Two Sub-Earths Around the K-Type Dwarf HIP 56998

HIP 56998 is a K4/5V star 41.7 light-years away, a main-sequence dwarf whose leading letter and number place it in the cooler, redder part of the temperature sequence running from M through K, G, F, and A. Its reported mass estimate is 0.653 solar masses, its radius estimate is 0.63 solar radii, and its temperature is 4680 K; each of these figures is smaller or cooler than the Sun's corresponding value. The star is 6.88 billion years old. Two planets are known to orbit this host.

HD 101581 b and HD 101581 c were both discovered in 2025 by the transit method, in which a planet passes in front of its star from our viewpoint and produces a small dip in observed brightness. Both are Sub-Earths, meaning their radii fall below Earth's. HD 101581 b completes an orbit in 4.47 days and has a radius of 0.956 Earth radii. HD 101581 c has an orbital period of 6.2 days and a radius of 0.99 Earth radii. Among the listed planets, HD 101581 b has the shortest year by reported estimates, at 4.47 days, and the smallest radius by reported estimates, at 0.956 Earth radii, while HD 101581 c has the longest year by reported estimates, at 6.2 days, and the largest radius by reported estimates, at 0.99 Earth radii.