HATS-18: A Sun-Like Star and Its Close-Orbiting Giant

HATS-18 is a G V star located 2040 light-years away. Its spectral type marks it as a main-sequence dwarf of the same temperature class as the Sun, and its measured temperature of 5600 K is cooler than the Sun's. The star has a mass of 1.04 solar masses, a radius of 1.02 solar radii, and an age of 4.2 billion years. One planet is known to orbit this host.

That planet, HATS-18 b, was discovered by the transit method in 2016. A transit occurs when a planet crosses in front of its star from our viewpoint and causes a small dip in observed brightness; repeated dips help establish orbital periods. HATS-18 b completes one orbit in 0.838 days. Its mean density is 1.05 g/cm³, 0.19 times Earth's. The planet is classified as Jupiter-like, a size class that exceeds 4 times Earth's radius, and its radius of 14.9 Earth radii is larger than Earth's. Its mass of 629 Earth masses is also larger than Earth's, and is roughly 1.98 times Jupiter's mass.