The Jovian Planets
The Jovian Planets
The Jovian Planets
Far beyond Earth in the solar nebula lies an ice belt and beyond that lay the four Jovian planets. They are Jupiter, Saturn, Uranus and Neptune. Jovian means "Jupiter- like" in which the rest of the jovian planets do coincide with the name. Uranus Neptune and Saturn, all carry the same traits as Jupiter. The jovian planets are large gas giants that contain mainly a thick atmosphere of Hydrogen and helium. These planets do not have solid surfaces, rather they just get denser with depth. They contain high mass and are usually anywhere from 15 to 318 times the mass of earth. They also contain many satellites and the gravity is much stronger than that of earth. The jovian planets inner structure probably consists of a rocky core of metals, water, ammonia and methane. Usually these cores are about the same size as earth possibly a little larger. It is also possible that Uranus and Neptune�s core is a liquid instead of a solid. The Jovian planets also have about the same rotational characteristics and all have rings around them.
Jupiter, the first of the jovian planets, reigns supreme throughout the solar system. Named after the Roman god Jove, the ruler of Olympus; Jupiter is the fifth planet from the sun and is also the largest planet in the Earth�s solar system. It is 318 times more massive than Earth and is two thirds of the planetary mass in the solar system. Jupiter�s surface, unlike earth, is gaseous and not a solid. It is about 90% hydrogen and 10% helium with traces of methane, ammonia, water and rock. Jupiter�s interior is very similar to the Sun�s interior but with a far lower temperature. However, it is still unknown but Jupiter is believed to have a core of liquid metallic hydrogen. This exotic element can only be achieved at pressure greater than 4 million bars. Jupiter radiates more energy in space than it receives from the sun. The interior of Jupiter is hot and has been estimated to be 20000 degrees Kelvin. The heat is generated by the Kelvin- Hemholtz mechanism, or the gravitational compression of a planet. It gives off about 1.5 to 2 times more energy than the sun. It is speculated that the source of this heat is due to the rapid rotation of the planet and it�s liquid metallic hydrogen core.
Liquid Metallic hydrogen consists mainly of ionized protons and electrons and is the electrical conductor and the source of Jupiter�s magnetic field. This magnetic field "spins in less
than 10 hours and is stirred by convection currents. The results are the strongest magnetic field in the solar system�." ( Seeds, 516). This magnetic field is so large that it extends beyond Saturn and is electrified enough to send charges into the earth�s magnetic field.
In the 1970�s, Pioneer and Voyager flew past Jupiter and discovered the large magnetic field or magnetosphere. The magnetosphere is not a true sense a perfect sphere. It is highly flattened due to the rapid rotation of Jupiter. This magnetic field causes phenomenon such as strong lightening and even an aurora similar to earth�s aurora borealis .
Jupiter, unlike earth, has three distinct weather producing zones or a troposphere. They are believed to contain Ammonia ice, ammonium hydrosulfide, and water and ice. In the apparent or uppermost atmosphere, ammonia ice crystals thrive in a temperature of about 150 degrees Kelvin. Most astronomers theorize that the next level of the atmosphere is primarily made up of Ammonium hydrosulfide crystals in a temperature of 200 degrees Kelvin. It is also theorized that the third and final level before the liquid metallic hydrogen is a layer of liquid ammonia and water droplets. Jupiter�s atmosphere is also plagued by high velocity winds that move in wide bands. These winds blow in opposite directions along the latitude of the planet. Because of chemical reactions and differences, they can be seen wrapping around Jupiter in colorful bands. The light colored bands are called zones and the dark colored bands are called belts. It is not known whether the belts and zones are permanent, they have not changed in eighty years of observance. "One theory is that the jet stream at the belt-zone boundaries are linked to circulation patterns deep in the liquid interior" (Seeds, 520)
One of the most prominent features in Jupiter�s atmosphere is the Great Red Spot or GRS. The GRS is an oval about 12000 by 25000 km. At first sight the GRS is similar to a hurricane on earth but with infrared observations and by observing the direction of rotation, scientists have concluded that the GRS is a high pressure region whose cloud tops are higher and colder than surrounding regions. Similar animosities exist on the other Jovian planets but it is not known how long they will last.
Like all Jovian planets, Jupiter has it�s own ring system. Jupiter�s rings are less than 30 kilometers thick and with a distance of 1.81 planetary radii. The rings are at least 100 times harder to see than Saturn�s rings. Most of the particles found in Jupiter�s rings are small and have a diameter about the same size as a light wave length. This causes the light to bounce off of the particles and scatter making the rings look bright. The particles found in Jupiter�s rings are believed to be the remains of a moon that moved in too close to the Roche limit and was torn apart.
