Every 165 days, the giant planet dives toward its star, nearly grazing its fiery corona, then flies off into the icy void. This is TIC 241249530 b — an exoplanet with a record eccentricity of 0,94. Discovered through photometry by the TESS telescope and refined with spectroscopy, it showed a barely perceptible transit dimming but a huge amplitude in the star's radial velocity. Such behavior is a sure sign of a transit planet, whose orbit resembles a mad swing.

The culprit behind this sweeping dance is a distant companion star, whose gravity rocks the orbit through von Zeipel–Lidov–Kozai oscillations. This mechanism turns the orbit into a cosmic swing: under the influence of the foreign pull, the planet's eccentricity periodically soars to enormous values, and then might drop if not for tidal forces. It is they, like friction in a hinge, that gradually damp the swing and bring the planet closer to the star — that's how hot Jupiters are born. We have a rare chance to catch migration in the act.

Astrophysicists tested which type of tidal braking is responsible for the present orbit. In numerical simulations, they ran through thousands of variations, including general relativity effects and two competing scenarios. Equilibrium tides — where the planet behaves like a viscous ball: the tidal bulge lags behind the star's motion and brakes the planet. Chaotic dynamical tides — where nonlinear oscillations are excited inside the giant, dumping energy through stochastic kicks. Calculations with the MESA code, originally designed for stellar evolution, even accounted for heating and inflation of the planet from friction. The verdict was unambiguous.

Only equilibrium tides could reproduce the observed state. The chaotic scenario invariably sent the planet into too tight a pericenter: the key conserved quantity — the reduced angular momentum j² = a(1−e²) — would have dropped to 0,026 AU instead of the actual 0,074. This little formula — a constant of tidal evolution — ruled out chaos. Moreover, an analysis of all known eccentric giants showed that none violate this threshold. Cosmic swings are arranged so that chaos either never kicks in or quickly ends, leaving behind only hot Jupiters.

It seems equilibrium tides are the principal conductor of the migrating planet orchestra. The observational hunt for new 'swing systems' with distant companions will continue, and each discovery will shed light on the birth of the most unusual worlds.