TOI-5789: A K-Type Dwarf with Four Known Planets

TOI-5789 is a K1 V star located 66.7 light-years away, with four planets in orbit around it. The star is a main-sequence dwarf of the cooler K class, with a reported age of 9.4 billion years. Its mass is 0.821 solar masses, its radius is 0.833 solar radii, and its effective temperature is 5190 K. Each of these stellar values is smaller or cooler than the corresponding value for the Sun.

TOI-5789 b was discovered by the radial velocity method. Its minimum mass is 2.12 Earth masses, larger than Earth's, and its orbital period is 2.76 days, the shortest among the listed planets. TOI-5789 c is a Neptune-like planet, with a reported mass of 5 Earth masses and a radius of 2.86 Earth radii. Its mass and radius are both larger than Earth's, and its mean density is 1.18 g/cm³, 0.214 times Earth's. It completes an orbit in 12.9 days, the second-shortest period among the listed planets. TOI-5789 d has a minimum mass of 4.29 Earth masses, also larger than Earth's, and an orbital period of 29.7 days, the second-longest among the listed planets. TOI-5789 e has a minimum mass of 11.6 Earth masses, larger than Earth's, and its orbital period of 63 days is the longest among the listed planets. Planets b, d, and e were each identified through the radial velocity method, which detects a star's wobble caused by an orbiting planet's gravity; repeated wobbles reveal the planet and its orbital period. Planet c was found by the transit method, in which a planet passing in front of its star causes a small dip in observed brightness. All four planets were discovered in 2026.