Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gravity & Our Gas Giant Planets

  1. Aug 11, 2005 #1
    Why doesn't the immense gravity of Jupiter and the others turn the gases into solids? (More than just a tiny core, that is.) Does the "gas" at the surface act like a hard solid? About 10 years ago that comet, Shoemaker-Levy 9, entered Jupiter's atmosphere, broke up, and caused explosions on the surface. If the surface was just gas wouldn't it have gone through it until it hit liquid or solid? In a nutshell, I'm trying to imagine the physical nature of the surface.

    Thanks in advance
  2. jcsd
  3. Aug 11, 2005 #2


    User Avatar

    Staff: Mentor

    Jupiter has no surface as such. Natrually, the gravitational force is lower the further out you go, so the pressure/density are lower. So there is a pressure/density gradient - the pressure/density get higher as you go in, eventually to the point where you can't distinguish between liquid and gas.
  4. Aug 12, 2005 #3
    Thank you, Russ, this helps me understand the planetary surface. I assume SL9 exploded at the surface because the speed of decent made the gas "feel" like a solid, and/or the atmospheric pressure came into play. I still wonder why the tremendous gravity doesn't force more of the liquid/gas into still more solid. I don't question why larger obects of the universe, such as stars, become solid because of the nuclear reactions.
  5. Aug 12, 2005 #4


    User Avatar

    Staff: Mentor

    Hydrogen is tough to make solid, so very little is known about it. Anyway, consider that Jupiter's specific density is about 1.3 (times the density of water) while earth's is 5.5. That implies a pretty shallow density gradient (you have to go pretty far in before it gets as dense as a liquid).
  6. Aug 12, 2005 #5
    As you descend into the atmosphere of Jupiter, you'll encounter the cloudtops at right around 1 atm (coincidence). The temperature there is way cold, about 160 K. Over the next 100 km or so, the temperature inceases at about 2 K/km but the pressure is building up as well. The atmosphere is mostly H2 and He, of course. As you go deeper and the pressure increases, this gas just gets denser and denser without ever becoming a liquid because it is above its critical temperature.

    I don't have the depths available to me here, but as the pressure builds, the gas becomes much denser than water and, at even deeper, becomes a metal. Once again, it isn't really a liquid, gas or solid; just a supercritical fluid. A little hard to imagine. That big hunk of hydrogen metal is where Jupiter gets its immense magnetic field.

    Near the center is a little Earth-sized silicate rocky core, but the "atmosphere" around it is a very hot, super high P metallic H2/He material. Not really a solid, but much denser than a liquid. The exact depths and compositions aren't really known because we don't know much about the behavior of hydrogen at those temperatures and, especially, pressures.
  7. Aug 12, 2005 #6
    If you look at a phase diagram, at high temperatures and pressures, the line between liquid and gas ends.
  8. Aug 17, 2005 #7
    If the pressure/density factor was great enough, then it would have triggered thermonuclear reactions rather than becoming solid, since the Gas giants are mostly made of 'H' and 'He' and i dont believe we can reach critical densities for these gases to become solid without triggering thermonuclear reactions...
  9. Aug 17, 2005 #8


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Has anybody worked out the mass density requirement four four-proton fusion ignition?
  10. Aug 17, 2005 #9
    H and He can't become solid inside a gas giant because they are above their critical temperature.
  11. Aug 19, 2005 #10
    travelling towards the center of the gas giants ull find the that gases are being squashed into dense liquid under tremendous pressure,,, ull also find very violent temperature fluctuations in the inner atmosphere...
  12. Jan 20, 2006 #11
    Ok, I was flipping through astronomy books at the public library today and came across some illustrations that showed a cutaway model of the various layers of Jupiter (and this was true for Saturn to a degree as well).

    First drawn was a very thin atmoshpere, it gave the percent of gaseous He and H, CH4 (very small) and then trace gases. It then showed the next layer to be a a massive volume of liquid He and H, the next was a core of (solid) metallic H and then last was a core of "unknown" element.
    What I can make from this discussion is that the bonding in question (whether it be metal-nonmetal/nonmetal-nonmetal/homonuclear I do not know) among the two (He, H) cannot occure due to temperatures at the specific depths being excessive, and instead pressures caused by gravity along with density allow He and H to exhibit liquid and solid state characteristics.
    Is this correct?

    If correct, why then do these popular science books indicate that there are solid/liquid cores within Jupiter? I would think that it is layman language since they are pop scie books, but seems very very misleading. I should find the name of the books and author/editors.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Similar Threads for Gravity Giant Planets Date
Insights Either the Sun Is Getting Smaller or Gravity Is Getting Weaker Apr 8, 2018
B Grav-stars vs. Neutron Stars? Jan 15, 2018
I Star formation and heavy elements Jan 12, 2018
I Trying to understand gravity Nov 19, 2017