Alpha Centauri: Planets, Proxima b and the Search for Life

Alpha Centauri Is Next Door. We’re Finally Starting to See What’s There.

The nearest stellar system to the Sun is no longer just a destination for science fiction. We know planets orbit its faintest star, and JWST may have caught sight of a giant world around one of its Sun-like stars.

Alpha Centauri is our nearest stellar neighbor: a triple-star system made up of Alpha Centauri A, Alpha Centauri B, and the distant red dwarf Proxima Centauri.

Alpha Centauri is so close, astronomically speaking, that light can cross the gap in a little more than four years. On a map of the Milky Way, it is practically next door. For us, of course, four light-years is still an almost unimaginable distance.

For most of human history, Alpha Centauri was simply a bright point in the southern sky. Modern astronomy has turned that point into a place: two Sun-like stars circling one another, a faint red dwarf far outside them, and planets. One known world is roughly Earth-mass. Another is smaller still. And in 2025, the James Webb Space Telescope found a tantalizing candidate around Alpha Centauri A itself.

None of that means we have found a second Earth. The closer scientists look, the less tidy the story becomes. Alpha Centauri now sits at the center of several of exoplanet science’s hardest questions. Can rocky planets form in a multiple-star system? Can an atmosphere survive beside an active red dwarf? And if an Earth-like world is hiding around Alpha Centauri A or B, can we separate its faint light from two of the brightest nearby stars?

Three Stars, One Nearest Neighbor

Alpha Centauri is a triple-star system about 1.34 parsecs, or roughly 4.37 light-years, from Earth. Its architecture sounds exotic, yet it has remained stable for billions of years.

The inner pair, Alpha Centauri A and B, are both stars we would recognize as broadly Sun-like. A is a little larger and brighter than the Sun; B is smaller, cooler and more orange. Their orbit is elongated, not circular, and takes about 80 years. Much farther out sits Proxima Centauri, a dim red dwarf. It is slightly closer to Earth than A and B, but so distant from the inner pair that one orbit around them is thought to take roughly half a million years.

That complicated architecture does not rule out planets. A 2024 study of planet formation and orbital stability estimated the system’s age at about 5.3 billion years, broadly comparable to the Solar System. The gravity of A and B would have trimmed each other’s planet-forming disks, but not necessarily destroyed them. The simulations still leave room, and enough material, for rocky worlds on stable inner orbits.

Alpha Centauri is a hierarchical triple system: Alpha Centauri A and B form the central binary, while Proxima Centauri orbits much farther away.

The Worlds We Actually Know About

The clearest planetary system we know is around Proxima Centauri. The NASA Exoplanet Archive currently lists Proxima b and Proxima d as confirmed planets, with the more distant Proxima c still a candidate. Around Alpha Centauri A, a directly imaged source remains a planet candidate. Alpha Centauri B has no confirmed planets; the much-publicized ‘Alpha Centauri Bb’ announced in 2012 eventually turned out to be a false signal.

World	Current status	Orbit / scale	Why it matters
Proxima b	Confirmed	11.18-day orbit; minimum mass ≈1.06 Earths	Earth-mass world receiving ~64% of Earth’s stellar flux; in the classical habitable-zone range.
Proxima d	Confirmed	5.12-day orbit; minimum mass ≈0.26 Earths	A very low-mass inner planet; hotter and much closer to Proxima.
Proxima c	Candidate	Long orbit, ~5.2 years; minimum mass ≈5.8 Earths	Possible cold outer world; its status remains less secure.
Alpha Cen A candidate	Candidate	Possible ~2–3 year orbit, roughly a few AU	JWST/MIRI evidence for a temperate giant planet around the nearest Sun-like star.

Status note: Planet classifications above follow the current NASA Exoplanet Archive. “Candidate” means the signal has not yet met the evidentiary standard for confirmation.

Proxima b: The Nearest Potentially Temperate Rocky World

Proxima b changed the conversation about our stellar neighborhood. Discovered in 2016 through the tiny radial-velocity wobble it produces in its star, the planet has a minimum mass only slightly above Earth’s and completes an orbit every 11.18 days. That sounds scorchingly close — Mercury takes 88 days to circle the Sun — but Proxima is a faint red dwarf. At about 0.048 astronomical units, Proxima b receives only around 64% as much stellar energy as Earth receives from the Sun.

