Jupiter

Jupiter is the largest of the eight planets, more than 10 times the diameter of Earth and more than 300 times its mass. In fact, the mass of Jupiter is almost 2.5 times that of all the other planets combined. Being composed largely of the light elements hydrogen and helium, its mean density is only 1.314 times that of water. The mean density of Earth is 5.5 times that of water. The pull of gravity on Jupiter at the top of the clouds at the equator is 2.4 times as great as gravity's pull at the surface of Earth at the equator. The bulk of Jupiter rotates once in 9 hours, 55.5 minutes, although the period determined by watching cloud features differs by up to five minutes due to intrinsic cloud motions.

The visible surface of Jupiter is a deck of clouds of ammonia crystals, the tops of which occur at a level where the pressure is about half that at Earth's surface. The bulk of the atmosphere is made up of 89% molecular hydrogen (H₂) and 11% helium (He). There are small amounts of gaseous ammonia (NH₃), methane (CH₄), water (H₂O), ethane (C₂H₆), acetylene (C₂H₂), carbon monoxide (CO), hydrogen cyanide (HCN), and even more exotic compounds such as phosphine (PH₃) and germane (GeH₄). At levels below the deck of ammonia clouds, there are believed to be ammonium hydro-sulfide (NH₄SH) clouds and water crystal (H₂O) clouds, followed by clouds of liquid water. The visible clouds of Jupiter are very colorful. The cause of these colors is not yet known. Contamination by various polymers of sulfur (S₃, S₄, S₅, and S₈), which are yellow, red, and brown, has been suggested as a possible cause of the riot of color; but, in fact, sulfur has not yet been detected spectroscopically, and there are many other candidates as the source of the coloring.

Great Red Spot (NASA/JPL)

The meteorology of Jupiter is very complex and not well understood. Even in small telescopes, a series of parallel light bands called zones and darker bands called belts is quite obvious. The polar regions of the planet are dark. Also present are light and dark ovals, the most famous of these being the Great Red Spot. The Great Red Spot is larger than Earth, and although its color has brightened and faded, the spot has persisted for at least 162.5 years, with the earliest definite drawing of it done by Schwabe on September 5, 1831. (There is less positive evidence that Hooke observed it as early as 1664.) It is thought that the brighter zones are cloud-covered regions of upward moving atmosphere, while the belts are the regions of descending gases, the circulation driven by interior heat. The spots are thought to be large-scale vortices, much larger and far more permanent than any terrestrial weather system.

Jupiter movie

The zones and belts are zonal jet streams moving with velocities up to 400 miles/hr. Wind direction alternates between adjacent zones and belts. The light colored zones are regions of upward moving convective currents. The darker belts are made of downward sinking material. The two are therefore always found next to each other. The boundaries of the zones and belts (called bands) display complex turbulence and vortex phenomenon.

Note: Upward moving gases in Jupiter's atmosphere bring white clouds of ammonia/water ice from lower layers. Downward moving gases sink and allow us to view the top, darker layers.

The detailed structure in Jupiter's atmosphere is dominated by physics known as fluid dynamics. Note that the atmosphere of Jupiter so dense and cold that it behaves as a fluid rather than a gas. At the point were we see features the atmosphere pressure is 5 to 10 times that of the Earth's atmospheric pressure. The simplest theories in fluid dynamics predict two types of patterns. One pattern occurs when a fluid slips by a second fluid of a different density. Such an event is known as a viscous flow and produces wave-like features at the boundary of the two fluids. A second pattern is produced by a stream of fluid in a constant medium. The stream breaks up into individual elements. These smaller sections can develop into cyclones.

Cyclones develop due to the Coriolis effect where the lower latitudes travel faster than the higher latitudes producing a net spin on a pressure zone. The cyclones on Jupiter are regions of local high or low pressure spun in such a fashion. Note that the direction of the spin differs in the two hemispheres where counter-clockwise spin is in the North and clockwise spin is in the South.

Brown ovals are low pressure cyclones/storms in the North. White ovals are high pressure cyclones/storms in the South. Both can last on the order of tens of years.

The most obvious feature on Jupiter is the Great Red Spot

Redspot movie

Gas planets do not have solid surfaces, but rather build-up in pressure and density as one goes deeper towards the core. Different colors represent different depths into Jupiter's atmosphere. The colors (reds, browns, yellows, oranges) are due to subtle chemical reactions involving sulfur. Whites and blues are due to CO₂ and H₂O ices.

