One of the most massive volcanic eruptions in the solar system has been spotted on Jupiter’s moon Io – by a telescope perched on a volcano on Earth.

On 15 August the Keck II telescope on Mauna Kea in Hawaii recorded fountains of lava gushing from fissures in the Rarog Patera region of Io. Heated by gravitational squeezing from Jupiter and its other moons, Io is covered in volcanoes that erupt almost continuously. This event is easily in the top 10 yet seen on Io by humans, says Ashley Davies of NASA’s Jet Propulsion Laboratory in Pasadena, California.

“We try to look at Io at every opportunity, in the hope of seeing something like this,” says Davies. “This time we got lucky.” The lava fountains spouted molten rock hundreds of metres above Io’s surface, erupting over an area totalling 31 square kilometres.

Plasma donut

The Galileo spacecraft, which toured the Jovian system from 1995 to 2003, was the last mission to get a close, near-constant view of the action on Io. But other monitoring efforts like the Keck programme have helped make it clear just how much violence Io is capable of.

The biggest eruption seen so far happened in 2001, when the Keck observatory saw a lava flow that is thought to have spread many hundreds of square kilometres across Io’s surface. And in 2007 the New Horizons probe spotted huge plumes from a volcano called Tvashtar as it flew past Io on its way to Pluto.

A rocky body roughly the size of our moon, Io has relatively low gravity and almost no atmosphere, which is why its volcanic eruptions can spray much higher than those we see today on Earth. The blasts are also much more intense: an individual eruption can pump out 5 terawatts of energy. “It’s an astonishing amount of energy,” says Davies. Despite the differences, Io gives us a glimpse into the massive volcanism that dominated our home planet’s early years, he says: “Io is this wonderful volcanic laboratory.”

The recent eruption is especially timely, because it comes mere weeks before the launch of a Japanese spacecraft called Sprint-A. From its orbit around Earth, the probe will be able to see extreme ultraviolet light coming from the Io plasma torus – a donut-shaped ring of charged particles that surrounds Jupiter and that is fed by gases escaping Io.

If all goes to plan, Sprint-A may get a clear view of how an eruption affects the torus. We might also find out more about how Io influences Jupiter’s monster auroras.

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