This 47 cents postage stamp was issued by America on 31 May 2016 (= Scott Catalogue # 5073). It shows a false-color image of Planet Jupiter (plus some moons) and is part of a set depicting all the planets of the Solar System.
There are four types of planets in the Solar System: terrestrial planets, gas giant planets, ice giant planets, and dwarf planets. The terrestrial planets are Mercury, Venus, Earth, and Mars. The gas giant planets are Jupiter and Saturn. The ice giant planets are Uranus and Neptune. Dwarf planets include named and unnamed objects - for example, Ceres, Pluto, Quaoar, Sedna, Eris, Varuna, Makemake, and many others. Only two dwarf planets have been visited and imaged (Ceres and Pluto).
Planet Jupiter has been visited nine times. Seven visits were flybys (Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Cassini, and New Horizons) and two visits were orbiters (Galileo and Juno). The Galileo mission was mostly a failure, because the main antenna failed to open - little data was trasmitted back to Earth. The Juno mission is still active, as of 2025.
Jupiter is the 5th planet from the Sun (or 6th, if one counts Ceres, which one should) and ranges from about 5 to 5.5 astronomical units ("AU"). One astronomical unit is the average distance between the center of the Sun and the center of the Earth.
Both Jupiter's rotation and orbit around the Sun are prograde, meaning movement in a counter-clockwise direction when viewed above the North Pole of the Sun. The orbit is slightly non-circular.
Jupiter, the "King of the Planets", is a gas giant planet, and the # 1 largest world in the Solar System. Unlike the terrestrial planets and dwarf planets, Jupiter has no solid surface - it is mostly fluid. As such, no traditional geology is present (no rocks, no volcanoes, no faults, no quakes, no tectonics, no impact craters, no river valleys, no mountains, no glaciers, no oceans, no landslides, no sand dunes). The planet's average radius is about 69,911 kilometers. It has a rapid rotation rate, resulting in a slightly flattened shape - it is wider than tall. Jupiter's radius ranges from 66,854 kilometers (polar radius) to 71,492 kilometers (equatorial radius). Jupiter is about 11 times larger than Earth.
Being a gas giant planet and composed of very light elements, Jupiter has a low density of about 1.33 grams per cubic centimeter. However, it is the second-highest density giant planet. Saturn and Uranus have lower densities than Jupiter. Jupiter is so large that gravity has compressed its internal materials.
Jupiter spins rapidly - one Jupiter day is about 9.9 hours (Earth hours). One Jupiter year is about 11.9 Earth years. It takes about 4333 days for Jupiter to go once around the Sun.
Unlike Earth and Mars, Jupiter is oriented almost upright - its axial tilt is about 3.1 degrees from the vertical. Because of this, Jupiter has no seasons - no spring or summer or fall or winter.
The number of known moons increases with each successive study. As of this writing, Jupiter has 124 known moons, only four of which are large. It's been estimated that Jupiter may have as many as 600 moons that are over a kilometer in size. Most moons are unnamed. Inner satellites orbit around Jupiter in a prograde direction. Outer satellites are retrograde (orbit in a clockwise direction, when viewed above the North Pole).
Jupiter's four largest moons were discovered in 1610 by Galileo and are nicknamed the "Galilean moons" or "Galilean satellites". Starting with the closest-orbiting moon, these are: Io, Europa, Ganymede, and Callisto.
All four giant planets in the Solar System have ring systems - only Saturn's rings are obvious from Earth. Jupiter's thin rings were not observed until 1979 when the Voyager 1 spacecraft did a flyby. Jupiter's rings are composed of tiny dust particles derived from small inner moons. A planetary ring system is normally expected to be ~planar. In 1996, Jupiter's rings were seen to be distinctly rippled or corrugated. The gravitational influence of an impacting comet in June 1994 tilted Jupiter's rings by about 2 kilometers. Ever since then, the rings have been returning to equilibrium, becoming rippled in the process.
