Agoraphobia

Martians spend their entire lives inside domed cities and tunnels underneath the surface Mars, not experiencing the vastness of space the way that Belters do. Generations spent in the underground cities and tunnels of Mars mean many Martians suffer from agoraphobia, though few would characterize it as suffering. Martians exposed to the wide skies and seas of Earth are left gasping and hyperventilating, panicking at the shocking openness. The atmosphere is too thick, the sky too far. Martian visitors are often brought to Earth on the dark side of the planet, and told to focus only on the horizon when they leave. Compared to Mars, the average Earth city is an overcrowded assault on every physical and moral sense imaginable; their home tunnels are kept clean and well-lit, but even with teeming billions living in cramped quarters, there’s quiet to be found that is lost on Earth.