GJ 357 d: Potentially Habitable World or Agent of Chaos?

TL;DR

This study investigates the GJ 357 planetary system, revealing that the outer planet d likely causes orbital instability in the habitable zone, impacting the potential for habitability of other planets.

Contribution

The paper combines photometric analysis and dynamical simulations to assess the stability of habitable zone planets in the GJ 357 system, highlighting the destabilizing influence of planet d.

Findings

Planets c and d do not transit the star, implying higher masses.

Planet d likely causes orbital instability for Earth-mass planets in the HZ.

Small eccentricities of planet d significantly destabilize the HZ.

Abstract

Multi-planet systems provide important laboratories for exploring dynamical interactions within the range of known exoplanetary system architectures. One such system is GJ 357, consisting of a low-mass host star and three orbiting planets, the outermost (planet d) of which does not transit but lies within the Habitable Zone (HZ) of the host star. The minimum mass of planet d causes its nature to be unknown, both in terms of whether it is truly terrestrial and if it is a candidate for harboring surface liquid water. Here, we use three sectors of photometry from the Transiting Exoplanet Survey Satellite (TESS) to show that planets c and d do not transit the host star, and therefore may have masses higher than the derived minimum masses. We present the results for a suite of dynamical simulations that inject an Earth-mass planet within the HZ of the system for three different orbital and mass configurations of planet d. These results show that planet d, rather than being a potentially habitable planet, is likely a source of significant orbital instability for other potential terrestrial planets within the HZ. We find that relatively small eccentricities of planet d cause a majority of the HZ to be unstable for an Earth-mass planet. These results highlight the importance of dynamical stability for systems that are prioritized in the context of planetary habitability.