Like a great king with many followers, Jupiter also has an extremely large amount of satellites orbiting around it. Jupiter�s satellites can be divided into two groups. The smaller moons are merely captured asteroids but the larger moons are like a small planet. Callisto is one of the larger moons orbiting around Jupiter. It is slightly larger than the earth�s moon and has rocky core topped by a mantel of ice. Photographs of Callisto has shown that it is a dead world that is mostly dark and full of pot marks from meteors. Ganymede, the next moon of Jupiter is also an icy world. It is about fifty percent larger than the earth�s moon. Ganymede is full of craters but it also has a grooved surface which suggests that the water mantle must have been warm enough to leak and it was probably caused by tidal heating. Europa unlike Callisto and Ganymede is a rocky moon with a small icy crust. However, this moon is also an active moon. Voyager photos showed a icy surface that had almost no craters at all and cracks that seemed to be allowing water to seep through, so it is theorized that Europa is a moon that is still growing and changing. Io is the moon closest to Jupiter. Io is surrounded by a cloud of sulfur, oxygen and sodium. It was also discovered that Io has eight active volcanoes on it and it continues to grow and expand as the volcanoes spew gas and debree. It also gets all of it�s energy from the Io flux tube. The tube is thought to deliver ionized gas to the surface to give the volcanoes their energy.
Jupiter also has many other small moons called the Galilean moons. These moons are thought to be small asteroids that were captured. It is also believed that the moons were originally part of the planet itself when it first formed. However, Jupiter in all it�s glory and moons cannot live up to the beauty of the sixth planet away from the sun.
Saturn one of the most beautiful planets was discovered by Galileo with a telescope in 1609. Saturn is a very unique planet in that it is "lighter than water, with a density of .7 gram per cubic centimeter." ( Considine) Saturn is only slightly smaller than Jupiter and has many of the same attributes that Jupiter has. Saturn is thought to have a liquid metallic region and a small silicate core. It has also been shown that with "infrared observations that Saturn radiates 2.5 to 3 times more energy than it gets from the Sun�" (Seeds, 529) Like Jupiter, Saturn has belts and zones but they lie much deeper in the Atmosphere and contrast less. The atmosphere of Saturn is slightly different from Jupiter�s atmosphere. Saturn is much colder and the temperature seems to change as if there were seasons. The winds also blow much harder than on Jupiter . They can exceed 500 meters per second and they blow primarily in an eastward direction. Saturn also contains less helium in it�s composition than Jupiter. Saturn also has a large magnetoscope allowing the rings to exist but it is largely influenced by the solar winds.
Although all the Jovian planets have rings, Saturn is by far the best known. When Galileo discovered the rings in 1609, he thought that he saw three objects. A central form with two forms on either side. It was not until 1659, that Christiaan Huygens discovered the actual disc around the planet. Then in 1675, Giovanni Cassani discovered the gaps between the rings. The gaps are now called Cassani�s division. Saturn�s rings are named by the letter�s of the alphabet in the order they were discovered not in the order they actually appear. The outermost edge of ring A is about " 21 times the radius of earth" (Seeds, 532) The rings of Saturn are made up of millions of small particles mostly frozen water. Each ring rotates slower on the inside than on the outside. It is believed that the rings have a thickness of two kilometers.
As voyager passed by Saturn, it was discovered that there were many gaps between the rings and that there was as many as 100 rings around Saturn. It was also discovered that Saturn�s rings had spokes that radiated out radially from the ring. Scientists believe that the Magnetic sphere around Saturn caused microscopic particles to be pulled out radially from the rings and they scattered the light much like the rings around Jupiter. Voyager also sent back pictures of shepherd satellites or two moons that orbit around each other. The gravitational force of these moons are thought to be one of the leading causes of the many rings within a ring. While the rings are beautiful it is still a mystery whether the moon is primordial or part of an icy moon that got too close to Saturn�s Roche limit.
Saturn also has it own satellites beside it�s rings. Saturn has seventeen different moons. Most are dead icy worlds, but there is one large enough that it may contain oceans. Saturn�s biggest satellite is Titan, with a diameter of 5150 kilometers it is 6 percent larger than Mercury. It is the second largest satellite in the solar system. It is been proposed that Titan is made up of equal parts of rock and ice. It has a very opaque atmosphere. It is a very thick "photochemical haze" that is about 50 kilometers thick. The atmospheric pressure is about 60 percent greater than earth�s and it is mad up primarily of nitrogen. Most scientists agree that some form of liquid methane lies on the surface. Some even believe that the surface contains rivers, lakes and even oceans full of methane. It is also speculated that the slime made by the methane might have been the same slime that started life here on Earth many centuries ago. Unfortunately, not much more can be learned about Titan until we can go beyond it�s thick, hazy atmosphere.
