You’re probably familiar with Proxima b, the nearest exoplanet to us and often referred to as the “poster boy/girl” of Earth-like exoplanets. Now, let’s shift our focus to its planetary sibling, Proxima Centauri c, or simply Proxima c. Both orbit the Proxima Centauri star, which is situated 4.22 light years away from us – quite a distance, as it would take 63,000 years to reach it. Ready? Let’s delve into it!
Proxima c Planet Details
Proxima c is found in 2019 and reported by Italian astronomer, Mario Damasso and his team. Its orbit is much farther away from its parent star compared to Proxima b. Therefore it is situated outside a habitable zone and cold with an average temperature of −234.2 °C (Damasso et al., 2020). Here is the overview of Proxima c exoplanet against Proxima b:
| Feature | Proxima b | Proxima c |
| Orbital Period | Approximately 11.2 Earth days | Approximately 5.2 Earth years |
| Mass | At least 1.17 Earth masses | Estimated > 7 Earth masses |
| Type | Terrestrial (Rocky) | Likely a mini-Neptune or super-Earth |
| Distance from Star | 0.0485 AU (7.5 million km) | Approx. 1.5 AU (224 million km) |
| Surface Conditions | Potentially habitable but likely subject to intense stellar flares | Likely cold and inhospitable |
| Atmosphere | Possibly Earth-like, but unknown | Unknown; if present, likely thick and composed of heavy gases |
| Discovery Year | 2016 | 2019 |
| Habitability | Within the habitable zone, could potentially support liquid water | Outside the habitable zone, unlikely to support life as we know it |
| Detection Method | Radial Velocity & Transit Method (Hard to do) | Radial Velocity |
Research Findings on Proxima c
The atmospheric conditions of both Proxima exoplanets are uncertain. Many questions have been raised online about why it’s so difficult to study Proxima Centauri’s planets, given their proximity to us. The planet’s proximity to us astronomically may make it harder to study.
Astronomers have reported that the transit probability of exoplanets in the Proxima Centauri system is very low. Proxima b has a 1.5% probability of transit, while Proxima c has a probability of zero (Gilbert et al., 2021). The low probability of transit for Proxima b is due to its close orbit to the host star, orbiting 20 times closer than Earth does to the Sun. On the other hand, the far orbit of Proxima c from the host star results in a negligible transit probability.
Furthermore, the stellar flare from Proxima Centauri star also makes it hard for the James Webb Space Telescope (JWST) to detect the planet’s transit. Proxima is a M5.5 red dwarf star and notoriously emitting stellar flares. These flares would induce radial velocity shifts and produce noises in measurement, thus making the detection process harder.
Another possibility of difficulty in detecting the transit of Proxima planets is that those planets could be not crossing in front of the Proxima Centauri star from the Earth’s view. The transit method is crucial in investigating exoplanets. It has been used by astronomers to study the size and also the atmosphere of exoplanets.
Proxima Centauri c Rings
The presence of rings around Proxima c has been a subject of speculation among astronomers. To this day direct evidence of rings around Proxima c is yet to be confirmed. This is caused by the limitations of current observational technologies. Nonetheless, this possibility is intriguing and makes Proxima c an interesting exoplanet.
By analyzing the astrometry data and images from SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research), astronomers have found that Proxima c appeared to be brighter than expected. They reported the brightness is incomparable to the planet’s size. Therefore, it was speculated that Proxima c has dust clouds or a huge ring system that reflects light, thus making it look brighter (phys.org/news/2020-04-astronomers-imaged-planet-proxima-centauri.html).
Rings around planets, similar to those of Saturn in our own Solar System, can significantly affect the planet’s atmosphere, climate, and even its habitability. In the case of Proxima c, if rings were present, they could:
- Affect Temperature and Climate: Rings could reflect sunlight, potentially altering the planet’s temperature and climate patterns. Depending on their density and composition, rings might either cool the planet by reflecting sunlight or warm it by trapping heat.
- Influence Habitability: For a planet in the habitable zone, the presence of rings could impact its potential to support life. The rings could shield the planet from stellar flares and radiation, which are common from red dwarf stars like Proxima Centauri, potentially making the environment more stable for life as we know it.
- Impact Observations: Rings could complicate the observation and study of Proxima c. They might cause variabilities in the light curves of the planet as it transits its star, providing clues to its existence but also making it harder to determine other characteristics of the planet, such as its atmosphere.
Summary
Proxima Centauri c is indeed an interesting exoplanet. In our opinion, it is distinctly different and more enigmatic than Proxima b. Both planets are orbiting the red dwarf Proxima Centauri, the closest star to us. Proxima c resides far outside the habitable zone. Therefore, it could have an icy and inhospitable environment. This finding has offered compelling discoveries about the diversity of worlds beyond our Solar System.
Despite the proximity of the Proxima Centauri system, several factors have complicated the observations. This includes the low possibility of transits and the star’s intense stellar flares. However, the speculative existence of rings around Proxima c, hinted at by its unexpected brightness, opens new avenues for understanding its climate, potential habitability, and the broader dynamics of exoplanetary systems.
References
Damasso, Mario; et al. (January 2020). “A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5 AU”. Science Advances. 6 (3): eaax7467. doi:10.1126/sciadv.aax7467.
Gilbert, Emily A.; Barclay, Thomas; Kruse, Ethan; Quintana, Elisa V.; Walkowicz, Lucianne M. (2021), “No Transits of Proxima Centauri Planets in High-Cadence TESS Data”, Frontiers in Astronomy and Space Sciences, 8: 190, doi:10.3389/fspas.2021.769371
https://phys.org/news/2020-04-astronomers-imaged-planet-proxima-centauri.html
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