On the morning of April 5th, 2063, it was passing through the outskirts of the Sol system, when it detected Dr. Zefram Cochrane's warp signature during a test flight of the Phoenix from the vicinity of Earth, a planet which the Vulcan High Command had been monitoring for decades. As per Vulcan first contact protocols, they decided to land on Earth, to meet the person who flew the first warp ship of their world. They landed near a settlement in Montana. It was named for T'Plana-Hath, the matron of Vulcan philosophy. (Star Trek IV: The Voyage Home)