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 like Io, the third largest of Jupiter’s 80 moons. Io is really, really volcanic. In fact, it’s dotted with so many hundreds of mighty active volcanoes that there must be something unusual beneath its crust.

That something could be a thick lunar layer of molten rock, or a “subsurface ocean of magma,” according to a new study published in the Planetary science journal on Nov. 16 by Yoshinori Miyazaki and David Stevenson, planetary scientists at the California Institute of Technology.

That possible super-hot sea of ​​molten rock, which is unique to the solar system, could hold secrets, strange mechanisms for forming moons and planets, and even recipes for exotic alien life. Only further 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, captured by NASA’s New Horizon spacecraft.

NASA/JPL/University of Arizona

To peek beneath Io’s surface, Miyazaki and Stevenson revisited reams of data from NASA’s Galileo spacecraft, which orbited Jupiter for eight years starting in 1995. Initial analysis of the spacecraft’s magnetic data led to a vague consensus that Io’s mantle — the layer beneath the moon’s crust — includes a 30-mile-thick upper layer that is expected to be “melted or partially molten,” according to NASA.

Compare this to the mantle of Earth, as well as the mantles of every other planetary body in the solar system, which are mostly solid and consist largely of superheated ice or rock. In general, planetary scientists reading Galileo’s data assumed that Io had a subterranean magma ocean, or some kind of rocky, sponge-like 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 from analysis of Io’s volcanoes, which can spew magma hundreds of miles into the moon’s sulfur dioxide atmosphere. The upper mantle could record temperatures as high as 2,800 degrees Fahrenheit.

It’s hot. But not hot enough to sustain a spongy interior. The analysis is complicated, but it boils down to this: Like a pot of gravy on a stove, Io would need a lot of heat to remain consistently spongy in its upper coat. Without enough heat, the gravy—ahem, spongy rock—would separate: rock at the bottom, magma on top.

Miyazaki and Stevenson crunched the numbers, calculating the heat coming from Io’s core and the effects of its strange, highly elliptical orbit, which slides the mantle, spreads heat around and keeps Io from permanently cooling.

They concluded that the gravy would separate. “The amount of internal heating is insufficient to maintain a high degree of melting,” they wrote. So what they believe could be a magma ocean higher up.

Luckily we will know more soon. NASA’s Juno spacecraft, which arrived around Jupiter in 2016, is scheduled to take readings of Io in 2023 and 2024, specifically measuring the “love number,” an indicator of starvation or lack of a planet. “If a large number of Loves are found, we can say with greater certainty that there is a magma ocean beneath Io’s surface,” Miyazaki told The Daily Beast.

We already knew Io is weird. It is possible that it is even stranger— and that quirk could have implications in the space sciences. “I don’t think it changes our understanding of planetary formation much, but it does change how we view the internal structure and thermal evolution of tidally heated bodies like Io,” David Grinspoon, a senior scientist at the Arizona-based Planetary Science Institute he 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 shadow are astrobiologists. Experts on how and where life might have evolved in the universe. If there is extraterrestrial life out there somewhere and it looks like terrestrial life, we should expect to find it – or evidence of its extinction – on planets and moons that have, or have had, Earth-like environments. Mars. Venus. A moon of Saturn named Enceladus.

But volcanoes with their extreme energy transfers are widely regarded as key components of a living ecosystem. So planets and moons with lots of volcanoes are great places to look for ET. In theory, this should include Io.

However, I may have it too many volcanoes. So if there’s life evolving there, it’s probably very strange life loves the heat very much. “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 those implications.”

Dirk Schulze-Makuch, an astrobiologist at the Technical University of Berlin, has long advocated extensive research for life on Io. A magma ocean would only spoil that quest if it were really close to the surface. A nice thick crust should insulate the planet’s outermost regions from unbridled 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 only underscores 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 type of moon, very dynamic, and we shouldn’t discount that entirely.”

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