JUPITER: Lord of the Planets

  1. Formation of the Planet
  2. Composition
  3. Internal Heat
  4. Atmosphere, Including Recent Findings ( Aug 1997)
  5. Effects on the Rest of the Solar System
  6. The Jovian Moons
  7. NASA's Ron Baalke Answers Questions About Europa
  8. Possibility of Life on the Planet

Printed References:

Kaufmann,William. Universe.. Freeman. 1985
Kaufmann/Comins. Discovering the Universe. Fourth Edition.Freeman. 1996
Scientific American. Jupiter and Saturn. December 1981

Online References William Arnett:Nine Planets
also refer to The Jovian System ( NASA )

1. Formation

The formation of Jupiter and the rest of the outer planets differed from that of Mercury,Venus, Earth and Mars. There is a significant gap of 3.7 A.U. between the last of the rocky planets, Mars ,and Jupiter.( Since Jupiter is about 3.5 times as far from the sun, a protoplanet at Jupiter's distance from the sun receives only (1/3.5)2 = 1/12 of the sun's energy as compared to something as far as Mars). At a greater distance from the sun the original solar nebula was a rotating disk of snow and ice-coated particles that eventually broke up into discrete rings with little material in between. Within each ring the material coalesced to form a protoplanet. If Jupiter had originally formed from many planetesimals, each of which was in turn formed from the accretion of many ice-coated rocky particles, then it would have developed a strong gravitational pull. As the huge Jupiter-protoplanet presumably moved in its orbit, it would have easily and quickly swept large amounts of hydrogen and helium. This explains why Jupiter is a gas giant twelve times larger than the Earth and larger than any other planet.

2. Composition and Magnetic Field

From determining Jupiter's mass and volume, astronomers have easily calculated a density of only 1.33 g/cm3. This implies a mixture of mostly helium and hydrogen since they are the two elements with the lowest atomic masses. But Jupiter's dense core cannot consist of hydrogen and helium because there is insufficient pressure to compress a mixture of those gases to the required central density.

So there must be a rocky core in Jupiter, one that constitutes about 4% of its overall composition. In light of what was said earlier, keep in mind that the rocky core could be as big as 13 earth masses. After all, Jupiter is 318 earth masses and such a core would only account for only 4% of its mass.

At a certain compression which does exist within the core of our giant planet, (although it is insufficient to produce the densities mentioned above) electrons are stripped from their nuclei, and hydrogen acts as a metal. This thick metallic liquid layer gives the rotating planet a strong magnetic field. Its magnetosphere extends more than 650 million km, past Saturn's orbit. The field traps all sorts of high energy particles, all lethal to life. They are rotated and accelerated to such high speeds that Jupiter's plasma has a temperature of 300 to 400 million K. Naturally no fusion occurs because the density of the plasma is extremely low. The Galileo probe discovered an unexpected radiation belt with high energy helium ions between the planet's ring and upper atmosphere.

As pressure decreases with increasing distance from the core, the hydrogen exists in a molecular state along with helium. Neither is metallic. So to summarize: there is a rock-ice core , surrounded by metallic liquid hydrogen in turn wrapped by a mixture of molecular hydrogen and monoatomic helium.

3. Internal Heat

Measurements made by both Voyager and Pioneer suggest that Jupiter gives off 2.0 to 3.0 times as much as it receives. This internal heat must stem from gravitational potential energy that was converted into heat as the planet contracted from the solar nebula. This has produced a core of about 20 000 K, not hot enough for fusion, but warm enough to cause convective currents that lead to complex motions in its atmosphere.

4. Jupiter's Atmosphere

Relative to hydrogen, methane and ammonia have stronger absorption lines, and in the 1930's, these were seen in sunlight bouncing off Jupiter. The much more abundant hydrogen (86% of Jupiter's atmospheric mass ) and helium (13%) were detected later. Water vapour and ammonium hydrosulfide were detected in the early 1970's,leading to a model of three distinct layers of clouds consisting of ammonia ice in the upper atmosphere, ammonium hydrosulfide in between and ice and water in the lower layer. But data from Galileo's atmospheric probe indicate that there is far less water than expected. In general Galileo also found less clouds than predicted, but the probe's entry point might have been at an atypical and warm spot in Jupiter's atmosphere.

Confined in wide bands, Jupiter's high velocity winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences account for the planet's characteristic coloured bands. Galileo's data indicate that the winds are even faster than expected, exceeding 640 km per hour and possibly extending thousands of kilometres into the interior. Also high is atmospheric turbulence, which may also be caused by convective currents from the planet's hot interior.

Some Recent Findings About Jupiter's Atmosphere.


Diane Farrar, NASA Ames Research Center, August 13, 1997

Jupiter's hurricane-force winds greatly increase in speed in the depths of the giant planet's dense atmosphere, data from NASA's Galileo Probe show. The powerful atmospheric motions probably extend downward for thousands of miles, scientists now say.

The Galileo Probe craft made history's first entry into Jupiter's atmosphere in December 1995 and penetrated into what appears to be the region of Jupiter's large-scale interior circulation. The wind speed findings, just completed after detailed analysis, indicate that Jupiter's whole atmosphere circulates, perhaps down to its liquid metallic hydrogen core.

"The winds below Jupiter's cloud tops do not die off as they would if driven by solar heating, but persist and increase to gale force at depths extending 100 miles below the clouds," said Al Seiff, probe investigator at NASA Ames Research Center, Moffett Field, CA. Seiff was principal investigator on the probe's atmosphere structure experiment during the most difficult atmospheric entry in the solar system. (Jupiter contains 71 percent of all the planetary mass in the solar system. The planet's massive gravity produced intense heating by atmospheric friction -- with temperatures hotter than the surface of the sun -- during the probe's descent.)
"We have dipped into the planet's internal motions and have the first clue about the circulation of gases in the deep interior," he said.

Probe instruments made two independent measurements of the winds. Principal investigator David Atkinson, University of Idaho, conducted the Galileo Probe wind experiment using radio measurements as well as data from Seiff's atmospheric structure experiment, obtaining data from eight miles above the cloud tops to 80 miles below. The probe measured winds that increased from 192 mph to 400 mph during descent. Wind speed was 192 mph at eight miles above the cloud tops, rose to 391 mph at 28 miles down, and stayed between 380 and 390 mph down to about 80 miles, the end of wind measurements.

Independent of the radio tracking, Seiff measured the winds using two accelerometers on board the craft that reported speeds from 400 mph to 450 mph. W.M. Folkner, Jet Propulsion Laboratory, measured wind speeds by tracking the probe from Earth during the first 28 miles of descent. He used the Very Large Array of Earth-based radio telescopes to measure the Doppler shift of the probe's incredibly faint radio signal as it came to Earth from deep in Jupiter's atmosphere a half a billion miles away.

The final details on Jupiter wind speeds from Atkinson's data are as follows: Winds were 232 mph at the cloud tops, rose to 293 mph at seven miles down; to 313 mph at 10 miles down; 360 mph at 17 miles down; 391 mph at 28 miles down and to around 390 mph to the end of measurement at 60 miles.

Both Seiff's and Folkner's data are in essential agreement with Atkinson's findings. The findings eliminate the long-held idea that jovian winds are confined to a 35-mile-deep weather layer containing Jupiter's brightly-colored, east to west wind-driven clouds.

The probe also measured atmospheric pressures of one half the pressure of Earth's atmosphere (.5 bars) at the top, to 21 times Earth's atmospheric pressure (21 bars) at the lowest level measured. Temperatures during the Probe descent ranged from a low of -230 degrees Fahrenheit at the top to a broiling 306 degrees Fahrenheit at the lowest level.

The results from Seiff and Atkinson's probe investigations are published in the August 14 issue of Nature.

The Galileo Probe's findings of Jupiter's huge winds may strengthen some existing theories about the gas giant's interior flow, according to Andrew Ingersoll, planetary meteorologist at California Institute of Technology and Galileo interdisciplinary scientist. Several scientists have proposed that the dense atmosphere of Jupiter has a pattern of cylindrical atmospheric vortices parallel to the axis of rotation, some extending completely through portions of the planet. Effects of this interior flow may be visible on the planet's surface as evidenced in its colorful belts and zones, Ingersoll said.

"The winds reached almost 400 mph at 30 miles down and stayed that way. This massive flow of dense atmosphere has tremendous momentum, and may account for centuries-long persistence of some jovian surface features," Ingersoll said. In a fairly well-mixed gas planet, we know of few forces that would drastically change this pattern as you go deeper

The massive interior winds are probably driven by a balance of forces, solar heating at the top and internal heat elsewhere. Jupiter radiates 1.7 times as much heat as it absorbs from the Sun. The planet's surface radiates the same amount of heat at the equator and poles. Therefore, interior circulation is likely to move interior heat preferentially to the poles, balancing solar heating at the equator, he explained.

"We will be studying the parallel cylinders model to explain what we now know about interior atmosphere circulation. These cylinders may work like sets of counter-rotating gears moving heat and momentum from place to place," Ingersoll said.

The proposed atmospheric cylinders were first demonstrated in a series of laboratory experiments 25 years ago to chart atmospheric flow in a wholly gaseous planet. Friederich Busse, University of Bayreuth, Germany, and John Hart, University of Colorado, Boulder, used liquid-filled spheres with high rotation speeds and imposed interior-exterior temperature differences. The experiments showed that the convective and most other disturbances in these fast-rotating spheres of fluid almost always produced cylindrical vortices parallel to the test vessel's spin axis, called Taylor columns.

