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New results from NASA’s Juno probe show that a lava lake can be much cooler but still keep an active surface And those measurements give a more complete picture of how pervasive these lakes are on Jupiter’s moon Io, and, now, new light on volcanic processes at the moon’s surfaces. Juno’s Jovian Infrared Auroral Mapper (JIRAM) instrument, provided by the Italian Space Agency, effectively ‘sees’ in infrared light, and the researchers published Juno’s most recent volcanic discoveries on June 20 2022 in the journal Nature.

Communications Earth and Environment.

The Jovian moon, bigger than Earth’s Moon and always a bit of a headache for astronomers, has intrigued us since Galileo Galilei first noted its presence in 1610. In 2014, exactly 369 years later, NASA’s Voyager 1 spacecraft detected and captured a plume from the moon. Subsequent Jovian missions with a number of Io flybys uncovered more plumes – and lava lakes. Geologists now regard Io as the most volcanically active body in the solar system. Stretched and squeezed by the orbital resonance with neighboring moons and mighty Jupiter itself until it is almost an accordion, Io has inspired many hypotheses about the variety of eruptions on its surface, but almost no data to support them.

Oct. 15, 2023 raw infrared image data of Chors Patera, a lava lake located in the south polar region of Io captured by NASA’s Juno spacecraft JIRAM instrument. Team members believe that the lake is mostly hidden under a thick, molten crust, with a hot ring around the edges resulting from lava originating from Io’s interior being exposed to the void of space.

Another set of close approaches happened in May and October 2023, again about 21,700 miles (35,000 kilometers) and 8,100 miles (13,000 kilometers), respectively. JIRAM’s view also caught one of Io’s most captivating little moons.

Engineered to detect the corresponding invisible infrared light (emitted by the weather layer) rising up out of Jupiter’s depths, JIRAM penetrates to 30 to 45 miles (50 to 70 kilometers) below the giant planet’s cloud tops. During Juno’s extended mission, the instrument was applied to analyze the weather layers on Jupiter’s moons Io, Europa, Ganymede and Callisto as well. JIRAM Io images ‘reveal the presence of bright rings around the … floors of numerous hot spots.’

The infrared images captured with high spatial resolution by JIRAM, and Juno’s favorable close flyby positions, allowed for the discovery that the entire surface of Io is covered by lava lakes in calderas, or dip-like features, according to Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome, Italy. ‘In the region of Io’s surface with which we have the most complete coverage, we estimate that about 3 percent of that region is covered by one of the molten lava lakes.’ (A caldera is a large depression formed when a volcano explodes and collapses.)

Fire-Breathing Lakes

New images of Jupiter’s moon Io are giving hints of what goes on under the surface of this giant lava world. The Io flyby data collected by JIRAM not only show that Io harbours vast reserves of lava, but also that recycling of melt is likely taking place along the border between the central crust that covers most of all the lakes and the lake’s walls. This is apparent from infrared images of the lava lakes on Io, a few of which clearly show that the lake rims are bounded by a thin circular zone of lava, but no lava flows occur on and beyond the rim of the lake. The implication is that the amount of melt that is erupted into the lava lakes balances the amount of melt that is recycled back into the subsurface system.

We have an overall picture of what is the most common style of volcanism on Io: giant lakes of lava, where the magma rises and sinks,’ Mura said. ‘The lava crust is being forced to break against the walls of the boiling lava lake, forming the usual inner walls of Hawaiian lava lakes. The walls are probably 100–200 meters high and that is probably why magma in general is not seen spilling out of the paterae [basins, known on Io as patera, formed by volcanism] and flowing across the surface of Io.’

The JIRAM data reveal that most of the surface of those Io hot spots consists of a single, contiguous rocky crust that moves up and down in a cyclic manner, giving us the impression of multiple surface craters. This hypothesis assumes that, since the crust is in contact with the walls of the reservoir, a friction mechanism would keep it from moving, and hence it would be deformed as it was forced up the wall of the cavity in which the magma is centralized. It will literally break, exposing lava just beneath the crust.

While admitting that this was possible, an alternate hypothesis also lingers: Magma may be welling up in the middle of the lake, spreading toward the rim and floating a crust that will sink into the lake’s interior, exposing lava at the lake’s rim.

‘We are just starting to dig into the JIRAM observations from the December 2023 and February 2024 Io close flybys, and we observe previously-unseen features that are presenting us with new insights into Io’s volcanic activity,’ said Scott Bolton, Juno’s principal investigator with the Southwest Research Institute in San Antonio. ‘When we plug in the new results into Juno’s longer-term imaging campaign to map the location and volcanic activity of Io’s volcanoes — many of which are being seen up close for the first time at Poles north and south — JIRAM becomes yet another crucial tool in teaching us how this damaged world works.

June 13 saw Juno execute its 62nd flyby past Jupiter ­— this time including an ion flyby at an altitude of about 18,175 miles (29,250 kilometers) — with the next gas-giant flyby coming on 16 July.

More About the Mission

The Juno mission is part of NASA’s New Frontiers Programme. It is managed at NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, for the principal investigator Scott Bolton, also of the Southwest Research Institute in San Antonio. The Italian Space Agency (ASI) funded the Jovian InfraRed Auroral Mapper. Lockheed Martin Space in Denver built the spacecraft and is operating it.

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