The most tightly packed planetary system ever discovered may also be one of the most geologically violent.

In the TRAPPIST-1 system, seven Earth-sized planets orbit a cool red dwarf star in orbits so close together that their gravitational interactions constantly tug and flex each world from the inside out. Some planetary scientists believe this extreme configuration could be generating internal heating strong enough to drive Io-level volcanic activity, making parts of these worlds potentially reshaped by continuous eruptions and resurfacing.

In this episode, we explore how the James Webb Space Telescope (JWST) is being used to investigate whether any of these planets show signs of volcanic activity—or whether they remain geologically quieter than models predict.

We begin with what JWST has actually observed so far, particularly its secondary eclipse measurements of TRAPPIST-1b. These observations, which analyze the light from the planet as it disappears behind its star, currently suggest a surface consistent with a bare rocky world with little to no substantial atmosphere. While earlier speculation allowed for thicker atmospheres, the data so far has leaned toward a more exposed, airless surface—at least for this innermost planet.

From there, we move into the physics of tidal heating. Because the TRAPPIST-1 planets are locked into tightly interacting orbits, gravitational forces between them—and from the host star—can flex their interiors in a process similar to what powers Jupiter’s moon Io, the most volcanically active body in the Solar System. This constant deformation converts orbital energy into heat, potentially melting rock and driving persistent volcanic resurfacing.

We then examine what researchers expect from ongoing and future JWST campaigns. The focus is now shifting toward planets like TRAPPIST-1d and TRAPPIST-1e, where conditions are slightly more temperate and where atmospheres—if they exist—could preserve chemical traces of volcanic outgassing.

One of the key targets is sulfur dioxide (SO₂), a classic volcanic gas. Theoretical modeling work from 2026 suggests that if these planets are volcanically active at even moderate levels, SO₂ could accumulate in detectable quantities in their upper atmospheres, producing spectral fingerprints that JWST might be able to identify during transit observations. Alongside SO₂, scientists are also modeling plume heights and atmospheric escape rates to determine whether volcanic material would remain visible long enough to be measured.

At the same time, JWST is conducting phase curve observations, tracking how light from these planets changes over their full orbits. These measurements are crucial for breaking a major scientific ambiguity: whether observed signals come from a bare rock surface radiating heat directly, or from a thin or patchy atmosphere redistributing energy across the planet. The difference has major implications for understanding whether volcanic activity is actively shaping these worlds.

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