Kepler-139 is a Sun-like G-type star (about 1.08 solar masses, 5,630 K, 1.04 solar radii), 391 light-years from Earth. The system hosts 4 confirmed planets on orbits ranging from 7.3 days to 355 days. With 4 confirmed worlds, Kepler-139 is a densely packed system whose resonances, spacing, and formation history are active research topics. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly. Kepler-139 d orbits well inside Earth's distance from the Sun. At 1.7 Earth radii, Kepler-139 d is a compact world comparable in size to rocky planets in our Solar System.