Orilla was a planet in the Othala Galaxy. The planet was rich in neutronium, a key element in Asgard technology. This was one of the primary reasons the Asgard chose this as the planet on which to rebuild their civilization.
Several years into the Asgard's war against the Replicators, SG-1 discovered the android Reese, who had created the first generation of Replicators as "toys", on an abandoned planet whose civilization had been destroyed. The Asgard were able to use the android to call all Replicators in the known universe to the planet Hala, originally an important Asgard colony. The Replicators on the planet were eventually trapped inside a time dilation field, which should have given the Asgard years to solve the problem.
However, Asgard scientists calculated it would only take little over a year for the Replicators to escape, and the Asgard were forced to evacuate their original homeworld, Othala, to Orilla, while destroying Hala, and Othala as well, with a black hole. The consciousnesses of most Asgard citizens were stored into the databases of the evacuation fleet, waiting to be downloaded into new cloned bodies upon arrival.
The neutronium which made the Asgard originally choose Orilla however, was also necessary for the construction of human-form Replicators, like Fifth, and thus made it a prime target of the Replicators after they escaped their time-dilation prison, one and a half years later. The Replicators, commanded by Fifth, captured Samantha Carter, and set his ship, which consisted entirely of Replicator blocks, on course to Orilla. Unable to again evacuate the planet after the stored consciousnesses had been downloaded into new bodies, the Asgard positioned six O'Neill-class ships in orbit of Orilla to try to destroy the Replicator ship immediately after it emerged from hyperspace.
Their plan was successful, but Fifth and Major Carter were transported to the planet before the ship was destroyed, while countless Replicator blocks from the destroyed ship rained down on the planet. There, they started to mine the neutronium to build more human-form Replicators. The remaining members of SG-1, who had recently discovered a new weapon to use against the Replicators, were transported by the Asgard to the planet to stop the Replicators, while Thor was constructing a larger version of the weapon that would destroy all Replicators on the planet. Eventually, the weapon was able to destroy the Replicators on the planet, and the Asgard were finally able to rebuild their civilization on their new homeworld. (SG1: "New Order, Part 2")
Last hours of Asgard
In 2007, the Tau'ri vessel Odyssey visited Orilla, where the crew was informed that the Asgard had determined they were unable to stop the genetic deterioration that threatened their species existence, and would choose to commit mass suicide by destroying the planet, leaving only a knowledge base aboard the Odyssey as their legacy. Three Ori warships arrived shortly after they had installed the database, prompting the Asgard to put this plan into effect somewhat sooner than expected. A massive energy surge produced a series of explosions that completely destroyed the planet and two of the Ori warships as the Odyssey attempted to escape the Ori assault. (SG1: "Unending")