Proxima Centauri System

What planets orbit Proxima Centauri?

So far, two planets—b and d—have been confirmed around Proxima Centauri. A third object, c, has also been proposed as a planet, but the evidence is not yet strong enough, so it remains a candidate. The same periodic motion of the star appeared in multiple observations for b and d, while c's signal has not been clearly detected again.

Alpha Centauri A and B are two stars that orbit close to each other. Proxima travels around this pair from about 13,000 AU away on a very long orbit. Light itself takes more than four years to cross the distance from the Sun to Proxima, yet in astronomical terms it is our nearest stellar neighbour. Its tiny motions and changes in brightness can therefore be observed repeatedly in greater detail than in many other planetary systems.

• About 4.24 light-years Distance from the Sun to Proxima Centauri
• About 13,000 AU Roughly 13,000 times the distance between Earth and the Sun
• 2 confirmed Proxima b and Proxima d
• 1 candidate The Proxima c signal, not yet confirmed as a planet

How are the three Alpha Centauri stars connected?

Alpha Centauri A and B are two Sun-like stars that orbit each other about once every 80 years. Proxima is a much less massive and fainter red dwarf, located far from the A–B pair and orbiting outside them. The three stars are not arranged at equal distances in a row. Instead, a close pair, A and B, and the distant Proxima form one stellar system.

Proxima's planets orbit directly around this small star. Planet b's orbital distance is about 5% of the Earth–Sun distance, and d lies even closer. These orbits are hundreds of thousands of times smaller than the gap between Proxima and A–B. Over very long periods, A and B can affect the motion of Proxima and its planets, but Proxima's gravity has by far the greatest effect on b and d as they complete an orbit every few days.

How does the evidence differ for b, d and c?

Proxima b was discovered in a signal showing the star moving slightly toward and away from Earth every 11.2 days. The same period appeared across several instruments and analyses, and b is now listed as a confirmed planet. The smallest mass allowed by the observations is about 1.07 times Earth's mass. Because b has not been seen passing in front of its star, its size and true mass have not yet been measured directly.

The signal left by Proxima d in the star's motion repeats about every 5.12 days. It is an extremely small wobble: the star's speed changes by at most about 39 centimetres per second in one direction. The signal was proposed as a candidate in 2022 ESPRESSO observations and was detected again in 2025 with a different instrument, NIRPS. The smallest mass allowed by the observations is about 0.26 Earth masses.

Proxima c was proposed as a planet candidate because of a variation repeating roughly every 5.2 years. In the 2025 NIRPS analysis, however, the originally reported signal did not clearly reappear. The NASA Exoplanet Archive also classifies c as a candidate rather than a confirmed planet. The system should therefore not be described as having three confirmed planets.

The confirmed planets are b and d. Planet c remains a candidate that requires further observations.

How were these unseen planets discovered?

Proxima b and d were not discovered in photographs of the planets themselves. A planet and its star pull on each other, so the star also wobbles by a tiny amount. Starlight changes in a subtle way as the star moves toward Earth and then away from it. Repeatedly measuring this change to find an unseen planet is called the radial-velocity method.

The measured velocity contains more than planetary signals. Spots on Proxima's surface, flares, the star's rotation, and tiny changes in the instruments can all produce similar variations. Researchers test whether the same period appears at several wavelengths, whether it changes alongside indicators of stellar activity, and whether another instrument can reproduce it.

Radial velocity alone makes it difficult to know how much a planet's orbit is tilted to our line of sight. The calculated value is therefore not necessarily the true mass, but the smallest possible value, called the minimum mass. Because neither b nor d has been confirmed crossing in front of Proxima, their size, density, and surface materials are also not directly known.

The planets shown on this page are not photographs. They are illustrations based on the confirmed orbital periods and minimum masses; their surface colours, oceans, and clouds have not been observed.

1. Measure the starlight many times Record Proxima's light split into colours over many days and years.
2. Calculate the star's speed Convert tiny changes in the light into the speed at which the star moves toward or away from Earth.
3. Separate changes caused by the star Check whether spots, flares, or rotation vary at the same time.
4. Confirm with another instrument Look for the same repeating signal with a different instrument and a different part of the spectrum.
5. Classify according to the evidence Register a planet as confirmed when the evidence is sufficient; otherwise keep it as a candidate.

What can the habitable zone tell us?

Judged only by the energy it receives from its star, Proxima b lies in the habitable zone. This means it is at a distance where liquid water might exist on the surface if an atmosphere traps the right amount of heat. It does not mean that water, an atmosphere, a magnetic field, or life has been observed. Because b does not pass in front of the star, we have not yet measured which gases, if any, are in its atmosphere.

Proxima is smaller and cooler than the Sun, but it frequently produces eruptions that emit strong ultraviolet light and X-rays. This radiation can strip away the atmosphere of a nearby planet or change its chemistry. The effect could be different if the planet has a sufficiently thick atmosphere or a magnetic field. Current observations do not tell us what conditions are like on b's surface.

How does being nearby help us study the planets?

A distance of 4.24 light-years is close compared with other stars, but it is not a journey present-day spacecraft can complete quickly. For astronomy, however, this distance is a major advantage. Proxima appears relatively bright and its position on the sky changes by a more measurable amount, allowing researchers to keep testing small velocity signals and long-period orbits.

Observations using several methods must continue. Long-term measurements of the star's speed can show whether the c candidate signal repeats. Extremely precise measurements of the star's motion across the sky can narrow down the planets' orbital tilts and true masses. If instruments eventually block most of the starlight and analyse light from a planet separately, they may obtain the first information about its atmosphere. Until then, the confirmed properties of b and d must remain clearly separated from c's candidate status.

Sources

• NASA — Alpha Centauri: A Triple Star System
• NASA Science — Our Nearest Celestial Neighbor?
• NASA Science — Proxima Centauri
• NASA Exoplanet Archive — Proxima Centauri Overview
• NASA Exoplanet Archive — Targets Excluded from the Archive
• ESO — Planet Found in the Habitable Zone Around Nearest Star
• Astronomy & Astrophysics — Proxima Centauri with NIRPS
• NASA Science — Neighboring Star’s Bad Behavior