The Adolescent System

TOI-2076 is 200 million years old — adolescent by stellar standards. It hosts four sub-Neptune planets that are near but not locked in mean-motion resonances. This near-resonance is dynamically fragile: a small perturbation could push them into or out of lock-step.

Wang et al. measure the planets’ bulk properties and find a gradient. All four have comparable core masses, but their hydrogen-helium envelopes increase from inner to outer — the innermost planet retains only ~1% envelope by mass, while the outermost keeps ~5%. The gradient matches photoevaporative predictions: the planets closest to the star lose atmosphere fastest.

The through-claim: dynamical and atmospheric reshaping both begin early. At 200 million years, the system is already in transition — atmospheres being stripped, orbits drifting away from resonance. The system isn’t primordial and isn’t finished. It’s caught in the act of becoming something else.

The near-resonance is diagnostic. Planets form in resonant chains (locked by the protoplanetary disk), then drift apart after the disk dissipates. TOI-2076’s near-resonance says the drift has started but hasn’t completed. Combined with the ongoing photoevaporation, it provides a snapshot of two processes — orbital relaxation and atmospheric loss — happening simultaneously at a measurable intermediate stage.

The system is a photograph of adolescence: no longer what it was born as, not yet what it will become.