That puts it inside the classical habitable-zone range: the region where, with the right atmosphere, surface temperatures could allow liquid water.

The phrase ‘habitable zone’ is easy to overread. It says something about incoming energy; it does not tell us whether a planet has oceans, breathable air, a magnetic field, plate tectonics or even an atmosphere. Venus and Mars are enough to show how badly distance alone can mislead us.

For Proxima b, the atmosphere is the missing piece. The planet does not transit its star from our point of view, so astronomers cannot use the most straightforward form of transmission spectroscopy to inspect its air. At the moment, we do not know whether that atmosphere is thick, thin or absent.

The Problem With Living Next to a Red Dwarf

There is an obvious attraction to red dwarfs: they are small, cool and astonishingly long-lived. Some can keep shining for trillions of years. But Proxima also has a violent side. It is magnetically active, producing powerful flares, ultraviolet radiation and streams of energetic particles.

The danger is not one dramatic flare. It is what repeated activity can do over geological time. High-energy radiation can heat the upper atmosphere and help gases leak into space. Energetic particles can rewrite atmospheric chemistry, creating or destroying molecules that future telescopes might otherwise interpret as signs of biology.

Models do not converge on one neat outcome. Some show severe atmospheric erosion under Proxima’s activity. Others find that a sufficiently massive atmosphere, a different chemical mix, oceans, clouds or magnetic protection could change the result. A 2024 three-dimensional radiation study added another complication: both stellar particles and galactic cosmic rays may matter when estimating conditions at the planet.

So the answer is less satisfying than a headline: Proxima b may be hostile, or it may have kept conditions compatible with liquid water. We are still missing the observation that would tell us which picture is closer to reality.

Proxima b may lie in the habitable-zone range, but intense stellar flares and radiation from Proxima Centauri could strongly shape its atmosphere and surface conditions.

A Planet With an 11-Day Year May Also Have a Strange Day

Because Proxima b circles so close to its star, tides should have reshaped its rotation. If the orbit is close to circular, the planet is expected to drift toward synchronous rotation, keeping roughly the same hemisphere facing the star. Other spin states are possible, but a familiar Earth-like 24-hour day is unlikely.

That sounds catastrophic until climate enters the picture. A dense enough atmosphere or ocean can carry heat from the permanent dayside toward the nightside. Clouds may gather over the lit hemisphere and reflect some incoming energy. Tides can also heat the interior. A 2024 orbital-dynamics study found that plausible orbits for Proxima b and the inner planet Proxima d can remain stable, while tidal evolution may continue contributing internal heat over very long timescales.

Before asking whether Proxima b hosts life, we first have to answer a stranger question: what does an Earth-mass world become after five billion years beside an active red dwarf? We do not yet know.

Proxima d and the Possible Outer World

Proxima d is easy to overlook because it is both smaller and hotter. The NASA Exoplanet Archive lists a minimum mass of about 0.26 Earth masses and an orbital period of just 5.12 days. It receives roughly 1.8 times Earth’s stellar flux, so it is not the obvious place to look for an Earth-like climate. Its importance is different: the nearest red dwarf is not a star with one lucky planet. It is a planetary system.

Farther out sits the much less secure Proxima c, a candidate several times Earth’s mass on an orbit of roughly five years. If it exists, it would be cold at that distance from a faint star. Taken together, the system could contain a hot inner world, a temperate Earth-mass planet and a distant cold planet — a compact arrangement unlike our own Solar System.

The Bigger Surprise: JWST May Have Seen a Planet Around Alpha Centauri A

For years, Alpha Centauri A and B looked like the more promising places to find an Earth analogue. Both resemble the Sun far more closely than Proxima does. The difficulty was never imagining planets there. It was seeing them.

Then JWST changed the picture. In observations with its Mid-Infrared Instrument, astronomers found a point source near Alpha Centauri A. The source, labeled S1, appeared in the 2024 data but not in two follow-up visits in 2025. At first glance that weakens the case. Yet orbital modeling shows a real planet could have moved into parts of the later images where the telescope was much less sensitive.

