Jupiter
The fifth planet from the Sun and the solar system's largest planet by far is Jupiter. More than 1,300 Earths would fit inside it. The planet is one of the brightest objects in the night sky, and even a small telescope can reveal its multicolored stripes. These stripes are bands of clouds being pushed around the planet by strong east-west winds. Jupiter is a world of complex weather patterns. Its most prominent feature is an orange-red oval called the Great Red Spot. The oval is a storm system that has lasted at least 300 years and is bigger across than Earth and Mars combined.
Basic Planetary Data
Size, Mass, and Density Jupiter is named for the ruler of the ancient Roman gods, the equivalent of the ancient Greek god Zeus. The ancient Romans did not know how large the planet is, but the name turned out to be fitting. Jupiter encompasses more matter than all the other planets in the solar system combined. Its diameter at the equator is some 88,846 miles (142,984 kilometers). It is about 320 times as massive as Earth. Jupiter's large mass produces strong gravitational effects on other members of the solar system. It forms gaps, for instance, in the distribution of the asteroids in the main belt and changes the trajectory of comets. The planet's density is very low, only about 1.3 times that of water. By comparison, Earth is more than 5.5 times denser than water.
Orbit and Spin Jupiter, like all the other planets, travels around the Sun in a slightly elliptical, or oval-shaped, orbit. It completes one orbit in about 11.86 Earth years, which is the length of a year on Jupiter. Its average distance from the Sun is about 483 million miles (778 million kilometers), which is more than five times greater than Earth's.
Jupiter spins very quickly on its axis, faster than the other seven planets. It completes one rotation in about 9 hours and 55 minutes, which is the length of a day on Jupiter. The atmosphere spins at slightly different rates, with the clouds near the equator completing a rotation a few minutes faster than the clouds at higher latitudes. The force of a planet's rotation causes it to bulge slightly at the equator and to flatten slightly at the poles. Jupiter's rapid spin accentuates this, so it is less perfectly spherical than most of the other planets. Jupiter's spin axis is tilted only about 3 degrees. For this reason, it does not have seasons like Earth, Mars, and other planets with tilted axes.
Atmosphere
The clouds in Jupiter's atmosphere appear as alternating dark and bright bands roughly parallel to the equator. The darker bands are called belts, while the brighter bands are called zones. The clouds are also separated into different layers by depth. They range in color from white to tawny yellow, brown, salmon, and blue-gray. Scientists think that the clouds vary in color because they contain different chemicals.
Jupiter has a turbulent atmosphere, and its cloud systems form and change in a matter of hours or days. However, the underlying pattern of wind currents has been stable over decades. Strong winds blow east or west through the atmosphere in several alternating bands. They are interrupted in places by large whirling storm systems that appear from above as ovals.
The Great Red Spot projects higher than the planet's highest white clouds, and it probably also descends well below the main cloud layers. There is no clear evidence that the storm causes upwelling of material at its center, though some vertical movement would be expected. Scientists are not certain why the spot is reddish. They think its color might result from complex organic molecules, red phosphorous, or sulfur compounds. Any of these materials could be produced by lightning. They also could result from material upwelling to high altitudes, where it reacts chemically with ultraviolet radiation from the Sun.
Interior The atmosphere surrounding Jupiter makes up only a small percentage of the planet. Scientists cannot directly observe the planet below the atmosphere, however. Instead, they form theoretical models based on many known properties such as the planet's size, mass, density, rotation rate, heat balance, and atmospheric pressures and temperatures.
Like the atmosphere, the interior is composed mainly of hydrogen and helium. Inside the planet, pressures and temperatures increase greatly with depth, so the hydrogen and helium get denser and denser. Starting at about a quarter of the way down to the center, the pressure has probably squeezed the hydrogen into liquid metallic form. In this state, the electrons are stripped away from the atomic nuclei, so the fluid hydrogen would conduct electricity like a metal.
At Jupiter's center is probably a very dense core. Different models have the core about a third as big as Earth to a bit bigger than Earth. Temperatures there may reach nearly 45,000° F (25,000° C). The pressure in the core is likely 50 million to 100 million times the pressure at sea level on Earth.
