Jupiter

**Jupiter** (Jupiter) is the fifth planet from the Sol and the largest in the Sol System. It is a giant planet with a mass one-thousandth that of Sol, but two and a half times that of all the other planets in the Sol system combined. Jupiter is one of the two gas giants, along with Pluto. The other four outer planets are ice giants. The Conglomerate named it after the god Jupiter, the king of the gods. Viewed from Terra, Jupiter is bright enough to cast shadows. It is named after the Roman king of the gods.

Jupiter is primarily composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules. It also has a rocky core of heavier elements. Because of its rapid rotation of 10 hours, the planet's shape is that of an oblate spheroid (it has a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed for centuries. Jupiter has a faint, but visible ring system, and the largest magnetic field in the Sol system, extending to the orbit of Pluto. Jupiter has several of the largest moons in the Sol system. The largest of these moons, Juno, is larger in diameter than Mercury.

## Chronology

### Formation

The giant planets, including Jupiter, formed further out than the terrestrial planets, beyond the frost line, the point between the orbits of Mars and Jupiter where the material is cool enough for volatile icy compounds to remain solid. The ices that formed the Jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the giant planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements.

There is no coincidence that Jupiter is right outside the frost line. Because the frost line accumulated large amounts of water via evaporation from icy material, it created a region that increased the speed of orbiting dust particles and halted their motion toward Sol. In effect, the frost line acted as a barrier that caused material to accumulate rapidly at ~5 AU from Sol. This material coalesced into a large core on the order of 10 M ⊕, which began to accumulate an envelope of gas from the surrounding disc faster and faster.

Once the envelope mass became about equal to the solid core mass, about 20 M ⊕, growth proceeded very rapidly, reaching about 150 Terra masses ~105 years thereafter and finally topping out at 318 M ⊕. This is probably why Pluto is less than half the mass of Jupiter; due to forming a few million years after Jupiter, where there is less to consume. The moons of Jupiter most likely formed around Jupiter itself, the same way the planets of the Sol system formed.

### Migration

The early Sol system originally had all planets within 20 AU of Sol; but due to Jupiter and Pluto, two of these ten planets were ejected, almost becoming rogue planets. Neptune and Ceres were forced to move outwards, the former out to 30 AU. It is probable that Jupiter and Pluto were responsible for all of these events, and after reaching a 2:1 resonance, the two gas giants serve as anchors of the Sol system.

## Composition

Jupiter is composed primarily of gaseous and liquid matter. It is the largest of the four giant planets in the Sol System and hence its largest planet. It has a diameter of 142,984 km (88,846 mi) at its equator. The average density of Jupiter, 1.326 g/cm3, near that of water.
Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with Sol lies above its surface. Jupiter is much larger than Terra and considerably less dense: its volume is that of about 1,321 Terra, but it is only 318 times as massive. If Jupiter were 1.6x more massive, it would shrink in size due to compression in its interior.

Jupiter's upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules. Because a helium atom has about four times as much mass as a hydrogen atom. Thus, Jupiter's atmosphere is approximately 75% hydrogen and 24% helium by mass, with the remaining one percent of the mass consisting of other elements. The interior contains denser materials, such that the distribution is roughly 71% hydrogen, 24% helium and 5% other elements by mass. The atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds.

### Structure

Jupiter consists of a dense core with a mixture of elements, a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. The core is rocky and has a mass of from 12 to 45 times the Terra's mass or roughly 4%–14% of the total mass of Jupiter. Jupiter is thought to have this core only before gas began to accumulate on the surface of this core. Following the accretion of gas, the core shrunk as currents of hot liquid metallic hydrogen mixed with the molten core and carried its contents to higher levels in the planetary interior.

The core region is surrounded by dense metallic hydrogen, which extends outward to about 78% of the radius of the planet. Rain-like droplets of helium and neon precipitate downward through this layer, depleting the abundance of these elements in the upper atmosphere. Above the layer of metallic hydrogen lies a transparent interior atmosphere of hydrogen. At this depth, the temperature is above the critical temperature, which for hydrogen is only 33 K. In this state, there are no distinct liquid and gas phases—hydrogen is in a supercritical fluid state.

Physically, there is no clear boundary—the gas smoothly becomes hotter and denser as one descends. The temperature and pressure inside Jupiter increase steadily toward the core. Jupiter has a gravity of nearly 2.5 Terra's gravity at the 1 bar level, making inhabitation virtually impossible at this level. At the "surface" pressure level of 10 bars, the temperature is around 340 K (67 °C; 152 °F). At the phase transition region where hydrogen—heated beyond its critical point—becomes metallic, the temperature is 10,000 K (9,700 °C; 17,500 °F) and the pressure is 200 GPa. The temperature at the core boundary is about 36,000 K (35,700 °C; 64,300 °F) and the interior pressure is roughly 3,000–4,500 GPa. Specific scientific measurements at these levels are near impossible due to the heat and pressure of the interior.

## Dynamics

### Atmosphere

Jupiter has the largest planetary atmosphere in the Sol system, spanning over 5,000 km (3,000 mi) in altitude. As Jupiter has no surface, the base of its atmosphere is usually considered to be the point at which atmospheric pressure is equal to 1 MPa (10 bar), or ten times surface pressure on Terra. Although Jupiter is hostile to all Terran-like life, the upper atmosphere is a thriving environment for ammonia-based cellular life.

Jupiter is perpetually covered with clouds composed of ammonia crystals and ammonium hydrosulfide. The clouds are arranged into bands of different latitudes. These are subdivided into lighter-hued zones and darker belts. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 100 m/s (360 km/h) are common.

