Tau Ceti and Its Three Known Planets

Tau Ceti is a G8.5V star located 11.8 light-years from Earth, with three planets. The star has a mass of 0.8 solar masses, a radius of 0.83 solar radii, and a temperature of 5280 K. Its reported mass estimate is smaller than the Sun's, its reported radius estimate is smaller than the Sun's, and its reported temperature is cooler than the Sun's. Its spectral type indicates a main-sequence dwarf.

The three planets - tau Cet f, tau Cet g, and tau Cet h - were all discovered in 2017 using the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion. Each has a minimum mass larger than Earth's, and minimum mass is a lower bound on a planet's true mass, not an exact figure.

Tau Cet g has the shortest year among the listed planets at 20 days and the smallest minimum mass at 1.75 Earth masses. Tau Cet h orbits in 49.4 days, the second-shortest period among the three, with a minimum mass of 1.83 Earth masses, the second-smallest. Tau Cet f has the longest year at 636 days and the largest minimum mass at 3.93 Earth masses.

The radial wobbles that revealed these planets repeat at intervals of 20, 49.4, and 636 days, corresponding to each world's orbital period.