Jupiter has some sort of internal heat source. The planet emits nearly twice as much energy as it receives from the Sun, for reasons that are not entirely clear. Much of this heat was probably acquired during the planet's formation some 4.6 billion years ago. As the planet continues to cool off, it gradually emits heat. Scientists think that another process probably also generates some of the heat. This process involves helium separating out into droplets and sinking toward the planet's center. The friction of the helium droplets pushing against the liquid metallic hydrogen would convert some energy to heat.
Magnetic Field and Magnetosphere Jupiter has the largest and strongest magnetic field of all the planets. The planet's rapidly rotating, electrically conducting interior is thought to give rise to the strong field. Like Earth's magnetic field, it has two poles, north and south, like a giant bar magnet. The orientation of the poles is opposite that of Earth, so that a compass would point south on Jupiter. Jupiter's magnetic field is also tilted about 10 degrees relative to its spin axis.
The region of space dominated by Jupiter's magnetic field is called its magnetosphere. It is a huge teardrop-shaped area. On the side nearest the Sun it extends about 1.9 million miles (3 million kilometers). On that side, the magnetosphere holds off the solar wind, which is a flow of electrically charged particles from the Sun. This creates a large shock wave. On the opposite side of Jupiter, the solar wind pushes the magnetosphere's tail out to the orbit of Saturn, some 400 million miles (650 million kilometers) away.
Jupiter strongly emits radio waves in both intermittent bursts at longer wavelengths and steady streams at shorter wavelengths. Both types result from charged particles moving in the planet's magnetosphere. The bursts are sometimes the most intense source of radio “noise” in the sky. They were first detected in the 1950s, and they provided the first clues that Jupiter had a magnetic field. The steady emissions, which were discovered later, are radiated by the charged particles trapped in the radiation belts. This stream of radio waves varies somewhat in intensity and orientation as the planet rotates. The variations have a characteristic period, which is the rotation rate of Jupiter's magnetic field. The rotation rate of the magnetic field is also the rotation rate of the planet's interior, which produces the field.
The bursts of radio waves come from three distinct areas around Jupiter. The position of the moon Io as it orbits Jupiter is thought to strongly influence these bursts. Magnetic field lines connect Jupiter to Io. They enclose a doughnut-shaped region of space called a flux tube between the planet and the moon. This flux tube moves along with Io. In addition, volcanic eruptions on Io release a cloud of electrically charged particles that accompanies Io along its orbit. As the cloud passes through Jupiter's magnetic field, an electric current of some 5 million amperes is generated. Scientists believe that the radio bursts are probably emitted by electrons that spiral along the magnetic field lines in the flux tube connecting Io and Jupiter.
Ring System
Moons
The two inner Galilean satellites, Io and Europa, are much denser than the outer two, Ganymede and Callisto. Io and Europa are probably rocky bodies with compositions roughly similar to Earth's Moon. Ganymede and Callisto are probably roughly half rock and half water ice or some other substance of low density. The surfaces of three of the moons, Europa, Ganymede, and Callisto, are icy.
Io
Io orbits Jupiter at an average distance of about 262,000 miles (422,000 kilometers) from the planet's center. It completes one orbit and one rotation in 1.8 Earth days. The diameter at its equator is about 2,260 miles (3,630 kilometers). The moon is about 3.5 times as dense as water.
Europa
Europa's average distance from Jupiter's center is about 417,000 miles (671,000 kilometers). It completes one orbit and one rotation in 3.6 Earth days. The smallest of the Galilean moons, it has an equatorial diameter of about 1,940 miles (3,130 kilometers). It is about three times denser than water.
Ganymede
Ganymede is the only moon in the solar system that produces its own permanent, strong magnetic field. Its magnetic field is about the strength of Mercury's and creates its own magnetosphere and auroras.
Ganymede orbits Jupiter from an average distance of about 665,000 miles (1,070,000 kilometers) from the planet's center. It takes the moon about 7.2 Earth days to complete both one orbit and one rotation. It is not quite twice as dense as water.
Callisto
The most distant of the Galilean satellites, Callisto is on average about 1,170,000 miles (1,883,000 kilometers) from the center of Jupiter. It completes one orbit and one rotation in 16.7 Earth days. The diameter at Callisto's equator is some 3,000 miles (4,800 kilometers). The moon is only about 1.8 times as dense as water.
