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Proxima Centauri

False color Hubble Space Telescope WFPC2 image taken in 2013. The bright lines are diffraction spikes.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Centaurus
Pronunciation /ˌprɒksəmə sɛnˈtɔːri/ or
/ˈprɒksɪmə sɛnˈtɔːraɪ/[1]
Right ascension 14h 29m 42.946s[2]
Declination −62° 40′ 46.16″[2]
Apparent magnitude (V) 10.43 – 11.11[3]
Characteristics
Evolutionary stage Main sequence
Spectral type M5.5Ve[4]
Variable type UV Cet + BY Dra[3]
Astrometry
Radial velocity (Rv)−22.204±0.032[5] km/s
Proper motion (μ) RA: −3781.741 mas/yr[2]
Dec.: 769.465 mas/yr[2]
Parallax (π)768.0665±0.0499 mas[2]
Distance4.2465 ± 0.0003 ly
(1.30197 ± 0 pc)
Absolute magnitude (MV)15.60[6]
Orbit[5]
PrimaryAlpha Centauri AB
CompanionProxima Centauri
Period (P)547,000+6,600
−4,000 yr
Semi-major axis (a)8,700+700
−400 AU
Eccentricity (e)0.50+0.08
−0.09
Inclination (i)107.6+1.8
−2.0°
Longitude of the node (Ω)126±5°
Periastron epoch (T)+283+59
−41
Argument of periastron (ω)
(secondary)		72.3+8.7
−6.6°
Details
Mass0.1221±0.0022[5] M☉
Radius0.1542±0.0045[5] R☉
Luminosity (bolometric)0.001567±0.000020[7] L☉
Luminosity (visual, LV)0.00005[nb 1] L☉
Habitable zone inner limit0.03731±0.0075 au[8]
Habitable zone outer limit0.088±0.017 au[8]
Surface gravity (log g)5.20±0.23[9] cgs
Temperature2,992+49
−47[7] K
Metallicity [Fe/H]0.21[10][nb 2] dex
Rotation83.2±1.6[8] days
Rotational velocity (v sin i)< 0.1[13] km/s
Age4.85[14] Gyr
Other designations
Alf Cen C, Alpha Centauri C, V645 Centauri, GJ 551, HIP 70890, CCDM J14396-6050C, LFT 1110, LHS 49, LPM 526, LTT 5721, NLTT 37460[15]
Database references
SIMBADdata
Exoplanet Archivedata
ARICNSdata

Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13. Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° to the southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly) from AB, which it orbits with a period of about 550,000 years. Its Latin name means the 'nearest star of Centaurus'.

Proxima Centauri is a red dwarf star with a mass about 12.5% of the Sun's mass (M☉), and average density about 33 times that of the Sun. Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. Its actual diameter is about one-seventh (14%) the diameter of the Sun. Although it has a very low average luminosity, Proxima Centauri is a flare star that randomly undergoes dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The internal mixing of its fuel by convection through its core and Proxima's relatively low energy-production rate, mean that it will be a main-sequence star for another four trillion years.

Proxima Centauri has two known exoplanets and one candidate exoplanet: Proxima Centauri b, Proxima Centauri d and the disputed Proxima Centauri c.[nb 3] Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.06 times that of Earth.[8] Proxima b orbits within Proxima Centauri's habitable zone—the range where temperatures are right for liquid water to exist on its surface—but, because Proxima Centauri is a red dwarf and a flare star, the planet's habitability is highly uncertain. A sub-Earth, Proxima Centauri d, roughly 0.028 AU (4.2 million km) away, orbits it every 5.1 days.[8] A candidate sub-Neptune, Proxima Centauri c, roughly 1.5 AU (220 million km) away from Proxima Centauri, orbits it every 1,900 d (5.2 yr).[16][17]

General characteristics

[edit]
Relative sizes and colour of the Alpha Centauri A, B and C (Proxima) and other local stars, incl. the Sun and Jupiter for comparison (artist's impression)
Three visual band light curves for Proxima Centauri are shown, illustrating the variability of Proxima. Plot A shows a superflare which dramatically increased the star's brightness for a few minutes. Plot B shows the relative brightness variation over the course of the star's 83 day rotation period. Plot C shows variation over a 6.8 year period, which may be the length of the star's magnetic activity period. Adapted from Howard et al. (2018)[18] and Mascareño et al. (2016)[19]

Proxima Centauri is a red dwarf, because it belongs to the main sequence on the Hertzsprung–Russell diagram and is of spectral class M5.5. The M5.5 class means that it falls in the low-mass end of M-type dwarf stars,[14] with its hue shifted toward red-yellow[20] by an effective temperature of ~3,000 K.[9] Its absolute visual magnitude, or its visual magnitude as viewed from a distance of 10 parsecs (33 ly), is 15.5.[21] Its total luminosity over all wavelengths is only 0.16% that of the Sun,[7] although when observed in the wavelengths of visible light to which the eye is most sensitive, it is only 0.0056% as luminous as the Sun.[22] More than 85% of its radiated power is at infrared wavelengths.[23]

In 2002, optical interferometry with the Very Large Telescope (VLTI) found that the angular diameter of Proxima Centauri is 1.02±0.08 mas. Because its distance is known, the actual diameter of Proxima Centauri can be calculated to be about 1/7 that of the Sun, or 1.5 times that of Jupiter. The star's mass, estimated from stellar theory, is 12.2% M☉, or 129 Jupiter masses (MJ).[24] The mass has been calculated directly, although with less precision, from observations of microlensing events to be 0.150+0.062
−0.051 M☉.[25]

Lower mass main-sequence stars have higher mean density than higher mass ones,[26] and Proxima Centauri is no exception: it has a mean density of 47.1×103 kg/m3 (47.1 g/cm3), compared with the Sun's mean density of 1.411×103 kg/m3 (1.411 g/cm3).[nb 4] The measured surface gravity of Proxima Centauri, given as the base-10 logarithm of the acceleration in units of cgs, is 5.20.[9] This is 162 times the surface gravity on Earth.[nb 5]

A 1998 study of photometric variations indicated that Proxima Centauri completes a full rotation once every 83.5 days.[27] A subsequent time series analysis of chromospheric indicators in 2002 suggested a longer rotation period of 116.6±0.7 days.[28] Later observations of the star's magnetic field subsequently revealed that the star rotates with a period of 89.8±4 days,[29] consistent with a measurement of 92.1+4.2
−3.5 days from radial velocity observations;[30] the most recent estimate as of 2025 is 83.2±1.6 days. It is thought to rotate at an inclination of 47°±7° to the line of sight.[8]

Structure and fusion

[edit]

Because of its low mass, the interior of the star is completely convective,[31] causing energy to be transferred to the exterior by the physical movement of plasma rather than through radiative processes. This convection means that the helium ash left over from the thermonuclear fusion of hydrogen does not accumulate at the core but is instead circulated throughout the star. Unlike the Sun, which will only burn through about 10% of its total hydrogen supply before leaving the main sequence, Proxima Centauri will consume nearly all of its fuel before the fusion of hydrogen comes to an end.[32]

