Jupiter

Jupiter

**Jupiter** is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass
 one-thousandth that of the Sun, but two and a half times that of all
the other planets in the Solar System combined. Jupiter is a gas giant, along with Saturn, with the other two giant planets, Uranus and Neptune, being ice giants.

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 may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid
surface. Because of its rapid rotation, 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 since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere. Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a diameter greater than that of the planet Mercury.

## Physical Characteristics

Jupiter is composed primarily of gaseous and liquid matter. It is the
largest of the four giant planets in the Solar 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, is the second highest of the giant planets, but lower than those of the four terrestrial planets.

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 the Sun lies above the Sun's surface at 1.068 solar radii
 from the Sun's center. Jupiter is much larger than Earth and
considerably less dense: its volume is that of about 1,321 Earths, but
it is only 318 times as massive.

The best known feature of Jupiter is the Great Red Spot, a persistent anticyclonic storm that is larger than Earth, located 22° south of the equator. It is known to have been in existence since at least 1831. The storm is large enough to be visible through Earth-based telescopes. Storms such as this are common within the turbulent atmospheres of giant planets.
 Jupiter also has white ovals and brown ovals, which are lesser unnamed
storms. White ovals tend to consist of relatively cool clouds within the
 upper atmosphere. Brown ovals are warmer and located within the "normal
 cloud layer". Such storms can last as little as a few hours or stretch
on for centuries.

## Satellites

Jupiter has 67 natural satellites. Of these, 51 are less than 10 kilometres in diameter and have only been
discovered since 1975. The four largest moons, visible from Earth with
binoculars on a clear night, known as the "Galilean moons", are Io, Europa, Ganymede, and Callisto.

### Galilean Moons

The moons discovered by Galileo—Io, Europa, Ganymede, and Callisto—are
among the largest satellites in the Solar System. The orbits of three of
 them (Io, Europa, and Ganymede) form a pattern known as a Laplace resonance;
 for every four orbits that Io makes around Jupiter, Europa makes
exactly two orbits and Ganymede makes exactly one. This resonance causes
 the gravitational
 effects of the three large moons to distort their orbits into
elliptical shapes, because 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.

### Planetary Rings

Jupiter has a faint planetary ring system composed of three main segments: an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring. These rings appear to be made of dust, rather than ice as with Saturn's rings. The main ring is probably made of material ejected from the satellites Adrastea and Metis.
 Material that would normally fall back to the moon is pulled into
Jupiter because of its strong gravitational influence. The orbit of the
material veers towards Jupiter and new material is added by additional
impacts. In a similar way, the moons Thebe and Amalthea probably produce the two distinct components of the dusty gossamer ring. There is also evidence of a rocky ring strung along Amalthea's orbit which may consist of collisional debris from that moon.