The HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone

TL;DR

This study reports the discovery of at least three planets orbiting the nearby M dwarf GJ163, including a super-Earth potentially in the habitable zone, using eight years of radial velocity data from the HARPS spectrograph.

Contribution

It provides the first detailed detection and characterization of multiple planets around GJ163, including a super-Earth possibly in the habitable zone, based on long-term radial velocity monitoring.

Findings

Detected three planets with periods of 8.6, 25.6, and 604 days.

Identified a super-Earth in the habitable zone with a temperature around 302K.

System's inner planets are outside the 3:1 mean motion resonance.

Abstract

The meter-per-second precision achieved by today velocimeters enables the search for 1-10 M_Earth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting GJ163 (HIP19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ163 over a period of 8 years. We searched the RV time series for coherent signals and found 5 distinct periodic variabilities. We investigated the stellar activity and casted doubts on the planetary interpretation for 2 signals. Before more data can be acquired we concluded that at least 3 planets are orbiting GJ163. They have orbital periods of P_b=8.632+-0.002, P_c=25.63+-0.03 and P_d=604+-8 days and minimum masses msini = 10.6+-0.6, 6.8+-0.9, and 29+-3 M_Earth, respectively. We hold our interpretations for the 2 additional signals with periods P_(e)=19.4 and P_(f)=108 days. The inner pair presents an orbital period ratio of 2.97, but a dynamical analysis of the system shows that it lays outside the 3:1 mean motion resonance. GJ163c, in particular, is a super-Earth with an equilibrium temperature of T_eq = (302+-10) (1-A)^(1/4) K and may lie in the so called habitable zone for albedo values (A=0.34-0.89) moderately higher than that of Earth (A_Earth=0.2-0.3).