"Voyager 2" was the first to be launched. Its trajectory was designed to allow flybys of Jupiter, Saturn, Uranus, and Neptune. "Voyager 1" was launched after "Voyager 2", but along a shorter and faster trajectory that was designed to provide an optimal flyby of Saturn's moon Titan, which was known to be quite large and to possess a dense atmosphere. This encounter sent "Voyager 1" out of the plane of the ecliptic, ending its planetary science mission. Had "Voyager 1" been unable to perform the Titan flyby, the trajectory of "Voyager 2" could have been altered to explore Titan, forgoing any visit to Uranus and Neptune. "Voyager 1" was not launched on a trajectory that would have allowed it to continue to Uranus and Neptune, but could have continued from Saturn to Pluto without exploring Titan.