TOI-1266: A Cool Red Dwarf with Three Known Worlds

TOI-1266 is a red dwarf star of spectral type M2, sitting 117 light-years from us. It is a small, cool star: 0.437 solar masses and 0.423 solar radii, with a temperature of 3560 K, all below the Sun's corresponding values, and an age of 4.6 billion years. Three planets are known to orbit this star: TOI-1266 b and TOI-1266 c were both detected by the transit method, in which a planet passing in front of its star produces a small dip in observed brightness, and TOI-1266 d was detected through transit timing variations.

TOI-1266 b was announced in 2020. It is a Neptune-like planet with a radius of 2.52 Earth radii and a mass of 4.46 Earth masses, both larger than Earth's, and a mean density of 1.54 g/cm³, 0.279 times Earth's. It completes one orbit every 10.9 days, the shortest orbital period among the listed planets.

TOI-1266 c, also announced in 2020, is a Super-Earth with a radius of 1.98 Earth radii and a mass of 3.17 Earth masses, again both larger than Earth's. Its mean density is 2.25 g/cm³, 0.408 times Earth's, and it orbits once every 18.8 days, the second-shortest orbital period among the listed planets. It also has the smallest reported mass of the three.

TOI-1266 d was announced in 2025 after being found through transit timing variations, the slight shifts in the timing of the other planets' transits. It has a mass of 3.68 Earth masses, larger than Earth's and the second-smallest reported mass among the listed planets, and it orbits every 32.5 days, the longest orbital period among the listed planets.

The two 2020 discoveries orbit in 10.9 and 18.8 days, while the 2025 planet takes 32.5 days, giving the system a spread of orbital periods. TOI-1266 b's radius of 2.52 Earth radii is the largest of the trio, just above the Super-Earth limit and into Neptune-like territory. The star's mass of 0.437 solar masses and radius of 0.423 solar radii are both smaller than the Sun's, and its temperature of 3560 K is cooler. TOI-1266 d takes 32.5 days to complete one orbit.