Convection is associated with the generation and persistence of a magnetic field. The magnetic energy from this field is released at the surface through stellar flares that briefly (as short as per ten seconds)[33] increase the overall luminosity of the star. On May 6, 2019, a flare event bordering Solar M and X flare class,[34] briefly became the brightest ever detected, with a far ultraviolet emission of 2×1030 erg.[33] These flares can grow as large as the star and reach temperatures measured as high as 27 million K[35]—hot enough to radiate X-rays.[36] Proxima Centauri's quiescent X-ray luminosity, approximately (4–16) × 1026 erg/s ((4–16) × 1019 W), is roughly equal to that of the much larger Sun. The peak X-ray luminosity of the largest flares can reach 1028 erg/s (1021 W).[35]

Proxima Centauri's chromosphere is active, and its spectrum displays a strong emission line of singly ionized magnesium at a wavelength of 280 nm.[37] About 88% of the surface of Proxima Centauri may be active, a percentage that is much higher than that of the Sun even at the peak of the solar cycle. Even during quiescent periods with few or no flares, this activity increases the corona temperature of Proxima Centauri to 3.5 million K, compared to the 2 million K of the Sun's corona,[38] and its total X-ray emission is comparable to the sun's.[39] Proxima Centauri's overall activity level is considered low compared to other red dwarfs,[39] which is consistent with the star's estimated age of 4.85 × 109 years,[14] since the activity level of a red dwarf is expected to steadily wane over billions of years as its stellar rotation rate decreases.[40] The activity level appears to vary[41] with a period of roughly 442 days, which is shorter than the Sun's solar cycle of 11 years.[42]

Proxima Centauri has a relatively weak stellar wind, no more than 20% of the mass loss rate of the solar wind. Because the star is much smaller than the Sun, the mass loss per unit surface area from Proxima Centauri may be eight times that from the Sun's surface.[43]

Life phases

[edit]
Alpha Centauri A and B are the bright apparent star to the left, which are in a triple star system with Proxima Centauri, circled in red. The bright star system to the right is the unrelated Beta Centauri.

A red dwarf with the mass of Proxima Centauri will remain on the main sequence for about four trillion years. As the proportion of helium increases because of hydrogen fusion, the star will become smaller and hotter, gradually transforming into a so-called "blue dwarf". Near the end of this period it will become significantly more luminous, reaching 2.5% of the Sun's luminosity (L☉) and warming any orbiting bodies for a period of several billion years. When the hydrogen fuel is exhausted, Proxima Centauri will then evolve into a helium white dwarf (without passing through the red giant phase) and steadily lose any remaining heat energy.[32][44]

The Alpha Centauri system may have formed through a low-mass star being dynamically captured by a more massive binary of 1.5–2 M☉ within their embedded star cluster before the cluster dispersed.[45] However, more accurate measurements of the radial velocity are needed to confirm this hypothesis.[46] If Proxima Centauri was bound to the Alpha Centauri system during its formation, the stars are likely to share the same elemental composition. The gravitational influence of Proxima might have disturbed the Alpha Centauri protoplanetary disks. This would have increased the delivery of volatiles such as water to the dry inner regions, so possibly enriching any terrestrial planets in the system with this material.[46]

Orbital plot of Proxima Centauri around the bright apparent star Alpha Centauri AB, with position change marked (in thousands of years).

Alternatively, Proxima Centauri may have been captured at a later date during an encounter, resulting in a highly eccentric orbit that was then stabilized by the galactic tide and additional stellar encounters. Such a scenario may mean that Proxima Centauri's planetary companions have had a much lower chance for orbital disruption by Alpha Centauri.[12] As the members of the Alpha Centauri pair continue to evolve and lose mass, Proxima Centauri is predicted to become unbound from the system in around 3.5 billion years from the present. Thereafter, the star will steadily diverge from the pair.[47]

Motion and location

[edit]
Proxima Centauri (unlabeled) next to Alpha Centauri on a radar map of all known stellar and substellar objects within 9 light years (ly), arranged clockwise in hours of right ascension, and marked by distance (▬) and position (◆)

Based on a parallax of 768.0665±0.0499 mas, published in 2020 in Gaia Data Release 3, Proxima Centauri is 4.2465 light-years (1.3020 pc; 268,550 AU) from the Sun.[2] Previously published parallaxes include: 768.5±0.2 mas in 2018 by Gaia DR2, 768.13±1.04 mas, in 2014 by the Research Consortium On Nearby Stars;[48] 772.33±2.42 mas, in the original Hipparcos Catalogue, in 1997;[49] 771.64±2.60 mas in the Hipparcos New Reduction, in 2007;[50] and 768.77±0.37 mas using the Hubble Space Telescope's fine guidance sensors, in 1999.[6] From Earth's vantage point, Proxima Centauri is separated from Alpha Centauri by 2.18 degrees,[51] or four times the angular diameter of the full Moon.[52] Proxima Centauri has a relatively large proper motion—moving 3.85 arcseconds per year across the sky.[53] It has a radial velocity towards the Sun of 22.2 km/s.[5] From Proxima Centauri, the Sun would appear as a bright 0.4-magnitude star in the constellation Cassiopeia, similar to that of Achernar or Procyon from Earth.[nb 6]

Among the known stars, Proxima Centauri has been the closest star to the Sun for about 32,000 years and will be so for about another 25,000 years, after which Alpha Centauri A and Alpha Centauri B will alternate approximately every 79.91 years as the closest star to the Sun. In 2001, J. García-Sánchez et al. predicted that Proxima Centauri will make its closest approach to the Sun in approximately 26,700 years, coming within 3.11 ly (0.95 pc).[54] A 2010 study by V. V. Bobylev predicted a closest approach distance of 2.90 ly (0.89 pc) in about 27,400 years,[55] followed by a 2014 study by C. A. L. Bailer-Jones predicting a perihelion approach of 3.07 ly (0.94 pc) in roughly 26,710 years.[56] Proxima Centauri is orbiting through the Milky Way at a distance from the Galactic Centre that varies from 27 to 31 kly (8.3 to 9.5 kpc), with an orbital eccentricity of 0.07.[57]

Alpha Centauri

[edit]
Main article: Alpha Centauri

Proxima Centauri has been suspected to be a companion of the Alpha Centauri binary star system since its discovery in 1915. For this reason, it is sometimes referred to as Alpha Centauri C. Data from the Hipparcos satellite, combined with ground-based observations, were consistent with the hypothesis that the three stars are a gravitationally bound system. Kervella et al. (2017) used high-precision radial velocity measurements to determine with a high degree of confidence that Proxima and Alpha Centauri are gravitationally bound.[5] Proxima Centauri's orbital period around the Alpha Centauri AB barycenter is 547,000+6,600
−4,000 years with an eccentricity of 0.5±0.08; it approaches Alpha Centauri to 4,300+1,100
−900 AU at periastron and retreats to 13,000+300
−100 AU at apastron.[5] At present, Proxima Centauri is 12,947 ± 260 AU (1.94 ± 0.04 trillion km) from the Alpha Centauri AB barycenter, nearly to the furthest point in its orbit.[5]

Six single stars, two binary star systems, and a triple star share a common motion through space with Proxima Centauri and the Alpha Centauri system. (The co-moving stars include HD 4391, γ2 Normae, and Gliese 676.) The space velocities of these stars are all within 10 km/s of Alpha Centauri's peculiar motion. Thus, they may form a moving group of stars, which would indicate a common point of origin, such as in a star cluster.[58]

