TOI-4138 b

TOI-4138 b is a transiting exoplanet orbiting the G-type subgiant TOI-4138 1,674 light years away in the northern circumpolar constellation Ursa Minor.

TOI-4138 b

TOI-4138 b compared to Jupiter
Discovery[1]
Discovered by	Montalto et al.
Discovery site	TESS
Discovery date	13 October 2021
Detection method	Transit
Orbital characteristics[1]
Periastron	0.049 AU (7,300,000 km)
Apoastron	0.052 AU (7,800,000 km)
Semi-major axis	0.051 ± 0.002 AU (7,630,000 ± 300,000 km)
Eccentricity	0.03 ± 0.02
Orbital period (sidereal)	3.660028 ± 0.000006 d
Inclination	86.0°±0.7°
Time of periastron	2,458,708.9983 ± 0.0003 JD
Semi-amplitude	74±3 m/s
Star	TOI-4138
Physical characteristics[1]
Mean radius	1.49 ± 0.04 RJ
Mass	0.67 ± 0.03 MJ
Mean density	0.250 ± 0.020 g/cm3[citation needed]
Temperature	1,762 ± 21 K (2,711.9 ± 37.8 °F; 1,488.8 ± 21.0 °C)

Discovery

The planet was discovered by TESS using the transit method, which involves measuring light curves during a planet’s eclipse. The paper states that it’s inflated due to heating from its host star, which has a high luminosity.^[2] Its discovery was announced in October 2021.

Properties

Orbit and mass

TOI-4138 b has an orbital period of 3.6 days, typical for a hot Jupiter. This corresponds to a separation from its host close to one eighth of the distance of Mercury from the Sun. Since the inclination is known, doppler spectroscopy measurements give the planet a mass only 67% that of Jupiter.^[1] Its separation is comparable with HD 209458 b, but is much larger due to the evolved state of the host star.^[1]

Radius and density

TOI-4138 b’s transit gives it a radius 1.49 times that of Jupiter; this combined with its low mass of 0.67 M_J gives it a density only 25% that of water.^[1]

Host star

TOI-4138 b orbits TOI-4138, a subgiant star^[1] located in the constellation Ursa Minor. The star has an enlarged radius of 1.82 R_☉, a luminosity of 4.37 L_☉ and an effective temperature of 6,128 K (5,855 °C).^[1] It has 1.32 times the Sun's mass, and it has an intermediate age of around 3.5 billion years.^[1] The apparent magnitude of the star is 11.8, making it not visible to the naked eye.^[3]