A pot of boiling soup is shaken hard — the liquid sloshes, waves crash against the walls. Something similar happens inside a gas planet when it swings past its star on an elongated orbit. The star's gravity excites powerful internal waves in the planet, known as tidal fundamental modes. These waves can completely change the planet's fate.

For a long time, it was a mystery where the energy of these waves goes. The authors of the new study, using hydrodynamic simulations, have for the first time shown two scenarios. If the wave penetrates shallowly, its energy is lost through radiation and heating — the planet gradually calms down, its orbit becomes circular, and it joins the "pile" of hot Jupiters on orbits of 5–6 days. But if the planet gets too close to the star, the waves accelerate to supersonic speeds and turn into shock waves. They literally strip the gaseous envelope, leaving a bare core: this is how the "Neptune desert" arises on orbits shorter than three days.

This process also explains another oddity. Planets that survive envelope stripping should retain a memory of the catastrophe: their rotation axis will be strongly tilted relative to their orbit, and the process itself may be accompanied by bright flares. Thus, lone rocky cores in the "desert" become not a mystery but a natural result of a turbulent youth. And the fate of each planet, like the soup in the shaken pot, depends on how strongly its close star shook it.