Jupiter is the largest planet in the solar system. It is a giant ball of gas, mostly hydrogen and helium, with no hard ground to stand on. Jupiter is the fifth planet from the Sun, much farther out than Earth. It is so big that about 1,000 Earths could fit inside it.
Why Jupiter is tricky to understand
Jupiter looks like a bright star in the night sky, but it is a planet, not a star. It does not make its own light. The light we see is sunlight bouncing off its cloud tops.
Jupiter is huge, but it is not heavy the way a rock is heavy. It is made of gas, which is very light. Jupiter is the heaviest planet only because there is so much gas inside it. If you could weigh every other planet together on one side of a giant scale, Jupiter on the other side would still tip the scale.
The hardest thing to picture is that Jupiter has no surface. On Earth you can stand on the ground. On Jupiter there is no ground at all. The gas just gets thicker and thicker the deeper you go. A spaceship trying to land would have nowhere to stop.
Key facts about Jupiter
Jupiter is the biggest planet. It is about 11 times wider than Earth, which is about 89,000 miles (143,000 km) across.
Jupiter is the heaviest planet. It weighs more than all the other planets put together, more than twice over.
Jupiter is made of gas, mostly hydrogen and helium. These are the two lightest gases in the universe, the same ones that make up most of the Sun.
A day on Jupiter is short. Jupiter spins around once in only about 10 hours. That is the fastest spin of any planet. Earth takes 24 hours.
A year on Jupiter is long. It takes about 12 Earth years for Jupiter to travel once around the Sun, because it is so far away.
Jupiter has a giant storm called the Great Red Spot. It is wider than the whole Earth and has been swirling for hundreds of years.
Jupiter has more than 90 known moons. Scientists keep finding new ones, so the count keeps going up.
Jupiter’s moon Ganymede is the biggest moon in the solar system. It is even bigger than the planet Mercury.
Jupiter has faint rings. They are much thinner and dustier than Saturn’s bright rings, so they are hard to see from Earth.
Common myths about Jupiter
Myth: Jupiter is a failed star. Some people call Jupiter a failed star because it is made of the same main gases as the Sun. But Jupiter is a planet, not a star. To shine like a real star, it would need to be about 80 times heavier than it is now. It is nowhere close.
Myth: The Great Red Spot is getting bigger. The Great Red Spot is actually getting smaller. A hundred years ago it was much wider than it is today. Right now it is about 1.3 times as wide as Earth, and it is the smallest size people have ever measured.
Myth: You could land on Jupiter. You could not land on Jupiter, because it has no solid surface. It is a giant ball of gas, so there is no ground anywhere. A spaceship would just sink deeper and deeper into thicker gas.
Myth: Jupiter is bigger than the Sun. The Sun is much bigger than Jupiter. More than a thousand Jupiters could fit inside the Sun. Jupiter is the biggest planet, but the Sun is far larger than any planet.
Myth: Jupiter has only a few moons. Jupiter has a huge family of moons, more than 90 of them. Earth has only one moon. Jupiter has the most moons of any planet, along with Saturn.
Frequently asked questions about Jupiter
How big is Jupiter compared to Earth?
Jupiter is about 11 times wider than Earth. If you lined Earths up side by side across the middle of Jupiter, you would need about 11 of them. By size inside, about 1,000 Earths could fit within Jupiter.
Could you stand on Jupiter?
No. Jupiter is made of gas, not rock, so it has no hard surface to stand on. The deeper you went, the thicker the gas would get, but you would never reach solid ground.
Why does Jupiter have a giant red spot?
The Great Red Spot is a giant storm in Jupiter’s clouds, a little like a hurricane on Earth but much bigger. It has been spinning for hundreds of years. People first saw it through telescopes long ago, and it is still there today, though it has been shrinking.
How many moons does Jupiter have?
Jupiter has more than 90 known moons. The four biggest, called the Galilean moons, were first seen by the astronomer Galileo Galilei in 1610. The other moons are small, and new ones are still being found.
Why is Jupiter named Jupiter?
The ancient Romans named the bright planet after Jupiter, the king of their gods. It was a fitting name, because Jupiter is the largest and most powerful-looking planet. Many planets in our solar system are named after Roman gods.
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Jupiter is the fifth planet from the Sun and the largest planet in the solar system. It is a gas giant, which means it is made mostly of the gases hydrogen and helium and has no solid surface. Jupiter is about 11 times wider than Earth, at roughly 89,000 miles (143,000 km) across. It is so massive that it weighs more than all the other planets combined.
