OLD FRIENDS: JUPITER
THE STORY OF VOYAGER
Secrets
erupt from
Jupiter In January 1979, after a journey of 15 months, Voyager 1 began to photograph the ďŹ rst planet on its Grand Tour, the gas giant Jupiter. Voyager 2 followed a few months later, and together they rewrote almost everything we thought we knew about the Jovian system – not least the fact that volcanism exists beyond Earth Words: Ben Evans AT FIRST GLANCE, it resembled nothing more than a blemish on Voyager 1’s lens. But as 26-yearold engineer Linda Morabito peered closer at the image of Jupiter’s moon, Io, she realised she was looking at something extraordinary. The blemish was actually a faint, bluish crescent that was protruding from beyond the moon’s limb. This all occurred on 9 March 1979, four days after the probe had made its closest pass – 349,000km – of the broiling Jovian cloudtops. Morabito was part of the optical navigation team, plotting Voyager 1’s
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trajectory to Saturn, threequarters of a billion kilometres and 20 months away. She had MXVW PDGH WKH PRVW VLJQLĆ…FDQW discovery of the entire mission. The long-exposure shot, taken a day earlier, viewed Io from a parting distance of 4.5 million km. Analysis revealed the crescent to be a plume – rising over 280km into space – from a volcano. Later named ‘Pele’ after the Hawaiian goddess of YROFDQRHV LW ZDV WKH Ć…UVW RI hundreds of such features to be found on Io. As the days wore on, infrared data pinpointed regions rich in sulphur dioxide, where
temperatures soared up to 200°C higher than the surrounding terrain. Four months later, on 9 July, Voyager 2 revealed that Pele had fallen dormant, although several other volcanoes remained active.
Big surprises It was a big surprise on a natural satellite with a size and density roughly equal to that of our geologically inactive Moon. Io’s proximity to its giant host (it orbits just 421,800km from Jupiter’s centre) forces it to bear the brunt of a punishing PDJQHWLF ƅHOG 7KLV LV KXQGUHGV Z