NASA Finds Surprising Secret Beneath Jupiter Moon Io's Surface

Juno's Close Encounter Reveals Hidden Magma Layer

Jupiter's moon Io has long been known as the most volcanically active body in the solar system. But a new discovery from NASA's Juno mission suggests the moon is hiding something even more dramatic beneath its surface.

Scientists analyzing data from Juno's flybys have found evidence of a global subsurface magma ocean. Instead of a solid, rocky mantle, Io appears to have a layer of molten rock stretching across the entire moon.

The findings, published in the journal Nature and presented at a recent planetary science conference, overturn previous models that assumed Io's interior was mostly solid with isolated pockets of magma.

How Juno's Gravity Data Solved the Puzzle

The Juno spacecraft, which has been orbiting Jupiter since 2016, made several close passes by Io in recent months. Its instruments measured tiny changes in the moon's gravitational field.

These measurements revealed that Io's interior is more flexible than expected. A solid mantle would resist tidal forces from Jupiter's massive gravity. Instead, the data showed a deformation consistent with a liquid layer beneath the crust.

“We expected to see a signature of tidal flexing, but not this strong,” said a lead researcher from NASA's Jet Propulsion Laboratory. “The only way to match the data was a global magma ocean.”

What This Means for Io's Fiery Volcanoes

Io is home to hundreds of volcanoes, some spewing plumes hundreds of kilometres high. The new discovery explains why the moon is so violently active.

Jupiter's immense gravity pulls and stretches Io as it orbits, generating heat through friction. The subsurface magma ocean acts as a reservoir, feeding the constant eruptions that reshape the moon's surface every few years.

Previous theories suggested that Io's volcanoes erupted from isolated magma chambers. The Juno data indicates a far more connected system, with molten rock moving freely across the moon's interior.

Implications for Other Moons

The finding also has implications for other icy moons in the solar system, such as Europa and Enceladus. Both are thought to have subsurface liquid water oceans.

If a magma ocean can persist for billions of years on a small moon like Io, similar processes could sustain other liquid layers elsewhere. Scientists are already planning follow-up studies to compare Io's internal structure with data from future missions to the outer solar system.

“This changes how we think about the evolution of planetary bodies,” a NASA spokesperson said. “Io is not just a volcanic oddity — it's a window into how tidal forces shape worlds.”

Juno's mission has been extended through 2025, with additional flybys of Io planned. Each pass is expected to provide higher-resolution data, helping scientists map the magma ocean's depth and temperature.

What remains unclear is how long this magma layer has existed. Some models suggest it could be as old as the moon itself, while others argue it may be a more recent feature triggered by changes in Io's orbit. Future observations from Juno and ground-based telescopes will aim to settle that debate.