Exoplanet caught in 'hairpin turn' signals how high-mass gas giants form

07/17/2024 - 16:00

An international scientific team, in which the Instituto de Astrofísica de Canarias (IAC) participates, has discovered the extremely eccentric orbit of a gas giant exoplanet. This world, called TIC 241249530 b, not only follows one of the most drastically stretched-out orbits of all known transiting exoplanets, but also is also orbiting its star backwards, lending insight into the mystery of how these high-mass gas giants evolve into hot Jupiters, with very close and circular trajectories. The study is published in Nature.

Within the population of known exoplanets, there are those that belong to the class known as hot Jupiters: large, Jupiter-like exoplanets that orbit very close to their star, some even closer than Mercury to our Sun. How hot Jupiters end up in such close orbits is a mystery, as they cannot form there, but astronomers postulate that they begin in orbits far from their star and then migrate inward over time.

The early stages of this process have rarely been observed, but a new analysis of the exoplanet TIC 241249530 b, detected by NASA's Transiting Exoplanet Survey Satellite (TESS) in 2020, has revealed that its orbit is extremely eccentric, describing an ellipse with one axis much larger than the other. This peculiar trajectory suggests that the planet is in a hot Jupiter pre-migration phase. The data also confirmed that the exoplanet is about five times more massive than Jupiter.

TIC 241249530 b is only the second exoplanet ever discovered that is at a point in its evolution prior to its migration into tighter orbits. The detection of such exoplanets observationally affirm the idea that higher-mass gas giants evolve to become hot jupiters as they move from highly eccentric orbits toward closer, more circular orbits. This process is due to the fact that, as it approaches the host star, the tidal forces on the planet sap energy from the orbit and cause it to gradually shrink and circularize.

More:
https://www.iac.es/en/outreach/news/eccentric-exoplanet-reveals-how-hot-jupiters-form