S1 would not be a second Earth. If the signal really is a planet, published models point to a cool giant roughly Jupiter-sized, perhaps 90–150 Earth masses, on a two-to-three-year orbit. Its estimated temperature is around 225 K. Headlines sometimes place it in the star’s ‘habitable zone,’ but that phrase needs care: a gas giant has no Earth-like solid surface. The interesting questions would instead concern its atmosphere — and, more speculatively, whether large moons could exist around it.

Even if S1 disappears under further scrutiny, the observation still matters. JWST showed that direct mid-infrared imaging can probe the immediate neighborhood of the nearest Sun-like star at a sensitivity that was barely imaginable a few years ago. The same program also found remarkably little warm exozodiacal dust around Alpha Centauri A. That matters because dust is glare: the less of it there is, the easier it becomes to search for fainter planets.

JWST has provided strong evidence for a giant planet candidate around Alpha Centauri A, opening a new chapter in the search for worlds around the nearest Sun-like stars.

Could Earth-Like Planets Exist Around Alpha Centauri A or B?

Yes — dynamically, there is room for them.

The fact that A and B orbit each other does not make planet formation impossible. Their mutual gravity would have truncated the disks from which planets formed, but 2024 simulations still left enough material to build rocky worlds. The same study found broad regions of long-term stability inside roughly 2–3 astronomical units — exactly where temperate rocky planets would be especially interesting.

That is the key point: we have not failed to find an Earth around A or B because such a planet is forbidden. We have failed because an Earth-sized world next to a bright star is an exceptionally difficult thing to detect.

Why the Nearest Stars Are Still Hard to Search

Being nearby does not automatically make an exoplanet easy to see. Alpha Centauri A and B are among the brightest stars in the night sky, and their glare overwhelms anything orbiting them. Direct imaging is harder still because suppressing the light of one star does not make the second bright star disappear.

Transits are not much help either: the geometry appears unfavorable for Earth-like planets around A or B to cross their stars from our viewpoint. Radial velocity can detect tiny gravitational tugs, but an Earth-mass planet would produce a wobble that has to be teased apart from stellar activity, instrumental noise and the binary stars’ own motion.

Alpha Centauri has already demonstrated how treacherous that can be. The ‘Alpha Centauri Bb’ signal announced in 2012 looked persuasive until later analyses showed it was not a planet. Near an instrument’s detection limit, observing cadence, stellar behavior and noise can combine into something that looks remarkably real.

Why Alpha Centauri May Be the Best Place to Learn How to See Another Earth

There is a useful paradox here. Alpha Centauri is difficult, but its proximity also gives astronomers an advantage that more distant systems cannot offer. A planet on an Earth-like orbit appears farther away from its star on the sky than the same orbit would around a distant star. That extra angular separation gives a telescope more room to suppress starlight and isolate the planet itself.

That makes Alpha Centauri one of the most valuable testing grounds for direct imaging. Future observatories will rely on coronagraphs, extreme wavefront control and large space telescopes to suppress starlight by enormous factors while preserving the far fainter reflected light of a planet.

NASA’s Habitable Worlds Observatory concept is being designed around exactly that challenge: directly image Earth-like planets around Sun-like stars and read their atmospheric spectra. If a rocky world exists around Alpha Centauri A or B, its proximity could make it one of the most valuable targets in the entire sky.

The next major breakthrough may come not from faster spacecraft, but from telescopes capable of suppressing starlight and analyzing the faint light of distant planets.

What Would Count as Evidence for Life?

Finding a rocky planet at the right distance would be the beginning, not the finish. The real prize would be its atmosphere. By splitting the planet’s reflected or emitted light into a spectrum, astronomers can search for molecules and infer something about temperature, pressure and chemistry.

Water vapor would constrain climate and the possible presence of an active water cycle. Carbon dioxide would help reveal greenhouse conditions. Oxygen and ozone would draw immediate attention because, on Earth, biology maintains large amounts of them. Methane could become especially interesting if it appeared alongside gases that should rapidly react with it.

No single molecule, however, is a ‘life detected’ button. Geology and photochemistry can imitate biology. Around active red dwarfs, ultraviolet light and particle radiation can produce atmospheric chemistry that would look unusual by Solar-System standards. A convincing biosignature would need context: the star, the planet’s temperature, atmospheric pressure, companion gases, plausible geology and, ideally, several independent observations.

