Scientists analyzing high-resolution images from the Large Binocular Telescope Observatory in Arizona have discovered an enormous lava lake on Io, the fifth of Jupiter’s moons and the third largest.

Io is only slightly bigger than our own Moon, but is the most geologically active body in our Solar System. Hundreds of volcanic areas dot its surface, which is mostly covered with sulfur and sulfur dioxide.

The largest of these volcanic features, named Loki after the Norse god often associated with fire and chaos, is a volcanic depression called patera in which the denser lava crust solidifying on top of a lava lake episodically sinks in the lake, yielding a raise in the thermal emission which has been regularly observed from Earth.

Loki, only 200 km in diameter, was, up to recently, too small to be looked at in details from any ground based telescope.

Now, thanks to the Large Binocular Telescope Interferometer (LBTI), a group of astronomers was able to look at Loki Patera in details for the first time from Earth.

“We have seen bright emissions – always one unresolved spot – ‘pop-up’ at different locations in Loki Patera over the years. New images from the LBTI show for the first time that these emissions arise simultaneously from different sites in Loki Patera,” said Prof Imke de Pater of the University of California, Berkeley.

“This strongly suggests that the horseshoe-shaped feature is most likely an active overturning lava lake, as hypothesized in the past.”

Team member Dr Chick Woodward from the University of Minnesota added: “studying the very dynamic volcanic activity on Io, which is constantly reshaping the moon’s surface, provides clues to the interior structure and plumbing of this moon.”

“It helps to pave the way for future NASA missions such as the Io Observer. Io’s highly elliptical orbit close to Jupiter is constantly tidally stressing the moon, like the squeezing of a ripe orange, where the juice can escape through cracks in the peel.”

The results were published online in the May 2015 issue of the Astronomical Journal.

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Albert Conrad et al. 2015. Spatially Resolved M-band Emission from Io’s Loki Patera-Fizeau Imaging at the 22.8 m LBT. Astronomical Journal 149, 175; doi: 10.1088/0004-6256/149/5/175