On Thursday (May 9), the six residents of the station noticed frozen flakes of ammonia leaking from a coolant loop affixed to one of the eight solar arrays responsible for supplying power to the station. The crew is in no danger, NASA officials say, but if the leak continues, it could cause a shutdown in the loop, possibly preventing the array from generating power.

Space station commander Chris Hadfield of the Canadian Space Agency announced the possibility of the emergency spacewalk via Twitter (where he posts as @Cmdr_Hadfield) early on Friday. [See How the International Space Station's Cooling System Works]