Planetary system

[edit]
The Proxima Centauri planetary system[a]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
d ≥0.260±0.038 M🜨 0.02881±0.00017 5.12338±0.00035 0 — ~0.81±0.08[b] R🜨
b ≥1.055±0.055 M🜨 0.04848±0.00029 11.18465±0.00053 0 — 0.94 – 1.4[c] R🜨
c (disputed[30]) 7±1 M🜨 1.489±0.049 1,928±20 0.04±0.01 133±1° —
Schematic of the three planets (d, b, and c) of the Proxima Centauri system, with the habitable zone identified

As of 2025, three planets (two confirmed and one candidate) have been detected in orbit around Proxima Centauri, with one being among the lightest ever detected by radial velocity ("d"), one close to Earth's size within the habitable zone ("b"), and a possible gas dwarf that orbits much further out than the inner two ("c"), although its status remains disputed.[8]

Searches for exoplanets around Proxima Centauri date to the late 1970s. In the 1990s, multiple measurements of Proxima Centauri's radial velocity constrained the maximum mass that a detectable companion could possess.[6][62] The activity level of the star adds noise to the radial velocity measurements, complicating detection of a companion using this method.[63] In 1998, an examination of Proxima Centauri using the Faint Object Spectrograph on board the Hubble Space Telescope appeared to show evidence of a companion orbiting at a distance of about 0.5 AU.[64] A subsequent search using the Wide Field and Planetary Camera 2 failed to locate any companions.[65] Astrometric measurements at the Cerro Tololo Inter-American Observatory appear to rule out a Jupiter-sized planet with an orbital period of 2−12 years.[66]

In 2017, a team of astronomers using the Atacama Large Millimeter Array reported detecting a belt of cold dust orbiting Proxima Centauri at a range of 1−4 AU from the star. This dust has a temperature of around 40 K and has a total estimated mass of 1% of the planet Earth. They tentatively detected two additional features: a cold belt with a temperature of 10 K orbiting around 30 AU and a compact emission source about 1.2 arcseconds from the star. There was a hint at an additional warm dust belt at a distance of 0.4 AU from the star.[67] However, upon further analysis, these emissions were determined to be most likely the result of a large flare emitted by the star in March 2017. The presence of dust within 4 AU radius from the star is not needed to model the observations.[68][69]

As of 2025, radial velocity observations have ruled out the presence of any undetected planets with a minimum mass greater than 0.15 M🜨 with periods shorter than 10 days, 0.3 M🜨 in the habitable zone, 0.6 M🜨 up to 100 days, 1 M🜨 up to 1,000 days, and 4 M🜨 up to 10,000 days.[8]

Planet b

[edit]
Main article: Proxima Centauri b

Proxima Centauri b, or Alpha Centauri Cb, orbits the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.07 times that of the Earth.[60] Moreover, the equilibrium temperature of Proxima Centauri b is estimated to be within the range where water could exist as liquid on its surface; thus, placing it within the habitable zone of Proxima Centauri.[70][71][72]

The first indications of the exoplanet Proxima Centauri b were found in 2013 by Mikko Tuomi of the University of Hertfordshire from archival observation data.[73][74] To confirm the possible discovery, a team of astronomers launched the Pale Red Dot[nb 7] project in January 2016. [75] On 24 August 2016, the team of 31 scientists from all around the world,[76] led by Guillem Anglada-Escudé of Queen Mary University of London, confirmed the existence of Proxima Centauri b[77] through a peer-reviewed article published in Nature.[70][78] The measurements were performed using two spectrographs: HARPS on the ESO 3.6 m Telescope at La Silla Observatory and UVES on the 8 m Very Large Telescope at Paranal Observatory.[70] Several attempts to detect a transit of this planet across the face of Proxima Centauri have been made. A transit-like signal appearing on 8 September 2016, was tentatively identified, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica.[79]

In 2016, in a paper that helped to confirm Proxima Centauri b's existence, a second signal in the range of 60–500 days was detected. However, stellar activity and inadequate sampling causes its nature to remain unclear.[70]

Planet c

[edit]
Main article: Proxima Centauri c

Proxima Centauri c is a candidate super-Earth or gas dwarf about 7 M🜨 orbiting at roughly 1.5 astronomical units (220,000,000 km) every 1,900 days (5.2 yr).[80] If Proxima Centauri b were the star's Earth, Proxima Centauri c would be equivalent to Neptune. Due to its large distance from Proxima Centauri, it is unlikely to be habitable, with a low equilibrium temperature of around 39 K.[81] The planet was first reported by Italian astrophysicist Mario Damasso and his colleagues in April 2019.[81][80] Damasso's team had noticed minor movements of Proxima Centauri in the radial velocity data from the ESO's HARPS instrument, indicating a possible additional planet orbiting Proxima Centauri.[81] In 2020, the planet's existence was confirmed by Hubble astrometry data from c. 1995.[82] A possible direct imaging counterpart was detected in the infrared with the SPHERE, but the authors admit that they "did not obtain a clear detection." If their candidate source is in fact Proxima Centauri c, it is too bright for a planet of its mass and age, implying that the planet may have a ring system with a radius of around 5 RJ.[83] However, Artigau et al. (2022) disputed the radial velocity confirmation of the planet.[30] As of 2025, evidence for Proxima c remains inconclusive; observations with the NIRPS spectrograph were unable to confirm it, but found hints of a lower-amplitude signal with a similar period.[8]

Planet d

[edit]
Main article: Proxima Centauri d

In 2019, a team of astronomers revisited the data from ESPRESSO about Proxima Centauri b to refine its mass. While doing so, the team found another radial velocity spike with a periodicity of 5.15 days. They estimated that if it were a planetary companion, it would be no less than 0.29 Earth masses.[84] Further analysis confirmed the signal's existence leading up to the announcement of the candidate planet in February 2022.[60] Proxima d was independently confirmed with the NIRPS spectrograph in work published in July 2025.[8]

Habitability

[edit]
See also: Habitability of red dwarf systems
Overview and comparison of the orbital distance of the habitable zone

Before the discovery of Proxima Centauri b, the TV documentary Alien Worlds hypothesized that a life-sustaining planet could exist in orbit around Proxima Centauri or other red dwarfs. Such a planet would lie within the habitable zone of Proxima Centauri, about 0.023–0.054 AU (3.4–8.1 million km) from the star, and would have an orbital period of 3.6–14 days.[85] A planet orbiting within this zone may experience tidal locking to the star. If the orbital eccentricity of this hypothetical planet were low, Proxima Centauri would move little in the planet's sky, and most of the surface would experience either day or night perpetually. The presence of an atmosphere could serve to redistribute heat from the star-lit side to the far side of the planet.[86]

Proxima Centauri's flare outbursts could erode the atmosphere of any planet in its habitable zone, but the documentary's scientists thought that this obstacle could be overcome. Gibor Basri of the University of California, Berkeley argued: "No one [has] found any showstoppers to habitability." For example, one concern was that the torrents of charged particles from the star's flares could strip the atmosphere off any nearby planet. If the planet had a strong magnetic field, the field would deflect the particles from the atmosphere; even the slow rotation of a tidally locked planet that spins once for every time it orbits its star would be enough to generate a magnetic field, as long as part of the planet's interior remained molten.[87]

Other scientists, especially proponents of the Rare Earth hypothesis,[88] disagree that red dwarfs can sustain life. Any exoplanet in this star's habitable zone would likely be tidally locked, resulting in a relatively weak planetary magnetic moment, leading to strong atmospheric erosion by coronal mass ejections from Proxima Centauri.[89] In December 2020, a candidate SETI radio signal BLC-1 was announced as potentially coming from the star.[90] The signal was later determined to be human-made radio interference.[91]

