The Impact of Stellar Rotation on the Detectability of Habitable Planets Around M Dwarfs

TL;DR

Stellar rotation and activity significantly hinder the detection of habitable exoplanets around M dwarfs using radial velocity methods, especially for early M dwarfs with rotation periods similar to habitable zone orbital periods.

Contribution

This study compiles rotation data for late-type stars and M dwarf planet hosts to identify how stellar rotation affects habitable planet detectability across different M dwarf masses.

Findings

Rotation periods of 0.25-0.5 solar mass stars match habitable zone orbital periods, complicating detection.

Mid M dwarfs with longer rotation periods and shorter habitable zone periods are more favorable for detection.

Early M dwarfs pose a fundamental challenge due to overlapping stellar rotation and planetary orbital periods.

Abstract

Stellar activity and rotation frustrate the detection of exoplanets through the radial velocity technique. This effect is particularly of concern for M dwarfs, which can remain magnetically active for billions of years. We compile rotation periods for late-type stars and for the M dwarf planet-host sample in order to investigate the rotation periods of older field stars across the main sequence. We show that for stars with masses between 0.25 and 0.5 solar masses (M4V to M1V), the stellar rotation period typical of field stars coincides with the orbital periods of planets in the habitable zone. This will pose a fundamental challenge to the discovery and characterization of potentially habitable planets around early M dwarfs. Due to the longer rotation periods reached by mid M dwarfs and the shorter orbital period at which the planetary habitable zone is found, stars with masses between 0.1 and 0.25 solar masses (M6V to M4V) offer better opportunities for the detection of habitable planets via radial velocities.