Spacecraft Exploration The first three spacecraft missions to Jupiter—named Pioneer, Voyager, and Galileo—dramatically increased scientists' knowledge about the giant planet in the late 20th century. Two Pioneer spacecraft flew by Jupiter in the early 1970s to survey the planet's basic environment and assess whether its radiation levels would permit future spacecraft exploration. They were launched by the U.S. National Aeronautics and Space Administration (NASA). Pioneer 10 was the first spacecraft to travel beyond the asteroid belt to the outer part of the solar system. Flying within 80,000 miles (130,000 kilometers) of Jupiter's cloud tops in December 1973, it transmitted the first close-up images of the planet. It also discovered the huge “tail” of the planet's magnetosphere. Pioneer 11 followed, passing within about 27,000 miles (43,000 kilometers) of the cloud tops in December 1974.
Additional data and images of Jupiter were captured by NASA's Cassini spacecraft as it flew by the planet in 2000–01 on its way to Saturn. Among the phenomena studied through Cassini were large amounts of charged particles escaping from one side of Jupiter's magnetosphere. (See also space exploration.)
Additional references about Jupiter
- A map shows the entire visible “surface” of Jupiter, including its bands of clouds, the …
- Hot, glowing lava erupts from a volcano on Jupiter's moon Io in an image captured by the Galileo …
- An elaborate pattern of ridges and cracks is etched on the icy surface of Europa, one of Jupiter's …
Basic Planetary Data
- A computer animation shows what Jupiter would look like if seen from above its moon Io. The …
Size, Mass, and Density Jupiter is named for the ruler of the ancient Roman gods, the equivalent of the ancient Greek god Zeus. The ancient Romans did not know how large the planet is, but the name turned out to be fitting. Jupiter encompasses more matter than all the other planets in the solar system combined. Its diameter at the equator is some 88,846 miles (142,984 kilometers). It is about 320 times as massive as Earth. Jupiter's large mass produces strong gravitational effects on other members of the solar system. It forms gaps, for instance, in the distribution of the asteroids in the main belt and changes the trajectory of comets. The planet's density is very low, only about 1.3 times that of water. By comparison, Earth is more than 5.5 times denser than water.
Orbit and Spin Jupiter, like all the other planets, travels around the Sun in a slightly elliptical, or oval-shaped, orbit. It completes one orbit in about 11.86 Earth years, which is the length of a year on Jupiter. Its average distance from the Sun is about 483 million miles (778 million kilometers), which is more than five times greater than Earth's.
Jupiter spins very quickly on its axis, faster than the other seven planets. It completes one rotation in about 9 hours and 55 minutes, which is the length of a day on Jupiter. The atmosphere spins at slightly different rates, with the clouds near the equator completing a rotation a few minutes faster than the clouds at higher latitudes. The force of a planet's rotation causes it to bulge slightly at the equator and to flatten slightly at the poles. Jupiter's rapid spin accentuates this, so it is less perfectly spherical than most of the other planets. Jupiter's spin axis is tilted only about 3 degrees. For this reason, it does not have seasons like Earth, Mars, and other planets with tilted axes.
Atmosphere
- The Galileo spacecraft recorded lightning storms on Jupiter in 1997 during observations of the …
- A graph shows the temperatures and pressures at different levels of Jupiter's atmosphere, as …
The clouds in Jupiter's atmosphere appear as alternating dark and bright bands roughly parallel to the equator. The darker bands are called belts, while the brighter bands are called zones. The clouds are also separated into different layers by depth. They range in color from white to tawny yellow, brown, salmon, and blue-gray. Scientists think that the clouds vary in color because they contain different chemicals.
- A false-color mosaic of Jupiter's northern atmosphere shows features such as cloud bands, white …
Jupiter has a turbulent atmosphere, and its cloud systems form and change in a matter of hours or days. However, the underlying pattern of wind currents has been stable over decades. Strong winds blow east or west through the atmosphere in several alternating bands. They are interrupted in places by large whirling storm systems that appear from above as ovals.
- Ribbons of clouds wind through the area around Jupiter's huge Great Red Spot, an ancient, whirling …
The Great Red Spot projects higher than the planet's highest white clouds, and it probably also descends well below the main cloud layers. There is no clear evidence that the storm causes upwelling of material at its center, though some vertical movement would be expected. Scientists are not certain why the spot is reddish. They think its color might result from complex organic molecules, red phosphorous, or sulfur compounds. Any of these materials could be produced by lightning. They also could result from material upwelling to high altitudes, where it reacts chemically with ultraviolet radiation from the Sun.
