This Unnamed planet is a heavily populated planet in the Pegasus galaxy, which has a Stargate. In an alternate timeline, Michael Kenmore deliberately leaked false information, claiming that he would attack the planet, and led the Phoenix, captained by Colonel Samantha Carter, into an ambush above the planet.
The Phoenix took heavy damage during the fight and Sam beamed her crew to the surface so that they could get to the Stargate and then to safety. She then drove the Phoenix into the two Hive Ships, causing all three to be destroyed in the explosion at the cost of her own life. (SGA: "The Last Man")