Jupiter's Atmosphere & Interior
Despite its massive size, Jupiter is called a gas giant because it is made up primarily of gases. Jupiter's atmosphere is comprised mostly of hydrogen and helium—similar to the Sun and at roughly the same proportions of 74.9% and 23.8%, respectively. Small amounts of methane (0.3%), ammonia (0.03%), hydrogen sulfide and water have also been detected. Spectroscopic studies have also revealed traces of hydrogen deuteride (HD), ethane (C2H6), ethyne (C2H2) phosphine (PH3), carbon monoxide (CO) and germane (GeH4).
Jupiter's atmosphere is made up of four layers (in increasing altitude): troposphere, stratosphere, thermosphere and exosphere. Each layer has its own temperature gradient. The troposphere, which is closest to the planet's interior, is made up of layers of water, ammonia and ammonium hydrosulfide that create clouds and hazes of a complicated system. The upper layer of clouds that is visible on the surface of the planet is made up of ammonia ice; below these clouds are denser clouds that are believed to be made of ammonium hydrosulfide or ammonium sulfide and water. The densest layer of clouds in the troposphere is made of water. These water clouds have the biggest influence on the dynamics of the planet's atmosphere. They are believed to drive the weather patterns that are visible on the planet's surface such as storms and lightning.
Jupiter's surface appears as alternating bands of light and dark regions that run parallel to the equator. The light-colored regions are called zones and the dark-colored regions are called belts. It is not yet clear which chemicals give the bands their distinct color particularly the Great Red Spot, although it has been suggested that they may contain sulfur, phosphorus and carbon. What is known is that the whiteness in the light-colored zones is caused by dense clouds of ammonia ice that gather at higher altitudes in the upper troposphere where the temperature is lower. On the other hand, the clouds of ammonia ice are thinner in belts and are located at lower altitudes where the temperature is higher.
Like other gas planets, Jupiter has high velocity winds that are confined within its bands. These winds can have speeds of more than 640 km/h (400 mi/h) and are believed to be driven by the planet's interior heat (in contrast, the Earth's atmospheric winds are driven by solar heat and the condensation of water vapor). Jupiter's winds blow in opposing directions in adjacent bands. For instance, the winds within the equatorial zone blow in an eastward direction (westerly winds) following the planet's rotation, whereas the winds in the belts north and south of this zone blow in a westward direction (easterly winds). The edges where these bands of opposing winds meet are characterized by jet streams that create complex patterns of disturbances such as eddies, where the wind flows in a circular motion. The most well-known and biggest of these disturbances is the Great Red Spot, which is located within the dark belt between the equatorial and south tropical zones. The Great Red Spot is a circular storm that rotates in a counterclockwise fashion once every six days. It was first spotted probably 349 years ago and continuously by Earth-based telescopes since 1831. Its size has varied through the years and it is not known for how long it will continue to exist. Although the Great Red Spot appear reddish brown, most other circular storms on Jupiter's atmosphere are usually white and can exist for several years.
Jupiter's atmosphere is about 1,000 km thick. Below the troposphere, increasing pressure and temperature compresses the hydrogen gas into a liquid. Underneath this liquid layer, the hydrogen turns metallic and is able to conduct electricity. Within this metallic layer, electrical currents driven by the planet's high velocity rotation generate a powerful magnetic field. Jupiter's magnetic field is almost 20,000 times more powerful than the Earth's. Its magnetosphere, the area encircled by the planet's magnetic field extends up to 3 million kilometers towards the Sun and 1 billion km behind it, almost reaching Saturn's orbit. It is not known what constitutes the core of Jupiter, but it is theorized that the tremendous pressure may support a rocky interior bigger than the Earth.