Jupiter: Largest Planet of the Solar System
Jupiter was the king of the gods in Roman mythology — a fitting name for the largest of the planets. In a similar manner, the ancient Greeks named the planet after Zeus, the king of the Greek pantheon.
Jupiter helped revolutionize the way we saw the universe and ourselves in 1610, when Galileo discovered Jupiter's four large moons — Io, Europa, Ganymede and Callisto, now known as the Galilean moons. This was the first time celestial bodies were not seen circling the Earth, major support of the Copernican view that Earth was not the center of the universe.
Physical Characteristics of the Planet Jupiter
Jupiter is the most massive planet in our solar system, more than twice as massive as all the other planets combined, and had it been about 80 times more massive, it would have actually become a star instead of a planet. Its atmosphere resembles that of the sun, made up mostly of hydrogen and helium, and with four large moons and many smaller moons in orbit around it, Jupiter by itself forms a kind of miniature solar system. All told, the immense volume of Jupiter could hold more than 1,300 Earths.
The colorful bands of Jupiter are arranged in dark belts and light zones created by strong east-west winds in the planet's upper atmosphere traveling more than 400 miles per hour (640 kilometers per hour). The white clouds in the zones are made of crystals of frozen ammonia, while darker clouds of other chemicals are found in the belts. At the deepest visible levels are blue clouds.
The most extraordinary feature on Jupiter is undoubtedly the Great Red Spot, a giant hurricane-like storm seen for more than 300 years. At its widest, the Great Red Spot is three times the diameter of the Earth, and its edge spins counterclockwise around its center at a speed of about 225 miles (360 kilometers) per hour. The color of the storm, which usually varies from brick red to slightly brown, may come from small amounts of sulfur and phosphorus in the ammonia crystals in Jupiter's clouds. Every now and again, the Great Red Spot seems to fade entirely.
Jupiter's gargantuan magnetic field is the strongest of all the planets in the solar system at nearly 20,000 times the strength of Earth's. It traps electrically charged particles in an intense belt of electrons and other electrically charged particles that regularly blasts the planet's moons and rings with a level of radiation more than 1,000 times the lethal level for a human, damaging even heavily-shielded spacecraft such as NASA's Galileo probe. The magnetosphere of Jupiter, which is comprised of these fields and particles, swells out some 600,000 to 2 million miles (1 million to 3 million kilometers) toward the sun and tapers to a tail extending more than 600 million miles (1 billion kilometers) behind Jupiter.
Jupiter spins faster than any other planet, taking a little under 10 hours to complete a turn on its axis, compared with 24 hours for Earth. This rapid spin actually makes Jupiter bulge at the equator and flatten at the poles, making the planet about 7 percent wider at the equator than at the poles.
Jupiter broadcasts radio waves strong enough to detect on Earth. These come in two forms — strong bursts that occur when Io, the closest of Jupiter's large moons, passes through certain regions of Jupiter's magnetic field, and continuous radiation from Jupiter's surface and high-energy particles in its radiation belts.
Jupiter's Orbital Characteristics
Composition & Structure
- Atmospheric composition (by volume)
89.8 percent molecular hydrogen, 10.2 percent helium, minor amounts of methane, ammonia, hydrogen deuteride, ethane, water, ammonia ice aerosols, water ice aerosols, ammonia hydrosulfide aerosols
Nearly 20,000 times stronger than Earth's
A dense core of uncertain composition, surrounded by a helium-rich layer of fluid metallic hydrogen, wrapped up in an atmosphere primarily made of molecular hydrogen.
- Internal structure
A core less than 10 times Earth's mass (Tristan Guillot, "Interiors of Giant Planets Inside and Outside the Solar System." Science Vol. 286 (5437), p. 72-77, October 1, 1999.), surrounded by a layer of fluid metallic hydrogen extending out to 80 to 90 percent of the diameter of the planet, enclosed in an atmosphere mostly made of gaseous and liquid hydrogen.
Orbit & Rotation
Average Distance from the Sun
English: 483,682,810 miles
Metric: 778,412,020 km
By Comparison: 5.203 times that of Earth
English: 460,276,100 miles
Metric: 740,742,600 km
By Comparison: 5.036 times that of Earth
English: 507,089,500 miles
Metric: 816,081,400 km
By Comparison: 5.366 times that of Earth
Jupiter has at least 63 moons, which are often named after the Roman god's many lovers. The four largest moons of Jupiter, now called Io, Europa, Ganymede, and Callisto, were discovered by Galileo Galilei himself, and are appropriately known today as the Galilean satellites.
