NASA’s Juno Mission Challenges Theory of Magma Ocean Beneath Io, Jupiter’s Volcanically Active Moon

Io, Jupiter’s innermost moon, has long been known as the most volcanically active body in the solar system. It is covered with hundreds of volcanoes, some of which produce eruptions so intense that they can be observed from Earth using telescopes. For years, scientists hypothesized that beneath its surface, Io may harbor a shallow sea of magma that could be responsible for its extreme volcanic activity. However, new findings challenge this assumption, suggesting that a magma ocean does not exist beneath the moon’s surface as previously thought.

NASA’s Juno spacecraft, which has been orbiting Jupiter since 2016, has provided new insights into Io’s geology. In December 2023 and February 2024, Juno passed closer to Io than any spacecraft has in the past two decades, capturing detailed images from as close as 930 miles. These images were taken by Juno’s two-megapixel camera, JunoCAM, and aimed to shed light on whether magma is distributed in patches across the moon or exists as a more widespread, global layer beneath the surface.

The new data collected from Juno’s close flybys, along with experiments conducted during the mission, led to the conclusion that Io’s volcanic activity is not fueled by a global magma ocean. Scientists had hoped to use the spacecraft’s observations to determine how magma is distributed beneath Io’s surface, but the calculations of the moon’s tidal heating revealed that it is unlikely that a magma ocean exists. Instead, the intense volcanic activity seems to be a result of localized magma pockets rather than a widespread ocean of molten material.

Io’s unique position in the Jupiter system plays a significant role in its geological activity. The moon experiences immense tidal heating due to the gravitational forces exerted on it by Jupiter and its other large moons. This constant stretching and flexing as Io orbits Jupiter every 42 days generates significant friction, which produces the heat necessary to fuel its volcanic eruptions. However, the amount of tidal energy generated is insufficient to melt Io’s entire interior, indicating that the moon’s mantle remains mostly solid.

These findings have broader implications for understanding other moons and exoplanets. For example, moons such as Europa, Enceladus, and several moons of Uranus are also thought to experience tidal heating, potentially leading to subsurface oceans. However, the case of Io suggests that tidal heating alone may not always result in magma oceans, challenging previous assumptions about the geological processes occurring on these distant bodies. The research highlights the complexity of tidal heating and its varied effects on different celestial bodies.