M44-5Y9 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 occurrence, since there is no evidence to suggest the planet is home to a race of people.
In 2008, a team lead by Dr. Nichols set up a base near the glacier as it is melting. One day Nichol's team was late to report back, due to the fact that the glacier had melted enough to release the water trapped inside of or behind it, flooding the valley and submerging the Stargate.
Lt. Colonel John Sheppard's team traveled to the planet to check on the research team, and had to climb to the top of the Stargate to avoid drowning until a Puddle Jumper was able to rescue them; it is unknown what happened to Nichol's team. It was here that a parasite went into Dr. Rodney McKay's brain, infecting him with the Second Childhood. (SGA: "The Shrine")