NASA's Juno Probe Reveals Glass-Like Surface of Io's Giant Lava Lake

NASA’s Juno spacecraft was dispatched on a mission in 2011 to study the planet Jupiter. It has beamed back some truly stunning images and valuable data on the solar system’s largest planet. While in the neighborhood, Juno also took a closer look at some of the larger Jovian moons. The mission’s most recent triumph is a close-up view of the volcanic moon Io, depicting lakes of lava as smooth as glass.
Technically, the images you’ve seen around the internet are not real photos of the surface, but they’re based on data from the probe’s recent flybys of Io. These artist impressions of the moon’s lava lakes came from data Juno acquired on its recent low-altitude passes in December 2023 and February 2024. The probe passed within 930 miles (1,500 kilometers) of the surface during those flybys.
The image above depicts a lava lake known as Loki Patera, which measures about 127 miles (200 kilometers) across, making it the largest volcanic depression on the moon. You can see multiple islands inside the molten lake, which has a smooth, glass-like surface where the lava has started to cool. The data from this rendering comes mainly from the JunoCam imager, but its microwave scanner was also key.
Juno has an instrument called the Microwave Radiometer (MWR), which consists of antennas spread around the spacecraft. It operates between 600MHz and 22GHz, allowing it to penetrate the murky Jovian atmosphere. It can also relay important information about the surface of Io, like the presence of almost perfectly smooth volcanic lakes.
Io is the most geologically active moon in the solar system, possessing hundreds of active volcanoes. So, the existence of lava flows on the surface is not a shock. However, the reflectiveness of some parts caught the team off guard. “The specular reflection our instruments recorded of the lake suggests parts of Io’s surface are as smooth as glass, reminiscent of volcanically created obsidian glass on Earth,” said JPL’s Scott Bolton.
The team has found that Io is overall more reflective than other Jovian moons. That suggests lava flows like the one modeled from the recent flybys could be constantly remodeling the surface.
Juno has completed its primary mission to study Jupiter, but it’s still orbiting the gas giant. To avoid being fried by the planet’s intense radiation bands, Juno follows long elliptical orbits. That allows it to swing past moons like Io on occasion. It also lowers its altitude over Juputer’s north pole with each orbit, allowing the MWR to see deeper into its cloud layers. This has given scientists extensive data on Jupiter’s polar cyclones, and they’ll continue to get more until the mission wraps up next year after 76 orbits.
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