In a big day for planetary science, scientists have announced major news regarding the exploration of two different worlds in our solar system: Mars, and Jupiter’s moon Io.
The findings from Io resolve one longstanding mystery…and create a new one.
When NASA’s two Voyager spacecraft visited Jupiter in 1979, scientists were stunned to discover that Io was by far the most volcanically active place in the Solar System—so active that they wondered if its hundreds of active volcanoes might all be fuelled by a world-girdling subsurface ocean of lava.
Now, NASA’s Juno mission, which has been orbiting Jupiter since 2016, has the answer: there is no subsurface ocean. Instead, Io’s volcanoes, like those on Earth, are fuelled by a host of smaller, local magma chambers. The difference is just that there are a lot of those magma chambers.
The determination was made during two close flybys of Io in December 2023 and February 2024, Ryan Park, a researcher at NASA’s Jet Propulsion Laboratory (JPL), said today in a media briefing at the annual meeting of the American Geophysical Union (AGU) in Washington, D.C.
During the flybys, which came as close as 1,500 kilometers to Io’s surface, Park said, radio astronomers monitored frequency changes in the spacecraft’s radio signals, looking for Doppler shifts from which they could very precisely detect changes in the spacecraft’s speed. The method, Park says, is so sensitive it can measure speed variations of as little as 20 or 30 micrometers per second.
This allowed them to precisely map Io’s gravity field during each flyby. By comparing the two results, he said, they were able to see how much Jupiter’s gravity deforms Io at different points in Io’s orbit, when it is at different distances from Jupiter.
If Io didn’t have had a worldwide magma layer beneath its crust, Park said, there wouldn’t be much deformation. If it did, there would be more, “like a water balloon.” The deformation turned out to be relatively small, he said, ruling out the possibility of a subsurface magma ocean.
During the flybys, the team also took the opportunity to take close-up images of Io’s surface, both in visible light and infrared, the latter of which Alessandro Mura of Italy’s National Institute for Astrophysics noted is particularly useful for studying the heat signatures of Io’s volcanoes.
It was in the process of doing this that the team found the new mystery: a large lava sea on Io’s surface, called Loki, is peppered with islands.
It had long been known that Loki, which is 202 kilometers across, had a large central island. But it now proves to also have numerous small islands, at least 20 of them, Mura said, about 3 kilometers wide. How these islands could exist in a lake we know has been there for at least 44 years, without being eroded away by churning lava, is unknown, Mura said.
Perseverance Reaches the Top
The Mars news is simpler. After 3 ½ years and 30 kilometers of travel, the Perseverance rover has reached the rim of Jezero Crater, crossing a pass and starting down the other side.
Reaching the top wasn’t just an opportunity to take panoramic images (though of course, the rover did indeed do that). It’s a gateway to an entirely new landscape, Ken Farley, project scientist for Perseverance at California Institute of Technology, said today at another AGU briefing. “This is a really exciting geologic transition from rocks [in] the crater [that] probably date to about 3.7 billion years ago, to rocks that existed before the Jezero impact [and] are likely older than 4 billion years,” he said.
In fact, he says, “they could be 4.4 billion years old”—an age that would date them to very close to the dawn of the Solar System. “We don’t know. This is one of the most exciting things that this mission is going to do—to be looking at rocks formed so early in the history of the Solar System.”
Better yet, the rover remains in good health, according to Justin Maki, an imaging scientist and systems engineer at JPL. “The rover has been performing nicely,” he said, “[and] all the instruments are healthy and busy taking data.”
Juno nearly didnt make it to Io
