These figures can be used to verify Kepler’s law: (m₁+m₂)P²=a³

Visited by Pioneers 10 and 11, Voyagers 1 and 2 and currently circled by the Galileo spacecraft. The gas giant has 1400 times the volume and 318 times the mass of the Earth, 0.1% the mass of the Sun. To rate as a star a body needs about 7% of the suns mass, but any body rather more massive than Jupiter would actually be smaller because the core is crushed to higher and higher density as mass increases if gravitational contraction is the only source of energy. so Jupiter is about the largest but not most massive planet that can orbit a star.

The telescopic appearance of Jupiter is quite rewarding and captivated Galileo who studied the planet and especially the four bright Galilean satellites Io, Europa, Ganymede and Callisto. With a small telescope the planet reveals a number of tan belts with complex patterns of red orange and brown and white zones between the belts and a number of transient white and tan ovals spots and festoons.

Starting from the South Polar Region (SPR) we have a large darkish brown region with faint markings but no bands. at latitude -60 we reach the South Temperate Zone (not STZ). The white of the zone is interspersed with dark reddish brown streaks. Then we reach the wavy edge of the South Tropical Belt (STB) which is quite varied in contrast and colouring with red spots and white ovals North of the STB we reach the South Tropical Zone (STZ) then finally, separating them by a fine wavy brown streak, the South Equatorial Belt (SEB). A persistent feature called the Great Red Spot (GRS) is embedded in the STZ. The GRS is a reddish oval about the size of two earths side by side has been seen with variable visibility for over since Robert Hooke first recorded it in 1630. The GRS pushes the STZ/SEB boundary northwards. All of the features rotate with different periods so the appearance changes quite a bit from day to day and even hour to hour. Another persistent feature called the South Tropical Disturbance sometimes passes by the GRS and the two push each other aside. The GRS does not rotate as fast as the STZ which flows past. The spacecraft have returned movies of the Jovian weather patterns and show that the GRS is an anticyclone, a high pressure rising column with a counterclockwise period of about six days. Small white spots frequently circle the GRS with periods of seven days. We suspect the GRS

The planet has a rapid rotation, a bit shorter than 10h, and this results in a pronounced equatorial bulge. But as mentioned above the rotation rate is quite non-uniform so there are three rotation systems in use, the equatorial (system I) P_I=35430s, the mid-high latitude (system II) P_II=35740.6s and a system associated with magnetospheric radio emissions and most likely representative of the bulk of the planet (system III) P_III=35729.8s.

The reason for the appearance of the zones and belts has to do with the fact that Jupiter radiates twice as much energy as it receives from the sun. The atmosphere convects and the rotation stretches the convection cells into warm rising zones whose tops freeze and form white ammonia ice clouds. The material "rolls over" into the belts where it falls, heats and becomes transparent. So the dark belts are regions of falling material and we can see down to a level where chemical activity gives the belts their characteristic colours. The chemistry is not known in detail but probably involves solar UV radiation and lightning.

Na + NH₃^liq. ® Na⁺ + e^- (ammonia) blue

2Na + NH₃^liq. ® 2Na⁺ + 2e^- (ammonia) bronze

There is a question mark over the previous information on colours. There are those who would say that organic molecules are the colouring agents. Like asphalt (yellow) and azuline (blue). Organic molecules have been synthesized under Jovian conditions [Sagan, Khare, Woeller, Ponnamperuma, Miller, etc.].

In brief there is no universally accepted theory of Jovian cloud colours.

These images are an artist's rendition showng the collision of a fragment of the comet P/Shoemaker-Levy 9 with Jupiter from different viewing perspectives. The Jupiter images were taken by Voyager 2 in 1979, applied to a sphere and rotated to the proper view. These images are courtesy of Dave Seal and Paul Chodas of JPL. This was the first collision of two solar system bodies ever to be observed. The comet consisted of at least 21 discernable fragments with diameters estimated at up to 2 kilometers.

Theory: The internal structure of Jupiter was worked out by Rupert Wildt around 1938 who showed that a planet with the observed mass and density of Jupiter could only be composed of H and He. Jupiter is mostly H and He in ratio N(H)=9N(He), the same as the solar photosphere. In fact, if 0.1% of the sun's mass were scooped out of the solar photosphere and placed beyond 5AU you would get another Jupiter after a few billion years. The body would contract and the nonvolatile elements would settle to form a iron/silicate core somewhat larger than and 10-15 times the mass of the Earth but at a temperature of 25000-40000K and pressure of 80,000,000 bar. At 10,000km there may be a rock and water ice layer then out to 45,000-55,000km where the temperature is 11,000K and the pressure 3,000,000 bar hydrogen in an as yet unknown liquid/metallic phase. Above is liquid molecular hydrogen to the surface. The source of the heat is gravitational contraction but the actual mechanism may be the phase change from liquid to metal, the metal core creeping outwards a mm per year. The Galileo probe will map the gravitational potential of Jupiter which, due to the rapid rotation, should give information on the density structure which will give us information on the state of hydrogen at temperatures and densities unobtainable in terrestrial labs.

Moons. There are four moons and many rocks.

Since the orbital inclination (i=1.31) and obliquity (3.08) are small and the inner Jovian satellites are tidally locked to the equator. Eclipses occultations and transits are frequent and these timings are always predicted in astronomy magazines and the Astronomical Almanac. Anyone with access to binoculars or a small telescope should point it at Jupiter just to see the changing configurations.

The Galilean satellites were immediately recognized by Kepler and Galileo to form a mini solar system which obeyed Kepler's harmonic law. These were the first objects that obviously went around a body other than the earth or the sun. Now look at the periods. The moons and especially Io interact strongly and tidal heating provides substantial energy to Io and Europa.

Io is one of three moons along with Titan and Triton that has an atmosphere. A Sodium cloud surrounds the moon and extends some 200,000km along its orbit. The secret of this cloud was revealed by the Voyager spacecraft and suggested theoretically by Stanton Peale et al a week before Voyager detected active volcanoes on Io.