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Lecture20 - very different from the terrestrial planets...

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Gas Giants: Interiors very different from the terrestrial planets. ¾ larger and more massive but much less dense ¾ all have populous satellite systems which include bodies at least as large as the Moon ¾ all have ring systems. primarily light elements: H, He, some C, N, O ¾ most models are consistent with near-solar compositions from measurements of moment of inertia, they are much more centrally concentrated than Earth ¾ Models predict a total mass of elements heavier than He (Z>2) in the range of 10-30M Earth , some of which is concentrated in a central core. ¾ strong magnetic fields indicate internal convection in electrically conducting regions The presence of significant cores in all four suggests cores formed and eventually began to accrete gas from the solar nebula, once the core mass reached ~10M Earth . ¾ Given the high mass fraction of H, He in Jupiter and Saturn, this must have occurred before the solar nebula dissipated – i.e. <10 7 yr. ¾ The higher CNO fraction for Uranus and Neptune may be a clue that they formed closer to the Sun than did Jupiter and Saturn and then migrated to their current orbits.
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Gas Giants: Atmospheres All except Uranus emit more heat (as IR blackbodies) than they receive from the Sun ¾ Jupiter: this is mostly due to gravitational contraction ¾ Saturn: must have an additional heat source (radioactivity?) Temperature structure of atmospheres are qualitatively similar to terrestrial planets ¾ Insulating cloud decks various compounds which give rise to the colours ¾ Steep temperature gradient means the interiors must be convective Atmospheres contain H under great pressure and temperature ¾ This forms a conducting metallic liquid.
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