Why Jupiter is surprising
Jupiter spins faster than any other planet, even though it is the biggest. A full day on Jupiter, one complete spin, takes only about 10 hours. On Earth a day takes 24 hours. Because Jupiter spins so fast and is made of fluid gas, it bulges out a little at its middle, like a slightly squashed ball.
Jupiter is huge but not dense. Its average material is only a little heavier than water, far lighter than Earth’s rock and metal. The planet is enormous, so it adds up to a great deal of mass, but the stuff it is made of is light.
Jupiter also acts a bit like a giant shield. Its strong gravity pulls in or flings away many comets and asteroids that might otherwise travel deeper into the solar system. Some scientists think this helped keep the inner planets, including Earth, safer over billions of years.
Key facts about Jupiter
Jupiter is about 11 times wider than Earth. It measures roughly 89,000 miles (143,000 km) across, compared with Earth’s 8,000 miles (13,000 km).
A day lasts about 10 hours. Jupiter has the shortest day of any planet because it spins so fast.
A year lasts about 12 Earth years. Jupiter is about five times farther from the Sun than Earth, so it has a long way to travel around its orbit.
Jupiter has more than 90 known moons. The count keeps rising as scientists find new ones with powerful telescopes.
Ganymede is the largest moon in the solar system. This moon of Jupiter is bigger than the planet Mercury.
Europa probably hides a salty ocean. Beneath its icy crust, this moon may hold about twice as much water as all of Earth’s oceans combined.
Io is the most volcanic world we know. This moon has hundreds of active volcanoes, more than anywhere else in the solar system.
Jupiter has the strongest magnetic field of any planet, many times stronger than Earth’s. It traps charged particles and powers bright glowing lights near Jupiter’s poles.
Jupiter has faint rings, made mostly of dust. The Voyager 1 spacecraft discovered them in 1979.
NASA’s Juno spacecraft has been orbiting Jupiter since July 4, 2016, sending back close-up data on the planet.
Common myths about Jupiter
Myth: Jupiter is a failed star. People sometimes call Jupiter a failed star because it is made of the same main gases as the Sun. But Jupiter is a planet, and it formed as a planet. To begin the nuclear process that makes a star shine, Jupiter would need to be about 80 times more massive than it is. It falls far short.
Myth: The Great Red Spot is growing. The Great Red Spot has been shrinking for more than a hundred years. Long ago the storm was much wider. Today it is the smallest size ever recorded, about 1.3 times the width of Earth.
Myth: You could land a spacecraft on Jupiter. Jupiter has no solid surface, so there is nowhere to land. A spacecraft would sink into thicker and thicker gas, with the pressure and heat climbing the deeper it went. No rover could drive on Jupiter the way rovers drive on Mars.
Myth: Jupiter is the only planet with rings. Saturn is famous for its bright rings, but Jupiter, Uranus, and Neptune all have rings too. Jupiter’s rings are simply faint and dusty, which makes them hard to see from Earth.
Myth: Jupiter glows because it is on fire. Jupiter is not on fire. Most of the light we see is sunlight reflecting off its clouds. Jupiter does give off some heat of its own, but that comes from leftover warmth as the planet slowly shrinks, not from flames.
Frequently asked questions about Jupiter
Is Jupiter a star?
No. Jupiter is a planet. It is made of the same main gases as the Sun, which is why it is sometimes called a failed star, but it does not have nearly enough mass to shine. A real star needs about 80 times Jupiter’s mass to start fusing hydrogen and give off light.
What is Jupiter made of?
Jupiter is made mostly of hydrogen and helium, the two lightest gases in the universe. Deep inside, the pressure is so high that the hydrogen behaves more like a liquid metal. Jupiter may have a dense core at its center, but it has no solid outer surface.
Why is the Great Red Spot red?
The Great Red Spot is a giant storm in Jupiter’s clouds. Scientists think chemicals in the clouds, changed by sunlight, give it its reddish color. The exact recipe is still being studied. The storm spins around like a hurricane and is wider than Earth.
Does Jupiter have water?
Jupiter itself has water vapor mixed into its clouds, but no oceans on a surface, because it has no surface. Its moon Europa is the watery one: scientists believe a deep ocean of liquid water lies hidden beneath Europa’s icy crust.
How do we know so much about Jupiter?
Spacecraft have studied Jupiter up close. Voyager 1 flew past in 1979 and discovered the rings. NASA’s Juno spacecraft arrived in 2016 and has been orbiting ever since, measuring Jupiter’s gravity, magnetic field, and clouds in detail.
