Proxima Centauri b
The nearest exoplanet known: at least 1.07 Earth masses, a year of 11.19 days, orbiting the red dwarf 4.2465 light years from the Sun. Found in 2016 by radial velocity, which is why "at least" matters.
Updated on October 7, 2026
What the data say
The planet was detected from the wobble it induces in its star’s spectrum. That method gives m·sin i, the mass multiplied by the sine of the orbital inclination, so the true mass can only be higher than the figure quoted — never lower. No transit has been seen, so there is no measured radius and no direct evidence of an atmosphere.
- Host star
- Proxima Centauri
- Distance
- 4.2465 light years
- Minimum mass (m·sin i)
- 1.07 Earth masses
- Radius
- —
- Orbital period
- 11.187 days
- Semi-major axis
- 0.0486 ua
- Discovered
- 2016
- Detection method
- radial velocity
In the habitable zone is not the same as habitable
Proxima b receives roughly 65% of the light Earth gets, which puts it inside the conventional habitable zone, where liquid water could exist given a suitable atmosphere. That is a statement about distance and starlight, not about the planet being pleasant.
Against it: the orbit is 0.0486 AU, twenty times closer than Earth is to the Sun, so the planet is almost certainly tidally locked, with one hemisphere in permanent day. Proxima Centauri is also a flare star, capable of outbursts thousands of times brighter in X-rays than anything our Sun does, and over billions of years that can strip an unprotected atmosphere. Whether Proxima b has an atmosphere at all is simply unknown.
The other planets of Proxima, and the travel time
A second confirmed planet, Proxima d, was announced in 2022: a very light world of about 0.26 Earth masses on a 5.1-day orbit, far too hot. A third signal, Proxima c, with a period of about 5.2 years, remains a candidate.
At 4.2465 light years, light takes just over four years to arrive. The Voyager 1 probe, moving at about 17 km/s, would need roughly 75,000 years to cover the same distance. Proposals for lightsails pushed by ground-based lasers aim at 20 years of flight, but none of the required hardware exists.
The nearest systems with known planets
| Star | Distance (light years) | Spectral type | Known planets |
|---|---|---|---|
| Proxima Centauri | 4.2465 | M5.5V | 2 |
| Alpha Centauri A/B | 4.3441 | G2V + K1V | 0 |
| Barnard's Star | 5.9629 | M4.0V | 4 |
| Wolf 359 | 7.8560 | M6.0V | 2 |
| Lalande 21185 | 8.3070 | M2.0V | 2 |
| Ross 128 | 11.0070 | M4.0V | 1 |
| YZ Ceti | 12.1320 | M4.5V | 3 |
| Luyten's Star (GJ 273) | 12.3480 | M3.5V | 2 |
| Teegarden's Star | 12.4970 | M7.0V | 3 |
| TRAPPIST-1 | 40.6600 | M8.0V | 7 |
How to read this page
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Where the data comes from
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Linked to the rest of the module
"Proxima Centauri b" is one of this module’s reference pages; the glossary below defines the technical terms used here.
Words on this page
Atomic number
The number of protons in an atom’s nucleus, written Z. It is this number, not the mass, that defines which element an atom is: every atom with 8 protons is oxygen, whether it has 8 or 18 neutrons.
Standard definition by IUPAC · Atomic number
Atomic weight
The average weight of an element’s atoms, weighted by how abundant each isotope is in nature, in atomic mass units. For 14 elements CIAAW publishes a range instead of a single value, because that abundance varies a little from sample to sample.
Standard definition by CIAAW — Commission on Isotopic Abundances and Atomic Weights · Atomic weight
Isotope
Atoms of the same element (same number of protons) with a different number of neutrons, and therefore a different mass. Carbon-12 and carbon-14 are isotopes of carbon; only the second one is radioactive.
Mole
The SI counting unit for atoms, molecules or other entities: one mole is exactly 6.02214076 × 10²³ of them, by the definition fixed in 2019. It is what ties a mass in grams to a number of particles.
Standard definition by BIPM — Bureau International des Poids et Mesures (SI) · Mole
Standard uncertainty
The margin attached to a measured value, usually written in parentheses on the last digits. A constant that is "exact by definition" has zero standard uncertainty; a measured one, like the gravitational constant G, always carries some.
Standard definition by BIPM — Bureau International des Poids et Mesures (SI) · Standard uncertainty