Jupiter

Jupiter
NASA/STSCI (S.T.A.R.S) · Public domain · source
Name	Jupiter
Caption	Jupiter as imaged by the James Webb Space Telescope in 2022
Adjectives	Jovian
Discovery date	Prehistoric
Discovered by	Unknown

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant primarily composed of hydrogen and helium, with a mass more than two and a half times that of all other planets combined. The planet's prominent Great Red Spot is a giant storm larger than Earth that has been observed for centuries.

Physical characteristics

Jupiter is a massive gas giant with no well-defined solid surface. Its interior is thought to consist of a dense core of heavier elements, possibly surrounded by a layer of metallic hydrogen and an outer layer of predominantly molecular hydrogen. The planet's rapid rotation causes a noticeable flattening at the poles, a state known as oblateness. This immense size and composition give it a powerful gravitational field that profoundly influences the surrounding asteroid belt and the orbits of many comets.

Orbit and rotation

Jupiter orbits the Sun at an average distance of about 5.2 astronomical units, taking nearly 12 Earth years to complete one revolution. Its orbit is slightly elliptical and inclined relative to the ecliptic. The planet has the shortest day in the Solar System, completing a rotation on its axis in just under 10 hours. This fast rotation drives the complex banding of its clouds and generates a powerful dynamo effect responsible for its intense magnetic field. Its orbital period forms the basis of the Metonic cycle used in some ancient calendars.

Atmosphere and climate

The outer atmosphere of Jupiter is visibly organized into alternating dark belts and bright zones, created by strong zonal winds known as jet streams. The atmosphere is composed mainly of molecular hydrogen and helium, with traces of methane, ammonia, hydrogen sulfide, and water. Spectacular storms, including the persistent anticyclonic Great Red Spot and smaller white ovals, dominate its turbulent weather systems. These features are studied by missions like the Hubble Space Telescope and the Juno spacecraft, revealing complex cloud chemistry and lightning activity deep within the atmosphere.

Magnetosphere

Jupiter possesses the largest and most powerful magnetosphere of any planet in the Solar System, extending millions of kilometers into space, even beyond the orbit of Saturn. This magnetic field, likely generated by currents within its layer of metallic hydrogen, is about 20,000 times stronger than Earth's. The magnetosphere traps intense radiation belts of high-energy particles, creating hazardous conditions for spacecraft and spectacular aurorae near its poles. It interacts violently with the volcanic moon Io, stripping material to form a vast plasma torus along its orbit.

Moons and rings

Jupiter forms a miniature planetary system with 95 known moons, the four largest of which—Io, Europa, Ganymede, and Callisto—are known as the Galilean moons, discovered by Galileo Galilei in 1610. These moons are diverse worlds: Io is the most volcanically active body in the Solar System, Europa is believed to harbor a subsurface ocean, Ganymede is larger than Mercury and has its own magnetic field, and Callisto is heavily cratered. The planet also has a faint planetary ring system, discovered by the Voyager 1 probe, composed mainly of dust.

Exploration and observation

Jupiter has been a target of scientific inquiry since the invention of the telescope and the work of astronomers like Giovanni Cassini. Modern exploration began with flybys by Pioneer 10 and Pioneer 11, followed by more detailed studies from the Voyager program and the Galileo orbiter. The Hubble Space Telescope provides regular monitoring, while the Juno mission, which entered orbit in 2016, is conducting an in-depth investigation of its interior, atmosphere, and magnetosphere. Future missions, such as the European Space Agency's Jupiter Icy Moons Explorer, are planned to study the Galilean moons further.

Category:Planets of the Solar System Category:Gas giants Category:Astronomical objects known since antiquity