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Gas Giant composition
A fellow was telling me that Jupiter and other gas giants are supposed
to be about 99.9% Hydrogen and Helium. I am suspicious of this for the following reasons: 1. One cannot analize the spectra of the core of a planet, or anything but the cloud top layer. Do tell me if I am wrong on this, and how it could be done by us from earth or a human existing spacecraft. 2. Denser materials will tend to sink to the core of a gas giant. 3. While we can know the mass of a gas giant from the period of objects in orbit around it, the diameter will be more of a matter of opinion, as atmopheres do not have very sharp boundaries. 4. We will also not know the temperature gradiant of the planet as a function of distance from the center. While if we did I could buy that a computer model could be made that would account for different densities, not if you are not sure of the temperature gradiant. 5. Nuclear processes at the core (need not be fusion) can mess with assumptions about temperature gradiants, and said nuclear processes might involve large masses of Radium, Uranium and Thorium as in the earth's core, which will all sink to the core of a gas giant as while some ores of rock with Uranium ect are lighter than the mantle of the earth, they are all a lot hevier than air or H2 gas. Comments? |
#2
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Gas Giant composition
Hi there. You posted:
A fellow was telling me that Jupiter and other gas giants are supposed to be about 99.9% Hydrogen and Helium. That is pretty close to the acutal figures for the composition of the atmosphere. The most recent information I have puts the composition as 92.5% Hydrogen, 7.2% Helium, and 0.3% everything else. This means that the atmosphere is 99.7% Hydrogen and Helium. I am suspicious of this for the following reasons: 1. One cannot analize the spectra of the core of a planet, or anything but the cloud top layer. Do tell me if I am wrong on this, and how it could be done by us from earth or a human existing spacecraft. There is no need to be suspicious. The first hint that Hydrogen and Helium might be present in large quantities came from the low mean density of the planet (1.33 grams/cc) and large oblateness of Jupiter due to its rotation. Earth-based spectroscopy detected the presence of Methane and Ammonia, both of which contain Hydrogen. Various models based on this information indicated that a large portion of Jupiter was probably in the form of Hydrogen and possibly Helium. The Voyager spacecraft's infrared spectrometers detected the signature of molecular Hydrogen. Both Hydrogen and Helium emissions were also detected in the Ultraviolet using Voyager's Ultraviolet spectrometer. As a direct measurement, the entry probe from the Galileo spacecraft entered deep into the atmosphere of Jupiter and sampled it with its Neutral Mass Spectometer and Helium Abundance Detectors to determine its composition. 2. Denser materials will tend to sink to the core of a gas giant. That is correct. It is thought that Jupiter has a small rocky solid core perhaps several times as massive as the mass of the Earth, surrounded by a thick shell of liquid metallic hydrogen and a thick atmosphere rich in Hydrogen and Helium. This model is supported by the strong magnetic field of Jupiter along with the way the planet's mass distribution slightly perturbs the paths of spacecraft like Galileo. 3. While we can know the mass of a gas giant from the period of objects in orbit around it, the diameter will be more of a matter of opinion, as atmopheres do not have very sharp boundaries. The diameter is known to a fairly high degree of accuracy, but that doesn't make what you say exactly incorrect. However, the uncertainties in where the atmosphere fades away does not significantly change the density figure for the planet as a whole. 4. We will also not know the temperature gradiant of the planet as a function of distance from the center. While if we did I could buy that a computer model could be made that would account for different densities, not if you are not sure of the temperature gradiant. We do know the heat output from the planet, both from infrared measurements from space and from the direct measurements of temperature and pressure made during the Galileo probe's descent into Jupiter. Again, the model of a mostly-Hydrogen planet is supported by this data. 5. Nuclear processes at the core (need not be fusion) can mess with assumptions about temperature gradiants, and said nuclear processes might involve large masses of Radium, Uranium and Thorium as in the earth's core, which will all sink to the core of a gas giant as while some ores of rock with Uranium ect are lighter than the mantle of the earth, they are all a lot hevier than air or H2 gas. Nuclear fission processes would supply a little heat, but otherwise, they don't change the composition all that much. They would sink to the core where they would contribute to some degree to the heat flow from Jupiter, but again, the amounts present and their effects do not contradict the idea that Jupiter is mostly Hydrogen and Helium. Clear skies to you. -- David W. Knisely Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 10th Annual NEBRASKA STAR PARTY * * July 27-Aug. 1st, 2003, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** |
#3
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Gas Giant composition
Hi David With all that hydrogen,and all those lightning strikes there
can't be any oxygen. However Jupiters moons are said to have water(ice) surface,and that means they had oxygen. Do you think some day Jupiter and its watery moons might be used where are deep space rocket ships can fuel up? Bert. |
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