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Jupiter is the fifth planet from the Sun and the largest in the solar system, a gas giant composed mostly of hydrogen and helium with no solid surface. Its equatorial diameter is about 88,846 miles (142,984 km), roughly 11 times that of Earth, and its mass is about 318 times Earth’s. Jupiter is the closest of the four gas giants to the Sun, orbiting at about 484 million miles (778 million km), or 5.2 times Earth’s distance. It is more massive than all the other planets in the solar system combined, more than twice over.
What is often misunderstood about Jupiter
Jupiter is the most massive planet, yet one of the least dense. Its average density is about 1.33 grams per cubic centimeter, roughly a quarter of Earth’s rocky density and only slightly greater than water. Jupiter outweighs Earth not because its material is heavy but because there is so much of it. Mass and density are different measurements, and Jupiter sits at the high end of one and the low end of the other.
Jupiter spins faster than any other planet despite being the largest. It completes one rotation in about 9 hours and 56 minutes. Because it is a fluid body rather than a rigid one, different latitudes rotate at slightly different speeds, with the equator turning a few minutes faster than regions nearer the poles. The rapid spin flings the equator outward, so Jupiter’s equatorial radius is about 7 percent longer than its polar radius.
Jupiter is sometimes called a failed star, but the label is misleading. Jupiter and the Sun formed from the same kind of gas, but a star needs to fuse hydrogen in its core, and that requires roughly 0.08 solar masses, about 80 times Jupiter’s mass. Jupiter is far below even the brown-dwarf range. It is firmly a planet.
Key facts about Jupiter
Equatorial diameter: about 88,846 miles (142,984 km), the widest of any planet, roughly 11 times Earth’s diameter.
Mass: about 318 times Earth’s mass, the largest of any planet, exceeding the combined mass of all other planets by more than a factor of two.
Rotation period: about 9 hours 56 minutes, the fastest of any planet, giving Jupiter the shortest day in the solar system.
Orbital period: about 12 Earth years to complete one trip around the Sun.
Distance from the Sun: about 484 million miles (778 million km), or 5.2 astronomical units. Sunlight takes about 43 minutes to reach Jupiter, compared with about 8 minutes to reach Earth.
The Great Red Spot: a long-lived high-pressure storm, an anticyclone, currently the smallest size ever measured, roughly 10,000 miles across its long axis and about 1.3 times the width of Earth.
Wind speeds: jet streams near the equator can exceed 300 miles per hour (over 480 km/h), faster than the strongest hurricanes on Earth, with neighboring belts blowing in opposite directions.
Cloud-top temperature: averages about minus 234 °F (minus 145 °C); the temperature climbs sharply with depth inside the planet.
Magnetic field and auroras: the strongest planetary magnetic field in the solar system, which drives the most powerful auroras of any planet.
Moons: more than 90 known, the largest family of any planet. The count keeps rising as surveys detect more.
Ganymede: Jupiter’s largest moon and the largest moon in the solar system, bigger than the planet Mercury.
Rings: a faint, dusty ring system discovered by NASA’s Voyager 1 spacecraft in 1979, making Jupiter the second planet known to have rings after Saturn.
Common myths about Jupiter
Myth: Jupiter is a failed star. Jupiter is a planet, not a star that fell short. Sustained hydrogen fusion requires about 80 times Jupiter’s mass, near 0.08 solar masses. Jupiter is below even the brown-dwarf threshold of about 13 Jupiter masses, so it never came close to becoming a star.
Myth: The Great Red Spot is growing. The Great Red Spot has been shrinking for over a century. Historic measurements from the late 1800s put its long axis near 25,500 miles (41,000 km). By the 1979 Voyager flybys it had shrunk to about 14,500 miles (23,300 km), and Hubble measured it near 10,000 miles in the 2010s, the smallest on record.
Myth: You could land on Jupiter. Jupiter has no solid surface. A descending spacecraft would meet steadily denser gas, rising pressure, and rising temperature, with no firm boundary to land on. Below the visible clouds, hydrogen gradually transitions to a hot, dense fluid, never a rocky floor.
Myth: The Great Red Spot is a hurricane. Hurricanes on Earth are low-pressure cyclones. The Great Red Spot is a high-pressure anticyclone, so its winds circulate in the opposite sense to a terrestrial hurricane. It also sits in Jupiter’s southern hemisphere and is far larger and longer-lived than any storm on Earth.
