code/game/turfs/open/asteroid.dm

/turf/open/misc/asteroid	Asteroid
/turf/open/misc/asteroid/basalt/lava_land_surface	Surface. The surface is warm, but survivable without a suit. Internals are required. The floors break to chasms, which drop you into the underground.
/turf/open/misc/asteroid/basalt/lava_land_surface/no_ruins	Used for the lavaland icemoon ruin.
/turf/open/misc/asteroid/snow/icemoon/do_not_chasm	Exact subtype as parent, just used in ruins to prevent other ruins/chasms from spawning on top of it.