Jupiter

Jupiter is the largest planet in the solar system and the fifth outward from the Sun. Characteristics:

• 318 Earth masses (about 0.001 solar mass).
• 11 Earth radii.
• 10 hours - solar day.
• 11.9 years - orbital period.
• 5.2 AU - orbital radius (semi-major axis).
• 0.0489 - orbital eccentricity.

Jupiter's moons include Callisto, Europa, Ganymede, and Io, known as the four Galilean Moons, discovered in 1610. Since the late 19th century, more than 90 additional moons have been identified (the most recent discoveries announced in 2023) as well as a ring system.

Jupiter has a surface feature called the Great Red Spot (GRS), a visible red region presumed to be a storm in its atmosphere; such a spot was first observed in 1665 and it has been continuously monitored since 1830, apparently a storm that lasts for centuries. Jupiter's interior is of interest: it is presumed to be basically fluid, mostly metallic hydrogen, thus conductive, providing the material for a dynamo and magnetic field. The resulting strong magnetic field creates a substantial radiation belt (analogous to Earth's Van Allen belts) which emit microwave synchrotron radiation, allowing study of the belt, but also blocking microwave observation of the planet, and which would significantly damage any space probe that were to remain in it. Whether Jupiter has a rocky core is of interest; some planet formation theories assume gas giants form around rocky cores, but analysis indicates all the transitions between Jupiter's internal layers are gradual, with no distinct boundaries.

Space missions to Jupiter have included Galileo, Juno, and JUICE (en route), as well as flybys by Voyager, Ulysses, Cassini, and New Horizons. Plans and concepts/proposals include Europa Clipper and Europa Lander.

The term Jupiter is also used to indicate a Jupiter-like extra-solar planet, often qualified, e.g., a hot Jupiter.