Red Dots: A temperate 1.5 Earth-mass planet in a compact multi-terrestrial planet system around GJ1061 (1908.04717v1)

Abstract: Small low-mass stars are favourable targets for the detection of rocky habitable planets. In particular, planetary systems in the solar neighbourhood are interesting and suitable for precise characterisation. The Red Dots campaigns seek to discover rocky planets orbiting nearby low-mass stars. The 2018 campaign targeted GJ 1061, which is the 20$^{\rm th}$ nearest star to the Sun. For three consecutive months we obtained nightly, high-precision radial velocity measurements with the HARPS spectrograph. We analysed these data together with archival HARPS data. We report the detection of three planet candidates with periods of $3.204\pm 0.001$, $6.689\pm 0.005$ and $13.03\pm 0.03$ days, which is close to 1:2:4 period commensurability. After several considerations related to the properties of the noise and sampling, we conclude that a 4$^{\rm th}$ signal is most likely explained by stellar rotation, although it may be due to a planet. The proposed three-planet system (and the potential four-planet solution) is long-term dynamically stable. Planet-planet gravitational interactions are below our current detection threshold. The minimum masses of the three planets range from $1.4\pm 0.2$ to $1.8\pm 0.3$ M$\oplus$. Planet d, with $m \sin i = 1.68\pm0.25$ M$\oplus$, receives a similar amount of energy as Earth receives from the Sun. Consequently it lies within the liquid-water habitable zone of the star and has a similar equilibrium temperature to Earth. GJ 1061 has very similar properties to Proxima Centauri but activity indices point to lower levels of stellar activity.

• The paper identifies three planet candidates, including a temperate 1.5 Earth-mass planet in GJ1061's habitable zone.
• The paper employs high-precision HARPS radial velocity measurements and Gaussian Process models to distinguish planetary signals from stellar activity.
• The paper reveals a near 1:2:4 orbital commensurability among candidates, indicating a dynamically stable multi-terrestrial system.

Analysis of a Temperate 1.5 Earth-mass Planet in GJ 1061's Multi-terrestrial Planet System

The paper focuses on the discovery and analysis of a planetary system around the nearby star GJ 1061, a late-type M-dwarf located roughly 3.67 pc from the Sun. This research is part of the Red Dots campaigns, which aim to identify rocky exoplanets orbiting nearby low-mass stars. GJ 1061 is particularly significant as it is the 20th nearest star to our solar system.

Observations and Methodology

Using the HARPS spectrograph at the European Southern Observatory, the authors acquired highly precise radial velocity (RV) measurements over a three-month period. They combined this data with archival HARPS data to enhance the robustness of their findings. The data analysis primarily involved identifying potential planetary signals and assessing their statistical significance through likelihood periodograms. The paper also employed Gaussian Process models to distinguish between planetary signals and those caused by stellar activity.

Findings

The investigation revealed evidence of three planet candidates with respective orbital periods of approximately 3.2, 6.7, and 13.0 days, suggesting near 1:2:4 period commensurability. The proposed system is shown to be dynamically stable, although any planet-planet gravitational interactions remain below the detection threshold.

Notably, the paper identifies a fourth signal at approximately 53 days. This signal could alternatively be ascribed to the star's rotation period due to its overlap with expected rotational period ranges and potential stellar activity indications. Confirmation would require extended observations to determine temporal coherence and amplitude persistence.

Planetary Characteristics

The detected planets have minimum masses ranging from 1.4 to 1.8 Earth masses. The focus is on planet 'd', which, due to its similarity in receiving stellar energy as Earth does from the Sun, lies within the star's habitable zone. This condition potentially allows for liquid water, given a compatible atmospheric composition.

Implications and Future Work

These findings significantly contribute to understanding the formation and evolution of multi-planetary systems around M-dwarfs, supporting theoretical models that suggest such planets migrate towards their host stars post-formation. The potential presence of a fourth planet, if confirmed, could provide further insights into the dynamical interactions and stability patterns within such systems.

Future research should aim at securing long-term observations to explore potential outer companions suggested by a detected linear RV trend. This could involve complementary observational strategies, including transit photometry and direct imaging, to better understand the system's architecture and planetary characteristics.

In conclusion, this paper exemplifies the capability of high-precision RV surveys to uncover complex systems in our stellar neighborhood, broadening the prospects for finding Earth-like planets in temperate environments. Continued observation and analysis of GJ 1061 and similar systems will deepen our understanding of planet formation and habitability conditions across varying stellar environments.