Scientists reveal the mystery of disappearing exoplanet orbits

Schematic of tidal dissipation due to wave conversion. Credit: The Astrophysical Journal Letters (2024).

A recent study led by scientists at Durham University has unveiled a new discovery that sheds light on a puzzling phenomenon: the gradual decay of planetary orbits around stars like our sun.

Published in The Astrophysical Journal Letters, the study introduces a fresh idea suggesting that the magnetic fields of stars play a crucial role in causing the orbital decay of “hot Jupiter” exoplanets.

Hot Jupiters are gas giants similar to Jupiter but orbit very close to their parent stars, completing orbits in just a few days.

This close proximity subjects both the planet and the star to strong gravitational tides, which gradually pull the planet closer to the star over billions of years until it’s eventually swallowed.

The researchers focused on a particular system called WASP-12b, where the hot Jupiter planet’s orbit is decaying rapidly, eventually leading to its demise within a few million years.

Conventional theories couldn’t fully explain this orbital decay until now.

The study proposes that strong magnetic fields within sun-like stars can efficiently dissipate the gravitational tides from hot Jupiter planets.

Inside these stars, the tides create waves that move inward. But when these waves encounter the star’s magnetic fields, they transform into different types of magnetic waves that travel outward and eventually vanish.

Lead author Dr. Craig Duguid of Durham University expressed excitement about the findings, stating that this discovery has significant implications for understanding the survival of short-period planets like hot Jupiters.

He also noted that it provides astronomers with new targets to observe orbital decay, which could be tested within our lifetime.

The study suggests that certain nearby stars might host more hot Jupiter planets on decaying orbits, offering opportunities to gather more evidence about the impact of magnetic fields on these planets’ tides.

Furthermore, the research could help scientists understand where the energy dissipated from the tides goes within the star’s interior.

In summary, this study marks a significant step forward in unraveling the mysteries of exoplanetary orbits and highlights the crucial role that stellar magnetic fields play in shaping the fate of these distant worlds.