Is Proxima Centauri b habitable?

It lies in its star's habitable zone, so liquid water is possible in principle. But strong flares from its red dwarf star may have stripped its atmosphere, and no one yet knows whether it has one.

How long would it take to get to Proxima b?

At about 4.24 light-years, it would take today's fastest spacecraft thousands of years. Proposed laser-driven light sails might cut this to around 20 years, but they remain concepts.

Is Proxima b like Earth?

Its minimum mass is about 1.07 Earth masses, so it is probably rocky. However, it orbits much closer to a much cooler, more active star and is likely tidally locked, so conditions would be very different.

How many exoplanets have been discovered?

NASA's Exoplanet Archive passed 6,000 confirmed exoplanets in September 2025, and the total keeps rising. Thousands more candidates are waiting to be confirmed.

What is the closest exoplanet to Earth?

Proxima Centauri b, 4.24 light-years away, is the closest known exoplanet, along with the smaller planet Proxima d in the same system.

The nearest known world beyond the Solar System

Proxima Centauri b

Exoplanet · 4.24 ly

Proxima Centauri b is the closest known planet outside the Solar System. It orbits Proxima Centauri, a small red dwarf star 4.24 light-years away and the nearest star to the Sun. The planet has at least 1.07 times the mass of Earth and circles its star every 11.2 days, inside the zone where temperatures could in principle allow liquid water on the surface.

Found in 2016, it immediately became a prime target in the search for life beyond Earth. Whether it is actually habitable is uncertain: its star bombards it with powerful flares, and no one yet knows whether it has kept an atmosphere. It is also the most likely first destination for any future interstellar probe.

Key facts

Distance: 4.24 light-years≈ 40 trillion km
Minimum mass: ≈ 1.07 Earth massesTrue mass depends on orbital tilt
Orbital period: 11.2 days
Orbital distance: ≈ 7.3 million km≈ 0.05 AU, about one-eighth of Mercury's distance from the Sun
Starlight received: ≈ 65% of Earth's
Host star: Proxima CentauriM5.5 red dwarf, ≈ 0.12 solar masses
Discovered: 2016Pale Red Dot campaign, ESO
Detection method: Radial velocity
Constellation: CentaurusSouthern sky

Discovering the nearest exoplanet

Hints of a planet around Proxima Centauri had appeared in older data, but they were not convincing. In 2016 a team led by Guillem Anglada-Escudé ran an intensive campaign called Pale Red Dot, observing the star almost nightly with the HARPS spectrograph on ESO's 3.6-metre telescope at La Silla in Chile, supported by other telescopes that monitored its brightness.

They found that the star moves towards and away from us by about 1.4 metres per second, roughly walking pace, in a cycle that repeats every 11.2 days. This tiny wobble revealed a planet of at least Earth's mass. The discovery was announced in August 2016 and was later confirmed with greater precision by the ESPRESSO spectrograph on ESO's Very Large Telescope.

Could it be habitable?

Proxima b lies in its star's habitable zone, the range of distances where a planet with a suitable atmosphere could have liquid water on its surface. Proxima Centauri is so dim that this zone sits very close in, which is why a year on the planet lasts less than two Earth weeks. At that distance the planet is probably tidally locked, with one side always facing the star, although a thick atmosphere or ocean could spread heat around it.

The biggest worry is the star itself. Proxima Centauri is a flare star that regularly erupts with bursts of ultraviolet and X-ray radiation far stronger than anything the Sun produces. Over billions of years such activity could strip away a planet's atmosphere and water. Proxima b receives hundreds of times more X-ray radiation than Earth, so its habitability remains an open question.

Other planets in the system

A second, much smaller planet, Proxima d, was reported in 2022 with a minimum mass of about a quarter of Earth's and a 5-day orbit. A more distant candidate, Proxima c, proposed in 2019, has not been firmly confirmed, and some astronomers think its signal may have other causes.

What exoplanets are

An exoplanet is any planet orbiting a star other than the Sun. The first were found around a pulsar in 1992, and in 1995 Michel Mayor and Didier Queloz discovered 51 Pegasi b, a giant planet around a Sun-like star, earning a share of the 2019 Nobel Prize in Physics. As of September 2025, NASA's Exoplanet Archive listed more than 6,000 confirmed exoplanets, with thousands more candidates awaiting confirmation.

These worlds are astonishingly varied. They include hot Jupiters that orbit their stars in a few days, super-Earths and mini-Neptunes larger than Earth but smaller than Neptune, a type the Solar System lacks, and planets orbiting two suns. Statistics from missions such as Kepler suggest that most stars in the Milky Way host at least one planet.

How astronomers find exoplanets

Exoplanets are usually far too faint to photograph next to their bright stars, so astronomers detect them indirectly. The two most productive techniques measure the effect a planet has on its star's motion or its brightness. Other methods include gravitational microlensing, which uses a star's gravity as a natural lens, and direct imaging of young, hot giant planets far from their stars.

Radial velocity

As a planet orbits, its gravity makes the star move in a small circle. When the star moves towards us its light is shifted slightly to bluer wavelengths, and when it moves away, to redder ones. Precise spectrographs can detect these shifts and reveal the planet's period and minimum mass. This is how Proxima b was found.

Transits

If a planet's orbit is lined up edge-on from our point of view, it passes in front of its star once per orbit and blocks a tiny fraction of its light. The size of the dip reveals the planet's diameter. Missions such as Kepler and TESS found thousands of planets this way. Proxima b does not appear to transit.

Studying it in the future

Because Proxima b does not transit, astronomers cannot study its atmosphere by watching starlight filter through it. Instead they hope to separate the planet's own faint light from its star using the next generation of giant ground-based telescopes, such as ESO's Extremely Large Telescope, now under construction in Chile. That could reveal whether it has an atmosphere and how heat moves around it.

Proxima b is also the focus of interstellar ambitions. The Breakthrough Starshot initiative has studied whether tiny probes pushed by powerful lasers could reach a fifth of the speed of light and fly past the planet about 20 years after launch. For now, that remains a long-term research concept rather than a mission.

Surprising facts about Proxima Centauri b

A year on Proxima b lasts just over 11 Earth days.
Its star is so dim that, at noon on the planet, it would look about three times wider than the Sun in our sky but give off far less light overall.
The wobble that revealed the planet is slower than a person walking.
Even at the speed of the fastest spacecraft so far, reaching Proxima b would take thousands of years.
Proxima Centauri is too faint to see with the naked eye, even though it is the nearest star to the Sun.

Frequently asked questions

Is Proxima Centauri b habitable?: It lies in its star's habitable zone, so liquid water is possible in principle. But strong flares from its red dwarf star may have stripped its atmosphere, and no one yet knows whether it has one.
How long would it take to get to Proxima b?: At about 4.24 light-years, it would take today's fastest spacecraft thousands of years. Proposed laser-driven light sails might cut this to around 20 years, but they remain concepts.
Is Proxima b like Earth?: Its minimum mass is about 1.07 Earth masses, so it is probably rocky. However, it orbits much closer to a much cooler, more active star and is likely tidally locked, so conditions would be very different.
How many exoplanets have been discovered?: NASA's Exoplanet Archive passed 6,000 confirmed exoplanets in September 2025, and the total keeps rising. Thousands more candidates are waiting to be confirmed.
What is the closest exoplanet to Earth?: Proxima Centauri b, 4.24 light-years away, is the closest known exoplanet, along with the smaller planet Proxima d in the same system.

Keep exploring

The 3D views in Ember’s Universe are scientific visualisations: physically based where possible, compressed or exaggerated where the real scales would hide everything.

Sources