TOI-561: A Sun-Like Star and Its Four Known Planets

TOI-561 is a star 280 light-years from Earth. It is a G9 V main-sequence star, a class that includes the Sun. Its mass is 0.806 solar masses, its radius is 0.843 solar radii, and its temperature is 5370 K, all smaller or cooler than the Sun's corresponding values. Its age is 11 billion years. Four planets have been reported orbiting this star, all discovered in 2020 by the transit method.

TOI-561 b is classified as Earth-like, with a radius of 1.4 Earth radii and a mass of 2.02 Earth masses. It completes an orbit in 0.447 days. Among the listed planets, it has the shortest orbital period by reported estimates, the smallest radius, and the smallest reported mass. Its mean density is 4.08 g/cm³, 0.741 times Earth's.

The remaining planets are all Neptune-like. TOI-561 c has a radius of 2.87 Earth radii and a mass of 5.93 Earth masses, orbiting every 10.8 days. Among the listed planets, it has the second-shortest year, the largest radius, and the second-smallest reported mass. Its mean density is 1.39 g/cm³, 0.252 times Earth's.

TOI-561 d has a radius of 2.62 Earth radii and a mass of 13.3 Earth masses, with a period of 25.7 days. Among the listed planets, it has the second-longest year, the second-largest radius, and the largest reported mass. Its mean density is 4.11 g/cm³, 0.745 times Earth's.

TOI-561 e has a radius of 2.52 Earth radii and a mass of 12.4 Earth masses, completing an orbit in 77.1 days. Among the listed planets, it has the longest year, the second-smallest radius, and the second-largest reported mass. Its mean density is 4.28 g/cm³, 0.778 times Earth's.

Every reported planetary radius and mass at TOI-561 is larger than Earth's.