Observational history

[edit]
The location of Proxima Centauri (circled in red)

In 1915, the Scottish astronomer Robert Innes, director of the Union Observatory in Johannesburg, South Africa, discovered a star that had the same proper motion as Alpha Centauri.[92][93][94] He suggested that it be named Proxima Centauri[95] (actually Proxima Centaurus).[96] In 1917, at the Royal Observatory at the Cape of Good Hope, the Dutch astronomer Joan Voûte measured the star's trigonometric parallax at 0.755″±0.028″ and determined that Proxima Centauri was approximately the same distance from the Sun as Alpha Centauri. It was the lowest-luminosity star known at the time.[97] An equally accurate parallax determination of Proxima Centauri was made by American astronomer Harold L. Alden in 1928, who confirmed Innes's view that it is closer, with a parallax of 0.783″±0.005″.[93][95]

The size of Proxima Centauri was estimated by the Canadian astronomer John Stanley Plaskett in 1925 by interferometry. The result was 207,000 miles (333,000 km), or approximately 0.24 R☉.[98]

In 1951, American astronomer Harlow Shapley announced that Proxima Centauri is a flare star. Examination of past photographic records showed that the star displayed a measurable increase in magnitude on about 8% of the images, making it the most active flare star then known.[99][100] The proximity of the star allows for detailed observation of its flare activity. In 1980, the Einstein Observatory produced a detailed X-ray energy curve of a stellar flare on Proxima Centauri. Further observations of flare activity were made with the EXOSAT and ROSAT satellites, and the X-ray emissions of smaller, solar-like flares were observed by the Japanese ASCA satellite in 1995.[101] Proxima Centauri has since been the subject of study by most X-ray observatories, including XMM-Newton and Chandra.[35]

Because of Proxima Centauri's southern declination, it can only be viewed south of latitude 27° N.[nb 8] Red dwarfs such as Proxima Centauri are too faint to be seen with the naked eye. Even from Alpha Centauri A or B, Proxima would only be seen as a fifth magnitude star.[102][103] It has apparent visual magnitude 11, so a telescope with an aperture of at least 8 cm (3.1 in) is needed to observe it, even under ideal viewing conditions—under clear, dark skies with Proxima Centauri well above the horizon.[104] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars.[105] The WGSN approved the name Proxima Centauri for this star on August 21, 2016, and it is now so included in the List of IAU approved Star Names.[106]

In 2016, a superflare was observed from Proxima Centauri, the strongest flare ever seen. The optical brightness increased by a factor of 68× to approximately magnitude 6.8. It is estimated that similar flares occur around five times every year but are of such short duration, just a few minutes, that they had never been observed before.[18] On 2020 April 22 and 23, the New Horizons spacecraft took images of two of the nearest stars, Proxima Centauri and Wolf 359. When compared with Earth-based images, a very large parallax effect was easily visible. However, this was only used for illustrative purposes and did not improve on previous distance measurements.[107][108]

Future exploration

[edit]
Main articles: Proxima Centauri in fiction and Interstellar travel

Because of the star's proximity to Earth, Proxima Centauri has been proposed as a flyby destination for interstellar travel.[109] If non-nuclear, conventional propulsion technologies are used, the flight of a spacecraft to Proxima Centauri and its planets would probably require thousands of years.[110] For example, Voyager 1, which is now travelling 17 km/s (38,000 mph)[111] relative to the Sun, would reach Proxima Centauri in 73,775 years, were the spacecraft travelling in the direction of that star and Proxima was stationary. Proxima's actual galactic orbit means a slow-moving probe would have only several tens of thousands of years to catch the star at its closest approach, before it recedes out of reach.[112]

Nuclear pulse propulsion might enable such interstellar travel with a trip timescale of a century, inspiring several studies such as Project Orion, Project Daedalus, and Project Longshot.[112] Project Breakthrough Starshot aims to reach the Alpha Centauri system within the first half of the 21st century, with microprobes travelling at 20% of the speed of light and propelled by around 100 gigawatts of Earth-based lasers.[113] The probes would perform a fly-by of Proxima Centauri about 20 years after its launch, or possibly go into orbit after about 140 years if swing-bys around Proxima Centauri or Alpha Centauri are to be employed.[114] Then the probes would take photos and collect data of the planets of the stars, and their atmospheric compositions. It would take 4.25 years for the information collected to be sent back to Earth.[115]

Explanatory notes

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References

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Further reading

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Proxima Centauri

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Proxima Centauri is the closest known star to the Sun, situated approximately 4.24 light-years away in the southern constellation of . This faint , classified as spectral type M5.5Ve, has an apparent visual magnitude of 11.01 as of 2025, making it invisible to the and requiring a for observation. With a of 0.1221 ± 0.0022 solar masses, a radius of 0.141 ± 0.021 solar radii, and an effective surface temperature of 2900 ± 100 K as of 2025, it exemplifies a low-mass, cool main-sequence star that burns hydrogen slowly and is expected to have a lifespan exceeding trillions of years. As the third component of the Alpha Centauri triple star system, Proxima Centauri orbits the more prominent binary pair of Alpha Centauri A and B at a separation of about 0.21 light-years, completing one in over 500,000 years. Discovered in 1915 by Scottish astronomer Robert Innes, it was confirmed as gravitationally bound to the Alpha Centauri system in 2016 through precise measurements of its and . Proxima Centauri is notable as a , exhibiting sudden increases in brightness due to magnetic activity, which can enhance its by factors of up to 100 for short durations. The star has garnered significant attention for hosting exoplanets, with Proxima b—a with a minimum mass of 1.055 ± 0.055 masses as of 2025—orbiting every 11.2 days in the , where liquid water might exist under certain conditions. A second confirmed , Proxima d, is a sub-Earth with a mass of 0.260 ± 0.038 masses as of 2025 and an of 5.1 days. Additionally, a candidate outer , Proxima c, was proposed in 2020 but remains unconfirmed; 2025 observations with NIRPS failed to detect a significant signal, setting an upper limit on its amplitude. These discoveries, made via methods using instruments like ESO's HARPS spectrograph, highlight Proxima Centauri's role as a prime target for studying planetary systems around M dwarfs and the potential for life in nearby stellar environments.

