Contrary to previous beliefs, Io's volcanoes are not fueled by a global ocean of magma beneath the surface, but by local magma chambers. This revelation comes from the details uncovered by NASA’s Juno mission, which, through two close flybys, captured unprecedented images and data, allowing scientists to observe the moon's poles for the first time with precision and solving a decades-long mystery. The findings were presented at the annual meeting of the American Geophysical Union and were quickly published in the scientific journal Nature. "It's like an endless thunderstorm. It’s always erupting everywhere," commented Scott Bolton, a researcher passionate about Jupiter’s moon and co-author of the study published in Nature.
Discovered by Galileo Galilei in 1610, Io is one of Jupiter’s four major moons and is just slightly larger than Earth's moon. Its distinctive volcanic activity was first detected in 1979 by the Voyager 1 probe, which revealed a dynamic surface resembling a "pepperoni pizza," as researchers described it. Since then, scientists have speculated about the origin of this extreme volcanism, which was attributed to intense tidal flexing caused by Jupiter's gravity. Io's irregular orbit generates enormous compressive forces that heat the moon’s interior, causing it to melt. For decades, the prevailing theory suggested the presence of a vast magma ocean beneath the surface, feeding its approximately 400 active volcanoes.
However, the data collected by Juno during flybys in December 2023 and February 2024 revealed that the interior of the moon is largely rigid and solid, meaning it lacks a global magma ocean. Instead, the researchers explain, each volcano appears to be fueled by its own localized magma chamber. Furthermore, the observations went beyond just the internal structure: the probe captured detailed images of Io's surface, revealing lakes of lava—including one vast expanse comparable to a glowing sea—and islands never seen before. The discovery, in addition to solving a decades-old mystery, has broader implications. As the scientists explain, it pushes astronomers to reconsider the internal structure of other moons like Europa and Enceladus, which are dominated by underground oceans, and even extrasolar planets and super-Earths, revolutionizing our understanding of planetary evolution. “Juno’s discovery that tidal forces don’t always create global magma oceans pushes us to rethink not only what we know about Io’s interior,” confirmed lead author Ryan Park, who concluded by adding that the Juno probe will continue to provide new information on Jupiter and its moons, having recently completed a flyby of the swirling cloud tops of the gas giant, with plans to pass about 3,500 kilometers above the center of Jupiter on December 27, marking 1.04 billion kilometers since it began its investigation of Jupiter eight years ago.
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