Myth: Jupiter is the densest planet because it is the most massive. Jupiter is one of the least dense planets, about a quarter of Earth’s density. The densest planet is Earth, a rocky world. Jupiter’s enormous mass comes from its size, not from heavy material.
Frequently asked questions about Jupiter
Why is Jupiter not a star?
A star shines because hydrogen fuses into helium in its core, and that requires a core hot and dense enough to start the reaction. The minimum mass for sustained hydrogen fusion is about 0.08 solar masses, roughly 80 times Jupiter’s mass. Jupiter is far below that. It also lacks enough mass to be even a brown dwarf, which begins around 13 Jupiter masses.
What is the Great Red Spot?
The Great Red Spot is a giant high-pressure storm, an anticyclone, in Jupiter’s atmosphere. Astronomers have tracked it for hundreds of years. It is currently about 1.3 times the width of Earth and shrinking, now the smallest size ever recorded. Its reddish color likely comes from chemical compounds in the clouds altered by sunlight.
How many moons does Jupiter have?
Jupiter has more than 90 known moons, the largest family of any planet, and the number keeps rising as surveys find more. The four largest, the Galilean moons, are Io, Europa, Ganymede, and Callisto, first observed by Galileo Galilei in 1610. Ganymede is the largest moon in the solar system, bigger than Mercury.
Why is a day on Jupiter so short?
Jupiter rotates once in about 9 hours 56 minutes, faster than any other planet. A short rotation period combined with a fluid body produces the planet’s banded cloud pattern and a noticeable equatorial bulge. The fast spin is one reason Jupiter is wider across the equator than from pole to pole.
Does Jupiter have a solid surface?
No. Jupiter is a gas giant. Moving inward from the cloud tops, the atmosphere grows denser and hotter, and hydrogen gradually changes from gas to a hot fluid and then to a metallic fluid under crushing pressure. There may be a dense core deep inside, but there is no solid surface to stand on.
Why does Jupiter have such bright auroras?
Jupiter has the strongest magnetic field of any planet, which traps charged particles and funnels them toward the poles, where they collide with the atmosphere and glow. Much of the material feeding these auroras comes from volcanic gas erupting off the moon Io. The result is the most powerful aurora display in the solar system.
Source notes
Jupiter’s diameter, mass, rotation period, orbital period, distance, wind speeds, magnetic field, and moon count come from NASA’s Jupiter facts page and the NASA planet sizes overview. Moon details, including Ganymede as the largest moon in the solar system, are from the NASA Jupiter moons page. The Great Red Spot’s historic and current dimensions and its shrinking trend are documented in NASA JPL’s Great Red Spot report. Jupiter’s auroras are described in NASA JPL’s auroras feature, and the current orbiter is documented on the NASA Juno mission page.
Each of this topic’s quiz questions cites a source for the specific fact tested. You can play at any level: Rookie, Curious, Sharp, or Expert.
Jupiter is the fifth planet from the Sun and the largest in the solar system, a gas giant of roughly 318 Earth masses composed predominantly of hydrogen and helium in proportions close to those of the early Sun. Its equatorial diameter is about 88,846 miles (142,984 km), and its mean density is about 1.33 grams per cubic centimeter, lower than any of the terrestrial planets. Jupiter is the innermost of the four giant planets, orbiting at about 5.2 astronomical units, and it dominates the solar system’s planetary mass budget, outweighing the other seven planets combined by more than a factor of two. It has no solid surface: the atmosphere grades continuously into a fluid interior with increasing depth.
Why Jupiter’s physics is non-intuitive
Jupiter is the most massive planet and one of the least dense, which separates two quantities that everyday intuition tends to merge. Its mean density of about 1.33 grams per cubic centimeter is roughly a quarter of Earth’s. The planet’s mass arises from sheer volume: about 1,000 Earths would fit inside it, since volume scales with the cube of the linear size and Jupiter is about 11 times Earth’s diameter. Under its own weight, the interior is far denser than the cloud-top average, but the bulk composition of light elements keeps the mean low.
Jupiter is sometimes labeled a failed star, a description that conflates composition with the mass needed to ignite fusion. Sustained hydrogen fusion requires about 0.08 solar masses, roughly 80 Jupiter masses, the boundary between brown dwarfs and the lowest-mass red dwarfs. Objects between about 13 and 80 Jupiter masses are brown dwarfs, able to fuse deuterium transiently but not ordinary hydrogen. Jupiter sits well below even the deuterium-burning threshold, so it never approached stellar or substellar ignition. Its modest excess luminosity is not fusion at all: Jupiter radiates roughly twice the energy it absorbs from sunlight, powered by the Kelvin-Helmholtz mechanism, the slow release of gravitational energy as the planet contracts and cools from formation.
