GJ 3138 is a cool M-dwarf (about 0.68 solar masses, 3,717 K, 0.50 solar radii), 28.5 light-years from Earth. GJ 3138 b is a 1.8-Earth-mass planet, with an orbital period of 1.2 days, at 0.020 AU from its star, on an eccentric orbit (e ≈ 0.19), discovered in 2017 via radial velocity. GJ 3138 c is a 4.2-Earth-mass planet, with an orbital period of 6.0 days, at 0.057 AU from its star, on an eccentric orbit (e ≈ 0.11), discovered in 2017 via radial velocity.