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| ARTICLE |
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| Year : 2008 | Volume
: 1
| Issue : 5 | Page : 10 |
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The Gas Giants
Christopher Barry
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| Date of Web Publication | 17-Nov-2008 |
Correspondence Address:
Christopher Barry
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A Gas Giant is a large planet that is not predominantly composed of rocky material. The upper mass limit for gas giants is 8 times Jupiter's mass. Above this mass, the core will start to fuse hydrogen and the planet will ignite into a red dwarf.[Additional file 1]
The two types of gas giants that we know of are Jovian planets and Uranian planets. In our solar system, the Jovian planets are Jupiter and Saturn. These planets are mainly composed of metallic hydrogen (which forms at 4×10 6 bars of pressure; 1 bar = 0.987atm). They have a small rocky core and a thick atmosphere. The Uranian planets in our solar system are Uranus and Neptune. They are composed much more of ice and are sometimes called ice giants. They also have small rocky cores and thick atmospheres. In the outer solar system, rock refers to silicate material, ice refers to water, ammonia and carbon based compounds and gas refers to hydrogen and helium. Gas giants tend to oblate as they rotate which gives them a bulge in their equators. All the gas planets have bands of high velocity winds along the lines of latitude which blow in opposite directions to those opposite it. This is Belt-zone circulation.[Additional file 2]
| Jupiter | | |
Jupiter is the largest gas giant in the solar system, 2.5 times the mass of all the other planets in the solar system put together. It has 63 moons and three faint rings. Its largest four moons are Io, Europa, Ganymede and Callisto, as shown right in that order. Jupiter's most notable feature is its great red spot, which is an anticyclonic storm. The other spots are also storms; the white spots are higher in the atmosphere and cooler than the brown ones. Jupiter also has a large influence on the rest of the solar system; a large number of Trojan asteroids orbit in the same orbital path as Jupiter.[Additional file 3]
| Saturn | | |
Saturn has stunning rings made predominantly of water ice (as can be seen below as well as each ring labelled). They are 250,000 km wide but less than a kilometre thick. Saturn has 56 moons, the largest of which is Titan (right), which the only moon in the solar system with a well established atmosphere.[Additional file 4]
Saturn also has weather, although not as obvious as Jupiter's. In 1990, the great white spot was observed on Saturn, but it is no longer visible.[Additional file 5]
| Uranus and Neptune | | |
Uranus has eleven faint rings of similar sized particles to Saturn's and 27 moons, the largest of which is Titania. Uranus is notable for its almost ninety-degree tilt on its axis which creates extreme seasons, and although it appears dull, it does have a complex weather system (as can be seen by the clouds in the image to the far right). One of the greatest mysteries of Uranus is why although the Polar Regions receive more polar energy (due to its tilt); the equatorial regions are still hotter.[Additional file 6]
Neptune has faint rings and 13 moons. Its great dark spot (left) is an anticyclonic storm like Jupiter's, but it appears to have disintegrated now and is no longer visible. Its largest moon is Triton, which is icy, volcanically active and has a tenuous atmosphere of nitrogen.[Additional file 7]
| Extra-solar Gas Giants | | |
51 Pegasus B (left) - Bellerophon at 0.05 AU from its star is classified as a "hot Jupiter". It is probably around 1,300°K. It is thought that this heat would blow gas away from the planet in a feature similar to the tail of a comet. It is thought impossible for a gas giant to form so close to its parent star, but its orbital path may have migrated. It was the first gas giant to be discovered orbiting a sun-like star.[Additional file 8]
70 Virginis (right) - Goldilocks is about 7 times as massive as Jupiter. Jupiter's mass is 1.9×10 27 kg
Because of its massive gravity, this planet could hold more than 100 moons in its orbit.[Additional file 9]
The 55 Cancri system is a system in the constellation of cancer that is a binary system. One of the stars is a red dwarf that orbits the other star. There are 4 known planets in this system. Binary stars were previously thought too unstable to have solar systems. 55 Cancri e is actually rocky, about 10-20 times the mass of Earth and has been classified a "Super-Earth".
The planet in the picture to the right is 55 Cancri c.[Additional file 10]
HD 209458 b/Osiris orbits at 0.045 AU and is having its atmosphere stripped by the gravity of its parent star. It may become a Chthonian planet. A Chthonian planet is a gas giant that has been stripped of its atmosphere. There are no Chthonian planets known of, but it is thought that Mercury could be one due to its high metallic content.[Additional file 11]
| Possibilities of Life | | |
The chemicals that can form organic compounds and could serve as the basic building blocks for Earth-like life. However, these chemicals are forced down into Jupiter's interior. It was hypothesized that there could be ammonia or water-based life in Jupiter's upper atmosphere.[Additional file 12]
Ultra-violet radiation entering Titan's atmosphere could cause the formation of complex polymers such as tholin. There have been suggestions that liquid water could be present as the result of an impact. But limited sun-light could not provide for complex biota (collection of all organisms) on Titan.
Titan is the most important body in the solar system for consideration of colonization by humans. There is abundance in nitrogen, ammonia, water and methane present on Titan. Water can be used to produce oxygen and rocket fuel; nitrogen is required to make the air breathable and can be used to make fertilizers and so develop agriculture; methane is needed to produce rocket fuel and can be used in fertilizers and ammonia is used for the production of fertilizers.[Additional file 13]
There could be Earth-like moons orbiting the larger extra-solar gas giants which are inhabitable to humans. But due to the gravity of these planets, the moon is likely to be bombarded by asteroids and comets. Other problems are distance and alien disease, for which our immune systems will be entirely unprepared.
The possibility of colonizing the gas giants themselves remains science-fiction for now, but theories have been suggested that we could float giant balloons in the upper atmosphere of a gas giant (left).[Additional file 14]
How to cite this article:
Barry C. The Gas Giants. Young Scientists J 2008;1:10 |
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