Alien Atmospheres

It’s fun to speculate about what atmospheres on other planets look like, and doing so with a scientific approach is also an interesting and educational exercise.

Unlike what many people may believe, the default color of basically every atmosphere is blue.

Another common misconception is that it is oxygen that makes our sky blue, but this is not the case, since oxygen is actually a colorless gas.

The physics that makes our sky blue is a far more general process that, to some extent, goes beyond the simple atmospheric composition.

In fact, as light passes through gasses of any sort, the shorter wavelengths of light are scattered, making the light source appear redder and the rest of the sky bluer.

This is the same physics that makes the sunsets reddish, and it’s called Rayleigh scattering.

In our solar system, the sky of all gas giants would be bluish, as shown in these images:

Jupiter:

Saturn’s clouds with the robotic Cassini spacecraft burning in the upper atmosphere, an image taken to commemorate the end of Cassini’s mission.