HU-2340 is a super-heavy element. A small jar took Dr. Douglas MacLaren, its creator, five years to create. The jar was strapped to a MALP and sent through to the Asgard-protected planet K'tau. En-route it passed directly through K'Tau's star with the intentions to use the material to repair the stellar body following a dramatic shift to infrared.
It is unclear if the HU-2340 saved K'Tau, or the Asgard, or both. In her official report Major Samantha Carter referred to HU-2340 as Maclarium. (SG1: "Red Sky")