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We already know, we are even taught at school that planets of the Solar System beyond Mars (Jupiter, Saturn, Uranus and Neptune) are "gas-giants". But what does it mean exactly? Also, can any kind of ground vehicles land on its surface?

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closed as too broad by PearsonArtPhoto, James Jenkins, Gwen, Rory Alsop, Undo Jul 31 '13 at 15:17

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ This question seems overly broad. It has potential to be improved, so if it gets put on hold (likely) try improve it a bit. $\endgroup$ – James Jenkins Jul 30 '13 at 16:35
  • $\begingroup$ This is already a result of another improvement. =) $\endgroup$ – Zoltán Schmidt Jul 30 '13 at 16:40
  • $\begingroup$ "What is a gas giant?" is a basic question of Astronomy (which would make it Off-Topic for this SE, but not Astronomy.SE) , with an answer easily found on-line (Wikipedia, or any Astro-101 page) (which may or may not make it Off-T for SE, I'm not sure). // As you consider in your own answer, you may want to refine what you mean by "rovers" and "land" (a glider or airship could certainly travel on/through the upper atmosphere). $\endgroup$ – hunter2 Jul 31 '13 at 10:50
  • $\begingroup$ @hunter2 This question assumes that the definition of "gas giant" is clear, and we can easily decide about a planet that is it either a gas giant or not. $\endgroup$ – Zoltán Schmidt Jul 31 '13 at 10:53
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    $\begingroup$ OK. Then I stick by my first comment (that the question should be on Physics or Astro SE), but think that Quonux has a good Answer (which you could Accept). You could edit the lander question out again, and ask it seperately. $\endgroup$ – hunter2 Aug 2 '13 at 2:39
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Interesting question,

to answer the question, gas planets do probably have a solid core, because the pressure is so enormous that the atoms connect into a crystal-like structure.

We know that water for example can have more than 3 material states here.

It is even possible/hypothesized that you get an metal if you compress a gas highly enough. This can explain the extreme magnetic fields of Jupiter metallic hydrogen.

But you can't land on this solid core because the preasure is so enourmous.

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  • $\begingroup$ Actually, my original question wasn't properly useful, so I rewrote it. The main question is about the ability to land on these planets. Fortunately, your answer is also related to it, so +1. $\endgroup$ – Zoltán Schmidt Jul 30 '13 at 15:19
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    $\begingroup$ AFAIK, a solid metallic core is not yet accepted. Hypothesized and studied - absolutely. Maybe even likely, but not yet agreed-upon-as-fact. $\endgroup$ – hunter2 Jul 31 '13 at 10:45
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No, they don't have. Cores of these gas giants are actually solid, but above them, there's a thick layer of gas, with thousands of kilometres of thickness. Obviously, its concentration is increasing as you approach the core, but it's not solid. Bodies are sinking into it, like into wateror quicksand. Except if they have something with smaller density than the gas (like hydroplan's "foots" with full of air)

Because of it, ground vehicles (like rovers) can't be placed on these planets. However, some kind of gliders would be effective in the atmosphere of these planets.

(This is my first attempt to answer my own question, so I may be wrong. Please fix it if I am.)

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    $\begingroup$ If the core is solid, then they arguably do have a solid surface at some point under the gas $\endgroup$ – RhysW Jul 30 '13 at 13:09
  • $\begingroup$ The surface of the core, below thousand kilometres of superdense gas can hardly be called an actual surface, I think. $\endgroup$ – Zoltán Schmidt Jul 30 '13 at 13:14
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    $\begingroup$ Why not? Earth has gasses covering its surface, not as much but its still there. You asked if they are 'only' gases, if they contain solids then no they aren't 'only' gasses. Is there some depth limit before we accept that the solids matter? if so at what point does this change from being ok to not being ok? $\endgroup$ – RhysW Jul 30 '13 at 13:16
  • $\begingroup$ I think, in spacecraft defition, the surface is solid if bodies can stand on it without sinking down. For example, with this definition, I doubt that quicksand is solid, and actually (at least with some logic and sense), it must act like superdense gas: things are sinking in it while standing. $\endgroup$ – Zoltán Schmidt Jul 30 '13 at 13:23
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    $\begingroup$ @ZoltánSchmidt Could you reference a body of work to back up this assertion? Personal interpretations that don't have any supporting evidence -- especially regarding topics of this nature -- don't really make good accepted answers on Stack Exchange. $\endgroup$ – Anthony Neace Jul 30 '13 at 13:55

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