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.
The simple answer is that the composition in terms of elements doesn't matter for the colour, since that is determined by the molecular composition as well as state (pressure and temperature) of the visual layers (which contain a small but significant fraction of other elements than H and He). Given the differences in the giant planets temperature and pressure, this molecular composition is most likely different.
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:
- free within an ionized gas (can absorb in the presence of the electric field of an ion)
- attached to atoms and ions
- attached to molecules
- 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
