TOI-178: A K-Type Star and Its Six Worlds

TOI-178 is a K-type star 204 light-years away. Its reported mass estimate is 0.65 solar masses, its radius estimate is 0.651 solar radii, and its temperature is 4320 K - all smaller or cooler than the Sun's corresponding values. The star's age is 7.1 billion years. Six planets are known to orbit this host, all discovered by transit in 2021.

TOI-178 b is Earth-like, with a radius of 1.2 Earth radii and a mass of 0.96 Earth masses. Its year lasts 1.91 days, and its mean density is 3.06 g/cm³, 0.556 times Earth's. Among the listed planets, it has the shortest year and the smallest radius and reported mass.

TOI-178 c is a Super-Earth with a radius of 1.75 Earth radii and a mass of 4.64 Earth masses. Its year is 3.24 days, and its mean density is 4.74 g/cm³, 0.86 times Earth's. Among the listed planets, it has the second-shortest year and the second-smallest radius.

TOI-178 d, a Neptune-like planet, has a radius of 2.7 Earth radii and a mass of 5.2 Earth masses. It completes an orbit in 6.56 days, and its mean density is 1.46 g/cm³, 0.266 times Earth's. Among the listed planets, it has the second-largest radius and the second-largest reported mass.

TOI-178 e is a Super-Earth with a radius of 2.3 Earth radii and a mass of 3.48 Earth masses. Its year is 9.96 days, and its mean density is 1.57 g/cm³, 0.286 times Earth's. Among the listed planets, it has the second-smallest reported mass.

TOI-178 f, another Super-Earth, has a radius of 2.42 Earth radii and a mass of 5.63 Earth masses. Its orbital period is 15.2 days, and its mean density is 2.2 g/cm³, 0.399 times Earth's. Among the listed planets, it has the second-longest year and the largest reported mass.

TOI-178 g is Neptune-like, with a radius of 2.94 Earth radii and a mass of 4.4 Earth masses. Its year lasts 20.7 days, and its mean density is 0.955 g/cm³, 0.173 times Earth's. Among the listed planets, it has the longest year and the largest radius.