Jupiter does not rotate as a rigid body. Because it is fluid, it exhibits differential rotation, tracked by convention in three systems. System I applies to the equatorial zone and turns in about 9 hours 50 minutes. System II applies to higher latitudes and turns about 5 minutes slower. System III is keyed to the rotation of the magnetic field and stands in for the deep interior, giving the planet’s canonical rotation period of about 9 hours 56 minutes. The rapid spin produces strong oblateness: the equatorial radius is about 7 percent larger than the polar radius.
Key facts about Jupiter
Bulk properties. Mass about 318 Earth masses, equatorial diameter about 88,846 miles (142,984 km), mean density about 1.33 grams per cubic centimeter. Surface gravity at the 1-bar level is roughly 2.5 times Earth’s.
Rotation and oblateness. System III rotation period about 9 hours 56 minutes, the fastest of any planet. Differential rotation gives the equatorial System I a period a few minutes shorter than the higher-latitude System II. Equatorial radius about 7 percent longer than polar radius.
Interior. Beneath the molecular hydrogen envelope, pressure drives a transition to liquid metallic hydrogen, an electrically conducting fluid whose circulation generates the magnetic field. Juno gravity data favor a diluted, possibly partially eroded core rather than a sharp rock-ice boundary.
Magnetosphere. The strongest planetary magnetic field in the solar system and the largest planetary magnetosphere, with a magnetotail that extends past the orbit of Saturn on the anti-solar side. The surface field at the cloud tops is on the order of tens of times Earth’s field strength.
Atmospheric dynamics. Banded zonal jets alternate in direction with latitude. Peak winds exceed 300 miles per hour (over 480 km/h). The visible weather layer sits atop a deep, convecting atmosphere; cloud-top temperatures average about minus 234 °F (minus 145 °C).
The Great Red Spot. A high-pressure anticyclone in the southern hemisphere, persistent for well over a century. Its long axis spanned about 25,500 miles (41,000 km) in the late 1800s, about 14,500 miles (23,300 km) at the 1979 Voyager flybys, and near 10,000 miles by the 2010s, the smallest on record and roughly 1.3 times Earth’s diameter.
Galilean moons. Io, Europa, Ganymede, and Callisto, discovered by Galileo Galilei in 1610. Ganymede is the largest moon in the solar system and exceeds Mercury in diameter. Jupiter has more than 90 known moons in total, a count that continues to rise.
Laplace resonance. Io, Europa, and Ganymede occupy a 1:2:4 mean-motion resonance, first analyzed by Pierre-Simon Laplace: Io completes four orbits for every two of Europa and one of Ganymede. The resonance forces and maintains orbital eccentricity in the inner moons.
Io’s tidal heating. The forced eccentricity drives time-varying tides as Jupiter’s gravity flexes Io through each orbit. The resulting frictional dissipation, tidal heating, makes Io the most volcanically active body in the solar system, with hundreds of active volcanoes.
Galileo probe composition. The Galileo atmospheric probe entered Jupiter on December 7, 1995, and measured a helium abundance close to but slightly below the primordial solar ratio, consistent with helium settling toward the interior. Helium accounted for roughly 14 percent of the atmosphere by number of molecules.
Current exploration. NASA’s Juno spacecraft entered orbit on July 4, 2016, on a highly elliptical polar orbit. Each perijove dives close to the cloud tops, partly to limit cumulative dose in the intense radiation belts, while mapping gravity and the magnetic field to constrain the interior.
Common misconceptions at expert level
Misconception: Jupiter’s excess heat comes from residual or ongoing fusion. Jupiter’s interior is far too cool and low-pressure to fuse hydrogen. The roughly factor-of-two excess of emitted over absorbed energy is gravitational, released by the Kelvin-Helmholtz mechanism as the planet slowly contracts. Models suggest the planet shrinks on the order of a millimeter per year.
Misconception: The Great Red Spot is a cyclone like a terrestrial hurricane. The Great Red Spot is an anticyclone, a high-pressure system whose vorticity is opposite in sense to a low-pressure terrestrial hurricane in the same hemisphere. It is confined to the upper atmosphere, with Juno gravity and microwave data indicating roots a few hundred miles deep, not a conduit to the core.
