Confirmed planetProxima Centauri system
Proxima Centauri b
A roughly Earth-mass world in the temperate zone of the nearest star beyond the Sun — close enough to study, yet still far enough that every question about its surface remains open.
- Orbital period
- 11.186 days
- Distance from the star
- 0.0485 AU · 7.26 million km
- Minimum mass
- 1.055 ± 0.055 Earth masses
- Radius
- Not measured; about 1.02 Earth radii estimated
- Equilibrium temperature
- About 234 K without an atmosphere
- Stellar flux
- About 0.65 × Earth’s
- Eccentricity
- Consistent with a circular orbit
- Discovery
- 2016 · radial velocity
- Host star
- M5.5V red dwarf · about 0.12 solar masses
- Distance from the Sun
- 4.24 light-years
The nearest temperate world
Proxima b was announced in 2016 by Anglada-Escudé and colleagues, who found an 11.2-day periodic signal in HARPS radial-velocity data from the Pale Red Dot campaign. The discovery paper reported a minimum mass of about 1.3 Earth masses and placed the planet in the star’s habitable zone — the region where a rocky surface could, in principle, support liquid water.
Independent confirmation came from ESPRESSO in 2020. That analysis combined radial velocities with activity indicators and a Gaussian-process model of the star’s variability, confirmed the planet, and refined its parameters. In 2025 the NIRPS instrument detected the same signal in near-infrared light. Combining NIRPS with HARPS and archival data refined the minimum mass to 1.055 ± 0.055 Earth masses; the result is one of the most precise radial-velocity masses for any temperate exoplanet.
What the measurements actually tell us
Everything measured so far comes from the star’s motion, not from the planet’s light. Radial velocity gives a minimum mass: the true mass is larger if the orbit is tilted away from our line of sight, and the inclination is not known. No transit of Proxima b has been detected, so its radius has not been measured directly; the commonly quoted figure of about 1.02 Earth radii is a model-dependent estimate.
The orbit is consistent with circular, and the planet is close enough that tidal forces may have synchronized its rotation, leaving one hemisphere permanently facing the star. No atmosphere has been detected, and no moons are known. Its true composition, magnetic field, and surface conditions remain unmeasured.
Climate, flares, and habitability
Proxima b receives roughly 65% of the stellar energy Earth receives. Without a greenhouse atmosphere its equilibrium temperature is about 234 K (−39 °C); a sufficiently thick atmosphere could raise the surface temperature, but the planet’s actual atmosphere is unknown.
The host star matters as much as the orbit. Proxima Centauri is an active M dwarf that produces flares and enhanced X-ray and ultraviolet emission. Studies of ozone chemistry, atmospheric escape, and space weather explore whether a rocky atmosphere could survive that environment. Biosignature papers to date simulate what future telescopes might detect; they are not evidence that life exists there.
The honest summary is that Proxima b is a temperate-zone planet, not a confirmed habitable world. Its location makes it a prime target, but habitability depends on properties that have not yet been observed.
Open questions
- What is the true mass and orbital inclination?
- Does the planet have an atmosphere, and can it survive the star’s flares?
- What are the surface temperature, pressure, and composition?
- Is the rotation synchronized, and does the planet have a magnetic field?
- Can future direct-imaging or reflected-light instruments detect its atmosphere or a biosignature?
Recent publications
| Year | Study | What it adds | Paper |
|---|---|---|---|
| 2016 | Anglada-Escudé et al., Nature | Discovery of a temperate, roughly Earth-mass candidate on an 11.2-day orbit. | 10.1038/nature19106 |
| 2020 | Suárez Mascareño et al., A&A 639, A77 | ESPRESSO independently confirms the planet and refines its parameters. | 10.1051/0004-6361/202037745 |
| 2022 | Garraffo et al., ApJ Letters | Models the flare and XUV space-weather environment at Proxima b. | 10.3847/2041-8213/aca487 |
| 2024 | De Luca et al., MNRAS | Ozone chemistry and climate dynamics of a synchronously rotating Proxima b. | 10.1093/mnras/stae1199 |
| 2024 | Metz et al., Planetary Science Journal | Simulates whether a near-infrared surface biosignature could be detected by future observatories. | 10.3847/PSJ/ad769d |
| 2025 | Suárez Mascareño et al., A&A 700, A11 | NIRPS detects b in the infrared and refines its minimum mass to 1.055 ± 0.055 Earth masses. | 10.1051/0004-6361/202553728 |
| 2025 | Bugatti et al., A&A | Assesses the reflected-light detectability of Proxima b with the RISTRETTO instrument. | 10.1051/0004-6361/202556398 |
Values compiled on 17 October 2026 from the NASA Exoplanet Archive, the NASA Exoplanet Catalog, and the papers listed above. Minimum masses assume an unknown orbital inclination; the radius is a model estimate because no transit has been measured.