HD 89345 b

HD 89345 b
	Image from 2MASS Two Micron All-Sky Survey
Orbital characteristics
Semi-major axis	0.1086 AU
Eccentricity	0.25°
Orbital period (sidereal)	11.8143 day
Inclination	87.7°
Physical characteristics
Mean radius	0.616 RJ
Mass	0.103 MJ
Temperature	1059 K

HD 89345 b is a Neptune-like exoplanet that orbits a G-type star. It is also called K2-234b. Its mass is equivalent to 35.7 Earths, it takes 11.8 days to complete one orbit of its star, and is 0.105 AU away from its star. It was discovered by a team of 43 astrophysicists, one of which was V. Van Eylen, and was announced in 2018.^[1]

Overview

The exoplanet HD 89345 b, which has a mass of 0.1 M_J and a radius of 0.61 R_J, was assigned to the class of ocean planets. The parent star of the planet, which is about 5.3 billion years old, belongs to the spectral class of G5V-G6V. It is 66 percent larger and 22 percent more massive than the Sun, and is located 413 light-years away. The effective temperature of the star is 5609 K. Considering that HD 89345 b makes one revolution around the star in 11.8 days at a distance of 0.11 AU, this planet was described by researchers as a warm subterranean with an equilibrium temperature of 1059 K.^[2]

Discovery

HD 89345 b, a Saturn-sized exoplanet orbiting a slightly evolved star HD 89345, was discovered in 2018 using the transit photometry method, the process that detects distant planets by measuring the minute dimming of a star as an orbiting planet passes between it and the Earth. It is the only planet orbiting around HD 89345, a G5 class star, situated in the constellation of Leo in 413 light-years from the Sun. This star is aged 9.4 billion years. HD 89345 b orbits its star in about 12 terrestrial days in an elliptical orbit. The orbit is closer to the star than the inner limit of the habitable zone. It has a low density and can be composed of gas.

Its parent star, HD 89345, is a bright star (apparent magnitude 9.3) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. The data is collected by asteroseismology, which enables to determine the parameters of the star and find its mass and radius. Its mass is 1.12^+0.04
_−0.01 M_☉ and its mean radius is 1.657^+0.020
_−0.004 R_☉. The star appears to have recently left the main sequence, based on the inferred age, 9.4^+0.4
_−1.3 Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" with an orbital period of approximately 11.8 days and a radius of 6.86±0.14 R_🜨. Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7±3.3 M_🜨. The data also show that the planet's orbit is eccentric ( $e\thickapprox 0.2$ ).^[3]^[4]