A smoker was a conical underwater volcano built up by powerful vents in a planet's crust. Smokers spewed out superheated gases into the ocean, causing large pockets of seawater to flash instantly into steam. Cold ocean water typically cooled the lava pouring out of smokers much more quickly than land volcanoes, and as a result, smokers typically built up large spires on the ocean floor. Because of the heat smokers provided, they were often havens of varied sea life which included Shellfish, Tubeworms, and bioluminescent flora.
Smokers were a feature most notable on the planet Muunilinst, where smokers spewed forth lava from deep within the planet composed of precious metals and built up gigantic "vault-spires" of gold, silver, and platinum. As such smokers served as financial vaults for the most powerful and prosperous Muuns of Muunilinst.
- Hydrothermal vent on Wikipedia