Neptune (source code)
= Neptune
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<Neptune> is an <ice giant> in the outer <Solar system>. It has a <hydrogen>-<helium>-rich outer <atmosphere> containing <methane>, while a substantial fraction of its interior is material heavier than those two light elements. In the classification name, ice refers to volatile-rich constituents rather than proving that the deep interior is a rigid block of frozen material.<Neptune Facts by National Aeronautics and Space Administration>[Structure and atmosphere: ice-giant composition and methane-bearing outer layers]{ref}
Its appearance illustrates how selective molecular absorption changes reflected colour. Interior models must instead satisfy <hydrostatic equilibrium> and an <equation of state> under high <pressure>. <Hot Neptunes> are named by an approximate size or <mass> comparison; that name does not establish that they share <Neptune>'s present thermal state or composition.
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