In addition to Titan there are eight smaller moons and many more minor satellites. Most of these moons are geologically dead. Few show some signs of cracks and fissures. It is also interesting top point out that the moons are not all spherical in shape, there are a few that are highly irregular. Overall, these moons wobble and move about in a crazy orbiting pattern , unfortunately we have not learned enough to give much information about them.
The next planet in the wonderful series of the Jovian Planets is Uranus. Uranus was discovered by Herschel on March 13, 1781 while he was looking for stellar parallax. Uranus is named after the eldest of the Greek Gods. Uranus like Jupiter has no surface. It is mainly comprised of hydrogen and helium. It has no visible cloud patterns but it�s weather is shown to be similar to Jupiter�s and Saturn�s weather. It is thought to have three levels of atmosphere, with water clouds on the first level, followed by Ammonia clouds and then Methane clouds. Uranus also has the same characteristic of the belt- zone pattern that Saturn and Jupiter has. This has laid claim that the temperature of Uranus is directly related to seasons and the belt- zones wind pattern.
The interior of Uranus does not include the same liquid metallic hydrogen that makes up Jupiter and Saturn. It is believed that the core is made up of highly pressured water, ammonia and methane which becomes a strong enough conductor to create a magnetic field around the planet . The magnetosphere is also odd in that it does not center around Uranus, instead it slants to about 60 degrees relative to it�s axis. This magnetosphere is also known for causing the phenomenon known as electroglow or ultraviolet photons released into the solar winds. Unlike Jupiter and Saturn , Uranus barely releases more energy than it gets from the sun and is thought that it has lost most of it�s internal heat.
Like Saturn, Uranus also has rings that were discovered not very long ago. In 1977, James Elliot and a team discovered the rings accidentally. There are eleven known rings that range in size and shape. Unlike Saturn rings, Uranus�s Rings are dark in color and relatively thin. The brightest of these rings is known as the epsilon ring. It is filled with debree of fairly large particles and dust.
Uranus is also surrounded by about 15 satellites. The names of Uranus�s moons take from the writings of the bard William Shakespeare and Pope. Uranian moons are believed to be made up of dirty ice. Oberon the outermost moon, is named after the fairy king in Midsummer Night�s Dream, and is pot marked with craters and is fairly dark. It has a large fissure or fault were it was believed that water poured across and flooded the craters. Titania, respectively named for the fairy queen in the aforementioned play, is the largest of the uranian moons. Titania is littered with craters, faults and fissures. It has shown signs of being active but not recently. Uranus has other moons also but the most unique is Miranda. Miranda�s history is a violent one that tells us that she might have been broken apart. The surface of Miranda is also filled with ovoids or oval patterns that unknown in origin.
The last and final Jovian Planet is Neptune. Neptune was named for the sea god and is the eighth planet from the sun. Neptune was discovered in 1843 by two people Adams and Galle.
Very little is known about Neptune and most the information provided is from voyager2�s encounter. Neptune�s interior seems to be like Uranus�s in that it is comprised mainly of various ice�s and rocks. It is presumed that Neptune has a small rocky core with an icy mantle with a layer of liquid hydrogen. Like the typical gaseous planets, Neptune has wild winds confined to bands of latitude with large storms or vortices. Neptune unlike Uranus has an internal heat source that radiates twice as much energy as it gets from the sun. Neptune like all of the jovian planets has a magnetic field, though it is weaker than Uranus�s. However like Uranus�s magnetic field, the magnetic field of Neptune is off centered and tips at a fifty degree angle.
Neptune also has rings like the rest of the jovian planets. There are very few of them and they are considerably thin and dark . Probably the only reason they exist is because of the shepherding moons. Neptune has about eight moons with Triton being the largest. Triton is mainly composed of ice and is still active. It has very few craters but has seen a violent past. It has been pushed and pulled by tidal forces, which caused nitro gas volcanoes on it�s surface.
Different from the terrestrial planets, the Jovian planets are basically big balls of gas. The jovian planets seemed to be formed around the same time from the solar nebula. Jupiter and Saturn are the closest in nature to each other with Neptune and Uranus taking on a few of their traits. They all carry the same characteristics in their Classification. The Jovian planets are composed mainly of helium and hydrogen. They have a liquid or small rocky core. They are usually high in mass and low in density. They have many satellites and the gravity is much stronger than Earth�s. They also all share the same banding and zoning winds. With these characteristics defined with each description given it is easy to see how the planets, Jupiter, Saturn, Uranus and Neptune are Jovian or "Jupiter - like".
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Copyright 1995, Van Nostrand Rienholdt, NY
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