Jupiter's albedo (= light reflectivity) is about 50% - it has alternating bright and dark areas in the form of horizontal bands. On average, about 50% of the sunlight reaching Jupiter gets reflected back into space.
Jupiter has the # 1 strongest magnetic field of any planet. Only the Sun has a stronger magnetic field. Some worlds have magnetic fields, some have weak ones, and some have none. Jupiter's field is about 18 to 20 thousand times stronger than Earth's magnetic field. The field around Jupiter is generated by electrical currents in a moving liquid metallic hydrogen layer in Jupiter's interior. The magnetic field traps charged particles, resulting in intense radiation. The presence of a field results in permanent polar auroras, usually infrared and ultraviolet auroras, which are invisible to human eyes.
Jupiter is a differentiated planet - it has internal layers that differ in composition and physical characteristics. The composition and nature of these layers are quite different from the corresponding internal layers (core, mantle, crust) of terrestrial planets like Earth. Being far from the Sun, Jupiter's cloud tops are naturally very cold. The core of Jupiter is extremely hot - considerably hotter than the Sun's surface.
The current model of Jupiter's interior is based on information obtained during the Juno mission. Jupiter has four major internal layers. At the center of the planet is a relatively small, compact core composed of rocks and / or metal. This portion of the planet is extremely hot and extremely high pressure - about 15 to 20 thousand degrees Kelvin temperature and about 40 to 50 million bars of pressure. Surrounding the compact core is a thick dilute core, or "fuzzy core". Apparently, this refers to a mix of heavy material, such as silicates and "ice", with helium and metallic hydrogen. Surrounding the dilute core is a thick layer of liquid metallic hydrogen (H), an exotic substance that does not occur anywhere else in the Solar System, except in the interior of Saturn. Metallic hydrogen requires very high pressure to form - many millions of bars of pressure. The liquid metallic hydrogen layer is relatively rich in helium (He). Moving currents in this layer generate Jupiter's magnetic field. The outermost layer of Jupiter consists of molecular hydrogen gas (H2) and is relatively poor in helium. This layer extends from the cold cloud tops (~165 degrees Kelvin) to a deep level at 2 million bars of pressure and ~6500 degrees Kelvin.
Jupiter's atmosphere is ~90% hydrogen (H) and ~10% helium (He), the two lightest and most common elements in the Universe. Jupiter's air also includes trace amounts of water vapor (H2O), methane (CH4), ammonia (NH3), ethane (C2H6), semi-heavy hydrogen (HD), hydrogen sulfide (H2S), and other gases.
The atmosphere of Jupiter is strongly color-banded with numerous storms. Not surprisingly, lightning has been detected at Jupiter by Voyager 1, Galileo, and Juno. Jupiter lightning is most common in polar areas and can be hundreds of times more powerful than Earth lightning.
The alternating bands of Jupiter's atmosphere are called zones (if light-colored) and belts (if dark-colored). Winds in zones and belts are rapid - up to a couple hundred meters per second, which is faster than winds in the most powerful hurricanes on Earth.
The most famous storm on Jupiter is the "Great Red Spot", a huge, counter-clockwise rotating storm ("anticyclone") in Jupiter's Southern Hemisphere. It is a long-lived feature and has existed for centuries. It used to be ~40,000 kilometers in size, but is currently less than half that. The Great Red Spot storm rotates once every ~6 days. Smaller storms appear and disappear on the scale of years to decades.
Unexpectedly, the polar areas of Jupiter are bluish-colored. Polar areas have many storms, as do the temperate and equatorial areas. Juno has observed eight storms forming a square around the North Pole. It's also observed six storms forming a hexagon around a central storm at the South Pole.
Impacts do occur at Jupiter, but they don't leave impact craters, because there is no solid surface. Instead, incoming bodies form holes in Jupiter's clouds. A series of fragments from a highly-disrupted comet (Shoemaker-Levy 9 Comet) impacted with Jupiter in 1994. Individual impact events produced ~Earth-sized holes in the cloud tops. Another notable impact occurred in 2009, the scar from which persisted from July to November 2009.