Misconception: The Galilean moons orbit independently. The inner three are locked in the Laplace 1:2:4 resonance. The resonance is not a coincidence of initial conditions: it is maintained dynamically, and it sustains the orbital eccentricities that would otherwise damp away, which in turn powers Io’s volcanism and helps keep Europa’s subsurface ocean liquid.
Misconception: Io’s heat is primordial or radiogenic. For a body of Io’s size, radiogenic and accretional heat would have largely dissipated long ago. The observed heat flow, far higher than radiogenic models predict, is supplied continuously by tidal dissipation driven by the resonance-forced eccentricity.
Misconception: Jupiter’s atmosphere resembles Earth’s air. The Galileo probe confirmed a hydrogen-helium atmosphere, not a nitrogen-oxygen one. Helium relative to hydrogen came out close to the solar value, slightly depleted, evidence that Jupiter formed from the same reservoir as the Sun and that helium has been redistributing toward depth.
Misconception: Being a gas giant prevents a strong magnetic field. Jupiter has the strongest magnetic field of any planet. The dynamo is seated in the liquid metallic hydrogen layer, where high pressure makes hydrogen electrically conducting and convective motions sustain the field. Composition does not preclude a dynamo; it sets where the dynamo operates.
Frequently asked questions about Jupiter
Why is Jupiter not a star or even a brown dwarf?
Stellar ignition of hydrogen requires central conditions reached only above about 0.08 solar masses, roughly 80 Jupiter masses. Brown dwarfs, which fuse deuterium transiently, begin near 13 Jupiter masses. Jupiter is about one-eightieth of the lowest stellar mass and well under the deuterium threshold, so it is unambiguously a planet that formed by accretion in the Sun’s protoplanetary disk.
What is metallic hydrogen, and why does it matter for Jupiter?
At the pressures deep inside Jupiter, hydrogen transitions from a molecular fluid to a metallic, electrically conducting fluid. Convective motion of this conducting layer, combined with the planet’s rapid rotation, drives the dynamo that produces Jupiter’s magnetic field. The same layer carries much of the planet’s mass and shapes the interior structure that Juno’s gravity measurements probe.
How does the Laplace resonance power Io’s volcanoes?
The 1:2:4 resonance among Io, Europa, and Ganymede continually pumps Io’s orbital eccentricity. An eccentric orbit means the strength and direction of Jupiter’s tidal pull on Io vary through each orbit, flexing the moon. That mechanical flexing dissipates as heat through internal friction, the process called tidal heating, which melts rock at depth and feeds Io’s hundreds of active volcanoes.
Why does Jupiter rotate differentially?
Jupiter has no rigid surface to enforce a single rotation rate. As a fluid body, it supports zonal flows that vary with latitude, so the equatorial atmosphere (System I) laps the higher latitudes (System II) by a few minutes per rotation. The magnetically defined System III period stands in for the deep interior, where the metallic hydrogen and the dynamo it drives rotate more coherently.
What did the Galileo probe measure as it descended?
The probe, released from the Galileo orbiter, entered Jupiter’s atmosphere on December 7, 1995, and returned data during its descent before being destroyed by pressure and heat. It measured atmospheric composition, temperature, pressure, winds, and cloud structure, finding a hydrogen-helium atmosphere with helium close to the solar ratio and winds that strengthened with depth, evidence that Jupiter’s winds are not merely sunlight-driven surface weather.
How does Juno study Jupiter’s interior without landing?
Juno flies a highly elliptical polar orbit, repeatedly passing close to the cloud tops. Precise tracking of the spacecraft reveals tiny variations in Jupiter’s gravity field, which constrain how mass is distributed inside, including the nature of the core. Its magnetometer maps the field in detail, and microwave instruments probe below the visible clouds. The polar, looping orbit also limits the time spent in Jupiter’s harsh radiation belts.
Source notes
Bulk parameters (mass, diameter, density, rotation period, distance) are drawn from NASA’s Jupiter Fact Sheet and the NASA Jupiter facts page. The Kelvin-Helmholtz internal-heat mechanism, the three rotation systems and differential rotation, the metallic hydrogen interior, and the magnetosphere extending past Saturn’s orbit are documented in the Jupiter overview. The Galileo probe helium abundance near the solar ratio is from the atmosphere of Jupiter entry. The Laplace 1:2:4 resonance and Io’s tidal heating are described by The Planetary Society’s Galilean resonance and Io pages. The Great Red Spot’s historic and current dimensions and shrinking trend are from NASA JPL’s Great Red Spot report. The Juno orbit and objectives are from the NASA Juno mission page.
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