🪐 This planet combines every extreme

A planet approximately twelve times more massive than Jupiter orbits so close to its star that a full year there lasts only 3.25 days.

The object, named TOI-7475.01, had already been detected using the TESS space telescope. It regularly measures the brightness of numerous stars. When a planet passes in front of its star, it blocks a small part of its light and causes a temporary drop in brightness. For TOI-7475, this transit lasts about 4.5 hours.

These transits revealed the companion’s size and orbital period, but not its mass directly. Astronomers therefore observed its star with the PST1 telescope. They obtained 24 high-resolution spectra, which make it possible to measure tiny variations in the star’s speed.

To understand why, a planet does not orbit a perfectly stationary star. The two bodies revolve around a shared center of mass. The star therefore performs a small back-and-forth motion. This movement slightly alters the light received on Earth, making it possible to estimate the companion’s mass.

The new measurements indicate approximately 12.0 Jupiter masses, with an uncertainty of 1.0 Jupiter mass. This value places the object among the most massive giant planets. Its very short orbit also classifies it as a “hot Jupiter,” a gas giant located very close to its star.

The distance between TOI-7475.01 and its star is small on the scale of a planetary system. Such proximity explains its 3.25-day revolution. For comparison, Jupiter takes nearly twelve Earth years to complete one orbit around the Sun.

Another distinctive feature appears in the measurements: the orbit is not perfectly circular. Its eccentricity is approximately 0.16. This means that the distance separating the planet from its star varies noticeably during each revolution, unlike an almost circular trajectory.

This shape interests researchers because the gravitational interactions between a nearby giant planet and its star tend, over time, to make the orbit more circular. The authors therefore suggest that an orbit that is still elliptical could be consistent with a relatively young system. However, this interpretation requires additional observations.

Spectroscopic monitoring thus provides a measurement that was missing from TESS’s initial observations: the companion’s mass. Further measurements will now make it possible to determine the system’s age more precisely and test the evolution of this very close orbit.