Image Jupiter and Io with a high frame rate camera
It takes patience and a clear sky to capture the gas giant and its moon, Io
it still has to be warm for it to stay dark,” explains de Kleer. “If it were cooled completely the sulphur dioxide would freeze out of the atmosphere on to it and it wouldn’t be dark anymore. So even where you don’t see the infrared emission, you can infer that something’s been active within the past couple of years.”
De Kleer’s own work has involved looking at Io with powerful ground-based facilities, like the Keck Observatory telescope in Hawaii. By observing the moon at infrared wavelengths, de Kleer and her colleagues were able to get a very different view of Io. “The disc is bright because the sulphuric frosts on its surface are reflecting sunlight,” says de Kleer. “But then on top of that you see these really bright little spots all over Io’s surface. These spots are infrared emission from the heat coming off these individual active volcanic regions.”
The Juno spacecraft – currently whirling around Jupiter – also looks at Io in infrared; in imagery captured in 2017, it was able to detect signs of a glowing patch of volcanic activity where there seemingly hadn’t been one before. This thrilling level of geological dynamism is something that can be seen in Earth-based infrared observations too. “Taking pictures from night to night you can see the different volcanoes [that] are active or not active,” explains de Kleer. “They’re giving off different amounts of heat and you can see that by just observing several nights in a row at a telescope; you can see how it’s changing.”
Volcanic activity
If we were able to get up close to these volcanoes, the sulphur deposits may appear similar to those seen around volcanic features on Earth, such as in Lassen Volcanic National Park and Yellowstone in the US, expains de Kleer. “You can probably imagine something like that but scaled up,” she says.
The actual shapes of the volcanoes are likely to be a far cry from towering, pointed peaks, however, due to the nature of the material they form from. “We think the magmas that are erupting on Io are at the upper end of the temperatures for things we see on Earth – maybe hotter,” says de Kleer. This high temperature, along with the magma’s lower silica content compared to Earthly analogues, means that when lava does break out onto Io’s surface it’s thought to be particularly runny, and it can flow over long distances rapidly.
What, then, creates Io’s volcanism in the first place? It’s thought to arise from the gravitational dance the moon performs with Jupiter, Europa and Ganymede; this creates a force that repeatedly pulls and squashes the 3,640km-wide Io.
“You have this pretty rapid deforming of its shape every couple of days that generates friction in its interior and produces heat,” explains de Kleer.
“It’s sufficient to melt rock.”
One of the most spectacular results of the molten mayhem going on under Io’s surface is the volcanic feature in the moon’s northern hemisphere known as Loki Patera. This huge magma lake measures some 180km across and has been the focus of recent research by de Kleer and her colleagues.
Using the Large Binocular Telescope (LBT) – sited in Arizona, in the US – the scientists watched as Jupiter’s moon Europa passed in front of Io. Ordinarily it’s tricky to resolve detail on Loki Patera when observing in infrared light from the ground, but the passage of Europa allowed them to perform a clever observation. As Europa gradually obscured ▲ Seeing sulphur: if you were able to stand on it, Io’s surface might resemble California’s Lassen Volcanic National Park