GJ 3929 and Its Two Known Planets

GJ 3929 is an M3.5 V star, a small, cool red dwarf, located 51.6 light-years away. Its spectral type places it among the cooler, redder stars, and it is estimated to be 7.1 billion years old. The star's mass is 0.313 solar masses and its radius is 0.32 solar radii, both smaller than the Sun's, and its temperature of 3380 K is cooler than the Sun's. Two planets are known to orbit this host.

GJ 3929 b was discovered in 2022 by the transit method, which detects the small dip in a star's brightness when a planet passes in front of it. This Earth-like planet has a mass of 1.75 Earth masses and a radius of 1.09 Earth radii, both larger than Earth's. Its mean density is 7.45 g/cm³, 1.35 times Earth's. It completes an orbit every 2.62 days, the shortest year among the listed planets.

GJ 3929 c was also discovered in 2022, using the radial velocity method, which measures the wobble a planet's gravity induces in its star's motion. Its minimum mass is 5.71 Earth masses, a lower bound on its true mass, and it is larger than Earth in this respect. Its orbital period is 15 days, the longest year among the listed planets.