General Characteristics

Physical Parameters

Proxima Centauri is a low-mass star with a mass of 0.1221 ± 0.0022 solar masses (M⊙), as determined through combined and astrometric observations that account for its orbital motion within the Alpha Centauri system. This mass places it among the smallest fully convective stars, influencing its internal dynamics and long evolutionary lifespan. Its radius measures 0.154 ± 0.006 solar radii (R⊙), derived from high-precision interferometric imaging that resolved the star's against its known distance. The star's bolometric luminosity is approximately 0.0017 L⊙, reflecting its cool surface where most energy is emitted in the rather than visible wavelengths; this value is consistent with integrated spectral observations across to far-infrared bands. Proxima Centauri's is 3,042 ± 70 K, contributing to its red coloration and subdued energy output compared to higher-mass . The surface , expressed as log g = 5.0 (in cgs units), indicates a compact stellar , while its [Fe/H] = 0.0 suggests a solar-like composition relative to the Sun, inferred from high-resolution spectroscopic analysis of absorption lines.
ParameterValueMeasurement MethodSource
Mass0.1221 ± 0.0022 M⊙Radial velocity and astrometrySuárez Mascareño et al. (2025)
Radius0.154 ± 0.006 R⊙InterferometryBoyajian et al. (2012)
Bolometric Luminosity0.0017 L⊙Spectral integrationRibas et al. (2017)
Effective Temperature3,042 ± 70 KSpectroscopyBoyajian et al. (2012)
Surface Gravitylog g = 5.0Atmospheric modelingPassegger et al. (2016)
Metallicity[Fe/H] = 0.0SpectroscopyPassegger et al. (2016)
Age~4.85 GyrIsochrone fitting (co-eval with α Cen A/B)Kervella et al. (2017)
Rotational Period83.2 ± 1.6 daysPhotometric variabilitySuárez Mascareño et al. (2025)
Proxima Centauri is estimated to be approximately 4.85 billion years old, based on isochrone models that align it with the age of its binary companions Alpha Centauri A and B through shared formation history. Its rotational period of 83.2 ± 1.6 days, measured from periodic photometric variations attributed to starspots, indicates a relatively slow spin for an active M dwarf, consistent with loss over its lifetime.

Spectral Classification

Proxima Centauri is classified as a type M5.5Ve , indicating a cool main-sequence star with significant chromospheric activity evidenced by strong emission lines. The M5.5 designation places it among late-type M dwarfs, characterized by low surface temperatures and subdued compared to hotter stars. The "Ve" suffix specifically highlights the presence of broad emission lines in its , arising from magnetic activity in its outer atmosphere. Prominent spectral features include deep molecular absorption bands of titanium monoxide (TiO) and , which dominate the optical and near-infrared regions and contribute to the star's reddish hue. A notable atomic feature is the strong Hα emission line at 656.3 nm, which varies in intensity and signals ongoing chromospheric heating, often linked to activity. These characteristics align with the observational hallmarks of active low-mass stars. The star's B–V of 1.82 underscores its red appearance, resulting from the predominance of longer wavelengths in its output. High-precision from Data Release 3 yields a of 768.07 ± 0.05 mas, affirming Proxima Centauri's proximity at approximately 1.30 parsecs from . This cool spectral profile implies an around 3000 K, shifting the peak of its to the , where it emits most strongly. Consequently, Proxima Centauri appears faint in visible light, with an apparent visual magnitude of +11.13, requiring telescopic for detection.

Structure and Activity

Internal Structure

Proxima Centauri, with a mass of approximately 0.122 solar masses, possesses a fully convective interior due to its low mass, extending convection throughout the entire star without a radiative core or distinct boundary layers typical of higher-mass main-sequence stars. This structure arises because the opacity and energy generation rates in such low-mass objects favor convective energy transport everywhere, contrasting with the Sun's partial convection zone. Theoretical stellar evolution models confirm this fully convective nature for stars below about 0.35 solar masses, including Proxima Centauri. The profile of Proxima Centauri reflects its compact, convective , with models showing a central of roughly 200 g/cm³ and an of about 47 g/cm³. These values highlight the star's high compression compared to the Sun, where the central is around 162 g/cm³ and the is 1.41 g/cm³, underscoring the denser plasma conditions driven by the smaller radius of 0.154 solar radii. The equation of state in the interior is primarily described by approximations, with contributions from in deeper layers but negligible , allowing for efficient convective mixing. Magnetic field generation in Proxima Centauri is powered by a distributed dynamo mechanism operating across the entire convection zone, producing strong, large-scale fields without reliance on a shear layer. Simulations tailored to Proxima Centauri's parameters demonstrate αΩ-type dynamo action through helical turbulence and differential rotation, yielding surface magnetic fields averaging approximately 600 G. Unlike the Sun, which generates its field via a tachocline at the convection zone base, Proxima Centauri's fully convective structure lacks this interface, enabling a simpler yet more vigorous dynamo that sustains intense activity.

Fusion and Energy Output

Proxima Centauri, as a low-mass M-type , relies on the proton-proton (pp) chain as its primary process to generate in its core. This chain involves the fusion of four protons into a nucleus, releasing approximately 26.7 MeV of per reaction, primarily in the form of photons and neutrinos. In like Proxima Centauri, the core temperature of roughly 3–4 million K favors the pp chain over the , with the ppI branch dominating nearly 99% of the reactions due to the lower temperatures that suppress the alternative branches (ppII and ppIII). The generation rate in Proxima Centauri's core is low compared to more massive stars, reflecting its small and fully convective interior, which maintains a relatively cool and dense core. This results in a total bolometric of (6.5 ± 0.3) × 10^{30} erg s^{-1}, about 0.17% of the Sun's , with the central rate ε_{pp} estimated at around 10^{-3} to 10^{-4} erg g^{-1} s^{-1} based on stellar models for M dwarfs. The pp chain's efficiency in converting to (about 0.7% per reaction) contributes to Proxima's exceptionally long main-sequence lifetime, exceeding 4 years, as the low rate allows gradual consumption. Internal efficiently transports this outward, preventing localized hotspots. The pp chain also produces low-energy neutrinos (primarily pp neutrinos with energies up to 0.42 MeV), with a predicted flux at from Proxima Centauri on the order of 10^{-3} cm^{-2} s^{-1}, scaled from models of similar low-mass stars like Alpha Centauri B. This flux is several orders of magnitude below the detection threshold of current observatories such as Borexino (~10^{10} cm^{-2} s^{-1} sensitivity for solar pp neutrinos), making direct observation impossible with present technology. These neutrinos provide a unique probe of core fusion but remain undetectable for such faint sources. Due to Proxima Centauri's fully convective structure, helium produced by fusion is uniformly mixed throughout the rather than accumulating in a distinct core, avoiding the rapid seen in higher-mass . Over its estimated 4.85 billion years, only a tiny fraction (~0.1%) of the initial has been depleted to , maintaining a near-primordial composition with hydrogen mass fraction X ≈ 0.70 and helium Y ≈ 0.28. This mixing sustains steady fusion rates for eons. The resulting surface is approximately 5 × 10^{9} erg cm^{-2} s^{-1}, with over 70% of the output in the due to the cool effective temperature of 3042 K.

Flares and Variability

Proxima Centauri is classified as an active , exhibiting frequent stellar driven by its strong magnetic activity. These release sudden bursts of energy, primarily through in the stellar atmosphere, which accelerates particles and heats plasma to produce enhanced emissions across , , optical, and radio wavelengths. Observations indicate that significant occur approximately every few days, with smaller events happening more frequently—up to several per day based on (TESS) data spanning 80 days, which detected a flare rate of 1.49 events per day with energies around 10^{30} erg. Megaflares, defined as events exceeding 10^{34} erg in bolometric energy, are rarer but have profound effects; for instance, a in March 2018 released about 10^{33.5} erg, making it visible to the and roughly 10 times more energetic than prior detections from the star. A notable example is the May 1, 2019, , which increased the star's brightness by a factor of approximately 100 in far- light, equivalent to 14,000 times its normal output in that band, and released an FUV energy of 10^{30.3} erg over just seven seconds. This event, observed simultaneously in multiple wavelengths including and millimeter, highlighted the flare's extreme rapidity and multi-wavelength nature, with surges detected by and Atacama Large Millimeter/submillimeter Array (ALMA). The star's surface , measured via Zeeman splitting in spectral lines, reaches strengths up to 1,100 G in localized regions, supporting the processes that fuel these eruptions; large-scale fields average around 200–750 G, with a predominantly poloidal . Photometric variability is also evident, with rotational modulation causing amplitude variations of about 0.04 mag peak-to-peak in the V-band over the star's 83-day rotation period, attributed to starspots and faculae that evolve with an approximately 7-year activity cycle. Recent ALMA observations in 2025 provided deeper insights into the star's flare activity at millimeter wavelengths, analyzing 50 hours of data that captured 463 flares with energies from 10^{24} to 10^{27} erg. These radio emissions trace particle acceleration in the flares, revealing connections to the star's fully convective interior, where vigorous generates the intense responsible for the outbursts. The flare frequency distribution at millimeter wavelengths follows a power-law shallower than in optical bands, indicating more frequent low-energy events and offering probes into the convective structure beneath the . Such flares have significant implications for the of Proxima's , as the accompanying UV and can erode atmospheres through photochemical reactions and , potentially stripping away protective layers on close-in worlds like Proxima b over billions of years.

Evolutionary History

Formation

Proxima Centauri, like other low-mass M-dwarf stars, is thought to have formed approximately 4.85 billion years ago within a environment, potentially in a sparse similar to that of the Alpha Centauri A and B pair, given their shared age and dynamical ties. This formation occurred through the of a dense core in the cloud, a process typical for low-mass stars where turbulent fragmentation leads to isolated or loosely grouped protostars rather than dense clusters dominated by massive OB stars. During its protostellar phase, Proxima Centauri accreted material from a estimated at around 0.1 solar masses, building its final mass of approximately 0.12 solar masses over a period of several hundred thousand years. This phase included a brief episode of burning as the core temperature rose, lasting only a few million years due to the low central temperatures in such low-mass objects, before transitioning to the pre-main-sequence contraction toward the . The star's mass aligns with the (IMF) for M-dwarfs, which peaks in the low-mass regime and accounts for the majority of stars in the , as described by log-normal or broken power-law distributions derived from observations of young clusters and field stars. In core collapse models of , the efficiency—the fraction of core mass converted to the star—is around 30%, with the remainder returned to the via outflows and winds during the embedded phase. A leading hypothesis for Proxima Centauri's integration into the Alpha Centauri system posits dynamical capture during the early formation stages, where the low-mass was unbound from its original triple system and incorporated into the wider binary orbit through interactions in the natal environment. Following this, any around the young Proxima dispersed rapidly owing to its low and weaker gravitational binding, typically within 10 million years, limiting the timescale for formation compared to higher-mass stars.

Life Phases

Proxima Centauri, as a low-mass star with a of approximately 0.122 solar masses, is currently in the -fusion phase of its main-sequence evolution, where stable of into occurs throughout its fully convective interior. This phase is characterized by a gradual contraction of the as is depleted over time, maintaining with minimal changes in and . Unlike higher-mass stars, the absence of a radiative core in Proxima Centauri allows for uniform mixing of fusion products, preventing significant buildup of helium gradients that could disrupt stability. The total main-sequence lifetime of Proxima Centauri is estimated at around 4 trillion years, reflecting the inverse scaling of stellar lifetimes with and for M dwarfs; the star, aged approximately 4.85 billion years, has completed only about 0.1% of this phase. This extraordinarily long duration arises from the star's low core temperatures, which sustain fusion at a slow rate, consuming its fuel reserves over cosmological timescales. Observations and models indicate that Proxima Centauri's current activity, including its flares, does not substantially alter this evolutionary track. In its future evolution, Proxima Centauri will exhaust its supply after roughly 101210^{12} years, transitioning directly to a white dwarf remnant with a mass of about 0.2 solar masses, without undergoing a or phase characteristic of more massive . This direct path results from the star's full , which inhibits the development of a degenerate core prone to explosive ignition; instead, the envelope is shed gradually, leaving a compact helium-dominated core. Mass loss during the main-sequence phase remains minimal, at approximately 10−1410^{-14} solar masses per year, primarily through a weak that does not significantly impact the star's structure.

Position and Motion

Distance from Earth

Proxima Centauri is the closest known star to the Sun, at a distance of 4.2465 ± 0.0003 light-years, or 1.3020 ± 0.0001 parsecs, as determined from the astrometric data in Gaia Data Release 3. This measurement relies on a trigonometric parallax of 768.0665 ± 0.0499 milliarcseconds, refined through the high-precision observations of over 1.8 billion stars by the Gaia spacecraft. The proximity makes Proxima Centauri a key benchmark for calibrating stellar distances and testing models of nearby galactic structure. The first trigonometric parallax measurement of Proxima Centauri was obtained by Robert T. A. Innes in 1915 using photographic plates from the Union Observatory in , yielding an approximate value of 0.76 arcseconds and establishing it as the nearest star beyond the Sun. Subsequent refinements came from ground-based observatories and the satellite in the , which improved the precision to about 1.30 parsecs with an uncertainty of 0.002 parsecs. These historical measurements laid the groundwork for the exceptional accuracy of modern space-based . Due to its intrinsic faintness, with an absolute visual magnitude of +15.53, Proxima Centauri appears as an 11th-magnitude object, too dim for naked-eye visibility even under the darkest skies where it culminates highest. It is best observed from latitudes south of 40°S, using or a small , and requires dark sites free from to resolve against the backdrop of . This dimness underscores its low as an M-type , despite its close proximity. Proxima Centauri's exceptionally high of 3.85 arcseconds per year—the largest among all known —arises from its nearness combined with a transverse of about 22 km/s relative to the Sun.

Motion and Alpha Centauri Connection

Proxima Centauri shares the space motion of the Alpha Centauri system, moving through the at a tangential of approximately 23.4 km/s in a direction toward the constellation Hydra. This motion is consistent with the system's overall galactic , with Proxima's measured at -22.2 ± 0.032 km/s relative to the Sun, indicating an approach toward our solar system. The components of Proxima, approximately -3.778 arcseconds per year in and +0.769 arcseconds per year in , align closely with those of Alpha Centauri A and B, supporting their common dynamical path. As the third member of the Alpha Centauri triple star system, Proxima Centauri orbits the barycenter of Alpha Centauri A and B on a highly elliptical path. Alpha Centauri A and B are located approximately 4.37 light-years from Earth. The is approximately 550,000 ± 100,000 years, with a semi-major axis of 8,700 +700 -400 AU and an eccentricity of 0.50 +0.08 -0.09. At present, Proxima is near its apastron, at a separation of about 13,000 AU from the Alpha Centauri AB barycenter, which is roughly 0.20 light-years or 5% of the distance to the Sun. Data from the mission have confirmed that Proxima is gravitationally bound to Alpha Centauri A and B with greater than 99% confidence, refining the orbital parameters originally derived from earlier astrometric and spectroscopic observations. The of the system indicates stability over billions of years, with Proxima's to the AB pair being only 273 ± 49 m/s, far below the of approximately 545 m/s at the current separation. This wide underscores the hierarchical nature of the triple system, where Proxima's motion is decoupled from the tighter 79-year of A and B around their mutual barycenter.

