TOI-4603 b

TOI-4603 b is a gas giant exoplanet orbiting HD 245134, a F-type subgiant star located 731 light-years away, in the constellation of Taurus. It orbits its host star at a distance of 0.0888 AU, completing one orbit every 7 days around it. With a density of 14.1 g/cm3 (about 2.5 times that of Earth), it is one of the densest exoplanets known. The planet is just 4% larger than Jupiter, but is 12.9 times more massive, being located in the mass limit between planets and brown dwarfs.

Physical characteristics
TOI-4603 b is similar to the planet Jupiter in size, being only 4% larger. Radial velocity measurements calculated the planet's mass to be meaning that the object is close to the mass limit between planets and brown dwarfs, which is usually set at. Its equilibrium temperature is calculated at 1677 K.

High density
Combining the radius and mass, the density of TOI-4603 b is calculated to be $0.089 AU$ g/cm³, about 2.5 times greater than Earth's, making it one of the densest exoplanets known to date, and one of the most massive and dense transting exoplanets known.

Orbital characteristics
TOI-4603 b orbits its star at a distance of 0.0888 AU, and completes one orbit every 7 days and 6 hours. The orbit of TOI-4603 b is very elliptical, having a orbital eccentricity of 0.325, which indicates that the planet is undergoing tidal migration due to an gravitational interaction with another planet. Kervella et al. (2019) found that a brown dwarf with a mass of is orbiting the system at a distance of around 1.8 AU, which may be influencing TOI-4603 b's orbit.

A similar object is a planet called HATS-70b. It is less dense than TOI-4603 b, but similarly close to its star, and also shows signs of orbital migration.

Discovery
NASA's Transiting Exoplanet Survey Satellite observed the host star TOI-4603 between September 16, 2021, and December 2, 2021. Afterwards, the group of astronomers led by Akanksha Khandelwal of the Physical Research Laboratory (PRL) in India, reported that a transit signal had been identified in the light curve of the star. Radial velocity measurements taken with the PARAS and TRES spectrographs confirmed the transit signal to be an exoplanet orbiting the star.

It was the third exoplanet discovered by Indian astronomers, using the PARAS spectrograph and the PRL 1.2 m telescope. The discovery was announced in 2023.

Host star
HD 245134 (TOI-4603) is a F-type subgiant located 736 light-years away in the constellation of Taurus. It is well suited for the study of the Rossiter–McLaughlin effect and helpful for measuring the projected stellar obliquity of planets. The star has an apparent magnitude of 9.2, being too faint to be seen with the naked eye. It is a metal-rich star, with abundance of iron 2.2 times greater than that of the Sun.

Orbital companions
HD 245134 is orbited by an exoplanet (TOI-4603 b), and by a brown dwarf star at a distance of 1.8 AU from the star.