K2-141 b radial velocity and light curve

We confirmed the planet's existence and measured its mass with a series of follow-up observations: seeing-limited MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS high-precision radial-velocity monitoring. K2-141 b has a mass of 5.31+/-0.46M_{Earth}_ and radius of 1.54+0.10-0.09R_{Earth}_, yielding a mean density of 8.00^+1.83^_-1.45_g/cm^3^ and suggesting a rocky-iron composition.

Models indicate that iron cannot exceed ~70% of the total mass. With an orbital period of only 6.7 hours, K2-141 b is the shortest-period planet known to date with a precisely determined mass.