The Gaia spacecraft doesn’t land on anything. It’s just in orbit, a fair way from the Earth (actually at the Earth-Sun L2 point – look it up if your’e interested in the details).
In general, there are space telescopes for looking outside our solar system and planetary probes for looking at things inside the system, and they’re built very differently. The looking-out telescopes don’t need to land on things and would break if they tried to. Gaia is a telescope for mapping stars in our a galaxy, so it needs to stay in orbit well away from planets.