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 a "giant planet," with very different properties from the "terrestrial" planets we have studied so far.
(To left, from the Galileo Project, http://www.jpl.nasa.gov/pictures/jupiter/
Important characteristics of giant planets are:
Their average densities are low, similar to water: Jupiter is 1.3 grams/cm3 and Saturn is 0.7 grams/cm3 - compared with densities of 3 - 6 grams/cm3 for terrestrial planets.
Their composition is similar to Sun -- (especially Jupiter and Saturn)
whereas the terrestrial planets are made almost entirely of those "other elements."
They have liquid or icy surfaces and dense atmospheres with violent and long lasting storms.
|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)
(the dark dot the appears part way through is the shadow of a Galilean satellite)
Differential rotation implies that we are not seeing a solid surface, which would have to have a constant rotational speed.
|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.
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)|
|Jupiter has the strongest magnetic field of any body in the solar system. The magnetic field on Jupiter implies that it must contain a liquid metal which contradicts expectations from its density. However, at a depth of ~15,000 km below its cloud tops, the pressure becomes so great that hydrogen becomes a liquid metal (a rarity because both temperature and pressure must be very high). "Metallic" in this sense means it conducts electricity readily. Most of the interior of Jupiter is in this state. (http://www2.jpl.nasa.gov/galileo/jupiter/interior.html)|
Protons and electrons trapped by this magnetic field produce synchrotron radiation at radio wavelengths making Jupiter the only planet detectable easily by radio telescopes. The bands of charged particles surrounding Jupiter are so intense that they actually knock atoms off the surface of Io, the innermost of the Galilean moons. (http://www.astronomy.org.au/ngn/
Jupiter also has aurorae similar to those on Earth. (http://nssdc.gsfc.nasa.gov/
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
Exactly how giant planets form quickly, before the gas escapes from protoplanetary disks, is a problem we are still struggling to understand.
|Therefore, the interior structure of the planet is as shown to the right. In place of the molten rock mantle of Earth, Jupiter has a thick layer of liquid hydrogen. Far below this liquid hydrogen "mantle" the pressure is so great that the hydrogen changes state to become electrically conductive. The strong magnetic field is a product of the rapid rotation and this conductive layer. We suspect that the rocky materials have settled into a core not too different in size than the earth, but dwarfed in this case by the overlying layers of hydrogen and helium.|
|We do not believe Jupiter has any solid surface (despite what you may have seen in the movies!). Instead, the "surface" is probably liquid molecular hydrogen under great pressure from the thick atmosphere. Perhaps it would look like this artist's concept!|
Test your understanding before going on
|Horus, Egyptian god of Mars, http://grenier2clio.free.fr/egypte/horus.htm||
Shani, Vedic god of Saturn, http://www.payer.de/kommkulturen/kultur123.htm
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|Click to return to Mars||
hypertext G. H. Rieke
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