A giant planet located outside the Solar System is, before our eyes, leaving the configuration that makes it easy to observe from Earth.
Named TOI-1355 b, this exoplanet has about 5.8 times Jupiter’s mass and 1.4 times its radius. It orbits a very hot star in just 2.17 days. Its close proximity to its star places it among the “hot Jupiters,” large gaseous planets whose year sometimes lasts only a few days.
Artist’s view of a Jupiter-sized planet passing in front of its star.
Credit: NASA, ESA and G. Bacon (STScI).
To detect such a world, astronomers can wait for it to pass in front of its star. The planet then blocks a small part of its light, producing a regular decrease in brightness called a transit. The team studied TOI-1355 b notably with the TESS space telescope and several ground-based observatories.
But these passages are changing. Researchers found that the planet’s apparent path is gradually shifting relative to the disk of its star. This movement, called precession, slowly changes the orientation of the orbit in space. According to the measurements, TOI-1355 b should no longer pass in front of its star from our point of view around the middle of 2033.
The planet will therefore not actually disappear, nor will it stop orbiting its star. Researchers estimate that this configuration could then last for several centuries before the geometry might eventually allow these passages to be seen again.
Another feature makes TOI-1355 b interesting: its orbit is not perfectly circular. Its eccentricity reaches about 0.22, indicating a distinctly elliptical path. Yet at a short distance from the star, tidal effects generally tend to make the orbit gradually more circular.
This shape could preserve evidence of a turbulent history. Gravitational interactions with other bodies may once have placed the planet on a highly elongated trajectory. Tides exerted by the star would then have reduced this orbit, gradually bringing the gas giant closer. TOI-1355 b could therefore make it possible to observe a stage of this evolution that is still poorly documented.
The time available for certain measurements is now running out. The team plans to study the orbit’s inclination relative to the star’s rotation more precisely. The researchers are also considering observations with the James Webb Space Telescope to examine the planet’s atmosphere before its transits disappear.