Jupiter's moon Io has a 200km-wide lava lake with waves of molten rock that clash, according to new research.

Images were captured by ground-based telescopes, providing an exceptionally detailed map of the most volcanically active place in the solar system.

The breakthrough was possible thanks to an "occultation" - a rare astronomical event similar to an eclipse where the larger moon Europa passed in front of Io.

As Europa's surface is coated in water ice it reflects very little sunlight at infrared wavelengths.

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This allowed researchers to accurately isolate the heat emanating from volcanoes on Io.

The infrared data showed the surface temperature of Io's massive molten lake steadily increased from one end to the other.

It suggested the lava had swept from west to east in two waves - travelling about 1km day.

This would confirm the popular idea among scientists that the periodic brightening and dimming of Io's hot spot - called Loki Patera after the Norse god of fire and chaos - is caused by an overturning lava lake.

Loki Patera - a bowl-shaped volcanic crater - is about 200km across. Its hot region has a surface area of 21,500sq km, larger than Lake Ontario.

A bit larger than Earth's Moon, Io is the third largest of Jupiter's moons, and the fifth one in distance from the planet.

Lava lakes like Loki Patera overturn because the cooling surface crust slowly thickens until it becomes denser than the underlying magma and sinks, pulling nearby crust with it in a wave that propagates across the surface.