Io is the innermost of Jupiter's four moons that were discovered b Galileo in January 1610. Io is a bit bigger than our moon, but the most geologically active body in the solar system, according to a press release. The moon - mainly covered by sulfur and sulfur dioxide - is sprinkled with hundreds of volcanic areas.

(Photo : LBTO-USGS)
From the press release: "Io seen by LBT (left) on 2013 December 24 (left) compared to a USGS map (right) based on images from NASA’s Voyager 1 and 2 missions (acquired in 1979) as well as the Galileo orbiter (1995-2003). Loki Patera is the bright red spot on the LBT image."

The largest of these volcanic features, named Loki after the Norse god of fire and chaos, is a volcanic depression called a 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 kiliometers in diameter and at least 600 million kilometers from Earth, was, up to recently, too small to be looked at in detail from any ground-based optical or infrared telescope.

(Photo : LBTO- NASA)
From the press release: "The LBT image of Loki Patera (orange) laid over a Voayager [sic] image of the volcanic depression.The emission (in orange color) appears spread out in the north-south direction due to the telescope point-spread function; it is mainly localized to the southern corners of the lake."

With its two 8.4-meter mirrors set on the same mount 6 meters apart, the Large Binocular Telescope (LBT), by combining the light through interferometry, provides images at the same level of detail a 22.8-meter telescope would reach. Using the Large Binocular Telescope Interferometer (LBTI), an international team of researchers was able to look at Loki Patera, revealing details as never before seen from Earth.

"We combine the light from two very large mirrors coherently so that they become a single, extremely, large mirror," said Al Conrad, the lead author of the study and a scientist at the Large Binocular Telescope Observatory (LBTO), according to the press release. "In this way, for the first time we can measure the brightness coming from different regions within the lake."

(Photo : LBTO)
According to the press release, these two images are a "comparison between a simulated view of Io through an 8-meter telescope (left) and the final real LBTI reconstruction (right)"

"While we have seen bright emissions - always one unresolved spot - "pop up" at different locations in Loki Patera over the years," said Imke de Pater, a professor at the University of California in Berkeley, "these exquisite images from the LBTI show for the first time in ground-based images that emissions arise simultaneously from different sites in Loki Patera. This strongly suggests that the horseshoe-shaped feature is most likely an active overturning lava lake, as hypothesized in the past."

"Two of the volcanic features are at newly active locations," added Katherine de Kleer, a graduate student also at UC Berkley, according to the press release. "They are located in a region called the Colchis Regio, where an enormous eruption took place just a few months earlier, and may represent the aftermath of that eruption. The high resolution of the LBTI allows us to resolve the residual activity in this region into specific active sites, which could be lava flows or nearby eruptions."

"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, helping to pave the way for future NASA missions such as the Io Volcano Observer," said Chick Woodward of the University of Minnesota, according to the press release. "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."

(Photo : LBTO)
The LBTO calls this "a serendipitous movie of an occultation of Io by its neighboring moon Europa when the team re-observed Io on the night of March 7, 2015 for a follow up to the work done for the published study. Europa happened to pass in front of Io as observed from Earth. ... Loki is the bright volcano on the left and Pele the other one on the lower right. Europa appears dark because the water ice on its surface absorbs the incident sunlight at the wavelength used."

Astronomical Journal Publication
"Spatially resolved M-band emission from Io's Loki Patera - Fizeau imaging at the 22.8 meter LBT"
Albert Conrad, Katherine de Kleer, Jarron Leisenring, Andrea La Camera, Carmelo Arcidiacono, Mario Bertero, Patrizia Boccacci, Denis Defrère, Imke de Pater, Philip Hinz, Karl-Heinz Hofmann, Martin Kürster, Julie Rathbun, Dieter Schertl, Andy Skemer, Michael Skrutskie, John Spencer, Christian Veillet, Gerd Weigelt, Charles E. Woodward
http://iopscience.iop.org/1538-3881/149/5/175/article
doi: 10.1088/0004-6256/149/5/175