M44-5YN was a planet in the Pegasus galaxy which contained a Stargate in a valley, near a glacier. The planet was suffering from the effects of global warming, possibly as a natural occurance, since there is no evidence to suggest the planet is home to a race of people.
In 2008, a team lead by Dr. Nichol put up a base near the glacier, as it is melting. However, one day, Nichol's team was late to report back, mainly due to the fact that the glacier melted enough to release the water from inside or behind it, flooding the valley, and the Stargate was submerged, apart from the top. The First Atlantis Reconnaissance Team went to this planet, and had to climb to the stop and stay there until a Puddle Jumper was able to rescue them. It is unknown what happened to Nichol's team. It was at that planet, where a parasite went into McKay's brain, infacting him with the Second Childhood. (SGA: "The Shrine")