I looked at the atmospheres of the terrestrial planets in an earlier post and now it is time to look at the other planets especially Jupiter. These are just totally weird planets. it is not possible to land a spacecraft on the surface of Jupiter as, by today’s standards, your spacecraft would be crushed to nothing (including you of course!) and you would just make a headline for a day and then be forgotten about.
When the solar system formed, the elements that could exist near the Sun (the refractory elements, the ones that survived the heat and the solar wind) were the Rocky type of Elements and these went to form the terrestrial planets including Earth. Unfortunately (if you want a planet to live on that is) Further out beyond Mars and the asteroid belt where the sun’s heat is Weak the icy volatile materials remained. These materials are unable to form a Rocky Earth like planet and end up giving us a ball of gas.
This ball of gas in the case of Jupiter is massive and the masses of all the planets in the solar system could fit into Jupiter. Because Jupiter is so massive there is an immense amount of gravitational force which causes some extreme effects inside Jupiter. Really, most of Jupiter is atmosphere but it is a very odd atmosphere.
We don’t have a lot of information about the gas giants as the further they are away from the Sun The Harder They are to get to and retrieve information. There is also the problem that anything that enters the atmosphere will get crushed. Voyager and Galileo gave us a lot of information about Jupiter and Cassini is sending back information on Saturn At the moment.
So how can we work out what is inside an inaccessible gas giant? Sneaky scientists tend to use what they can see such as the degree of flattening of the planet, the changes in gravity and measurements of the magnetic fields. None of the planets are perfect spheres And Jupiter is no exception. This flattening affects gravity and And gives a few clues as to what lies below. Another way gravity can be used is to measure it and use this to work out the composition.
Density of Jupiter and Saturn is very low and the mass of material in these planets large Therefore the interior must be at a very high pressure. At the very edge of the atmosphere The pressure is the same as that on Earth but at the centre it is estimated that the pressure is 50 million times that of Earth. Because of this overall low-density Saturn and Jupiter must be made out of hydrogen and helium. Another indication that this is probably true is that the original elements that made up the solar system had a very high proportion of hydrogen and then, coming second in abundance, was helium.
The other part of Jupiter is hydrogen and helium and this then turns into helium and metallic hydrogen under the extreme pressures. This is quite a big layer and then we reach a small icy Layer and then getting to the core a Rocky/icy material.
There are Clouds on Jupiter With the topmost cloud layer consisting of ammonia. Ammonia is that smelly smell that takes no prisoners. The next layer down is a cloud of ammonium hydro-sulphide and then below this a good old layer of water vapour clouds.
It is not a very pleasant atmosphere with high-speed winds and turbulence. The most interesting storm that we can see is the great red spot. Observations have shown that this has been around for 470 years and might be there for a good time yet, around about 300 years. The spot rotates about every six days and rotates anticlockwise, a poor little earth could fit into it! Close to the red spot are three white vortices. These were observed by the Voyager and Galileo spacecraft. In between the time of observation between Voyager and Galileo the white vortices drifted eastwards and closer together. These white clouds are about 1000 km across and extend down to the water cloud layer.
The great red spot gives us a few clues as to what is going on lower down in the atmosphere but also raises a few as well. One of the main question is the obvious one of why it is such a lonely spot and why there isn’t another spot in the other hemisphere. The colours of the spot don’t really add up to the picture we have of the general atmosphere as it descends lower and changes colour.
The atmospheres of Saturn and Jupiter are roughly the same except Saturn has much higher winds than Jupiter.
Uranus and Neptune are much further out but are similar to each other. The densities of these two planets tell us that they have a higher ratio of the heavier elements compared to hydrogen and helium. Therefore they both have a hydrogen and helium outer layer which is smaller than Jupiter and Saturn’s and then a big icy layer with about the same size Rocky/icy core.
Uranus doesn’t have much of a cloud system and what it does have is methane clouds lower down. Neptune has the same methane clouds that Uranus has and also a few ethane and similar clouds.
Information on the giant planets atmospheres and composition are very scarce and some good results have been found using evidence from ground-based telescopes and the Hubble space telescope. As time goes by more information will probably prove the above wrong or right. As the case may be it is a good idea to have a general idea of what is going on in these type of planets anyway just in case you fancy a visit.