Detection and Characterization of the Temperate Super-Earth Ross 318 b

TL;DR

This study confirms the existence of a temperate super-Earth, Ross 318 b, orbiting an active M-dwarf, characterized its orbit and mass, and rules out transits, highlighting its potential habitability.

Contribution

It provides a comprehensive re-analysis combining radial velocities and TESS photometry to characterize Ross 318 b and assess its transiting potential.

Findings

Ross 318 b has a 39.63-day orbit with a minimum mass of 6.21 Earth masses.

No transits detected, ruling out a high-confidence transiting configuration.

Ross 318 b resides within the habitable zone of its star.

Abstract

Ross~318 is an M3.5V red dwarf exhibiting significant magnetic activity and a stellar rotation period of $\sim51.5$\,d. In this work we present a systematic re-analysis of radial velocities (RV) from CARMENES and decade-long HIRES observations, integrated with TESS space-based photometry. We identify a terrestrial-mass planet, Ross~318\,b, with an orbital period $P = (39.6299 \pm 0.29)$\,d and a minimum mass $M\sin i = (6.21 \pm 0.62)M_{\oplus}$. The dynamical nature of the signal is confirmed by its temporal coherence over a 15-year baseline and its achromaticity between visible and near-infrared channels. TESS photometry from Sectors 18, 19, 24, and 25 (218.6\,d total baseline, 66\,983 cadences) reveals no transit at $P = 39.63$\,d (FAP $> 10\%$, BLS). An injection-and-recovery test demonstrates that a $2200$\,ppm transit signal corresponding to a $1.74R_{\oplus}$ body would have been detected with Signal-to-Pink-Noise Ratio SPNR $> 12$, ruling out a transiting geometry with high confidence. The orbital inclination is constrained to $i < 88.5^\circ$. With an incident stellar flux $S_{eff} \approx 0.58\,S_\oplus$ and bolometric luminosity $L_* = (0.01478 \pm 0.00122)L_{\odot}$, Ross~318\,b falls within the Conservative Habitable Zone, making it one of the most interesting temperate Super-Earths orbiting an M-dwarf.