NASA's Spacecraft Reveals Io To Be A Hellishly Active Volcanic Moon

Forbes

07-05-2025

Io, one of the four Galilean moons of Jupiter, as seen by the Galileo probe, circa 1997. (Photo by ... More Space Frontiers/) Getty Images
New data from NASA's Juno $1.2 billion spacecraft now in orbit around Jupiter reveals that the massive planet's Galilean moon of Io has recently undergone the most massive eruptions ever observed in our solar system. Only about the size of our own moon, Io is much hotter and more volcanically active than the Juno team could have ever imagined.
There's nothing in our solar system that we've seen that has so many volcanoes all going off at the same time, continuously, hundreds of them, Scott Bolton, principal investigator of NASA's Juno at the Southwest Research Institute in San Antonio, tells me at the European Geosciences Union General Assembly in Vienna. Io has volcanoes all over the place, he says.
Juno was able to accomplish a couple of totally new things.
Because we were in a polar orbit, we saw the poles of Io for the first time and there were volcanoes all over both poles, says Bolton. There were multiple eruptions around the same area over the South Pole which suggested that maybe there was one reservoir that somehow got active, and a few eruptions all happened at the same time, he says.
Io is in orbit around Jupiter, but it's far from a perfectly circular orbit.
On one side of the orbit, it's a little bit closer to Jupiter than on the other side, says Bolton. Jupiter is pulling on the side that's closest to it a little bit more than the side that's far away from it and distorts its spherical shape, he says. So, Io itself is constantly being gravitationally squeezed by Jupiter, causing Io's insides to become very hot and molten and eventually erupt, says Bolton.
Why is studying such a volcanic, eruptive moon like Io important?
Here's this moon that's constantly spewing out volcanoes, says Bolton. By studying Io, he says, we can learn about the volcanoes here on the earth, what's similar, what's different, what are the conditions that cause these things?
On 30 December 2023, the Juno spacecraft, exploring the Jovian system, approached the volcanic moon ... More Io at a distance of just 1500 km (930 miles). A similar encounter is scheduled to take place on 3 February 2024. The probe is monitoring the moon's volcanic activity getty
No spacecraft has ever gone into this hazardous, high-radiation environment; the real danger is near Jupiter where we're in this elliptical, polar orbit, says Bolton. But Juno got within 1500 km above Io's surface, he says.
One reason the mission is a challenge is the nature of the planet Jupiter itself.
Jupiter is more massive than all the other planets in our solar system put together, says Bolton. It's got the strongest magnetic field, largest gravity field and the most ferocious aurorae, including the harshest radiation belts in the entire solar system, he says. Then sitting in the same system is another extreme object, Io, which is the most volcanic body in the solar system, says Bolton. Lava Lakes
We're possibly seeing lakes of lava, possibly that are kind of crusted over, like you see in Hawaii when lava flows get crusted over and look dark, says Bolton. People walk on them, even though it's quite dangerous, because underneath is unbelievably hot lava, he says.
Juno's data suggests that about 10 percent of Io's surface has these remnants of slowly cooling lava just below the surface, says NASA.
As for the overall mission's success?
Even though the mission had some minor hiccups, it's been a grand success.
Once we got there, we saw some symptoms with the rocket motor and its fuel that made us a little nervous about whether we should fire that or not, says Bolton. We were in an orbit that would work; it was just a longer orbit and so we decided not to fire the engine and just stay in that 53-day orbit, he says.
One of Juno's ten active instruments, the Microwave Radiometer (MWR) was specifically invented for the mission.
We're looking at maybe flying one of these instruments right here on Earth to study our own volcanoes, says Bolton. This microwave radiometer was invented for the Juno mission to look below the cloud tops of Jupiter and understand its composition, the dynamics of its storms, he says. But when we pointed at Io, somewhat serendipitously, it allowed us to see into the rock and lava to provide the first real look inside of the moon's subsurface structure, says Bolton.
A further extension notwithstanding, this coming September Juno will end its current extended mission. Launched in 2011, the spacecraft arrived at Jupiter in 2016 and has been scientifically prolific ever since.
The mission represents the best of NASA ingenuity.
One of the greatest things that we've been able to do as humans is figure out how to navigate around the planets and stars, says Bolton. I'm totally amazed that we're able to robotically visit Jupiter, Saturn, Uranus, Neptune, and once there, go into orbit and navigate around their moons, just like driving down to the gas station, he says. In one sense, we're navigating by the stars in the same way we used to do with ancient ships, but now we're navigating between bodies of the solar system, says Bolton. Forbes How Jupiter Helped Spawn Life On Earth By Bruce Dorminey