Proxima Centauri c: The Debate Over Our Nearest Neighbor's Second Planet
The search for planets orbiting Proxima Centauri, the closest star to our Sun, has long fascinated astronomers. While the existence of Proxima b is well-documented, a second candidate, Proxima Centauri c, has sparked a complex scientific debate. First proposed as a potential world, its existence has shifted from a promising discovery to a subject of significant skepticism and ongoing investigation.
The Initial Discovery
In April 2019, Italian astrophysicist Mario Damasso and his team reported the potential discovery of a second planet orbiting Proxima Centauri. The team identified minor movements of the star using radial velocity data—a method that detects a star's "wobble" caused by the gravitational pull of an orbiting body. This data was captured by the European Southern Observatory's (ESO) HARPS instrument and had been previously analyzed by Ukrainian astrophysicist Yakiv Pavlenko and colleagues at the Instituto de Astrofísica de Canarias.
The findings were officially published on January 15, 2020, suggesting that Proxima Centauri hosted more than one planetary companion.
[ไม่มีภาพประกอบ]Supporting Evidence and Theoretical Models
Following the initial report, several studies in 2020 sought to confirm the planet's existence through astrometry, which involves measuring the precise position of a star in the sky. By analyzing Hubble Space Telescope data dating back to approximately 1995, researchers attempted to determine the planet's true mass and orbital inclination.
In June 2020, an attempt was made to directly image the planet using the SPHERE instrument in the infrared spectrum. While a potential counterpart was detected, the researchers noted that they did not obtain a clear detection. Interestingly, the authors pointed out that if the detected source were indeed Proxima c, it would be too bright for a planet of its estimated mass and age. This led to the hypothesis that the planet might possess a ring system with a radius of approximately 5 Jupiter radii (RJ).
Growing Skepticism and Recent Findings
The scientific consensus began to shift in 2022 when a new study questioned the planetary nature of the radial velocity signal. Researchers were unable to recreate the detection, suggesting that the original signal might have been caused by systematic effects—errors or patterns inherent in the measuring equipment rather than a physical planet.
As of 2025, the evidence for Proxima c remains inconclusive. Observations conducted with the NIRPS spectrograph failed to confirm the planet, although they did find hints of a different, lower-amplitude signal with a similar orbital period. Furthermore, a 2025 reanalysis of Hubble and Gaia astrometry estimated the mass of Proxima c at 3.4-3.4+5.2 Earth masses (M🜨), assuming a circular, face-on orbit. While this aligns with earlier estimates, the study noted that the data is also consistent with a non-detection.
Key Facts
- First Reported: April 2019 by Mario Damasso and colleagues.
- Detection Methods: Radial velocity (HARPS), astrometry (Hubble/Gaia), and attempted direct imaging (SPHERE).
- Estimated Mass: Approximately 3.4 M🜨 (based on 2025 astrometry analysis).
- Current Status: Inconclusive; recent studies suggest the signal may be due to systematic effects.
- Theoretical Feature: A proposed ring system of ~5 RJ to explain infrared brightness.
Summary of Proxima Centauri c Observations
| Method/Instrument | Finding/Result | Conclusion/Status |
|---|---|---|
| Radial Velocity (HARPS) | Detected stellar wobble | Questioned as systematic effect (2022) |
| Astrometry (Hubble/Gaia) | Estimated mass of 3.4 M🜨 | Consistent with both planet and non-detection |
| Direct Imaging (SPHERE) | Infrared candidate source | No clear detection; suggested ring system |
| Spectrograph (NIRPS) | Lower-amplitude signal | Unable to confirm original Proxima c |
Frequently Asked Questions
Who first discovered Proxima Centauri c?
The planet candidate was first reported in April 2019 by Italian astrophysicist Mario Damasso and his colleagues, based on data from the HARPS instrument.
Is Proxima Centauri c a confirmed planet?
No, its existence remains inconclusive. While early data suggested a planet, later studies in 2022 and 2025 have questioned the results, attributing some signals to systematic effects.
What is the estimated mass of Proxima Centauri c?
A 2025 study reanalyzing Hubble and Gaia data estimated its mass at 3.4-3.4+5.2 Earth masses, assuming a circular, face-on orbit.
Why did some scientists suggest the planet has rings?
Because a potential infrared detection by SPHERE was too bright for a planet of its mass and age, researchers hypothesized that a ring system with a radius of about 5 Jupiter radii could account for the extra brightness.
What are systematic effects in this context?
Systematic effects are non-random errors or artifacts produced by the observing instruments or data processing that can mimic the signal of a planet, leading to a false detection.