13point8100 ly map
The nearest star system · 4.2–4.4 light years

Alpha Centauri, the way astronomers see it.

Three stars, two confirmed planets and one tantalising candidate. Everything below is drawn from measurements; star and planet sizes are enlarged so you can see them, distances and speeds are not.

Year 0.0

The three stars

Alpha Centauri A

Rigil Kentaurus

Type
G2V, like the Sun
Size
1.22 × the Sun
Mass
1.10 × the Sun
Brightness
1.5 × the Sun
Surface
≈ 5,790 K
Facts and sources →
Alpha Centauri B

Toliman

Type
K1V, orange
Size
0.86 × the Sun
Mass
0.91 × the Sun
Brightness
0.5 × the Sun
Surface
≈ 5,260 K
Facts and sources →
Alpha Centauri C

Proxima Centauri

Type
M5.5Ve red dwarf
Size
≈ 0.15 × the Sun
Mass
≈ 0.12 × the Sun
Brightness
≈ 0.0016 × the Sun
Surface
≈ 3,040 K
Facts and sources →

The planets

Around Proxima

Proxima b

Year
11.2 days
Distance from star
≈ 0.049 AU
Mass
at least ≈ 1.1 Earths
Found
2016, wobble (HARPS)
Confirmed · in the habitable zone
Around Proxima

Proxima d

Year
5.1 days
Distance from star
0.029 AU
Mass
at least 0.26 Earths
Found
2022, wobble (ESPRESSO)
Confirmed · too hot
Around A

S1

Year
≈ 2–3 years (model)
Distance from star
≈ 1–2 AU
Mass
≈ Saturn (estimate)
Seen
Aug 2024, Webb image
Candidate · not seen again in 2025

A third Proxima signal, "c", reported in 2020, remains unconfirmed and is not drawn. Masses from the wobble method are minimums, because the orbit's tilt is unknown.

What the telescopes actually see

Hubble image: two bright stars, Alpha Centauri A on the left and B on the right
Real image · HubbleA (left) and B (right): two Sun-like stars that look like one to the naked eye.ESA/Hubble & NASA · CC BY 4.0
Hubble image of Proxima Centauri, a bright point with diffraction spikes
Real image · HubbleProxima Centauri: even to Hubble the nearest star is a single point of light.ESA/Hubble & NASA · CC BY 4.0
Artist's impression: a rocky surface under a dim red sun, with a double star in the sky
Artist's impression · not a photographHow Proxima b's surface might look, with A and B in its sky. Nobody has seen the planet itself.ESO/M. Kornmesser · CC BY 4.0

Webb's own images of the S1 search, from glare to the masked view to the candidate dot, are on NASA JPL's release.

How we know

The wobble

Proxima b and d have never been seen. They tug their star back and forth by less than a metre per second, and spectrographs such as ESPRESSO on ESO's Very Large Telescope measure that shift in the star's light. That gives each planet's year and a minimum mass.

Blocking the glare

S1 was found the hard way: Webb's mid-infrared camera hid Alpha Centauri A behind a mask, then subtracted models of both stars' light. A faint dot remained. It was missing in two later looks, which orbit models say can happen if the planet swung close to its star.

Sources

  1. Positions and catalogue values: HYG Database v4.1 (CC BY-SA 4.0).
  2. A–B orbit (≈ 79.8 years, 23.3 AU, e ≈ 0.52) and star properties: Alpha Centauri summary and the references it cites.
  3. Proxima b mass and confirmation: University of Geneva, ESPRESSO result.
  4. Proxima d: Faria et al. 2022, A&A.
  5. S1 candidate: NASA JPL, Aug 2025.
  6. Habitable zones are a simple estimate from each star's brightness (√L × 0.95 to 1.67 AU), shown as a guide.
← Back to the 100-light-year map