Jovian Planet Systems: Interiors and Atmospheres

The jovian planets are truly different from the terrestrial worlds:

· Huge mass and volume difference.

· The overall composition difference: Jovian planets have relatively small, dense cores surrounded by massive layers of gas (CH₄, H₂O, NH₃).

· Jovian planets lack of a solid surface and rotate very rapidly which causes their ‘‘surface’’ to undergo differential rotation and flatten out their spherical shape.

· Jovian planets are orbited by many moons and rings.

These differences between the jovian and the terrestrial worlds can be understood by recalling the different circumstances of their formation.

Inside the Jovian Planets

The jovian planets have no solid surfaces, but they still have distinct interior layers defined by the phase of their materials.

· Jupiter’s interior structure:

o Gaseous hydrogen layer (0 – 7,000 km)

o Liquid hydrogen layer (7,000 – 14,000 km)

o Liquid metallic hydrogen layer (14,000 – 60,000 km)

o Core of rock, metals and hydrogen compounds; about 10 times as massive as Earth (60,000 – 71,500 km)

Jupiter emits more energy than it receives from the Sun. The excess heat, which drives strong convection activity, is created because the planet is still slowly contracting.

· Saturn less massive than Jupiter but only slightly smaller because its weaker gravity does not compress its layers as much. Interior is similar to Jupiter’s interior but less liquid metallic hydrogen because of lower pressure inside. Like Jupiter, it emits more energy than it receives; the excess heat is created by unusual planetary differentiation, helium rain.

· Uranus and Neptune contain larger fraction of higher-density materials (hydrogen compounds (water) and rock). Their interiors are similar but different from Jupiter’s; no liquid metallic hydrogen (gaseous hydrogen; water, methane and ammonia oceans, rock and metal). Uranus emits no excess energy but Neptune does due to a yet to understand process.

Jovian Planet Atmospheres

The atmospheric processes are quite similar to those we saw in the case of the terrestrial planets.

· Jupiter’s atmosphere:

o It consists of 75% hydrogen, 25% helium, and 1% hydrogen compounds (CH₄, NH₃, H₂O); it is similar to the composition of the primordial solar nebula.

o Structure:

§ Thermosphere heated by solar X rays

§ Stratosphere heated by solar UV radiation (haze formation)

§ Troposphere: Cloud layers (water (H₂O), ammonium hydrosulfide (NH₄SH), and ammonia (NH₃). Jupiter’s clouds are confined to narrow bands; zones (white ammonia clouds), belts (reddish ammonium hydrosulfide clouds).

o Weather and climate on Jupiter: Rapid winds (600 km/h); storms (ovals) and the Great Red Spot (Cassini, 1665). Jupiter’s climate is steady.

· Saturn’s atmosphere: Very similar to Jupiter’s atmosphere, however Saturn is colder so the different cloud layers occur deeper giving a less colorful appearance to Saturn.

· The atmospheres of Uranus and Neptune: The distinctive blue color of the atmosphere is caused by the abundant methane gas. The upper cloud layers are formed from methane snow; we do not know what kind of clouds are below that. Uranus’ storms are induced by seasonal changes. Neptune’s winds are among the fastest in the solar system (2,000 km/h); the Great Dark Spot.

Last updated 01/25/2006