The 1970s are often remembered for political and economic successes, such as the signing of the SALT treaties, and the end of the Vietnam War. Yet few will recall the peculiar natural phenomenon that sparked the creation of the Voyager 1 and 2 space probes, launched during that same decade.
The 1970s experienced a rare geometric alignment, occurring once every 175 years, in which the four gas giants — Jupiter, Saturn, Uranus, and Neptune — were arranged to allow for a four-planet tour using a minimum of time and propellant. The planetary arrangement meant that flying by each planet would alter the craft’s flight path and increase its velocity just enough to deliver it to its next destination.
Although a four-planet mission was believed to be possible, it was considered too expensive to construct a space probe that would last 10 years. Consequently, the Voyager space probes were initially designed and funded solely for studying Jupiter, Saturn, their rings, and their larger moons. From the ten thousand trajectories considered, two were chosen — the second reserving the possibility of continuing to Uranus and Neptune.
Voyager 2 was the first of the space probes to be launched, on August 20, 1977, while its counterpart had a faster route with a shorter trajectory, and was launched on September 5, 1977. Voyager 1 reached Jupiter in late March 1979, and provided images showing Jupiter’s swirling turbulence within its atmosphere, along with the giant storm about three times the size of the Earth, aptly named the Great Red Spot. Voyager 1 also identified nine volcanoes erupting on Jupiter’s moon Io, eight of which were still erupting when Voyager 2 visited 4 months later.
In their encounter with Saturn, the probes provided high-resolution photographs that noted waves and kinks in the planet’s rings, most likely caused by the tug from its nearby moons. Voyager 1’s Saturn investigation showed that seven per cent of Saturn’s upper atmosphere is made of helium, while the remainder is mostly hydrogen. The space probes also identified aurora-like emissions not only at the poles, but also at mid-latitudes. The presence of mid-latitude auroras is puzzling, since on Earth the auroras caused by electron and ion collision mostly occur at high latitudes.
After having analyzed both Saturn and its moons — with particular interest paid to its largest satellite, Titan — Voyager 1 began its trip out of the solar system, still conducting studies of interplanetary space while its twin continued to Uranus and Neptune. Voyager 2’s examination of Uranus’ five largest moons unveiled intricate geologic variations.
In total, the two space probes were able to explore all the outer gas giants, along with 48 of their moons, their unique ring systems, and their magnetic fields. The space probes are both currently travelling through the heliosheath, where the Sun’s magnetic influence ebbs and interstellar forces dominate.
Although the Voyager space probes were launched almost 40 years ago, they continue to transmit information to Earth, which takes 13 hours, travelling at the speed of light to reach us. This time lag creates difficulties within the probe’s communication system, as was the case in its May 2010 glitch. Nevertheless, the Voyagers continue to make important space discoveries, including that of the “local fluff” with which we will familiarize ourselves next week. Until then, your fantastic space voyages await.