- As of 2006, Jupiter had two large red spots. The Great Red Spot, below the equator at right, and …
Interior The atmosphere surrounding Jupiter makes up only a small percentage of the planet. Scientists cannot directly observe the planet below the atmosphere, however. Instead, they form theoretical models based on many known properties such as the planet's size, mass, density, rotation rate, heat balance, and atmospheric pressures and temperatures.
Like the atmosphere, the interior is composed mainly of hydrogen and helium. Inside the planet, pressures and temperatures increase greatly with depth, so the hydrogen and helium get denser and denser. Starting at about a quarter of the way down to the center, the pressure has probably squeezed the hydrogen into liquid metallic form. In this state, the electrons are stripped away from the atomic nuclei, so the fluid hydrogen would conduct electricity like a metal.
At Jupiter's center is probably a very dense core. Different models have the core about a third as big as Earth to a bit bigger than Earth. Temperatures there may reach nearly 45,000° F (25,000° C). The pressure in the core is likely 50 million to 100 million times the pressure at sea level on Earth.
Jupiter has some sort of internal heat source. The planet emits nearly twice as much energy as it receives from the Sun, for reasons that are not entirely clear. Much of this heat was probably acquired during the planet's formation some 4.6 billion years ago. As the planet continues to cool off, it gradually emits heat. Scientists think that another process probably also generates some of the heat. This process involves helium separating out into droplets and sinking toward the planet's center. The friction of the helium droplets pushing against the liquid metallic hydrogen would convert some energy to heat.
Magnetic Field and Magnetosphere Jupiter has the largest and strongest magnetic field of all the planets. The planet's rapidly rotating, electrically conducting interior is thought to give rise to the strong field. Like Earth's magnetic field, it has two poles, north and south, like a giant bar magnet. The orientation of the poles is opposite that of Earth, so that a compass would point south on Jupiter. Jupiter's magnetic field is also tilted about 10 degrees relative to its spin axis.
The region of space dominated by Jupiter's magnetic field is called its magnetosphere. It is a huge teardrop-shaped area. On the side nearest the Sun it extends about 1.9 million miles (3 million kilometers). On that side, the magnetosphere holds off the solar wind, which is a flow of electrically charged particles from the Sun. This creates a large shock wave. On the opposite side of Jupiter, the solar wind pushes the magnetosphere's tail out to the orbit of Saturn, some 400 million miles (650 million kilometers) away.
- The Cassini spacecraft mapped Jupiter's radiation belts by measuring the strength of their radio …
Jupiter strongly emits radio waves in both intermittent bursts at longer wavelengths and steady streams at shorter wavelengths. Both types result from charged particles moving in the planet's magnetosphere. The bursts are sometimes the most intense source of radio “noise” in the sky. They were first detected in the 1950s, and they provided the first clues that Jupiter had a magnetic field. The steady emissions, which were discovered later, are radiated by the charged particles trapped in the radiation belts. This stream of radio waves varies somewhat in intensity and orientation as the planet rotates. The variations have a characteristic period, which is the rotation rate of Jupiter's magnetic field. The rotation rate of the magnetic field is also the rotation rate of the planet's interior, which produces the field.
The bursts of radio waves come from three distinct areas around Jupiter. The position of the moon Io as it orbits Jupiter is thought to strongly influence these bursts. Magnetic field lines connect Jupiter to Io. They enclose a doughnut-shaped region of space called a flux tube between the planet and the moon. This flux tube moves along with Io. In addition, volcanic eruptions on Io release a cloud of electrically charged particles that accompanies Io along its orbit. As the cloud passes through Jupiter's magnetic field, an electric current of some 5 million amperes is generated. Scientists believe that the radio bursts are probably emitted by electrons that spiral along the magnetic field lines in the flux tube connecting Io and Jupiter.
- Auroras light up Jupiter's poles in images taken by the Hubble Space Telescope. The two lower …
Ring System
- Jupiter's ring system and small inner moons are depicted in a schematic illustration. Impacts of …
- Two images taken by the Galileo orbiter show the thin main ring of Jupiter nearly edge-on. The top …
Moons
- Jupiter's Galilean moons—from left to right, Io, Europa, Ganymede, and Callisto—appear …
- The four innermost moons of Jupiter are, from left to right, Metis, Adrastea, Amalthea, and Thebe. …
- The large moon Io appears above Jupiter's clouds in an image taken by the Voyager 1 spacecraft.
