Indeed, Jupiter is about 90 percent hydrogen, 9.99 percent helium. The rest is made up of substances such as phosphorus, sulfur, methane, ammonia and various hydrocarbons.
Hydrogen and helium are transparent gases and make up 99.9% of the mass of Jupiter. It would seem that Jupiter should be transparent. Why is it not so? Let’s figure it out.
On the Internet, you can find such an explanation that they say the color of Jupiter is explained by just this 0.01% of impurities. This is not so, or rather not quite so.
Undoubtedly, the impurities of heavy substances in the composition of Jupiter affect its color, but it cannot be explained only by it. Yes, indeed, hydrocarbons and water vapor mix with convection flows of hydrogen and helium and form vortices and gas flows in the atmosphere of Jupiter well known to us from the photographs.
However, if that were all, Jupiter would be much paler. than now. Much of Jupiter’s color comes from «colorless» hydrogen and helium.
Hydrogen and helium are transparent and colorless under normal conditions, however, in the atmosphere of Jupiter, a significant part of hydrogen and helium atoms are in an excited (i.e. high-energy) or ionized state, and it is the excited and ionized atoms of these gases that, when colliding with photons, are colored in one way or another. color. Most often in various shades of red.
The mechanism for this glow is simple. Ionized hydrogen is essentially free protons and electrons. When a proton captures an electron, light is emitted, usually red in color, depending on what energy level the electron is at.
Ionized and excited atoms will never end, since their appearance is due to processes inside the gas giant, and convection processes will always carry them to the surface.
In addition, even in the normal state, any gas causes light scattering and a large thickness of a perfectly normal hydrogen-helium mixture would also not be completely transparent.
This is why Jupiter is colored in a wide variety of shades of red, yellow and orange. The reason for this: ionization and excitation of atoms, as well as impurities of other substances.