Io is the most volcanically active body in our solar system. The sulfur these volcanoes spew out gives Io a blotted yellow-orange appearance that is often compared to a pepperoni pizza. As Io orbits Jupiter, the planet's immense gravity causes 'tides' in Io's solid surface that rise 300 feet (100 meters) high, generating enough heat for volcanic activity.
The frozen crust of Europa is made up mostly of water ice, and it might hide a liquid ocean holding twice as much water as Earth does. Icy oceans might also exist beneath the crusts of Callisto and Ganymede.
Callisto has the lowest reflectivity, or albedo, of the four Galilean moons. This suggests that its surface might be composed of dark, colorless rock.
The main ring is flattened. It is about 20 miles (30 kilometers) thick and more than 4,000 miles (6,400 kilometers) wide.
The inner cloud-like ring, called the halo, is roughly 12,000 miles (20,000 kilometers) thick. The halo extends halfway from the main ring down to the planet's cloudtops and expands by interaction with Jupiter's magnetic field. Both the main ring and halo are composed of small, dark particles.
The third ring, known as the gossamer ring because of its transparency, is actually three rings of microscopic debris from three of Jupiter's moons, Amalthea, Thebe and Adrastea. It is probably made up of dust particles less than 10 microns in diameter, about the same size of the particles found in cigarette smoke, and extends to an outer edge of about 80,000 miles (129,000 kilometers) from the center of the planet and inward to about 18,600 miles (30,000 kilometers).
Research & Exploration
Seven missions have flown by Jupiter — Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Cassini and New Horizons — while another, NASA's Galileo, actually orbited the planet.
Pioneer 10 revealed how dangerous Jupiter's radiation belt is, while Pioneer 11 provided data on the Great Red Spot and close-up pictures of its polar region. Voyager 1 and 2 helped astronomers create the first detailed maps of the Galilean satellites, discovered Jupiter's rings, revealed sulfur volcanoes on Io, and saw lightning in Jupiter's clouds. Ulysses discovered the solar wind has a much greater impact on Jupiter's magnetosphere than before suggested. New Horizons took close-up pictures of Jupiter and its largest moons.
In 1995, Galileo sent a probe plunging towards Jupiter, making the first direct measurements of its atmosphere and measuring the amount of water and other chemicals there. When Galileo ran low on fuel, the craft was intentionally crashed into Jupiter's atmosphere to avoid any risk of it slamming into and contaminating Europa, which might have an ocean below its surface capable of supporting life.
NASA is now planning a mission named Juno scheduled to launch in 2011. It will study Jupiter from a polar orbit to figure out how it and the rest of the solar system formed, which could shed light on how alien planetary systems might have developed.
Jupiter's Gravitational Impact on the Solar System
As the most massive body in the solar system after the sun, the pull of Jupiter's gravity has helped shape the fate of our system. It might have violently hurled Neptune and Uranus outward. Jupiter, along with Saturn, might have slung a barrage of debris toward the inner planets early in the system's history. It might even nowadays help keep asteroids from bombarding Earth, and recent events certainly have shown that it can absorb potentially deadly impacts.
Currently, Jupiter's gravitational field influences numerous asteroids that have clustered into the regions preceding and following Jupiter in its orbit around the sun. These are known as the Trojan asteroids, after three large asteroids there, Agamemnon, Achilles and Hector, names drawn from the Iliad, Homer's epic about the Trojan War.
Possibility of Life on the Planet Jupiter
If one were to dive into Jupiter's atmosphere, one would discover it to grow warmer with depth, reaching room temperature, or 70 degrees F (21 degrees C), at an altitude where the atmospheric pressure is about 10 times as great as it is on Earth. Scientists have conjectured that if Jupiter has any form of life, it might dwell at this level, and would have to be airborne. However, researchers have found no evidence for life on Jupiter.
RELATED: See our Solar System Planets overview, or our broader Solar System Facts overview, or learn more about each of the other planets: Mercury, Venus, Earth, Mars, Saturn, Uranus, Neptune and the demoted dwarf planet Pluto.