FIRE JOVIAN SKY
In the As Jupiter reaches opposition this month Will Gater explores the secrets of its enigmatic volcanic moon, Io
ith Jupiter at opposition this month, we have a chance to observe a planet that, along with its moons, has spent centuries in the limelight of scientific study. Jupiter’s icy moons Europa, Ganymede and Callisto, continue to attract immense interest, not least because liquid water may be sloshing under their frozen shells. But there’s another Jovian satellite every bit as interesting as its ice-encrusted compatriots: Io.
The third largest of the four ‘Galilean’ moons, Io is a volcanic hell – a world stained with putrid hues of yellow, brown and red. It is, in many ways, the antithesis of the likes of Europa. Yet that hasn’t stopped researchers from poring over every detail of its surface. With ever improving ground-based technology and the Juno mission currently in the Jovian system, new insights into the activity of this pockmarked moon are being revealed every day. There are even calls for a dedicated mission to explore this oddity among the outer planets.
One researcher whose work has recently attempted to shed light on Io’s violent volcanism is Professor Katherine de Kleer of the California Institute of Technology. The varied colours across Io’s famously blotchy disc are almost all a result of some form of volcanic activity, she says. “It’s all different sulphur-containing molecules that produce those different colours. Except for the dark regions – the black and grey deposits and lava flows are probably silicate.”
The volcanoes that create Io’s striking surface are
Wlittered all over the moon. The Galileo probe
– which took what are still the best close-up images of Io when it swooped past in the late 1990s and early 2000s – caught sight of glowing lava flows. Meanwhile, other missions – including New Horizons and Hubble – have imaged vast, dome-shaped plumes of material erupting over Io’s limb.
Heat seeking
Hundreds of volcanoes are located across Io’s globe. Sometimes they stand out because scientists can detect their heat as an infrared glow, while others can be revealed thanks to tell-tale surface colouration. “You assume that a dark lava flow is young because> ▲ A giant volcanic plume from
Io’s Tvashtar volcano was spotted by NASA’s New Horizons spacecraft in 2013