The interior of Jupiter is totally unlike that of Earth. Earth has a solid crust floating on a denser mantle that is fluid on top and solid beneath, underlain by a fluid outer core that extends out to about half of Earth's radius and a solid inner core of about 1,220-kilometer (758-mile) radius. The core is probably 75 percent iron, with the remainder nickel, perhaps silicon, and many different metals in small amounts. Jupiter, on the other hand, may well be fluid throughout, although it could have a small solid core (say up to 15 times the mass of Earth!) of heavier elements such as iron and silicon extending out to perhaps 15% of its radius. The bulk of Jupiter is fluid hydrogen in two forms or phases, liquid molecular hydrogen on top and liquid metallic hydrogen below; the latter phase exists where the pressure is high enough, say 3-4 million atmospheres. There could be a small layer of liquid helium below the hydrogen, separated out gravitationally, and there is clearly some helium mixed in with the hydrogen. The hydrogen is convecting heat (transporting heat by mass motion) from the interior, and that heat is easily detected by infrared measurements, since Jupiter radiates twice as much heat as it receives from the Sun. The heat is generated largely by gravitational contraction and perhaps by gravitational separation of helium and other heavier elements from hydrogen, in other words, by the conversion of gravitational potential energy to thermal energy. The moving metallic hydrogen in the interior is believed to be the source of Jupiter's strong magnetic field.

Comparison of all gas giants (Lunar and Planetary Institute)

Jupiter's magnetic field is much stronger than that of Earth. It is tipped about 11° to Jupiter's axis of rotation, similar to Earth's, but it is also offset from the center of Jupiter by about 10,000 kilometers (6,200 miles). The magnetosphere of charged particles which it affects extends from 3.5 million to 7 million kilometers (2.2 to 4.3 million miles) in the direction toward the Sun, depending upon solar wind conditions, and at least 10 times that far in the anti-Sun direction. The plasma trapped in this rotating, wobbling magnetosphere emits radio frequency radiation measurable from Earth at wavelengths from 1 meter (3 feet) or less to as much as 30 kilometers (19 miles). The shorter waves are more or less continuously emitted, while at longer wavelengths the radiation is quite sporadic. Scientists will carefully monitor the Jovian magnetosphere to note the effect of the intrusion of large amounts of cometary dust into the Jovian magnetosphere.

The two Voyager spacecraft discovered that Jupiter has faint dust rings extending out to about 53,000 kilometers (33,000 miles) above the atmosphere. The brightest ring is the outermost, having only about 800-kilometer (500-mile) width. Next inside comes a fainter ring about 5,000 kilometers (3,100 miles) wide, while very tenuous dust extends down to the atmosphere.

The innermost of the four large satellites of Jupiter, Io, has numerous large volcanoes that emit sulfur and sulfur dioxide. Most of the material emitted falls back onto the surface, but a small part of it escapes the satellite. In space, this material is rapidly dissociated (broken into its atomic constituents) and ionized (stripped of one or more electrons). Once it becomes charged, the material is trapped by Jupiter's magnetic field and forms a torus (donut shape) completely around Jupiter in Io's orbit. Accompanying the volcanic sulfur and oxygen are many sodium ions (and perhaps some of the sulfur and oxygen as well) that have been sputtered (knocked off the surface) from Io by high energy electrons in Jupiter's magnetosphere. The torus also contains protons (ionized hydrogen) and electrons. It will be fascinating to see what the effects are when large amounts of fine particulates collide with the torus.
Movie of Jupiter's Magnetic Field

Formation of Jupiter
The formation of Jupiter (and the other Jovian worlds) starts with the accretion (build-up) of ice-covered dust in the outer, cold solar nebula

The formation of Jupiter (and to some extent Saturn) has recently come under scrutiny as some pieces don't entirely fit convenient theory any more. There are two basic possible formation histories:

• Standard One: Acretion of Icy Material onto a rocky core.

  But this model now has several problems:

  • Why is Jupiter so big? (318 earth masses)
  • At that size, the accretion process takes a very long time (hundreds of millions of years)
  • Turns out that Jupiter's rocky core is too small to allow for significant early acretion - so again, why is Jupiter this big.
  • There are new details about the chemical composition of the atmosphere of Jupiter that are not completely consistent with formation by accretion.

• A new model: Disk Instability.

  • While this model is technically difficult to explain at this level, the bottom line is that it suggests that Jupiter forms mostly as a whole object and not by accretion.
  • This model is consistent with its large mass and indeed in the theory, only objects with masses greater than 50 earth masses could form in this way.
  • This model also explains other features of the solar system. For instance, its hard to understand why we have an asteroid belt if Jupiter grows slowly via acretion.

  • The model suggests that Jupiter formation via disk instability can take as little as one million years.
  • The main problem with this model is that is not a "natural" way to make planets but it appears to be ubiqitous as there are plenty of extra solar planets discovered with Jupiter masses.