Jupiter’s moon Io may have a hellish magma ocean beneath its surface

There are more than 200 moons in the solar system, but none resemble Io, the third largest of Jupiter’s 80 moons. Io is really quite volcanic. In fact, it is laced with so many hundreds of powerful active volcanoes that there must be something unusual under its crust.

That something could be a thick moon-wide layer of molten rock — or an “underground magma ocean,” according to a new study published in the Journal of planetary science on Nov. 16 from Yoshinori Miyazaki and David Stevenson, planetary scientists at the California Institute of Technology.

That potentially super-hot sea of ​​molten rock — which is unique in the solar system — could hold secrets, weird mechanisms for forming moons and planets, and even recipes for exotic alien life. Only closer examination of the 2,200-mile-diameter moon will tell.

Miyazaki and Stevenson aren’t the first scientists to make an educated guess about what lies beneath Io’s potentially 20-mile-thick rocky crust. It has been the subject of heated debate for years. But their new peer-reviewed study of the lunar mantle may be the most thorough yet.

A volcanic explosion on Io, Jupiter’s third-largest moon, as captured by NASA’s New Horizon spacecraft.

NASA/JPL/University of Arizona

To peer beneath Io’s surface, Miyazaki and Stevenson re-examined large amounts of data from NASA’s Galileo probe, which orbited Jupiter for eight years starting in 1995. Initial analysis of the probe’s magnetic data led to a loose consensus that Io’s mantle — the layer beneath the moon’s crust — contains a 30-mile-thick top layer that NASA says should be “molten or partially molten.”

Compare this to Earth’s mantle itself, as well as the mantles of every other planetary body in the solar system, which are mostly massive and made up largely of ice or superheated rock. Broadly speaking, planetary scientists reading the Galileo data assumed that Io either has a subsurface magma ocean or some kind of spongy rocky outer mantle soaked in magma.

A fresh look at the data led Miyazaki and Stevenson to conclude that it is the molten sea. They based their conclusion on mantle temperature estimates via analysis of Io’s volcanoes, which can spew magma hundreds of miles into the moon’s sulfur dioxide atmosphere. The top of the mantle can be as hot as 2800 degrees Fahrenheit.

That’s hot. But not hot enough to maintain a spongy interior. The analysis is complicated, but it boils down to this: Like a pot of gravy on a hotplate, Io would need a lot of heat to stay consistently spongy in its upper mantle. Without enough heat, the gravy – er, the spongy rock – would separate: rock on the bottom, magma on top.

Miyazaki and Stevenson crunched the numbers, calculating the heat of Io’s core and the effects of its weird, highly elliptical orbit, which sloshes the mantle, scattering heat and keeping Io from cooling permanently.

They concluded that the gravy would separate. “The amount of internal heating is insufficient to maintain a high rate of melting,” they wrote. Hence what they believe could be an upper magma ocean.

Fortunately, we will know more soon. NASA’s Juno probe, which arrived around Jupiter in 2016, is scheduled to take measurements of Io in 2023 and 2024, specifically measuring the “love number,” a measure of a planet’s rigidity or lack thereof. “If a large Love number is found, we can say with more certainty that a magma ocean exists beneath Io’s surface,” Miyazaki told The Daily Beast.

We already knew that Io is weird. It is possible that it is right stranger— and that weirdness could have implications for space science. “I don’t think this changes the understanding of planetary formation hugely, but it does change how we see the internal structure and thermal evolution of tidally heated bodies like Io,” said David Grinspoon, a senior scientist at Arizona-based Planetary Science. Institute, told The Daily Beast.

Io and Europa, Jupiter’s two largest moons, captured by NASA’s Juno spacecraft.

NASA/JPL-Caltech/SwRI/MSSS/Roman Tkachenko

Lurking in the academic shadows are the astrobiologists. The experts in how and where life could evolve in the universe. If there is extraterrestrial life somewhere and it resembles terrestrial life, we should expect to find it – or evidence of its extinction – on planets and moons that have or had Earth-like environments. Mars. Venus. A moon of Saturn called Enceladus.

But volcanoes with their extreme energy transfers are widely regarded as the most important components of a living ecosystem. So planets and moons with lots of volcanoes are great places to look for ET. In theory, that should be Io as well.

However, Io could too many volcanoes. So if life evolves there, it’s probably very strange life that really likes heat. “Lava tubes could create a favorable condition for microbes,” Miyazaki said.

The question for astrobiologists is whether a magma ocean would create more or fewer lava tubes than a magma sponge. “I don’t have an explicit answer,” Miyazaki said. “But it’s interesting to think about such implications.”

Dirk Schulze-Makuch, an astrobiologist at the Technical University of Berlin, has long advocated a thorough search for life on Io. A magma ocean would only spoil that search if it were very close to the surface. A nice thick crust should insulate the outer regions of the planet from abrasive heat and preserve the potential for evolution. “There seems to be quite a bit of crust,” Schulze-Makuch told The Daily Beast.

If anything, the possibility of a magma ocean on Io underscores just how interesting and exciting the moon is — and why it should be a prime target for future space probes, Schulze-Makuch said. “Io is a unique kind of moon, very dynamic, and we shouldn’t reject it altogether.”

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