The two inner Galilean satellites, Io and Europa, are much denser than the outer two, Ganymede and Callisto. Io and Europa are probably rocky bodies with compositions roughly similar to Earth's Moon. Ganymede and Callisto are probably roughly half rock and half water ice or some other substance of low density. The surfaces of three of the moons, Europa, Ganymede, and Callisto, are icy.
Io
- A false-color infrared image shows the surface of Io, one of the satellites of Jupiter. The …
- Volcanoes erupt on Io, one of Jupiter's Galilean satellites, in a mosaic of images captured by the …
Io orbits Jupiter at an average distance of about 262,000 miles (422,000 kilometers) from the planet's center. It completes one orbit and one rotation in 1.8 Earth days. The diameter at its equator is about 2,260 miles (3,630 kilometers). The moon is about 3.5 times as dense as water.
Europa
- Part of the icy surface of Europa, one of Jupiter's large Galilean moons, appears in a composite of …
- A small, elaborately patterned area of Europa's ice crust appears in an enhanced-color image that …
Europa's average distance from Jupiter's center is about 417,000 miles (671,000 kilometers). It completes one orbit and one rotation in 3.6 Earth days. The smallest of the Galilean moons, it has an equatorial diameter of about 1,940 miles (3,130 kilometers). It is about three times denser than water.
Ganymede
- Ganymede, one of Jupiter's major moons and the largest moon in the solar system, appears in a …
- A close-up of Ganymede's surface taken by the Galileo spacecraft shows a region of diverse terrain …
Ganymede is the only moon in the solar system that produces its own permanent, strong magnetic field. Its magnetic field is about the strength of Mercury's and creates its own magnetosphere and auroras.
Ganymede orbits Jupiter from an average distance of about 665,000 miles (1,070,000 kilometers) from the planet's center. It takes the moon about 7.2 Earth days to complete both one orbit and one rotation. It is not quite twice as dense as water.
Callisto
- Callisto, one of Jupiter's Galilean moons, appears in an image taken by the Galileo spacecraft. The …
- A heavily cratered and pitted region of Callisto's ancient surface appears in an image (bottom …
The most distant of the Galilean satellites, Callisto is on average about 1,170,000 miles (1,883,000 kilometers) from the center of Jupiter. It completes one orbit and one rotation in 16.7 Earth days. The diameter at Callisto's equator is some 3,000 miles (4,800 kilometers). The moon is only about 1.8 times as dense as water.
Spacecraft Exploration The first three spacecraft missions to Jupiter—named Pioneer, Voyager, and Galileo—dramatically increased scientists' knowledge about the giant planet in the late 20th century. Two Pioneer spacecraft flew by Jupiter in the early 1970s to survey the planet's basic environment and assess whether its radiation levels would permit future spacecraft exploration. They were launched by the U.S. National Aeronautics and Space Administration (NASA). Pioneer 10 was the first spacecraft to travel beyond the asteroid belt to the outer part of the solar system. Flying within 80,000 miles (130,000 kilometers) of Jupiter's cloud tops in December 1973, it transmitted the first close-up images of the planet. It also discovered the huge “tail” of the planet's magnetosphere. Pioneer 11 followed, passing within about 27,000 miles (43,000 kilometers) of the cloud tops in December 1974.
- This animation shows the paths of Voyagers 1 and 2, a pair of spacecraft that explored the outer …
- Artwork depicts the journey of the Galileo spacecraft to Jupiter. Galileo's multiple gravity-assist …
- The Galileo atmospheric probe (shown before its launch) became the first man-made object to make …
- An artist's rendering shows the Galileo spacecraft making its 559-mile (900-kilometer) flyby of Io, …
- Several enormous, dark scars temporarily formed in Jupiter's atmosphere when pieces of Comet …
Additional data and images of Jupiter were captured by NASA's Cassini spacecraft as it flew by the planet in 2000–01 on its way to Saturn. Among the phenomena studied through Cassini were large amounts of charged particles escaping from one side of Jupiter's magnetosphere. (See also space exploration.)
Additional references about Jupiter