Pretty sure they use directional SSAO and in some cases use it to have some form of shadowing for lights without shadow maps.Because the entire sky from horizon to horizon is a light source in atmosphere due to atmospheric scattering. That's not the case in space. It should actually be computationally easier to achieve realistic lighting in space because almost all of the light is or can be reasonably approximated as direct light from point sources, even reflections off of things like moons and planets which despite their size are relatively narrow and highly directional compared to the sky while being in atmo.
Should become useful in nebula, animated objects etc.