M5S-224
From The Stargate Omnipedia
Planet in the Pegasus Galaxy, home to a non-corporeal race of beings who appear as an imposing fog. The Stargate on this planet draws power from the beings themselves, killing many when the device is active.
M5S-224 is 840 light years away from Atlantis via Puddle Jumper. This is either from takeoff at Lantea, or the nearest Stargate in the network to 224, though the former is more likely.
DETAILS
HOME TO - Inhabitants of M5S-224
FIRST APPEARED - Home
KEY EPISODE
Home - Sheppard agrees to take his team to explore M5S-224 after Dr. McKay believed the planet to be inhabited, but Rodney soon discovers something of greater value -- an endless power supply for the Stargate that could allow the expedition to contact Earth.