From The Stargate Omnipedia
Nickname for "Ernest's Planet," PB2-908. After failed experiments to uncover the mysteries of the Stargate
, Dr. Ernest Littlefield
became trapped on this world.
During his more than 50 years there, Littlefield determined that the planet was once a meeting place for the exchange of knowledge and culture for four great races -- who SG-1 later identified as the Asgard, the Nox, the Furlings, and the Ancients.
SG-1 rescued Dr. Littlefield from Heliopolis, only to discover that the planet's Stargate has fallen into the ocean. The planet is no longer reachable by Stargate.
HOME TO - Uninhabitable
FIRST APPEARED - The Torment of Tantalus
The Torment of Tantalus - SG-1, having discovered a freak Stargate accident in the 1940's, journeys to the planet in question to uncover a very-much alive Dr. Littlefield.
The Fifth Race - O'Neill learns from the Asgard the identity of the four races that once met at Heliopolis: the Asgard, the Nox, the Furlings, and the Ancients.