The Loneliest Probe in the Universe

Thirty-five years ago (the anniversary is on September 5), Voyager 1 began a historic journey across the universe. During the 1970s, a rare alignment of all the Solar System's outer planets--Jupiter, Saturn, Uranus, Neptune, and then-planet Pluto--offered a once-in-several-lifetimes opportunity to get tremendous bang for one's space exploration buck. NASA scientists, long on ambition and imagination but short on budgetary politics sense, envisioned a Planetary Grand Tour of a fleet of space probes continuously hopping from one of those distant worlds to the next. Fiscal reality reduced that fleet to a duo, the Voyagers, intended to study Jupiter and Saturn.

It was at Saturn that the twins' destinies diverged. Voyager 2 was given the go-ahead for an extended mission following its successful flyby of the planet: it was to salvage the majestic concept of the Planetary Grand Tour. It would go on to give us our first (and to date, only) close-up looks at Uranus and Neptune. It then continued on into deep space.

Meanwhile, mission scientists made a different decision about Voyager 1's post-Saturn destination. A proposal to send it on a Pluto flyby was rejected (Pluto remains unvisited; the arrival of the New Horizons probe in 2015 will mark mankind's first exploration of that world). Instead, it was diverted to take a closer look at Saturn's enigmatic moon, Titan. The probe's instruments had difficulty penetrating Titan's thick, hazy atmosphere but produced tantalizing hints that conditions on the moon might allow for the existence of seas--this was confirmed in 2006, when the Cassini-Huygens mission found lakes of ethane and methane, the only standing liquid known to exist in the universe off of the Earth.

Voyager 1's flyby of Titan was the end of its own planetary tour, as the process jettisoned it out of the plane of the planets' orbits. It now headed off to deep space. Aided by its interactions with Saturn and Titan, Voyager 1 was receding from the Sun faster than any other probe. Today, Voyager 1 is the farthest piece of humanity in the universe, a whopping 11.1 billion miles from home. Wiki has a sobering simulation of what its view would be were it gazing homeward: