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Proxima Centauri is the closest star to the Sun after the Sun itself, but it is far too faint to see without a telescope. It is a small, dim red dwarf that flares often and strongly, and it has at least one known planet in its habitable zone. That last point is the one most often overstated, so this article separates what is established about the star and its planets from what remains uncertain.
How close is Proxima Centauri, and can you see it?
NASA places Proxima Centauri in the constellation Centaurus, a little over four light-years from Earth. NASA’s facts page for the Sun gives the more precise figure of 4.24 light-years. A light-year is the distance light travels in one year, roughly 6 trillion miles (9.5 trillion kilometers), so the star is close by astronomical standards even though the trip would take tens of thousands of years at the speed of current spacecraft.
You cannot see it with the naked eye. NASA states that Proxima Centauri is not visible to the naked eye because its average luminosity is very low. Telescopes show it easily, but it does not appear as a point of light in the night sky the way the brighter stars of the Alpha Centauri pair do.
What kind of star is it?
Proxima is a red dwarf with about one-eighth the mass of the Sun. Its small size and low energy output are the reason it is so dim. NASA’s Proxima Centauri page, first published in 2013 and updated in 2025, says the star is expected to remain on the main sequence for another four trillion years. That figure is NASA’s prediction from models of stellar evolution, not a measured countdown, and the same page notes that four trillion years is about 300 times the current age of the universe.
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A flare star that complicates planet hunting
Proxima is a flare star. NASA explains that convection processes inside the star contribute to sudden, dramatic changes in brightness. In a 2021 NASA Science account, observations made over 40 hours in 2019 captured an extremely high-energy flare along with many other large, medium and small flares.
The flares matter for planets. Radiation from an active star can strip or chemically alter atmospheres and bombard surfaces, and a planet close enough to sit in the habitable zone of a red dwarf receives a larger share of that activity. Meredith MacGregor, an astronomer at the University of Colorado and lead author of the study, put the concern this way: “It’s hard to imagine that life could emerge, being subjected to radiation that frequently.” That is MacGregor’s assessment of the environment, not a settled conclusion about whether life can or cannot exist there.
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- Proxima Centauri b is an exoplanet orbiting in the habitable zone of the star Proxima Centauri, which is the closest star to the Sun, making it the closest known exoplanet to the Solar System.
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The Alpha Centauri neighborhood
Proxima is part of the Alpha Centauri system, which contains three stars. Alpha Centauri A and Alpha Centauri B form a close pair, and Proxima orbits that pair from a much greater distance. NASA’s overview says Proxima takes more than half a million years to complete one orbit around them. Because of that separation, Proxima is best described as the nearest star and the nearest member of a triple system, not as one of three equally spaced suns.
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What planets does Proxima have?
NASA’s overview of the system says at least one planet orbits Proxima, and possibly two more. Two of these candidates have been named and cataloged, and they are not equally well established.
Rank #3
- Proxima Centauri b is an exoplanet orbiting in the habitable zone of the star Proxima Centauri, which is the closest star to the Sun, making it the closest known exoplanet to the Solar System.
- Astronomy and science fans will love this design.
- Hardcover journal with 240 line-ruled pages (120 sheets)
- Built-in elastic closure and ribbon bookmark
- Includes an expandable inner storage pocket and a pen holder
Proxima b
Proxima b was announced in 2016. NASA describes it as roughly Earth-sized and located in the habitable zone. NASA’s Proxima b model page lists a mass of 1.27 Earth masses and an orbital period of 11.2 days. The orbit is tight: a year there takes less than two Earth weeks.
Proxima d
NASA’s catalog lists Proxima d as a terrestrial planet, with an estimated radius of 0.692 Earth radii, a mass of 0.26 Earth masses, an orbital period of 5.1 days and an orbital radius of 0.02881 AU. Its discovery was announced in 2025, so it is much newer than Proxima b and should be read with that in mind. Popular overviews sometimes present the planets as a settled set; NASA’s own catalog wording is more cautious about how many are confirmed.
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| Parameter | Proxima b | Proxima d |
|---|---|---|
| Announced | 2016 | 2025 |
| Type | Roughly Earth-sized (NASA description) | Terrestrial (NASA catalog) |
| Radius | Roughly Earth-sized; exact value not stated in the NASA sources cited here | 0.692 Earth radii (estimated, NASA catalog) |
| Mass | 1.27 Earth masses (NASA model page) | 0.26 Earth masses (NASA catalog) |
| Orbital period | 11.2 days (NASA model page) | 5.1 days (NASA catalog) |
| Orbital radius | Not stated in the NASA sources cited here | 0.02881 AU (NASA catalog) |
| Habitable zone | Yes, per NASA | Not stated in the NASA sources cited here |
| Atmosphere | Not known | Not stated in the NASA sources cited here |
Habitable zone is not the same as habitable
A habitable zone is the range of distances from a star where liquid water could potentially exist on the surface of an orbiting planet. It describes the energy a planet receives, not whether water or life is actually there. A planet inside the zone could have no atmosphere, a thin one, or one that has been eroded by flares.
NASA is direct about the gap. Its Proxima Centauri overview states: “Whether the planet first discovered around this nearest star, nicknamed Proxima b, might be potentially habitable is so far unknown.” The same overview says Proxima b’s atmosphere is not known, and it describes the high-energy radiation around close-in planets of red dwarfs as a possible challenge.
The accurate summary is this: Proxima b sits where liquid water could in principle exist, but no one has detected water, an atmosphere or life on it. Any statement that it is habitable, inhabited or an Earth twin goes beyond the evidence.
Reading new claims about Proxima
Because the planetary picture has changed within the last decade, check the date and the source before accepting a count of planets or a property of a world. Look for three things:
- The date of the announcement. Proxima b dates from 2016, and Proxima d from 2025.
- Whether the value is a model or a measurement. Mass, radius and orbital period in NASA’s catalogs are estimates derived from observations and models.
- Whether the claim is about orbit or about conditions. Being in the habitable zone says nothing about water, air or life.
Used this way, Proxima Centauri is a good example of a nearby star whose most important questions are still open.
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