K2-141 b: A 5-M$_\oplus$ super-Earth transiting a K7 V star every 6.7 hours

TL;DR

K2-141 b is a newly discovered ultra-short-period super-Earth with a 6.7-hour orbit, confirmed through multiple observations, and characterized as a dense, rocky-iron planet, making it the shortest-period planet with a precisely measured mass.

Contribution

This paper reports the discovery and precise mass measurement of K2-141 b, the shortest-period super-Earth known, using combined photometric and spectroscopic follow-up observations.

Findings

K2-141 b has a mass of 5.31 ± 0.46 M⊕ and radius of 1.54 R⊕.

It has a high density of approximately 8 g/cm³, indicating a rocky-iron composition.

The planet's orbital period is only 6.7 hours, the shortest for a planet with a well-measured mass.

Abstract

We report on the discovery of K2-141 b (EPIC 246393474 b), an ultra-short-period super-Earth on a 6.7-hour orbit transiting an active K7 V star based on data from K2 campaign 12. 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 \pm 0.46 $ $M_{\oplus}$ and radius of $1.54^{+0.10}_{-0.09}$ $R_{\oplus}$, yielding a mean density of $8.00_{ - 1.45 } ^ { + 1.83 }$ $\mathrm{g\,cm^{-3}}$ and suggesting a rocky-iron composition. Models indicate that iron cannot exceed $\sim$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.