The Adara System lies within our Milky Way galaxy. The second planet in the system has an inhospitable environment with a very thick atmosphere composed of more than 80% carbon dioxide and surface temperatures reaching 420° Fahrenheit. It had been a protected planet under the terms of the Protected Planets Treaty, and the Asgard had maintained a research laboratory deep underground, believing it to be safe from the Replicators and the Goa'uld. It was there that Heimdall conducted his vital research into Asgard physiology until he was threatened by Anubis. SG-1 rescued Heimdall and his research, and the laboratory had to be abandoned.
Cross Reference: Anubis, Asgard, Freyr, Heimdall, Osiris, Protected Planets Treaty, Thor
Episode Reference: Revelations