Jupiter

The planet Jupiter, due to its size and brightness, was known to the ancients. It is named after Jupiter, the chief god in Roman mythology. This name is appropriate, since Jupiter is the largest and most massive planet in our solar system. It has a mass of (1.8988 × 10²⁷ kg), more than three times that of Saturn, and more than 300 times that of Earth. Its equatorial radius 44.4 mi (71,492 km) is more than 11 times that of Earth.

Jupiter is at a distance of 7.783 × 10⁸ km from the Sun, or about 5.2 times the distance of Earth. Because the planet is so far from the Sun, it receives much less solar radiation than Earth, and is consequently much colder, with a temperature of only -184°F (-120°C) at the top of its clouds. This temperature is actually higher than would be expected from the input of solar energy alone, since the planet generates some of its own heat internally, most likely due to the energy from its gravitational collapse.

Jupiter is one of four gas giants in the outer solar system. These planets differ substantially from the rocky bodies found closer to the Sun. Jupiter does not have a solid surface at all, and is hypothesized to have a lower atmosphere of molecular (gaseous) hydrogen that is 8.699–12,427 mi (14,000–20,000) km thick, which is underlain by a mantle of metallic (liquid) hydrogen that is 18,641 mi–24,855 mi (30,000–40,000 km) thick. This mantle surrounds an inner core of rock and ice thought to be 6,214 mi (10,000 km) thick. When we look at the planet, we see only the ammonia ice clouds in a hydrogen-helium mixture at the top of the atmosphere. These clouds rotate with different periods. The Jovian cloud structure consists of bands (divided into zones [light color] and belts [dark color]) and inter-band shear zones (characterized by streaks, loops, plumes, and spots [storms]). Because of the atmospheric motion, there is no single rotation period that can be associated with visible features on this gaseous planet like there would be with a terrestrial planet.

The most commonly used rotation period, referred to as System III, corresponds to the period of the planet's periodic radio emissions, which is the rate of rotation of the interior of the planet. This period is 9 hours, 55 minutes, 30 seconds. The Jovian year, which is the time for the planet to complete an orbit about the Sun, is 11.86 Earth years long.