Proxima Centauri c

A proposed cold outer world, first inferred from a long-period wobble in the star’s motion. The signal is still not confirmed, and the planet remains a candidate.

Radial-velocity candidate · proposed 1,900-day orbit · status unresolved

Proposed orbital period: About 1,900 days · 5.2 years
Proposed distance: About 1.48 AU · 221 million km
Proposed minimum mass: About 5.8 Earth masses
Radius: Unknown
Equilibrium temperature: Roughly 40–50 K if the planet exists
Detection method: Radial-velocity candidate
Status: Unconfirmed candidate
Proposed: 2020 · Damasso et al.
Host star: M5.5V red dwarf · about 0.12 solar masses
Distance from the Sun: 4.24 light-years

A candidate in the cold outer system

In 2020, Damasso and colleagues reported a long-period signal in radial-velocity data of Proxima Centauri, with a period close to 1,900 days and a minimum mass of about 5.8 Earth masses. If the signal comes from a planet, it would orbit at roughly 1.48 AU — far outside the temperate zone — and would be a very cold super-Earth or mini-Neptune.

That interpretation has never become a confirmed detection. The original paper described the signal as a planet candidate, and later observations have not produced a decisive confirmation.

Why the case is still unresolved

Long-period radial-velocity signals are difficult to separate from stellar activity and instrument systematics. Proxima’s magnetic cycle and flare behaviour can introduce slow variations that mimic a distant companion. A 2025 NIRPS analysis searched for the 1,900-day signal and found only inconclusive evidence for it, even while the same data confirmed planets b and d.

Direct imaging has not found the planet either. Gratton and colleagues used SPHERE high-contrast imaging to search for a near-infrared counterpart and reported no detection, placing upper limits on what could be there. The mass estimate from Kervella and colleagues depends on an assumed orbital inclination, so it is not an independent confirmation of the candidate.

Dynamical work does show that a planet at the proposed distance could remain stable in the system, so stability arguments neither confirm nor exclude it. The question is observational: whether the long-period signal is planetary or stellar.

What would settle it

A longer radial-velocity baseline with multiple instruments would help distinguish a coherent planetary signal from activity. Direct imaging and astrometry at higher sensitivity could detect the planet itself, or rule it out over the relevant separation. Combining visible and near-infrared velocimetry, as NIRPS and HARPS now allow, is the most direct route to a firmer answer.

What we know — and what we do not

The period, distance, and minimum mass above are proposed values, not confirmed measurements. There is no measured radius, no detected atmosphere, and no direct image of the planet. Its composition, surface conditions, rotation, and magnetic field are unknown. For now, Proxima c is best treated as a scientifically interesting candidate rather than a confirmed world.

Recent publications

Year	Study	What it adds	Paper
2020	Damasso et al., Science Advances 6	Proposes a roughly 5.8-Earth-mass planet candidate at about 1.48 AU with a 1,900-day period.	10.1126/sciadv.aax7467
2020	Kervella et al., A&A	Estimates the orbital inclination and mass of the candidate under stated assumptions.	10.1051/0004-6361/202037551
2020	Gratton et al., A&A	SPHERE high-contrast imaging finds no near-infrared counterpart to the candidate.	10.1051/0004-6361/202037594
2023	Ipatov, arXiv	Studies stable orbits in the feeding zone of the proposed planet c.	arXiv:2309.00492
2024	Livesey et al., arXiv	Examines the long-term orbital stability of the full Proxima system, including c.	arXiv:2401.08773
2025	Suárez Mascareño et al., A&A 700, A11	NIRPS finds only inconclusive evidence for the 1,900-day signal attributed to c.	10.1051/0004-6361/202553728

Values compiled on 17 October 2026. Proxima c is an unconfirmed candidate; its period, distance, and mass are proposed parameters, and its radius and atmosphere have not been measured. See the NASA Exoplanet Archive for the current catalog status.