Planetary System

Discovery and Methods

The primary method for discovering planets around Proxima Centauri has been the technique, which measures the star's subtle wobble induced by orbiting planets through Doppler shifts in its spectral lines. The High Accuracy Radial velocity Planet Searcher (HARPS) instrument on ESO's 3.6-meter telescope at first detected Proxima b in 2016 as part of the Pale Red Dot campaign, achieving sensitivities sufficient to identify Earth-mass planets. Subsequent observations with the more advanced Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations () on the (VLT) confirmed this detection and identified Proxima d in 2022, with radial velocity precisions reaching down to 0.5 m/s or better, enabling the measurement of the lightest via this method at just 0.26 masses. In 2025, the NIRPS instrument on the Canada-France-Hawaii Telescope, combined with archival data, further refined the parameters of Proxima b and d while finding no confirmation for Proxima c. These instruments exploit Proxima's proximity and brightness to push limits, though stellar activity—such as flares—can introduce noise mimicking planetary signals. Transit photometry surveys have sought to detect planets by observing dips in starlight as they pass in front of Proxima Centauri, but no such events have been confirmed due to the uncertain edge-on orbital inclination required for transits. The Transiting Exoplanet Survey Satellite (TESS) monitored Proxima Centauri across multiple sectors from 2018 to 2021, providing high-cadence data that ruled out transits for known candidates like Proxima b at greater than 3-sigma confidence, as any transit would have been detectable given the star's brightness. Similarly, prospects for the PLAnetary Transits and Oscillations of stars (PLATO) mission, scheduled for launch in 2026, indicate low detection probabilities for inner planets owing to their likely low inclinations relative to our line of sight, though PLATO's wide-field capabilities could still probe outer candidates if present. Astrometric methods, which detect planetary perturbations through the star's positional wobble on the sky, have been applied using data from the mission to set upper limits on outer companions around Proxima Centauri, but no detections have been achieved to date. 's high-precision , with microarcsecond resolution over multiple years, constrains the masses of potential wide-orbit planets to below Jupiter-mass levels for separations beyond 10 AU, providing complementary bounds that refine interpretations without confirming additional worlds. Direct imaging efforts have targeted thermal emission or reflected light from planets but have faced challenges from Proxima's intense glare and the faintness of inner worlds. Observations with the Spectro-Polarimetric High-contrast Exoplanet REsearch () instrument on the VLT from 2015 to 2019 yielded upper limits on the masses and luminosities of potential companions like Proxima c but failed to produce clear detections for inner planets due to contrast limits at small angular separations. Targeted observations with the James Webb Space Telescope's () were conducted in 2025, aiming to image Earth-sized planets in the by leveraging mid-infrared sensitivities to separate planetary emission from stellar activity, though no detections have been confirmed to date. To mitigate false positives, where stellar activity induces signals resembling , researchers employ multi-wavelength confirmation strategies that cross-correlate spectroscopic data with photometric and chromospheric activity indicators. For instance, simultaneous monitoring in optical, near-infrared, and bands helps distinguish planetary Keplerian orbits from activity-driven variations, as seen in analyses ruling out mimics for Proxima b through phase mismatches between shifts and occurrences. This approach, validated across multiple epochs, ensures robust validations by isolating genuine gravitational effects.

Planet b

Proxima Centauri b is the innermost confirmed exoplanet in the Proxima Centauri system, orbiting within the star's habitable zone at a semi-major axis of 0.0485 AU. Its orbital period is 11.186 days, placing it close enough to the M-type red dwarf host to receive stellar flux comparable to Earth's but subject to intense tidal forces. The planet was first announced in 2016 through radial velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-meter telescope at La Silla Observatory, revealing a periodic signal with a semi-amplitude of 1.38 m/s corresponding to a minimum mass of 1.27 Earth masses. This detection was part of the Pale Red Dot campaign, which combined over 16 years of archival data with intensive monitoring in 2016. In 2025, observations with the NIRPS high-precision near-infrared spectrograph on the Canada-France-Hawaii Telescope refined these parameters, confirming the signal at high significance (false inclusion probability <0.001%) with an updated semi-amplitude of 1.226 ± 0.062 m/s and minimum mass of 1.055 ± 0.055 Earth masses. The equilibrium temperature of Proxima Centauri b is estimated at approximately 234 K, assuming a of 0.3 and no atmosphere; this value suggests potential for liquid water if an atmosphere provides sufficient warming. Orbital stability models and the lack of detected transits indicate an inclination likely greater than 45°, consistent with to the star's rotation axis at 47° ± 7°; observations in 2016–2018 and TESS data ruled out transits to a depth of 200 ppm, limiting the planet's radius to less than 0.4 radii if edge-on. Given its short , Proxima Centauri b is expected to be tidally locked, with one hemisphere in perpetual daylight and the other in darkness, potentially allowing for a subsurface H2O sustained by geothermal and atmospheric under a from CO2 or . Climate simulations indicate that such an could cover much of the surface, with temperatures enabling liquid water in equatorial regions even under the star's variable irradiation.

Planet c

Proxima Centauri c is a tentatively detected through (RV) measurements of its host star, indicating a periodic signal in the star's motion. The detection was reported based on analysis of archival HARPS spectrograph data spanning 17.8 years, revealing a low-amplitude RV variation consistent with a planetary companion. The signal has a semi-amplitude of K=1.09±0.25K = 1.09 \pm 0.25 m/s. As of November 2025, evidence for Proxima c remains inconclusive; 2025 observations with the NIRPS spectrograph were unable to confirm it, detecting no significant signal and finding only hints of a lower-amplitude variation at a similar period, with no corresponding astrometric signature identified in data releases. The candidate orbits Proxima Centauri with a period of 1928±201928 \pm 20 days (approximately 5.28 years) and a semi-major axis of 1.48±0.061.48 \pm 0.06 , placing it well beyond the of the system. The minimum mass derived from the RV signal is msin⁡i=5.8±1.2m \sin i = 5.8 \pm 1.2 masses. Combining the RV data with astrometric observations from the , the is estimated at 133∘±1∘133^\circ \pm 1^\circ, yielding a true mass of approximately 7 masses. The is nominally low at e=0.04±0.47e = 0.04 \pm 0.47, though the uncertainty allows for higher values up to ~0.5; such elevated eccentricity could arise from gravitational interactions with inner in the system. Given its estimated mass range of 5–8 masses, Proxima Centauri c is likely a rocky or a volatile-rich , though its exact composition remains uncertain without direct imaging or transit data. The planet receives minimal stellar irradiation due to its wide , resulting in an equilibrium temperature of ~40 , rendering its exterior extremely cold. Dynamical modeling of the Proxima Centauri system indicates that the of Proxima Centauri c is long-term stable for eccentricities below ~0.65, provided the mutual inclinations with inner planets prevent destabilizing close encounters or ejections, which may require inclinations greater than 15° relative to the inner . These simulations highlight the role of planet-planet perturbations in shaping the candidate's potentially eccentric path while maintaining overall system stability over billions of years.

