AU Mic: A Young Red Dwarf and Its Four Worlds

AU Mic is an M1 V star, a small, cool red dwarf, located 31.7 light-years away. It is extremely young, with an age of 0.019 billion years, placing it well under the 0.1-billion-year threshold that marks a very young star. The star has a mass of 0.635 solar masses, smaller than the Sun's, and a radius of 0.862 solar radii, also smaller than the Sun's. Its temperature of 3540 K is cooler than the Sun's. Four planets are known to orbit this host.

AU Mic b is a Jupiter-like planet discovered by transit in 2020. It has a mass of 8.99 Earth masses, larger than Earth's, and a radius of 4.79 Earth radii, also larger than Earth's. Its mean density is 0.451 g/cm³, 0.0818 times Earth's. It completes an orbit in 8.46 days, the shortest year among the listed planets.

AU Mic c is Neptune-like, discovered by transit in 2021. Its mass is 14.5 Earth masses, larger than Earth's, and its radius is 2.79 Earth radii, larger than Earth's. Its mean density is 3.67 g/cm³, 0.666 times Earth's. It orbits once every 18.9 days, the second-longest year among the listed planets. Among the listed planets, AU Mic c has the second-largest reported mass at 14.5 Earth masses.

AU Mic d was discovered in 2023 through transit timing variations. It has a mass of 1.05 Earth masses, the smallest reported mass among the listed planets, and an orbital period of 12.7 days, the second-shortest year among the listed planets.

AU Mic e was discovered in 2025 by radial velocity, a method that measures the wobble a planet's gravity induces in its star's motion. It has a mass of 21.1 Earth masses, larger than Earth's and the largest reported mass among the listed planets. Its orbital period is 33.1 days, the longest year among the listed planets.