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 microwavesynchrotron 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.