Why are gas giants colored the way they are?

  • As I understand it, Jupiter, Saturn, Uranus, and Neptune are all made primarily from varying proportions of hydrogen and helium. Despite this, Jupiter is very red, Saturn is yellow, and Uranus and Neptune are blue. Why the difference in colors for planets with similar chemical makeups? Or do they not have similar chemical makeups?

    If such an explanation is available, I would like specific descriptions of why each planet is colored the way it is.

  • You could just have Googled this question.

    Post #5 from the first hit:

    First off, by "wondering what colors different gas giants can be", you
    are presumably asking about their light spectra through the visible
    range of wavelengths (380-720 nm), right?**

    Light interacts primarily with electrons. It is scattered or absorbed
    in the presence of electrons, which come in a variety of "phases".
    Here are the most relevant:

    1) free within an ionized gas (can absorb in the presence of the
    electric field of an ion)

    2) attached to atoms and ions

    3) attached to molecules

    4) attached to molecules that have condensed into solid state aerosols and grains, or liquid droplets.

    The most important thing to take away from this is that every type of
    material, in terms of composition and "phase", absorbs and scatters
    light uniquely.

    The prevalence and importance of each of the above four "phases"
    depend on (a) the elemental composition of the giant planet's
    atmosphere (defined as that layer responsible for light
    reflected/emitted by planet), and (b) its equation of state (how
    pressure changes as a function of density and temperature). The first
    of these provides the raw materials, and the second arranges them in
    "phase". Very roughly speaking, one may assign decreasing temperatures
    (T) to the above 4 "phases" moving down the list 1-->4. Pressure (P)
    also plays a role, and in general one may place the above phases on a
    P-T diagram. Physics and Chemistry are at work to determine what kind
    of "stuff" is present as a function of depth through the giant planet
    atmosphere. One rule of thumb is that chemistry is much more effective
    at higher temperatures (to a point) and/or in the presence of
    moderately energetic light.

    Next, before proceeding, go back and read the bold statement, above.

    To finish off this overly long post: Two giant planets of equal bulk
    compositions will almost certainly appear differently if their P vs. T
    profiles differ, or if their atmospheric compositions differ (e.g.,
    due to convective mixing from the interior, mixing due to wind
    currents, heterogeneous settling of heavier matter towards the center
    over time). Two giant planets of equal bulk compositions, but
    differing ages will appear differently, since a planet's interior
    cools over time, affecting P-T relation within the planet as well as
    its thermally emitted spectrum. The intensity and spectral shape of
    the light incident from the parent star will affect the P-T diagram,
    the chemistry and phase of the matter, the thermally emitted spectrum,
    as well as the distribution of photons available for scattering.

    From the second hit:

    Jupiter is a giant gas planet with an outer atmosphere that is mostly
    hydrogen and helium with small amounts of water droplets, ice
    crystals, ammonia crystals, and other elements. Clouds of these
    elements create shades of white, orange, brown and red. Saturn is also
    a giant gas planet with an outer atmosphere that is mostly hydrogen
    and helium. Its atmosphere has traces of ammonia, phosphine, water
    vapor, and hydrocarbons giving it a yellowish-brown color. Uranus is a
    gas planet which has a lot of methane gas mixed in with its mainly
    hydrogen and helium atmosphere. This methane gas gives Uranus a
    greenish blue color Neptune also has some methane gas in its mainly
    hydrogen and helium atmosphere, giving it a bluish color

    Your google search results almost certainly differ from mine, or from Joshua (the person who asked the question). Don't assume your first hit is my first hit, or Joshua's. See Reasons your Google search results are different than mine for more info.

    So what? Did you or the OP do a Google search? What were your hits, where they all about the colour of hot air balloons? Are you telling me that your Google search turned up noting about the colours of gas giants? Your hits may well differ, your first hit may be irrelevant, what you do is look at the hits until you find one which is relevant, I doubt you will have had to look far. The only significant difference between mine and others' searches might well be the fierceness of ad blocking. Effective use of Google is a very low grade type of research and everyone should learn how to do it.

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Content dated before 7/24/2021 11:53 AM