogen (~90%) and helium (~10%) by volume, with trace amounts of methane, ammonia, water vapor, and hydrogen sulfide that create the colorful cloud bands visible from space.
At a depth of roughly 20,000 km below the cloud tops, the pressure exceeds 2 million atmospheres, compressing hydrogen into a liquid. Deeper still — at about 40,000–50,000 km down — hydrogen enters a metallic phase, a state of matter that exists only under extreme pressure. In this layer, hydrogen atoms are squeezed so tightly that their electrons flow freely, conducting electricity like a metal. This metallic hydrogen layer, churning as Jupiter rotates, generates the planet's extraordinarily powerful magnetic field.
Jupiter's magnetic field is roughly 20,000 times stronger than Earth's, creating a magnetosphere so vast that it extends up to 7 million km toward the Sun and stretches beyond the orbit of Saturn on the tail side. This magnetosphere traps charged particles in intense radiation belts that are lethal to unshielded electronics — a major engineering challenge for every Jupiter mission. At the planet's center, there may be a dense core of heavier elements roughly 10–20 times Earth's mass, though Juno's gravity measurements suggest this core may be "fuzzy" — partially dissolved and mixed into the surrounding metallic hydrogen rather than being a distinct solid body.
Jupiter's 95 Moons: The Galilean Satellites
Jupiter has 95 confirmed moons as of 2024, forming a miniature solar system of its own. The vast majority are small, irregularly shaped captured asteroids, but four stand out as worlds in their own right: the Galilean moons, discovered by Galileo Galilei in January 1610. These four moons — Io, Europa, Ganymede, and Callisto — were the first objects confirmed to orbit another planet, providing crucial evidence for the Copernican heliocentric model.
Io is the most volcanically active body in the solar system. Tidal forces from Jupiter's immense gravity, amplified by orbital resonances with Europa and Ganymede, constantly flex Io's interior, generating enough heat to power over 400 active volcanoes. Some eruptions launch sulfur plumes 500 km above the surface. Europa is arguably the most compelling target in the search for extraterrestrial life. Beneath its smooth, cracked ice shell — estimated to be 15–25 km thick — lies a global saltwater ocean containing roughly twice as much water as all of Earth's oceans combined. The Hubble Space Telescope has observed what appear to be water vapor plumes erupting through cracks in the ice.
Ganymede is the largest moon in the solar system — at 5,268 km in diameter, it is larger than Mercury and would be classified as a planet if it orbited the Sun independently. It is the only moon known to generate its own magnetic field. Callisto is the most heavily cratered object in the solar system, its ancient surface a record of 4 billion years of impacts. Callisto may also harbor a subsurface ocean, making three of Jupiter's four Galilean moons potential habitats for life.
Jupiter: The Solar System's Gravitational Guardian
Jupiter's enormous mass — 2.5 times that of all other planets combined — makes it the gravitational anchor of the outer solar system. Its influence shapes the orbits of asteroids, deflects incoming comets, and has been credited with reducing the rate of catastrophic impacts on Earth over billions of years. Without Jupiter, some models suggest the inner solar system would experience significantly more frequent asteroid and comet collisions.
The most dramatic demonstration of Jupiter's role as cosmic catcher came in July 1994, when Comet Shoemaker-Levy 9 collided with Jupiter. The comet had been captured by Jupiter's gravity and torn into 21 fragments during a close approach in 1992. Over six days, these fragments slammed into Jupiter's atmosphere at 60 km/s, creating fireballs larger than Earth and dark impact scars visible for months. The event was the first directly observed collision between two solar system bodies and underscored just how powerful Jupiter's gravitational influence really is.
However, the "Jupiter shield" narrative is more nuanced than popularly believed. Some computational simulations suggest that while Jupiter deflects many long-period comets from the Oort Cloud, it can also redirect asteroids from the asteroid belt toward the inner planets. Jupiter's gravity is responsible for the Kirkwood gaps in the asteroid belt — orbital resonances that clear out certain zones and scatter asteroids into Earth-crossing orbits. So Jupiter is both a shield and, occasionally, a slingshot.
Missions to Jupiter: From Pioneer to Europa Clipper
Jupiter has been visited by nine spacecraft since the early 1970s. Pioneer 10 (1973) and Pioneer 11 (1974) were the first to fly through the asteroid belt and return close-up images of Jupiter, revealing the intensity of its radiation belts and the complexity of its cloud patterns. Voyager 1 and Voyager 2 (both in 1979) transformed our understanding with detailed observations of Jupiter's atmosphere, ring system, and moons — including the stunning discovery of active volcanism on Io and the smooth ice surface of Europa.
