The mystery of the radius valley — a sharp drop in the number of exoplanets with radii ~1.8 Earth — haunts astronomers. JWST, transit surveys like Kepler and TESS draw a clear gap: rocky super-Earths and gaseous sub-Neptunes are separated by almost a chasm. Yet the hottest worlds, bathed in harsh ultraviolet from their stars, sometimes look too puffed up for their age, as if refusing to age by the textbooks. That’s where an unexpected ally appears: interior geochemistry.

Imagine a super-Earth as a bathyscaphe stuffed with heavy ballast. The ballast is a primordial atmosphere of carbon monoxide (CO), exhaled by a reduced mantle where iron hasn’t yet oxidized. The star, like a relentless pump, sucks out this gas, and the bathyscaphe begins to rise. But its magma ocean already holds giant reserves of dissolved hydrogen. As pressure drops, H₂ breaks free, instantly puffing up the outer envelope. For a while, the planet fluffs up: its average density crashes by 60%. (For comparison: Earth would suddenly become lighter than Mercury.) That’s reflation — a planetary inhale after a long exhale.

The mass-loss rate follows the law of universal gravitation and boils down to a simple rule: the more massive the planet, the tighter it clings to its atmospheric coat. But if the coat is too heavy (like carbon dioxide), it’s stripped away faster, making room for a light hydrogen cloud.

The idea of reflation, grown from the pioneering searches of Michel Mayor and Didier Queloz and the atmosphere spectroscopy refined by David Charbonneau, promises a revolution in observations. When you spot a super-Earth with anomalously low density, don’t rush to label it a water world or gas dwarf: perhaps we’re catching it in the act of reflation. That’s a direct signal of reducing conditions in the interior, meaning its geochemical kitchen may resemble young Earth.

Next-generation instruments (PLATO, ARIEL, and numerical models that include fractionation and photochemistry) will help find these ‘breathing’ planets. We’re entering an era where stellar evolution and interior chemistry merge into a single story, and every super-Earth will tell its tale through the rhythm of inhales and exhales.