An amateur astronomer first discovered an asteroid, 137 kilometers long, located in Cassiopeia, declination 61 degrees, 6 minutes, right ascension 2 hours, 48 minutes. Traveling in an atypical path outside the plane of the solar system, it was on a collision course for Earth, expected to strike the Arctic Circle in 11 days, with the potential to wipe out all life on the planet. Approximately 45% of its total mass was composed of naquadah, an element not native to the solar system.
SG-1 landed a cargo ship on the asteroid with the original intention of destroying it, but a nuclear detonation, enhanced by the naquadah, would create a small nova that would set Earth's atmosphere on fire and cause the oceans to boil. Anubis had deliberately used the asteroid as part of a plan to circumvent the Protected Planets Treaty by destroying Earth with what would appear to be a natural disaster. SG-1 was unable to destroy the asteroid before the failsafe position, 39 minutes before impact, however the collision was avoided by creating a hyperspace field to take the asteroid out of normal space long enough to pass through the Earth and reappear on the other side.
Episode Reference: Fail Safe