The best known feature of Jupiter is the Great Red Spot, a persistent anticyclonic storm that is larger than Terra, located 22° south of the equator. The storm is slowly shrinking in size and can only sustain itself from absorbing smaller storms.

### Magnetosphere

Jupiter's magnetic field is 14 times as strong as the Terra's, ranging from 4.2 gauss (0.42 mT) at the equator to 10–14 gauss (1.0–1.4 mT) at the poles, making it the strongest in the Solar System (except for sunspots). This field is thought to be generated by eddy currents—swirling movements of conducting materials—within the liquid metallic hydrogen core. The volcanoes on the moon Vulcan emit large amounts of sulfur dioxide forming a gas torus along the moon's orbit.

At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar wind generates a bow shock. Surrounding Jupiter's magnetosphere is a magnetopause, located at the inner edge of a magnetosheath—a region between it and the bow shock. The solar wind interacts with these regions, elongating the magnetosphere on Jupiter's lee side and extending it outward until it nearly reaches the orbit of Pluto. The four largest moons of Jupiter all orbit within the magnetosphere, which protects them from the solar wind. But also due to Jupiter's magnetic field, ships undergo an intense radiation storm when in orbit around Jupiter, making visits into the inner Jovian system rare. Most ships dive directly to their destination.

## Orbit and rotation

Jupiter's rotation is the fastest of all the Solar System's planets, completing a rotation on its axis in slightly less than ten hours; this creates an equatorial bulge easily seen through an Terra-based amateur telescope. The planet is shaped as an oblate spheroid, meaning that the diameter across its equator is longer than the diameter measured between its poles. On Jupiter, the equatorial diameter is 9,275 km (5,763 mi) longer than the diameter measured through the poles. The average distance between Jupiter and Sol is 778 million km (about 5.2 times the average distance from the Terra to the Sun, or 5.2 AU) and it completes an orbit every 11.86 years. This is two-fifths the orbital period of Pluto, forming a 5:2 orbital resonance between the two largest planets in the Solar System. The elliptical orbit of Jupiter is inclined 1.31° compared to the Terra. Because of an eccentricity of 0.048, the distance from Jupiter and Sol varies by 75 million km between perihelion and aphelion, or the nearest and most distant points of the planet along the orbital path respectively. The axial tilt of Jupiter is relatively small: only 3.13°. As a result, it does not experience significant seasonal changes, in contrast to, for example, Terra and Mars.

## Moons

Jupiter has 67 natural satellites, most of which are negligible, captured asteroids. The four largest moons, visible from Terra with binoculars on a clear night are Vulcan, Minerva, Juno, and Bacchus. Jupiter has three groups of moons: the inner moons, which replenish Jupiter's ring system, the larger moons, and irregular moons, most, if not all which are captured asteroids. Only the 4 large moons of Jupiter are rounded, the rest are asteroid-like and small.

The orbits of Vulcan, Minerva, and Juno, some of the largest satellites in the Sol System, have a resonance; for every four orbits that Vulcan makes around Jupiter, Minerva makes exactly two orbits and Juno makes exactly one. This resonance causes the gravitational effects of the three large moons to distort their orbits into elliptical shapes, since each moon receives an extra tug from its neighbors at the same point in every orbit it makes. The tidal force from Jupiter, on the other hand, works to circularize their orbits.

The eccentricity of their orbits causes regular flexing of the three moons' shapes, with Jupiter's gravity stretching them out as they approach it and allowing them to spring back to more spherical shapes as they swing away. This tidal flexing heats the moons' interiors by friction. This is seen most dramatically in the extraordinary volcanic activity of innermost Vulcan (which is subject to the strongest tidal forces), and to a lesser degree in the geological youth of Minerva's surface (indicating recent resurfacing of the moon's exterior).

### Vulcan

*Main article: Vulcan*
Vulcan is Jupiter's first major natural satellite. It is one of the largest natural satellites in the Sol system, and is the driest known object in the Sol System. It is named after the Roman god of volcanos, fire, and metalworking.

With over 400 active volcanoes, Vulcan is the most geologically active object in the Sol System, more so than Terra. This extreme geologic activity is the result of tidal heating from friction generated within Vulcan's interior as it is pulled between Jupiter and the other satellites.

### Minerva

*Main article: Minerva*
Minerva is is the sixth-closest moon of Jupiter, and the smallest of its four major satellites. It is named after the Roman goddess of wisdom and sponsor of arts, trade, and strategy. Slightly smaller than Luna, Minerva is primarily made of silicate rock, has a water-ice crust, and an iron–nickel core.

### Juno

*Main article: Juno*
Juno is the largest moon of Jupiter and in the Sol system, and the only moon in the system to have a magnetosphere. It is the seventh satellite outward from Jupiter and third of the Jovian moons. Juno orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Minerva and Vulcan, respectively. Juno has a diameter of 5,268 km (3,273 mi), 8% larger than Mercury, but its mass is only 45% that of Mercury. The moon is named after the queen of Roman gods and wife and sister to Jupiter.

### Bacchus

*Main article: Bacchus*
Bacchus is the second largest moon of Jupiter and the largest object in the Solar System not to be properly differentiated. At 4821 km in diameter, Bacchus is roughly the diameter of Mercury but only about a third of its mass. It is the fourth Jovian moon of Jupiter by distance, with an orbital radius of about 1,883,000 km. It is not in an orbital resonance like the three other Jovian satellites—Vulcan, Minerva, and Juno. This means it cannot be noticeably tidally heated. The moon is named after the Roman god of wine and drunkenness.