Jupiter’s moon Io may have a hellish ocean of magma beneath its surface
There are more than 200 moons in the solar system, but none look like Io, the third largest of them 80 moons of Jupiter. Io is really, really volcanic. In fact, it is dotted with so many hundreds of powerful active volcanoes that there must be something unusual beneath its crust.
This thing could be a thick layer of molten rock covering the entire moon, or a “subterranean ocean of magma,” according to a new study published in Planetary Science Journal on Nov. 16 by Yoshinori Miyazaki and David Stevenson, planetary scientists at the Cal Institute of Technology.
This possible super-hot sea of molten rock – which is unique in the Solar System – may hold secrets, strange mechanisms for the formation of moons and planets, and even recipes for exotic alien life. Only a more in-depth study of the 2,200-mile-diameter moon will tell.
Miyazaki and Stevenson aren’t the first scientists to make an educated guess as to what lies beneath Io’s potentially 20-mile-thick rocky crust. This has been the subject of heated debate for years. But their new peer-reviewed study of the moon’s mantle may be the most thorough yet.
Volcanic explosion on Io, Jupiter’s third largest moon, imaged by NASA’s New Horizon spacecraft.
NASA/JPL/University of Arizona
To peer beneath Io’s surface, Miyazaki and Stevenson reviewed troves of data from NASA Galileo probewhich orbited Jupiter for eight years beginning in 1995. Initial analysis of the probe’s magnetic data led to a loose consensus that Io’s mantle—the layer beneath the lunar crust—includes a 30-mile-thick upper layer that must be “ molten or partially molten,” according to NASA.
Contrast this with Earth’s own mantle, as well as the mantles of every other planetary body in the Solar System, which are mostly solid and consist mostly of ice or superheated rock. Generally speaking, planetary scientists who read the Galileo data assume that Io has either an underground magma ocean or a kind of sponge-like rocky outer mantle soaked in magma.
A new look at the data led Miyazaki and Stevenson to conclude that it was the molten sea. They based their conclusion on estimates of mantle temperature through analysis of Io’s volcanoes, which can spew magma hundreds of miles into the moon’s sulfur dioxide atmosphere. The upper mantle can register up to 2,800 degrees Fahrenheit.
That’s hot. But not hot enough to support a spongy interior. The analysis is complicated, but it boils down to this: like a pot of sauce on the stove, Io will need a lot of heat to stay permanently spongy in its upper mantle. Without enough heat, the sauce—er, the sponge rock—would separate: rock below, magma above.
Miyazaki and Stevenson crunched the numbers, calculating the heat from Io’s core as well as the effects of its strange, highly elliptical orbit, which splashes the mantle, spreads heat around and keeps Io from constantly cooling.
They concluded that the sauce would separate. “The amount of internal heating is insufficient to maintain a high degree of melting,” they wrote. Therefore, what they believe may be the uppermost magma ocean.
Fortunately, we’ll soon learn more. of NASA Juno probe, which arrived around Jupiter in 2016, is scheduled to take readings on Io in 2023 and 2024 — specifically measuring the “love number,” an indicator of a planet’s hardness, or lack thereof. “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 Yo was weird. It may be equal more strange– and this oddity may have implications in the space sciences. “I don’t think this significantly changes the understanding of planet formation, but it does change the way we look at the internal structure and thermal evolution of tidally heated bodies like Io,” David Grinspoon, senior scientist at the Arizona-based Planetary Institute sciences, said The Daily Beast.
Io and Europa, Jupiter’s two largest moons, imaged by NASA’s Juno spacecraft.
NASA/JPL-Caltech/SwRI/MSSS/Roman Tkachenko
Astrobiologists lurk in the academic shadows. The experts on how and where life might develop in the universe. If alien life exists somewhere and it looks like life on Earth, we should expect to find it—or evidence of its disappearance—on planets and moons that have, or have had, terrestrial environments. Mars. Venus. It is called a moon of Saturn Enceladus.
But volcanoes, with their extreme energy transfers, are widely regarded as key components of living ecosystems. So planets and moons with lots of volcanoes are great places to look for aliens. In theory this should include Io.
However, Yo may have too much volcanoes. So if there is life going on there, it’s probably a very strange life really likes the heat. “Lava tubes may create conditions favorable to 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 a clear answer,” Miyazaki said. “But it’s interesting to think about those kinds of implications.”
Dirk Schulze-Makuh, an astrobiologist at the Technical University of Berlin, has long advocated a thorough search for life on Io. An ocean of magma would only spoil this search if it was really close to the surface. A nice thick crust should insulate the outermost regions of the planet from searing heat and preserve the potential for evolution. “There seems to be quite a bit of bark,” Schulze-Makuh told The Daily Beast.
If anything, the possibility of a magma ocean on Io just underscores how interesting and exciting the moon is — and why it should be a prime target for future space probes, Schulze-Makuh said. “Io is a unique kind of moon, very dynamic, and we shouldn’t dismiss it completely.”
