While browsing Emily Lakdawaller’s inestimable blog at the Planetary Society’s site the other day, I came across this great list of active planetary probes - where they are and what they are doing in various parts of the Solar System. What really caught my attention was the entry right at the end of the list: a reminder that the two Voyager probes are still going strong.
Voyager 1 and 2 were launched in 1977 on Grand Tour trajectories that took advantage of a favourable alignment of the outer planets. I was in the middle of my Ph.D studies back then; the space shuttle prototype Endeavour flew for the first time; Elvis died; and Star Wars was released. In 1979 both Voyagers swung past Jupiter, discovering volcanoes on Io and evidence for an ocean beneath the surface of Europa. I gained my Ph.D that year and began my first stint of postdoctoral research; Margaret Thatcher was elected Prime Minister; Sid Vicious died in New York; Y.M.C.A. was the best-selling single in the UK. The next year Voyager 1 reached Saturn and swung past Titan to investigate the moon’s dense atmosphere, a manoeuver that flung it out of the plane of the ecliptic and ended its planetary tour (instead of flying past Titan, it could have gone on to reach Pluto, in hindsight a better option, but back then we didn’t know that Pluto had three moons and an active atmosphere).
Voyager 2 reached Saturn in 1981, the year I started work in the University of California, Los Angeles. Prince Charles and Lady Diana Spencer married; President Reagan was shot in a failed assassination attempt; the first personal computer was launched by IBM. In 1986, when Voyager 2 swung past Uranus and discovered that one of its moons, Miranda, looked as if it had been shattered and badly reconstructed, I was working in Oxford University, Chernobyl blew its top, the space shuttle Challenger disintegrated soon after launch, and Phil Collins won a Grammy. Not a great year, all in all. Voyager 2 reached Neptune in 1989, discovering evidence for active geysers on the ice giant’s largest moon, Triton. In the same year I moved
to St Andrew’s University in Scotland to take up my first (and last) real job after a decade of scraping by on postdoctoral grants; the Berlin Wall came down and the Soviet Empire began to crumble away; George Bush the First succeeded Ronald Reagan as US President; the Chinese pro-democracy movement was crushed at Tiananmen Square; the first full episode of The Simpsons was screened.
Twenty years later, The Simpsons is still going; I’ve written a bunch of short stories and two novels that have made extensive use of images of the outer planets and their moons taken by Voyager 1 and 2; and the two probes are still sending data back to Earth. Voyager 1 is 110 Astronomical Units - 16.5 billion kilometres - from the sun, beyond the Kuiper Belt and every known large body in the Solar System apart from long-term comets; Voyager 2 is presently some 90 AU from the sun. Both probes have passed through the termination shock point, where the velocity of solar wind particles falls below its speed of sound and becomes subsonic. At some point, as yet unknown, they will pass through the heliopause where the flow of solar wind particles is halted by pressure of gases in the interstellar medium, and enter true interstellar space. They will continue to transmit data about the Solar System’s boundary until they no longer have enough power to run any instruments, around 2025, 48 years after they were launched. They’ll continue to fall through interstellar space (unless they are intercepted by alien probes) until, after a couple of billion years or so, their fabric finally disintegrates. They carry with them greetings from Earth, including two golden phonograph records (remember them?) containing images and sounds from Earth. One of the musical tracks is Blind Willie Johnson’s haunting blues lament, ‘Dark Was Night, Cold Was The Ground.’ Never as dark, nor as cold, on Earth, as the long night through which Voyager 1 and 2 are sailing.
(Clip from Wim Wenders' contribution to Martin Scorsese's The Blues; Ry Cooder used Johnson's music in his soundtrack for Wenders' Paris, Texas, released in 1984, two years before Voyager 2 reached Uranus.)