Jupiter is a giant gas planet, comprised mostly of hydrogen, that rotates on its axis once every 10 hours. Because its gravity is so huge, much of its hydrogen is compressed into a liquid metal. This dense "liquid" extends from Jupiter's central area to 80 percent of the planet's radius, Ingersoll explained. Rotating cylinders of atmosphere extending through Jupiter parallel to its spin axis would run into the dense metallic hydrogen and be cut off, or otherwise modified. This would make interior circulation more complex than if the planet were uniformly gaseous, he said.

The Galileo Probe mission was managed by NASA Ames Research Center, Moffett Field, CA, as part of the Galileo spacecraft mission conducted by the Jet Propulsion Laboratory, Pasadena, CA. The probe was built by Hughes Space and Communications Group, Redondo Beach, CA.

5. Jupiter's Effects on the Rest of the Solar System

In 1992 Jupiter's gravity ripped a comet into 21 pieces. Two years later the fragments of Comet Schumacher-Levy crashed into the planet. It's unlikely that this event was unique in Jupiter's history. This implies that throughout the history of the solar system, Jupiter has either deflected or intercepted comets that would otherwise have penetrated towards the terrestrial planets.

Gravitational perturbations by Jupiter deplete certain orbits within the asteroid belt. The resulting gaps, called Kirkwood gaps, occur at simple fractions of Jupiter's orbital period. Its gravity also captures asteroids in two locations ( called Lagrange points ) along its orbit.

All of these effects can be attributed to Jupiter's large size and consequent strong gravity.

6. Its Moons

Jupiter is gradually slowing down due to the tidal drag produced by its four large, Galilean satellites. In addition Jupiter has 12 other but much smaller moons. The same tidal forces are slowly forcing the moons away from the giant planet.

Io, Europa and Ganymede are locked together by tidal forces into a 1:2:4 orbital resonance. ( Io goes around Jupiter every 1.77 days. It takes Europa almost exactly twice as long and Ganymede almost four times as long: 7.15 days, instead of 7.08 .) Eventually, in a few hundred million years, Callisto will be part of a 1:2:4:8 system. (Presently it takes Callisto 16.7 days, not 14 .)

Note how much shorter their periods are compared to that of the Earth's moon. Io has a comparable mass to that of our moon and is at a similar distance from its mother planet , but Io moves much faster because Jupiter' s mass is much larger than that of the Earth.

Let's look at this more closely: Io is 1.14 times as massive as the earth's moon but also 1.10 times as far from its parent planet. Therefore if the earth and Jupiter's mass were equal, then the force between Io and its mother-planet would be 1.14/1.10^2 = 0.94 of the force between the moon and the earth. But Jupiter's mass is 318 times that of the earth, accounting for a force that is 318*0.94 =300 times stronger. Since centripetal force is proportional to the square of the velocity, Io should be moving 17.3 times faster than the moon. It takes the moon 27.3 days to make one revolution. Since Io's orbit is 1.1 times as long, it should take it 27.3/17.3 *1.10 = 1.74 days---not a bad estimate for neglecting the influence of other Galilean moons on Io.

Tidal forces flex Io's crust as it passes through the point when it is closer to Jupiter. Io's orbit is more elliptical precisely because of the influence of the other satellites. Since it moves faster at that proximity point, it is placed out of sync with its rotation about its own axis, which Jupiter's tug then "corrects". This is responsible for Io's high volcanic activity.

Europa is covered with a smooth layer of ice, and is crisscrossed by an intricate pattern of long cracks, likely also caused by tidal flexing.

The other 2 Galilean moons are highly cratered but neither presently has plate tectonics. They are, not coincidentally, the outer of the Galilean satellites, and not significantly influenced by the 8 much smaller moons of Jupiter that exist beyond their orbits.

The Galilean satellites, Jupiter's ring and other inner moons formed by accretion in a process similar to the one that formed the solar system's planets. The outer moons may be captured asteroids.

7. Possibility of Life on the Planet

The intense radiation and wild turbulence in the planet's atmosphere and surface create an environment hostile to life. In fact scientists seem so certain of this that they did not even bother to equip Galileo with probes for verifying the absence of life on Jupiter. Some of Jupiter's moons, however, especially Europa, are better candidates for the existence of microbial life. The icy coating may be occasionally churned and melted, covering craters, sheltering some form of chemical evolution. In March,1997, the Galileo probe revealed an icy layer that is thinner than previously believed, suggesting that liquid water probably exists on the moon's surface.
Born on: April, 1996
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