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| Comparative Planetology: the Giant Jovian Planets
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Relate the overall size, internal structure, and composition of the giant planets to their location in the solar system.
Distinguish between Jupiter's magnetosphere and that of the Earth based upon its source (how it is generated, what is doing it) and its overall strength.
List 5 of the main accomplishments of the Galileo satellite and its probe.
Explain why Jupiter seems so colorful and Saturn does not.
Explain why Uranus and Neptune are blue.
Describe the internal heat sources for Jupiter and Saturn.
Using the approximate phase diagram for hydrogen, state why Uranus and Neptune lack metallic hydrogen whereas Jupiter and Saturn both have a metallic hydrogen region.
Describe what is so weird about the magnetic fields of Uranus and Neptune, and give a possible explanation for what is observed.
Explain why the Great Red Spot of Jupiter has been such a long-lived storm.
Compare the aurorae seen on Jupiter and Saturn to those seen on Earth, giving one similarity and one difference.
Outline why we expect Uranus's atmosphere to start to look more active based upon the characteristics of its seasons.
List 5 of the goals of the Cassini spacecraft and its Huygens probe to Saturn.
Structure and Composition
Heat Sources
Uranus "YOOR a nus" not "your anus" or "urine us"
Take the Quiz!
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Saturn |
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| Uranus |  |
Neptune |
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Interiors
Structure and Composition
Illustration from Bennett et al A Cosmic Perspective, the Brief Edition
Hydrogen Phase Diagram
This illustration is based upon a photocopied figure from
a text or article--I have lost track of the source. My apologizes.
Click on the image to the left to take a closer look at an approximate
phase diagram for hydrogen. There are a number of features you should note.
First of all, the temperature and pressure diagram the interior structure
of the planets or brown dwarf, starting with close to the surface in the
lower left-hand corner and progressing to the core. Secondly, the pressure is
in millions of bars. Third, there is a region where dissolved helium will
form droplets and sink to the core. Saturn's structure cuts across this
region, where the temperature of the hydrogen is too low to hold helium in
suspension (just as cold water cannot hold dissolved sugar like hot water can).
Jupiter and Saturn reach high enough pressures and temperatures within their
interiors to have hydrogen in its liquid metallic phase--a state that is
conducive for producing strong magnetic fields.
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Both Jupiter and Saturn give off more heat than they receive from the Sun, but their heat sources are different. Jupiter retains some of its heat from contraction; it is probably in its last stages of contract ing from the protosolar nebula. Saturn, on the other hand, is in the process of differentiating. Helium, being heavier than hydrogen, is raining onto the depths of Saturn. The gravitational potential energy is being converted to kinetic energy (heat) as the helium descends.
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 Uranus as seen by Voyager 2
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 Neptune as seen by Voyager 2
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| URANUS: Uranus appears to have very little, if any, generating of internal heat. Each hemisphere directly faces the Sun for a couple of decades, and its northern hemisphere is just coming out of the deep freeze. By 2007, the Sun will be shining directly on the equator. As the position of the planet with respect to the Sun changes, its atmosphere appears to be waking up and showing hotspots. | NEPTUNE: Neptune radiates about 2 times as much heat as it gets from the Sun (it gets about 1/900 as much energy from the Sun as the Earth does). When Voyager 2 flew by in 1989, Neptune had a Great Dark Spot. Although that particular storm disappeared, another appeared in the opposite hemisphere. It had to have been a new storm since Neptunes 2000 km/hr winds at its equator would destroy any migrating storm. |
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| JUPITER An enormously strong magnetic field |
SATURN magnetic field perfectly aligned with its rotation axis; 5% the size of Jupiter's field |
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| URANUS Axis tilted about 59 degrees and offset from center of planet by 30% of its radius, placing magnetic poles nearer the equator. |
NEPTUNE Field highly tilted: 47 degrees from rotational axis and offset at least 0.55 radius from physical center of planet. |
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| Comparing the two magnetic fields, scientists think that the unusual orientations may be characteristic of flows in the interior of both Uranus and Neptune and not the results of magnetic field reversals, or, in Uranus' case, of the planet being tipped on its side. From Voyager: A Grand Tour | |
The largest entity in the Jovian system is the invisible force of the planet's magnetic field. Planetary magnetic fields are created by the motion of fluid interiors. Fifteen thousand miles deep within Jupiter's interior, hydrogen undergoes a dramatic change. At a pressure three million times that at Earth's surface, and at temperatures exceeding 19,000 degrees Fahrenheit, the hydrogen changes from molecular liquid to a state called liquid metallic hydrogen, an excellent electrical conductor.The liquid metallic hydrogen and the planet's rapid rotation (9 hours 55 minutes) generate electric currents that create Jupiter's magnetic field, which is more than 10 times stronger than that of Earth.
Jupiter's ring and moons are embedded in an intense radiation belt of electrons and ions trapped in the magnetic field. The Jovian magnetosphere, which comprises these particles and fields, balloons two or three million miles towards the Sun and tapers into a wind sock-shaped tail extending at least 465 million miles behind Jupiter as far as Saturn's orbit.
The relationship between the magnetic field and Io is unique. As the magnetosphere rotates with Jupiter, it sweeps past Io, stripping away about a ton of matter per second and forming a torus—a doughnut-shaped ring around Jupiter predominantly composed of electrified oxygen and sulfur glowing in the ultraviolet.
As these heavy ions migrate outward, their pressure inflates the magnetosphere to more than twice its expected size. Some of the more energetic ions fall into the atmosphere along the magnetic field to create Jupiter's auroras.
