The Habitable-zone Planet Finder Detects a Terrestrial-mass Planet Candidate Closely Orbiting Gliese 1151: The Likely Source of Coherent Low-frequency Radio Emission from an Inactive Star

The coherent low-frequency radio emission detected by LOFAR from Gliese 1151, a quiescent M4.5 dwarf star, has radio emission properties consistent with theoretical expectations of star–planet interactions for an Earth-sized planet on a 1- to 5-day orbit. New near-infrared radial velocities from the Habitable-zone Planet Finder (HPF) spectrometer on the 10 m Hobby–Eberly Telescope at McDonald Observatory, combined with previous velocities from HARPS-N, reveal a periodic Doppler signature consistent with an $m\sin i=2.5\pm 0.5M_{\oplus }$ exoplanet on a 2.02-day orbit. Precise photometry from the Transiting Exoplanet Survey Satellite (TESS) shows no flares or activity signature, consistent with a quiescent M dwarf. While no planetary transit is detected in the TESS data, a weak photometric modulation is detectable in the photometry at a ∼2-day period. This independent detection of a candidate planet signal with the Doppler radial velocity technique adds further weight to the claim of the first detection of star–exoplanet interactions at radio wavelengths and helps validate this emerging technique for the detection of exoplanets.