Some rocky planets around alien suns orbit so close to their star that their gas envelopes should have vanished long ago. Yet the James Webb Space Telescope and brightness measurements reveal dense atmospheres. The answer lies in computer simulations. First, heavy carbon dioxide escapes from the scorching magma and wraps the planet in a thick shroud. Under the onslaught of changing starlight, this wrapping gets blown away, the pressure drops, and light hydrogen bursts out. It instantly inflates the remaining envelope, just like a compressed balloon expands when you remove its tight packaging. This effect, reflation, only works on planets with reduced interiors (rich in iron); on oxidized ones, like Earth, hydrogen is locked away. Surprisingly, triggering the process requires entire oceans of water hidden inside. These findings build on the pioneering work of discoverers Michel Mayor and Didier Queloz, as well as atmospheric studies by David Charbonneau. Reflation can be detected by brightness changes during a planet’s transit across the star’s disk and by the rainbow fingerprints of the atmosphere. This is how astronomers peer inside distant worlds. Future missions like PLATO and ARIEL will map these inflated envelopes.