NASA has been testing the next engine to land the Altair spacecraft on the moon. This is a test-firing of the engine which produces 13,000lbs of thrust as the exhaust heats up to 5,000 F. But....look at the rim of the engine bell, there are icicles forming on the edge.
The reason, the fuel for the engine is Cryogenic - which means it's very cold. -297 F liquid oxygen and -423 F liquid hydrogen. The nozzle is cooled by fuel running through the pipes which then cools the steam from the exhaust (at least on the outer parts) to freeze in to ice on the edge of the engine. Cool - really!