A terrestrial planet candidate in a temperate orbit around Proxima Centauri

Abstract: At a distance of 1.295 parsecs, the red-dwarf Proxima Centauri ($\alpha$ Centauri C, GL 551, HIP 70890, or simply Proxima) is the Sun's closest stellar neighbor and one of the best studied low-mass stars. It has an effective temperature of only $\sim$ 3050 K, a luminosity of $\sim$0.1 per cent solar, a measured radius of 0.14 R$_\odot$ and a mass of about 12 per cent the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is $\sim$ 83 days, and its quiescent activity levels and X-ray luminosity are comparable to the Sun's. New observations reveal the presence of a small planet orbiting Proxima with a minimum mass of 1.3~Earth masses and an orbital period of $\sim$11.2 days. Its orbital semi-major axis is $\sim0.05$ AU, with an equilibrium temperature in the range where water could be liquid on its surface.

• The paper presents the discovery of Proxima b, a 1.3 Earth-mass planet candidate, validated through robust Doppler and statistical analyses.
• Researchers used high-precision HARPS and UVES data to detect an 11.2-day periodic signal with a false alarm probability below 0.1%.
• The findings offer a promising target for future studies on habitability and atmospheric characterization around low-mass stars.

Analysis of a Terrestrial Planet Candidate in a Temperate Orbit Around Proxima Centauri

The paper presents the discovery and analysis of a terrestrial planet candidate, referred to as Proxima b, orbiting the red dwarf star Proxima Centauri. Proxima Centauri, located approximately 1.295 parsecs away, is the closest stellar neighbor to the Sun, making it an ideal target for detailed astronomical studies. The discovery was facilitated through precise Doppler measurements using the High Accuracy Radial velocity Planet Searcher (HARPS) and the Ultraviolet and Visual Echelle Spectrograph (UVES) at the European Southern Observatory (ESO). These instruments enabled the detection of radial velocity variations indicative of an orbiting planet.

Observations and Data Analysis

The research combines existing Doppler data and a focused follow-up campaign utilizing HARPS in 2016. The primary goal was to confirm a signal initially detected in the pre-2016 data. The Doppler measurements achieved a precision of approximately 1 m/s, essential for identifying planetary signals in stars with low relative velocities. Proxima b was identified through statistical analysis, which revealed a significant periodic signal at 11.2 days. This was further reinforced by Bayesian and frequentist methods, revealing a low false alarm probability (< 0.1%), underscoring the robustness of the detection.

Characteristics of Proxima b

Proxima b is characterized by a minimum mass of 1.3 Earth masses and resides at a semi-major axis of approximately 0.05 AU. It orbits within the classical habitable zone of its host star, suggesting that liquid water could exist on its surface under favorable conditions. The presence of a second, less clear signal hints at additional planets, which requires further investigation due to uncertainties induced by stellar activity and sparse data sampling.

Implications for Habitability and Future Research

The potential habitability of Proxima b is heavily debated, impacted by factors such as tidal locking and high stellar activity including flares and X-ray radiation. Despite these challenges, theoretical studies propose mechanisms, such as atmospheric circulation, that could enable a stable climate conducive to habitability. The findings fuel discussions on planetary formation, particularly around low-mass stars, highlighting migration theories or in-situ assembly as plausible formation scenarios.

Future Directions

The discovery of Proxima b positions it as a prime candidate for further exploration using advanced observational techniques. Future efforts may involve high-resolution spectroscopy, direct imaging, and potentially transit observation campaigns to further elucidate its atmospheric and surface conditions. The research sets a foundational framework for understanding terrestrial planets in habitable zones around M-dwarf stars, significantly contributing to the broader quest of identifying potentially life-supporting exoplanets.

In conclusion, the detection of Proxima b represents a compelling step forward in exoplanetary science, demonstrating state-of-the-art observational capabilities and offering an exceptional opportunity for in-depth studies of terrestrial planets in proximity to our solar system.