As Io moves through Jupiter's magnetic field, it acts as an electrical generator, developing 400,000 volts across its diameter and generating an electrical current of three million amperes. The current flows along the magnetic field to Jupiter's ionosphere.
From Voyager, the Grand Tour NASA and JPL
| Requirements for a planet (or moon) to generate a magnetic field |
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| Jupiter |  | Saturn |
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(Per cent by volume)
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(Per cent by volume)
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| Uranus |  | Neptune |
(Per cent by volume)
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(Per cent by volume)
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Galileo Home Page (JPL) |
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Galileo Probe Mission Science Summary in non-technical terms |
Galileo's Probe of Jupiter's Atmosphere |
Determine the atmosphere's temperature and pressure structure
Determine the chemical composition of Jupiter
Determine the cloud layer characteristics
Measure the ratio of helium to hydrogen to high accuracy
Measure the winds and determine how deep in the atmosphere the winds exist
Measure how sunlight and energy coming from the deep interior are distributed
Detect lightning, measure its energy, and observe how often it occurs
Measure the characteristics of energetic protons and electrons trapped in Jupiter's magnetic field
Answers to these questions and the figures shown in class can be found at: Galileo Probe Mission Science Summary in non-technical terms
The direction and speed of the jets partially determine what colors are seen. Most of the differences in coloration is due to the composition of the atmosphere and the abundance of trace elements present. Although there isn't much carbon in Jupiter's atmosphere, carbon easily combines with hydrogen and small amounts of oxygen to form a variety of organic compounds. The orange and brown colors in Jupiter's clouds may be due to the presence of these organic compounds, or sulfur and phosphorus.
Here is an image of Jupiter's northern hemisphere showing the distinctive orange and brown colors:
Hotspots are thought to be areas of downwelling with dry (low ammonia and water) air. The hotspots and ovals remain for an extremely long time. The great red spot has been observed for at least 300 years. These hot spots and ovals (ovals being a gigantic storm, much like our anticyclones here on Earth) are driven by the internal heat of Jupiter. Unlike storms here on Earth, there are no land masses on Jupiter to dampen the storms; thus, once formed, they remain. During its tour of Jupiter, Galileo scientists observed two large cold storms, called "white ovals", merge to form one larger storm. This new white oval is the strongest storm observed in our solar system, with the exception of Jupiter's Great Red Spot, and is the diameter of the Earth.
Jupiter's Red Spot is 20,000 km long and has been followed by observers on Earth since the telescope was invented 300 years ago. It is a huge storm made visible by variations in the composition of the cloud particles and the amount of cloud cover. Winds in the outer part of the Red Spot reach 250 mph while the center remains quiescent.
The striped cloud bands on Jupiter are not uniform. The striped pattern is divided into belts and zones. Winds flow first in one direction, then in the opposite direction. The cloud tops rise in a belt, and drop down in a zone. Wind speeds blow east to west in a belt, and west to east in a zone. The extremely rapid rotation of Jupiter relative to an object of it's size (10 hours) causes the pattern to be reinforced such that it becomes the dominant dynamics of Jovian meteorology.)
There is no clear consensus yet on the details of why these
bands, zones, and jets look the way they do.
Without knowing that Jupiter has aurorae, why might you predict (knowing what you do about how the Earth's aurorae are created) that Jupiter would have very active, strong auroral displays? Knowing how the atmosphere of Earth and the atmosphere of Jupiter differ, would you guess that the auroral displays would be similar between these two planets?
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The space probe Cassini is on its way to Saturn. ETA: 1 July 2004.
CAPTION: Image of the planet Uranus taken using the new adaptive optics system at the 10-meter diameter Keck II Telescope on the Mauna Kea volcano in Hawaii. The image uses infrared light with a wavelength of 2 micro-meters to outline the planet and its rings in reflected sunlight. The planet itself is artificially darkened by a factor of about 20. Clearly visible are the methane haze layer on Uranus's south polar cap and the tiny cloud features at high northern latitudes. The latter features are located well above the methane haze in altitude. Inside the bright epsilon ring three fainter rings can be discerned, which each consist of multiple ringlets. These are barely resolved in the image.
These images were obtained on June 18, 2000, by a team from the University of California, Berkeley, and the Lawrence Livermore National Laboratory. Team members were Professor Imke de Pater and her student Henry Roe, and Livermore scientists Claire Max, Bruce Macintosh, Seran Gibbard and Don Gavel. (CREDIT: Imke de Pater/UC Berkeley)
Huge Spring
Storms Rouse Uranus from Winter Hibernation Although the color in this image
has been enhanced, there is little question but that Uranus is starting to change.
Be sure to follow this link for an explanation of why we are seeing these changes.
CAPTION: Image of the planet Neptune taken using the new adaptive optics system at the 10-meter diameter Keck II Telescope on the Mauna Kea volcano in Hawaii. The image uses infrared light with a wavelength of 2 micro-meters to outline the planet in reflected sunlight. The bright bands are haze layers in Neptune's upper atmosphere. By compensating for the blurring effects of turbulence in the earth's atmosphere, adaptive optics has shown much more detail in the haze bands than has been previously observed from earth-bound telescopes. The dark stripe is a very narrow slit through which light was directed onto a spectrograph in order to characterize the chemical composition of Neptune's atmosphere and the heights of the haze layers.
These images were obtained on June 17, 2000, by a team from the University of California, Berkeley, and the Lawrence Livermore National Laboratory. Team members were Professor Imke de Pater and her students Shuleen Chau Martin and Henry Roe, and Livermore scientists Claire Max, Bruce Macintosh and Seran Gibbard. (CREDIT: Imke de Pater/UC Berkeley)
Here is an excellent exercise leading to the comparative study of the giant planets. |
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