Volatiles are the hidden engines driving both planetary atmospheres and explosive volcanic eruptions

Nature · Published 3 October 2026 Swipe more like this →

In short: Whether shaping the icy depths of distant gas giants or triggering violent volcanic blasts on Earth, volatiles are substances that vaporize with ease. These chemical compounds, ranging from water and carbon dioxide to hydrogen, dictate the behavior of magma and the evolution of planetary bodies across our solar system.

In astrogeology, volatiles are elements and compounds that vaporize readily, contrasting with refractory substances. Scientists classify them based on melting points: those below 100 K are often called gases, while those above are termed ices. This terminology is fluid; for instance, Jupiter and Saturn are gas giants, yet their interiors consist of dense, hot fluids reaching extreme temperatures. Even at 25.8 AU from the Sun, supervolatiles like carbon monoxide drive cometary activity.

On Earth, volatiles are critical to igneous petrology. Magma is typically 95-99% liquid rock, but the small percentage of dissolved gases—primarily water and carbon dioxide—determines a volcano's character. In high-viscosity felsic magma, these volatiles often trigger explosive eruptions. As magma rises, pressure drops, causing dissolved gases to exsolve and form bubbles. If the magma is supersaturated, these bubbles expand rapidly, fragmenting the liquid into spray or clots. The process is governed by complex solubility laws, where pressure and magma composition dictate when and how these gases escape.

Bubble formation, or nucleation, is a delicate physical process. While molecules can aggregate spontaneously, solid crystals within a magma chamber often act as nucleation sites. If nucleation is delayed, the magma becomes significantly supersaturated, leading to more intense activity upon reaching the surface. Because carbon dioxide has lower solubility than water, it often exsolves at greater depths, sometimes leaking through caldera cracks before an eruption even begins. Ultimately, understanding these volatile interactions—from the deep mantle to the surface—is essential for predicting volcanic behavior and interpreting the geological history of planets.

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