Jupiter

Key points: "Weather" features; internal energy; nature of surface; interior composition; contrast of a giant planet with the terrestrial ones

Jupiter is the largest planet in the Solar System (as massive as all the rest together). It is is a "giant planet," with very different properties from the "terrestrial" planets we have studied so far.

jupiter-brihaspati.jpg (20208 bytes)

(To left, from the Galileo Project, http://www.jpl.nasa.gov/pictures/jupiter/

above, an Indian miniature painting of Brihaspati, the planet Jupiter, divine sage and tutor of the Gods, from The Black Peacock, http://www.goloka.com/index.html)

Rotation

Jupiter rotates in 9 hr 50 minutes at its equator. However, careful observation shows that the rotational rate is slower moving towards the pole -- 9 hr 56 minutes.

This effect of rotation rate varying with latitude is called differential rotation. It is dramatized here by "freezing" the polar motions and letting the rest move relatively. (From NASA, JPL, Cassini/Huygens Project, http://saturn.jpl.nasa.gov/index.cfm)

Differential rotation implies that we are not seeing a solid surface, which would have to have a constant rotational speed.

Weather on Jupiter

Jupiter's atmosphere displays colored bands and changing features indicative of weather. The Galileo orbiter has returned images of cloud tops that look very similar to thunderheads on Earth.

The exact cause of the colors is still not understood but they are likely to result from sulfur or phosphorus compounds found in trace amounts. Light colored clouds are ammonia ice crystals. The clouds show powerful turbulent motions indicating high winds. (all from Galileo Project)

Storms have been seen to last for very long times -- the Great Red Spot has existed for over 300 years. (NASA via Astronomy Picture of the Day)

Voyager images of the Great Red Spot showed a whirlpool character confirming that it is a large high-pressure cell like some on Earth.

Internal Energy

The inner terrestrial planets have a close balance between the energy absorbed from the sun and the energy radiated into space.

To observe in the far infrared, in 1969 a 12 inch telescope was mounted in the escape hatch of a Lear Jet so it could be carried above most of the atmosphere (which absorbs far infrared light) (from http://www.nasm.si.edu/research/dsh/artifacts/SS-LearJetScope.htm). It was discovered that Jupiter emits twice as much energy as it absorbs from the sun. Subsequently, it was found that Saturn and Neptune (but not Uranus) also emit about twice as much energy as they absorb from the sun.

For Jupiter, this can be trapped heat from the time of its formation; the cause is not well understood for Saturn and Neptune.

The convection from the internal heat contributes to the extreme activity of atmospheric motions. Convection arises when we heat a liquid or gas under a cooler layer, the heated part expands and floats up to the top where it cools, contracts, and sinks down to the bottom. We see it in everyday experiences like LavaLamps. (From http://www.ihatemycubicle.com/2004/12/stupid_man_dies.html and Windows to the Universe, http://www.windows.ucar.edu/tour/link=/jupiter/interior/J_int_motions_overview.html&edu=high)

Galileo Probe

Not long after the Galileo mission arrived at Jupiter, a probe that fell through the atmosphere was released. As the probe fell, it returned data on temperature, pressure, composition, wind speeds, and prevalence of clouds. These results showed that

The hydrogen and helium abundances are close to those found in the sun, but the next 4 most abundant elements (oxygen, carbon, neon and nitrogen) are quite different. Oxygen is much less abundant while carbon in the form of methane is much more abundant.
These differences in abundances of the elements suggests that Jupiter did not form by simple collapse of a part of the cloud which ultimately formed the Sun, that is the way a stellar companion to the sun would have formed. It is more plausible that Jupiter formed by accretion beginning with a small icy core, a process that is analogous with the way the terrestrial planets formed rather than with the way stars form.