Jupiter: The Giant of the Solar System
Jupiter is the fifth planet from the sun and the largest in the solar system. It is a gas giant with a mass more than two and a half times that of all the other planets in the solar system combined. Jupiter is primarily composed of hydrogen, but helium constitutes one quarter of its mass and one tenth of its volume. It likely has a rocky core of heavier elements, but like the other giant planets, it lacks a well-defined solid surface.
Physical Features
Jupiter has a slight but noticeable bulge around the equator, giving it the shape of an oblate spheroid.
The outer atmosphere is visibly segregated into several bands at different latitudes, with turbulence and storms along their interacting boundaries.
The planet is known for its giant storm called the Great Red Spot, which has been observed since at least the 17th century.
Jupiter has a faint planetary ring system and a powerful magnetosphere.
It has 80 known moons, including the four large Galilean moons discovered by Galileo Galilei in 1610.
Exploration
Jupiter has been explored by several robotic spacecraft missions:
Pioneer 10 was the first spacecraft to visit Jupiter in December 1973.
The Voyager missions flew by Jupiter from 1973 to 1979, providing valuable data.
The Galileo orbiter arrived at Jupiter in 1995 and studied the planet and its moons.
The New Horizons probe used Jupiter's gravity to increase its speed and trajectory on its way to Pluto in 2007.
The Juno probe entered orbit around Jupiter in July 2016, becoming the largest probe to visit the planet.
Formation and Migration
Jupiter is believed to have formed at or beyond the snow line, where volatile substances like water can condense into solids. It first assembled a large solid core before accumulating its gaseous atmosphere. The core must have formed before the solar nebula began to dissipate.
There are different theories about Jupiter's migration. The "Grand Tack Hypothesis" suggests that Jupiter migrated inward due to interactions with the gas disk and orbital resonance with Saturn. This migration caused disturbances in the orbits of other planets, leading to their destructive collisions and ultimately allowing the formation of the inner planets, including Earth.
Another theory proposes that Jupiter formed at extreme distances, possibly even outside the molecular nitrogen snow line. It then migrated inward over a long period of time, along with Saturn, Uranus, and Neptune.
Composition
Jupiter's atmosphere is primarily composed of hydrogen (90%) and helium (10%). It also contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. The interior of Jupiter is denser, with hydrogen and helium making up around 95% of its mass. Neon and helium are depleted compared to their abundances in the Sun.
Size and Mass
Jupiter is the largest planet in the solar system, with a diameter of 142,000 km (88,000 miles) at its equator. Its mass is 2.5 times that of all the other planets combined. Despite its size, Jupiter is less dense than Earth, with similar densities due to its composition. Jupiter's mass is often used as a unit to describe the masses of other objects, such as extrasolar planets and brown dwarfs.
Jupiter still radiates more heat than it receives from the sun. The amount of heat produced inside it is similar to the total solar radiation. This additional heat is generated by the Kelvin-Helmholtz mechanism through contraction. When formed, Jupiter was hotter and about twice its current diameter. Most scientists expected Jupiter to either consist of a dense core surrounded by a layer of liquid metallic hydrogen and helium, or to have no core at all. However, the Juno mission found that Jupiter has a diffuse core that mixes into its mantle, possibly due to an impact from a planet. The core is estimated to be 30 to 35% of the planet's radius and contains heavy elements.
Above the layer of metallic hydrogen lies a transparent interior atmosphere of hydrogen. At this depth, the pressure and temperature are above molecular hydrogen's critical pressure and temperature, resulting in a supercritical fluid state. Below this layer, there is no clear boundary as the gas smoothly becomes hotter and denser. Rain-like droplets of helium and neon precipitate downward through the lower atmosphere, depleting their abundance in the upper atmosphere. Rainfalls of diamonds have also been suggested.
The temperature and pressure inside Jupiter increase steadily inward. The hydrogen is always supercritical and never encounters a first-order phase transition. The temperature of Jupiter's diluted core is estimated to be around 20,000 K. Jupiter has a deep planetary atmosphere composed of clouds made of ammonia crystals. The clouds are in bands of different latitudes known as tropical regions, which consist of lighter-hued zones and darker belts. These clouds generate thunderstorms and lightning, and contribute to the colorful compounds observed in Jupiter's atmosphere. Jupiter's low axial tilt and convection within its interior balance out the temperatures at the cloud layer.
The Great Red Spot is a persistent anticyclonic storm located 22° south of Jupiter's equator. It has existed since at least 1831 and possibly since 1665. The storm rotates counterclockwise and has significantly decreased in size since its discovery. There are also polar cyclone groups at Jupiter's poles, similar to the hexagon at Saturn's north pole. Other features include Red Spot Junior and the Great Cold Spot.
Jupiter's magnetic field is the strongest in the solar system and is thought to be generated by eddy currents.
