Unprecedented images reveal stunning features of Jupiter’s ‘tortured moon’

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Close flights past Io, one of Jupiter’s moons and the most volcanically active world in our solar system, have revealed a lava lake and a towering feature called “Steeple Mountain” on the moon’s alien surface.

NASA’s Juno spacecraft, which first arrived in 2016 to study Jupiter and its moons, flew within about 900 miles (1,500 kilometers) of the lava world’s surface in December and February to capture the first detailed images of Io’s northern latitudes.

It’s been more than two decades since a mission flew this close to Io, and the spacecraft’s camera, called JunoCam, captured high-resolution images showing active volcanic plumes, mountain peaks and a glass-smooth lake of cooling lava.

“Io is simply littered with volcanoes, and we were able to see some of them in action,” Scott Bolton, Juno’s principal investigator at the Southwest Research Institute, said in a statement.

“We also got some great close-ups and other data from a 200-kilometer-long lava lake called Loki Patera. There are amazing details showing these crazy islands embedded in the middle of a potential magma lake rimmed with hot lava,” he added. “The specular reflection that our instruments captured from the lake suggests that parts of Io’s surface are as smooth as glass, reminiscent of volcanically created obsidian glass on Earth.”

Bolton announced the findings on April 16 at the General Assembly of the European Geophysical Union in Vienna. The new data paints a clearer portrait of Io, which has intrigued scientists for centuries.

“Other than Earth, this is the only place in our solar system where we see active magma volcanoes,” says Bolton.

Animate an alien world

The team translated parts of Juno’s data into animations that dramatically visualize some of the surface features of the infernal world, such as Loki Patera and Steeple Mountain.

Juno discovered the mountain using the sun shining on Io’s surface, creating dramatic shadows that revealed a very sharp peak.

“We used the science to understand the shadows and measure the distance,” Bolton said. “It may not be completely accurate, but this is roughly what it would be like if you went there. We call this Steeple Mountain because it is so steep at the edge that it could be Io’s version of the Matterhorn.”

Although the temperature of the magma on Io is thousands of degrees, the moon’s surface is likely minus 148 degrees Fahrenheit (minus 100 degrees Celsius), Bolton said.

“If the magma comes out while a volcano is going off, it will freeze immediately and probably create sulfuric snow,” he said.

As an outdoor enthusiast, Bolton joked that Io’s Steeple Mountain should be one of the solar system’s skiing and snowboarding destinations.

Meanwhile, Loki Patera is another place with hot and cold extremes. Although the lava lake itself is likely very hot, the top of the islands is likely very cold, and a cold crust may also surround the edges of the lake, Bolton said.

The mission team used Juno’s Microwave Radiometer instrument to create maps of Io’s surface, showing how incredibly smooth it is.

The topography lacks contours because Io is so volcanically active that the world is constantly being resurfaced by lava, which erases impact craters from its surface, according to a new study from a separate research team, published in the journal Science on April 18.

The team also used the Atacama Large Millimeter/submillimeter Array of telescopes in Chile to observe gases in Io’s atmosphere. The researchers found evidence of an abundance of enriched sulfur and chlorine, suggesting that Io has likely been volcanically active, releasing the gases for most or all of its history over the past 4 billion years.

Uncovering Io’s mysteries

First discovered by Galileo Galilei in 1610, Io is just slightly larger than our moon, but unlike anywhere else in the solar system.

The moon’s rocky surface is covered with hundreds of volcanoes, drawing comparisons to the fictional volcanic planet Mustafar and its lava rivers from the “Star Wars” films.

Scientists have observed Io’s powerful volcanoes spewing lava fountains tens of kilometers high that can be seen even with large telescopes on Earth, according to NASA.

The name of the moon comes from a Greek myth in which a mortal woman is turned into a cow during a marital conflict between the god Zeus and his wife Hera. The nickname is appropriate, as Io is in a constant state of tug-of-war, pulled by the enormous gravity of Jupiter, as well as its large moons Europa and Ganymede.

These three worlds are pulling on Io so violently that its surface bulges in and outward by 100 meters, like the tides on Earth – but it’s happening on solid ground, rather than in an ocean. Bolton said he often calls Io “Jupiter’s tortured moon” because of the ferocious forces it regularly encounters.

The forces exerted on Io by Jupiter, Europa, and Ganymede cause Io’s surface to experience a tremendous amount of heat, leaving the moon’s subsurface as liquid rock. Researchers believe that liquid rock is made of molten sulfur or silicate rock, and that volcanic eruptions help relieve the moon’s gravity.

Io has been studied by several spacecraft, including the Pioneer and Voyager probes in the 1970s and the Galileo spacecraft in the 1990s. And now Juno’s revelations are helping scientists understand the forces behind the moon’s volcanic activity like never before.

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