HD 219134 d is a planet whose mass depends on whom you ask. It orbits HD 219134, an orange dwarf star about 21 light-years away, every 46.7 days, and was found in 2015 by two teams independently, both measuring the slight back-and-forth motion its gravity gives the star.
A team led by Fatemeh Motalebi, using the HARPS-N spectrograph in the Canary Islands, reported it with a minimum mass of about 8.7 Earth masses on a noticeably oval orbit. They noted that its period is close to the star's rotation period of about 42 days, which can produce false planet signals, but found no matching variation in the star's activity and so favoured a planet. A team led by Steven Vogt, using the Keck and Automated Planet Finder telescopes, found the same 46.7-day period with a minimum mass of about 21 Earth masses. The NASA Exoplanet Archive currently lists about 16 Earth masses. Because the planet has not been seen crossing its star, its size is unknown; the archive's radius is an estimate.
It is the outermost of the system's inner group: HD 219134 b and c, which do transit, orbit in under a week, and HD 219134 f lies between them and d. According to the archive, HD 219134 d receives nearly five times the light Earth gets from the Sun, so it is too hot for liquid water. A 2026 study of the star, which reconstructed how its X-ray output changed over its roughly nine-billion-year life, found that the innermost planets were probably stripped of their original gas early on, while HD 219134 d experienced only moderate erosion.