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.^{[3][note 1]} It orbits its host star at a distance of 0.0888 astronomical units (13,280,000 km), completing one orbit every 7 days around it.^[2] With a density of 14.1 g/cm³ (about 2.5 times that of Earth), it is one of the densest exoplanets known.^[2] 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.^[2]

Quick Facts Discovery, Discovered by ...

TOI-4603 b

Discovery
Discovered by	Khandelwal et al.[1]
Discovery site	India
Discovery date	2023
Detection method	Transit
Orbital characteristics
Semi-major axis	0.0888±0.001 AU[2]
Eccentricity	0.325±0.02[2]
Orbital period (sidereal)	7.246[2] d
Inclination	80.21°[2]
Star	HD 245134 (TOI-4603)
Physical characteristics
Mean radius	1.042+0.035 −0.038 RJ[2]
Mass	12.89+0.57 −0.58 MJ[2]
Mean density	14.1+1.6 −1.7 g/cm3[2]
Temperature	1,677±24 K (1404 °C)[2]

Close

TOI-4603 b is similar to the planet Jupiter in size, being only 4% larger.^[2] Radial velocity measurements calculated the planet's mass to be 12.89+0.58
−0.57 M_J^[4] meaning that the object is close to the mass limit between planets and brown dwarfs, which is usually set at 13 M_J.^[2] Its equilibrium temperature is calculated at 1,677 K (1,404 °C).^[2]

TOI-4603 b orbits its star at a distance of 0.0888 astronomical units (13,280,000 km), and completes one orbit every 7 days and 6 hours.^[2] 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.^[2] Kervella et al. (2019) found that a brown dwarf with a mass of 20.5 M_J is orbiting the system at a distance of around 1.8 AU, which may be influencing TOI-4603 b's orbit.^[2]

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.^[4]

NASA's Transiting Exoplanet Survey Satellite observed the host star TOI-4603 between September 16, 2021, and December 2, 2021.^[2] 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^{[note 3]} spectrographs confirmed the transit signal to be an exoplanet orbiting the star.^[6]

It was the third exoplanet discovered by Indian astronomers, using the PARAS spectrograph and the PRL 1.2 m telescope.^[7] The discovery was announced in 2023.^[8]

HD 245134 (TOI-4603) is a F-type subgiant located 736 light-years away in the constellation of Taurus.^{[1] [note 1]} It is well suited for the study of the Rossiter–McLaughlin effect and helpful for measuring the projected stellar obliquity of planets.^[2] The star has an apparent magnitude of 9.2, being too faint to be seen with the naked eye.^[1] It is a metal-rich star, with abundance of iron 2.2 times greater than that of the Sun.^[2]