There are more than 200 moons in the solar system, but none quite like Io, the third largest of them Jupiter’s 80 moons. Io is really, really volcanic. In fact, it is studded with so many hundreds of powerful active volcanoes that there must be something unusual beneath its crust.
That something could be a thick lunar-wide layer of molten rock — or, accordingly, a “subterranean magma ocean.” a new study published in Planetary Science Journal he Nov. 16 by Yoshinori Miyazaki and David Stevenson, planetary scientists at the California Institute of Technology.
This potentially super-hot sea of molten rock – unique to the solar system – could hold secrets, strange mechanisms for the formation of moons and planets, and even recipes for exotic extraterrestrial life. Only further study of the moon, 2,200 miles across, will tell.
Miyazaki and Stevenson aren’t the first scientists to make an educated guess at what lies beneath Io’s potentially 20-mile-thick rock crust. It has been the subject of heated debate for years. But their new peer-reviewed study of the lunar mantle could be the most thorough yet.
To look beneath the surface of Io, Miyazaki and Stevenson revisited reams of data from NASA Galileo trialsorbited Jupiter for eight years beginning in 1995. Initial analyzes 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 upper layer that should be “molten or partially molten.” according to NASA.
Compare this to the Earth’s mantle, as well as the mantles of all other planetary bodies in the solar system, which are mostly solid and mostly made of ice or superheated rock. Roughly speaking, planetary scientists reading the Galileo data assumed that Io has either a subsurface magma ocean or some sort of spongy, rocky outer mantle saturated with magma.
A fresh look at the ice data Miyazaki and Stevenson conclude it’s the molten sea. They based their conclusion on estimates of mantle temperature by analyzing Io’s volcanoes, which can spew magma hundreds of kilometers into the moon’s sulfur dioxide atmosphere. The top of the mantle could be as hot as 2,800 degrees Fahrenheit.
That’s hot. But not hot enough to endure 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 mantle. Without enough heat, the sauce—er, the spongy rock—would separate: rock at the bottom, magma at the top.
Miyazaki and Stevenson crunched the numbers, calculating the heat from Io’s core as well as the effects of its odd, highly elliptical orbit, which billows the mantle, dispersing heat and keeping Io from ever permanently cooling.
They concluded that the sauce would separate. “The amount of internal heating is insufficient to maintain a high degree of fusion,” they wrote. Therefore, they believe it could be an uppermost magma ocean.
Luckily we’ll know more soon. NASA’s Juno Samples, which arrived around Jupiter in 2016, is scheduled to take measurements of Io in 2023 and 2024 – specifically the “love number,” a measure of a planet’s rigidity or lack of rigidity. “If a large love number is found, we can say with greater certainty that a magma ocean exists beneath the surface of Io,” Miyazaki told The Daily Beast.
We already knew Io was weird. It’s possible, it’s even possible stranger— and this madness could have implications for space science. “I don’t think it changes our understanding of planet formation much, but it does change how we view the internal structure and thermal evolution of tidally heated bodies like Io,” says David Grinspoon, a senior scientist at the Planetary Science Institute in Arizona . said The Daily Beast.
Astrobiologists lurk in the academic shadows. The experts on how and where life could develop in the universe. If there is extraterrestrial life out there somewhere and it looks like life on Earth, we should expect to find it – or evidence of its extinction – on planets and moons that have or have had an Earth-like environment. Mars. Venus. A moon of Saturn called Enceladus.
But volcanoes, with their extreme energy transfers, are widely considered key components of a living ecosystem. So planets and moons with lots of volcanoes are great places to look for ET. In theory, that should include Io.
However, Io too many volcanoes. So if life develops there, it’s probably a very strange life likes heat very much. “Lava tubes could create a favorable condition for microbes,” Miyazaki said.
The question for astrobiologists is whether a magma ocean would produce more or fewer lava tubes than a magma sponge. “I don’t have a definite 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 interfere with this search if it was really close to the surface. A nice thick crust should protect the planet’s outermost regions 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 only underscores how interesting and exciting the moon is — and why it should be a top target for future spacecraft, Schulze-Makuch said. “Io is a unique type of moon, very dynamic, and we shouldn’t dismiss it entirely.”