The Galileo mission (1995–2003) was the first to orbit Jupiter, spending eight years studying the planet, its moons, and its magnetosphere. Galileo deployed an atmospheric probe that descended 150 km into Jupiter's clouds, measuring wind speeds, temperatures, and chemical composition before being crushed by pressure. The mission confirmed Europa's subsurface ocean and provided the strongest evidence yet for liquid water beyond Earth.
NASA's Juno spacecraft has been orbiting Jupiter since 2016, using highly elliptical polar orbits to study the planet's interior structure, magnetic field, and polar regions. Juno's microwave radiometer has peered hundreds of kilometers below the cloud tops, revealing that Jupiter's atmospheric features extend far deeper than expected. The mission has been extended through 2025, with close flybys of Io, Europa, and Ganymede. Looking ahead, NASA's Europa Clipper — launched in October 2024 — will arrive at Jupiter in 2030 to conduct nearly 50 close flybys of Europa, using ice-penetrating radar, a magnetometer, and mass spectrometers to assess whether Europa's ocean could support life. ESA's JUICE (Jupiter Icy Moons Explorer), launched in April 2023, will arrive in 2031 to study Ganymede, Callisto, and Europa.
Frequently Asked Questions About Jupiter
▶How big is Jupiter?
Jupiter is the largest planet in our solar system with an equatorial diameter of 142,984 km (88,846 miles) — more than 11 times wider than Earth. Its volume is so vast that approximately 1,321 Earths could fit inside it. Despite its enormous size, Jupiter is composed mostly of hydrogen and helium gas, giving it a mass of 1.898 × 10²⁷ kg — about 318 times Earth’s mass but only 2.5 times the mass of all other planets combined.
▶What is the Great Red Spot on Jupiter?
The Great Red Spot is a persistent anticyclonic storm in Jupiter’s southern hemisphere that has been observed for over 350 years. It is currently about 16,350 km wide — large enough to swallow Earth entirely. The storm’s winds reach speeds of up to 680 km/h (432 mph). NASA’s Juno mission has revealed the storm extends at least 300–500 km deep into Jupiter’s atmosphere. The reddish color is likely caused by complex organic molecules broken apart by ultraviolet sunlight.
▶How many moons does Jupiter have?
As of 2024, Jupiter has 95 confirmed moons — the most of any planet in our solar system. The four largest are the Galilean moons, discovered by Galileo Galilei in 1610: Io (the most volcanically active body in the solar system), Europa (which harbors a subsurface ocean beneath its icy crust), Ganymede (the largest moon in the solar system, bigger than Mercury), and Callisto (one of the most heavily cratered objects known).
▶What is Jupiter made of?
Jupiter is composed primarily of hydrogen (~90%) and helium (~10%) by volume, with traces of methane, ammonia, water vapor, and hydrogen sulfide. It has no solid surface. As depth increases, the immense pressure compresses hydrogen into a liquid state, and deeper still into metallic hydrogen — a bizarre phase where hydrogen conducts electricity like a metal. Jupiter may have a dense core of heavier elements roughly 10–20 times Earth’s mass, though Juno data suggests the core may be partially dissolved.
▶How far is Jupiter from the Sun?
Jupiter orbits the Sun at an average distance of 778.5 million km (5.2 AU). At this distance, sunlight takes about 43 minutes to reach Jupiter, compared to 8 minutes to reach Earth. Jupiter’s orbital period is 11.86 Earth years, meaning a single Jovian year lasts nearly 12 times as long as one on Earth. Despite this vast orbit, Jupiter has the shortest day of any planet at just 9 hours and 56 minutes.
▶Does Jupiter protect Earth from asteroids?
Jupiter’s massive gravity acts as a cosmic shield, deflecting or capturing many comets and asteroids that might otherwise enter the inner solar system. The most dramatic example was Comet Shoemaker-Levy 9, which Jupiter’s gravity tore apart and then absorbed in a spectacular series of impacts in July 1994. However, some simulations suggest Jupiter can also redirect objects toward Earth, so its role as a “protector” is more nuanced than commonly believed.
Explore More
Want to test your knowledge of Jupiter and the other planets? Our Solar System games challenge you to sort planets by properties, identify worlds from clues, and explore the wonders of our cosmic neighborhood. Jupiter is just the beginning.
Sources
- NASA Planetary Fact Sheet. "Jupiter Fact Sheet." nssdc.gsfc.nasa.gov.
- NASA Jet Propulsion Laboratory. "Juno Mission to Jupiter." nasa.gov/juno.
- NASA Science. "Jupiter: Facts." science.nasa.gov/jupiter/facts.
- NASA Jet Propulsion Laboratory. "Europa Clipper." europa.nasa.gov.
- ESA Space Science. "JUICE: Jupiter Icy Moons Explorer." esa.int/Science_Exploration.
- Southwest Research Institute. "Juno Reveals Jupiter's Interior Structure." swri.org.