Discovery of a Nearby Habitable Zone Super-Earth Candidate Amenable to Direct Imaging

TL;DR

This paper reports the discovery and characterization of a super-Earth candidate in the habitable zone of the nearby star GJ 251, highlighting its potential for future direct imaging with next-generation telescopes.

Contribution

It provides improved parameters for the known planet GJ 251 b and constrains the minimum mass of the new candidate GJ 251 c using multiple high-precision RV datasets and activity mitigation techniques.

Findings

GJ 251 c is a plausible terrestrial super-Earth in the habitable zone.

GJ 251 b's parameters are refined with high-precision RV data.

GJ 251 c is a prime target for future direct imaging efforts.

Abstract

We present the discovery of GJ 251 c, a candidate super-Earth orbiting in the Habitable Zone (HZ) of its M dwarf host star. Using high-precision Habitable-zone Planet Finder (HPF) and NEID RVs, in conjunction with archival RVs from the Keck I High Resolution Echelle Spectrometer (HIRES), the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrograph (CARMENES), and the SPectropolarim\`etre InfraROUge (SPIRou), we improve the measured parameters of the known planet, GJ 251 b ($P_{b}$ = 14.2370 days; $m \sin(i)$ = 3.85$^{+0.35}_{-0.33}$ M$_{\oplus}$), and we significantly constrain the minimum mass of GJ 251 c, placing it in a plausibly terrestrial regime (P$_{c}$ = 53.647 $\pm$ 0.044 days; $ m \sin i_{c}$ = 3.84 $\pm$ 0.75 M$_{\oplus}$). Using activity mitigation techniques that leverage chromatic information content, we perform a color-dependent analysis of the system and a detailed comparison of more than 50 models that describe the nature of the planets and stellar activity in the system. Due to GJ 251's proximity to Earth (5.5 pc), next generation, thirty meter class telescopes will likely be able to image terrestrial planets in GJ 251's HZ. In fact, GJ 251 c is currently the best candidate for terrestrial, HZ planet imaging in the Northern Sky.