Unseen Cosmos

Exoplanets

Proxima Centauri b

The nearest planet beyond the Solar System, lit by a dim red star that often flares

Artist's impression · drag to rotate
Distance about 4.2 light-years 1.30 parsecs, the closest known exoplanet [1]
Minimum mass 1.06 × Earth the true mass is higher; the orbit's tilt is unknown [1]
Radius ≈ 1.0 × Earth calculated, not measured [1]
Year length 11.2 days [1]
Distance from its star 0.048 AU [1]
Equilibrium temperature 218 K (−55 °C) [1]
Host star red dwarf, M5.5 V, 2 900 K (2 630 °C) [1]
Announced 24 August 2016 [2]

About the image. Drawn as a bare rocky world in red light. Its radius has never been measured, only estimated, because it does not pass in front of its star. Whether it has air or water is unknown.

2.9× as wide as our Sun looks from Earth

54% of the light Earth gets

Probably tidally locked: the star stays put

The sky from Proxima Centauri b

Proxima Centauri would look 2.9× as wide as the Sun does from Earth, and the planet gets 54% of the light Earth gets from the Sun. Its colour comes from its surface temperature of 2 900 K (2 630 °C); the Sun's is about 5 772 K (5 500 °C).

Proxima Centauri b is probably tidally locked: one side always faces the star. There are no sunrises. Where you stand decides where the star hangs, overhead on the day side, low at the edge, gone on the night side.

Apparent size = star radius ÷ orbit; light = size² × (temperature ÷ 5 772 K)⁴. Both from the values on this page. The landscape is imagined.

In January 2016 a team of astronomers began the Pale Red Dot campaign: an intensive watch on Proxima Centauri, the star nearest to the Sun, looking for the faint back-and-forth wobble a planet would cause. On 24 August 2016 the team, led by Guillem Anglada-Escudé, announced it had found one.

Close, and still unseen

Proxima Centauri b is about 4.2 light-years away, the closest known exoplanet. It goes around its star in just over 11 days. Proxima is a small, dim red dwarf, so even that tight orbit lies inside the star’s habitable zone: the planet receives about 65% of the light Earth gets from the Sun.

The planet has never been seen to cross in front of its star, so its size has never been measured. Its mass is a minimum: at least about 1.06 Earth masses. If the orbit is tilted, as one 2025 analysis assumes, the true mass would be about 1.44 Earth masses.

A hard neighbour

Proxima is a flare star. Its brightness can jump a hundredfold within hours, and the planet takes 10 to 60 times more ultraviolet and X-ray radiation than Earth. That could strip away an atmosphere. The planet is also probably tidally locked, with one side in endless day and the other in endless night.

It is still the obvious first target for any journey to another star. The Breakthrough Starshot project aims to develop light-sail probes that could reach Proxima Centauri within this century.

Proxima b

Its orbit, to scale

Proxima Centauri b goes around once every 11 days, at 0.04848 AU from its star. The whole view is tiny on Solar System scale: Mercury orbits the Sun about 8 times farther out than the outermost orbit shown here.

Earth days passing: 0

How hot is it?

Earth (average)288 K · 15 °C
Water boils373 K · 100 °C
Venus surface737 K · 464 °C
Iron melts1 811 K · 1 540 °C
Sun's surface5 772 K · 5 500 °C
Proxima Centauri b218 K · -55 °C
Proxima Centauri b: equilibrium temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.

How long to get there?

Proxima Centauri b is about 4.24 light-years away.

  1. Light299 792 km/s 4.2 years
  2. Breakthrough Starshotplanned light sail, 20% of light speed 21 years
  3. Parker Solar Probefastest spacecraft so far, 192 km/s 6 620 years
  4. Voyager 1leaving the Solar System, 17 km/s 74 772 years
At Voyager 1's speed the trip would take about 935 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.

Gallery

Artist's impressions rendered from the same model as the view at the top of this page.

Timeline

  1. 2016 The Pale Red Dot campaign begins in January; the planet is announced on 24 August.
  2. 2025 New measurements refine its minimum mass to about 1.06 Earth masses.

Questions people ask

What is the closest exoplanet to Earth?

Proxima Centauri b, about 4.2 light-years away, orbiting the nearest star to the Sun.

Can we travel to Proxima Centauri b?

Not with today's spacecraft: at Voyager 1's speed it would take tens of thousands of years. Breakthrough Starshot aims for light-sail probes that could make the trip in about two decades.

Is Proxima Centauri b habitable?

It is in its star's habitable zone, but the star flares violently and the planet gets far more ultraviolet and X-ray radiation than Earth, which could strip away an atmosphere.

Sources

  1. NASA Exoplanet Archive: Proxima Cen b (Suárez Mascareño et al. 2025)
  2. Wikipedia: Proxima Centauri b (Anglada-Escudé et al. 2016; Ribas et al. 2016)
  3. NASA Planetary Fact Sheet (planet temperatures, orbits, Jupiter's gravity)
  4. IAU 2015 Resolution B3 (nominal solar values)
  5. NASA: Voyager mission
  6. NASA: Parker Solar Probe
  7. Breakthrough Starshot

Keep exploring

Exoplanets TRAPPIST-1 Seven Earth-sized worlds circling an ultra-cool red dwarf, all closer to it than Mercury is to the Sun Exoplanets Kepler-452b A world about 60% wider than Earth, circling a star very much like our Sun Exoplanets K2-18b A world between Earth and Neptune in size, where JWST found methane, and the most argued-about planet in the search for life Exoplanets Kepler-22b Twice Earth's width, in the habitable zone of a Sun-like star, and possibly covered by a single ocean