That is why the search for life is moving beyond the old question, ‘Did we find oxygen?’ The harder test is whether an entire planetary environment can be explained without biology. Our broader guide to the cosmic search for life explores that problem in more detail.

Could We Ever Go There?

Alpha Centauri plays a trick on intuition. Four light-years is tiny on a galactic map and brutally large for a spacecraft.

At Voyager 1’s current speed, crossing a comparable distance would take tens of thousands of years. Laser-driven light sails try to change the scale of that problem by accelerating gram-scale probes to a meaningful fraction of the speed of light. Breakthrough Starshot made the idea famous: tiny sails, pushed by powerful lasers, reaching the Alpha Centauri system in decades rather than millennia.

We keep the engineering deliberately short here. For a full comparison of propulsion concepts and realistic travel times, see How Long Would It Take to Reach Alpha Centauri?

For the projects researchers are actually pursuing now — from laser sails to interstellar-probe concepts — see What Interstellar Projects Are Scientists Working on Right Now?

What Happens Next?

First: confirm — or lose — the Alpha Centauri A candidate

The immediate task is straightforward to describe and technically hard to do: see S1 again. If it reappears where orbital motion predicts, the case for a planet becomes far stronger. If future observations should have seen it and do not, the candidate will weaken or disappear. Either result would be scientifically useful.

Then: close the hiding places for rocky planets

Better radial-velocity instruments, astrometry and extreme high-contrast imaging should keep shrinking the range of masses and orbits where unseen planets could hide around A and B. Even a non-detection is information: every excluded orbit tells us more about how similar — or different — our nearest stellar neighbors are from the Solar System.

The next generation: stop counting worlds and start reading them

The bigger transition will come when discovery gives way to characterization. Extremely large ground telescopes and future space observatories such as the Habitable Worlds Observatory are designed to separate faint planetary light from bright stars and turn it into spectra. If a temperate rocky planet is eventually found around Alpha Centauri A or B, astronomers could begin asking genuinely Earth-like questions: Does it have clouds? Oceans? Seasons? Oxygen? Methane? A climate held out of chemical equilibrium by something alive?

That would not guarantee a discovery of life. It would do something almost as profound: turn a neighboring planetary system from a set of dots and numbers into a place we can begin to describe.

The Nearest Answer May Still Be Invisible

Alpha Centauri is compelling precisely because we do not already know the ending.

We know enough to make the mystery concrete. Proxima b is a real Earth-mass planet in a temperate orbit, but its atmosphere may have been altered or stripped by its star. Proxima d proves the nearest star hosts more than one small world. Proxima c remains an intriguing outer candidate. Around Alpha Centauri A, JWST may have glimpsed a cool giant. And around A and B, simulations leave room for rocky worlds that our instruments have not yet been able to reveal.

That mix of confirmed planets, uncertain candidates and still-empty discovery space is more interesting than a simple ‘nearest Earth’ story.

The first major surprise may not be that Alpha Centauri resembles the Solar System. It may be that our nearest stellar neighbor shows us another way for planets to form, survive — and perhaps become habitable.

FAQ

How far away is Alpha Centauri?

The Alpha Centauri A/B system is about 4.37 light-years from Earth. Proxima Centauri is slightly closer, at about 4.24 light-years, making it the nearest individual star to the Sun.

Is Proxima Centauri b habitable?

We do not know. Its mass and stellar energy place it among the most interesting nearby rocky planets, but its atmosphere has not been detected and Proxima’s flares and particle radiation may make surface conditions harsh.

How many planets are known in Alpha Centauri?

The current NASA Exoplanet Archive lists Proxima b and Proxima d as confirmed planets, Proxima c as a candidate, and a candidate giant planet around Alpha Centauri A. No planet is currently confirmed around Alpha Centauri B.

Did JWST discover a planet around Alpha Centauri A?

JWST found strong evidence for a cool giant-planet candidate, but it is not yet confirmed. Additional observations are required to show that the source follows the expected planetary orbit.

Could there be an Earth-like planet around Alpha Centauri A or B?

Yes. Dynamical simulations show that stable rocky-planet orbits are possible around both stars, including regions relevant to habitability. The challenge is detecting such faint worlds next to two extremely bright nearby stars.