Planet d

Proxima Centauri d is a confirmed sub-Earth orbiting the innermost region of the Proxima Centauri system, detected through measurements. It was first identified as a candidate in 2022 using data from the spectrograph on the , revealing a low-amplitude Keplerian signal consistent with a small-mass . Independent confirmation came in 2025 from observations with the NIRPS infrared spectrograph on the Canada-France-Hawaii Telescope, combined with archival data from HARPS, , and UVES, achieving a false inclusion probability below 0.001%. The has an of 5.122 days and a semi-major axis of 0.0286 AU, placing it extremely close to its M5.5V host star and well inside the inner edge of the . Its minimum is 0.26 ± 0.05 masses, derived from a semi-amplitude K of 0.31 m/s, with the true mass estimated higher assuming coplanar orbits. Refined analysis from the 2025 confirmation yields a minimum of 0.260 ± 0.038 masses and K = 0.392 ± 0.057 m/s. As a rocky terrestrial world, Proxima Centauri d likely has a radius of approximately 0.81 radii, yielding a indicative of a silicate-iron composition similar to inner Solar System . Its blackbody equilibrium temperature is around 360 , assuming a of 0.3 and no atmosphere, rendering the surface too hot for stable liquid and potentially featuring a molten lava on the dayside. Due to its proximity, tidal forces from the star are expected to enforce synchronous , locking one hemisphere in perpetual daylight. Additionally, Proxima Centauri's frequent stellar flares could erode any primordial atmosphere through intense and particle bombardment, limiting the planet's volatile retention.

Habitability and Biosignatures

Proxima Centauri b orbits within the star's , defined as the region between approximately 0.04 and 0.08 AU where liquid water could potentially exist on a , assuming Earth-like atmospheric conditions. This zone is much closer to the star than 's due to Proxima Centauri's low luminosity, placing planet b at a semi-major axis of about 0.05 AU. However, the planet's is severely challenged by the star's frequent flares, which deliver (UV) radiation up to 400 times higher than what receives from the Sun in the relevant spectral range, potentially sterilizing surface environments during active periods. Models of atmospheric evolution suggest that Proxima Centauri b could retain a substantial atmosphere of (N₂) and oxygen (O₂) if it possesses an intrinsic , which would shield against erosion. Without such protection, hydrodynamic escape driven by high XUV fluxes could strip away volatiles over billions of years, but magnetized scenarios predict retention of 1–10 bars of pressure, sufficient for a dense atmosphere capable of mitigating some effects. Prospective observations target biosignatures such as molecular oxygen (O₂), (CH₄), and (H₂O) to assess biological potential. The James Webb Space Telescope's NIRSpec instrument is optimized for detecting these gases via transmission during planetary transits, though the faint signal from Proxima b requires long integration times. Complementarily, the high-contrast spectrograph, planned to begin operations in 2025 on the , aims to constrain the planet's and orbital properties through reflected light, enabling indirect inferences. Tidal locking, likely due to the close orbit, confines to synchronous rotation, creating extreme temperature contrasts between the permanent dayside and nightside, with potential confined to region where moderate conditions might persist. The candidate c and confirmed d fall outside viable parameters: c, at ~1.5 AU, experiences equilibrium temperatures below freezing (~40 ), rendering it uninhabitable, while d, orbiting at ~0.029 AU, suffers surface temperatures exceeding 400 from intense stellar heating. Hypothetical concepts propose artificial magnetic shields or orbital sunshades to deflect flare-induced radiation and stabilize climates, though these remain speculative and untested for exoplanetary applications.

Observational History

Initial Discovery

Proxima Centauri was discovered on May 16, 1915, by Robert T. A. Innes, director of the Union Observatory in , , through astrometric comparison of photographic plates using a blink comparator; the plates, one from 1894 and the other from 1915, revealed the faint 11th-magnitude star's large matching that of Alpha Centauri, suggesting it was a distant companion to the binary system. Innes announced the find in a circular from the observatory, noting its position near Alpha Centauri but too faint for naked-eye visibility. In 1917, Dutch astronomer Joan Voûte conducted trigonometric parallax measurements at the Royal Observatory, Cape of Good Hope, yielding a value of 0.755 ± 0.028 arcseconds, which confirmed Proxima Centauri as the nearest star to the Sun at approximately 4.2 light-years and led Voûte to coin the name "Proxima Centauri," denoting its status as the closest member of the Centaurus constellation. That same year, Ejnar Hertzsprung obtained the first spectroscopic observations of the star at Leiden Observatory, classifying it as an M-type based on its late-type spectral features indicative of low temperature and high . In the , parallax measurements were refined using additional photographic plates from multiple observatories, stabilizing the value at around 0.76 arcseconds and solidifying the star's proximity to .

Modern Era Observations

In the latter half of the , ultraviolet spectroscopy of Proxima Centauri using the International Ultraviolet Explorer (IUE) revealed strong emission lines during flaring events, providing early evidence of the star's intense chromospheric and transition region activity. Coordinated observations with the Einstein Observatory in 1980 captured a major flare, where UV lines such as C IV and Si IV showed fluxes increasing by factors of over 100, indicating heating to temperatures exceeding 10^5 K in the star's atmosphere. These IUE spectra, spanning multiple wavelengths from 1150 to 3200 Å, confirmed the presence of quiescent and flaring plasma, distinguishing Proxima Centauri's activity from less dynamic M dwarfs. High-resolution optical in the late 1990s and early further characterized the star's flaring nature through variations. Observations with instruments like CORALIE on the 1.2-m Euler Telescope and HARPS detected periodic signals modulated by stellar activity, with flare-induced Doppler shifts up to several m/s, ruling out massive companions and attributing variability to surface phenomena such as starspots and flares. Subsequent monitoring with the HARPS spectrograph on the 3.6-m telescope at La Silla, starting in the early , refined these measurements, confirming that flares contribute significantly to the observed , with emission in lines like Hα strengthening during events. Interferometric observations in the early provided direct measurements of Proxima Centauri's size. Using the Interferometer (VLTI) with the VINCI instrument, angular diameters were resolved for low-mass stars, yielding a uniform-disk value of 1.02 ± 0.08 milliarcseconds for Proxima Centauri, corresponding to a linear of approximately 0.14 solar radii at its known . This resolution, achieved with baselines up to 140 m, marked the first such measurement for an M5.5V star and highlighted its compactness relative to solar-type stars. Photometric monitoring advanced in the mid-2000s with space-based observations from the Microvariability and Oscillations of STars (MOST) . Between 2007 and 2008, MOST captured continuous white-light photometry over several months, detecting the star's 83-day rotational period through spot modulation and identifying dozens of with energies up to 10^33 erg, occurring at a rate of about one per day. These data underscored Proxima Centauri's persistent variability, with flare amplitudes reaching 20% in optical bands. The (TESS) extended flare studies in , producing a comprehensive catalog from high-cadence photometry in Sectors 11 and 12. Analysis identified 72 flares over ~50 days, with a detection rate of 1.49 events per day and total flaring time comprising 7.2% of the observation period; energies ranged from 10^30 to 10^33 erg, revealing quasi-periodic oscillations during decay phases suggestive of magnetohydrodynamic processes. Recent ground-based observations in 2025 utilized the Atacama Large Millimeter/submillimeter Array (ALMA) for mm-wave imaging at 1.3 mm (233 GHz), constraining flare rates and probing convective dynamics. Over ~50 hours of integration, ALMA detected millimeter flares with energies exceeding 10^32 erg, occurring at a frequency consistent with optical rates but with distinct spectral evolution, indicating accelerated electron populations in the corona; no resolved imaging of flare loops was achieved, but the data provided the first cumulative flare frequency distribution at these wavelengths for an M dwarf. Astrometric data from Data Release 3 (DR3) in 2022 refined Proxima Centauri's to 3784.28 ± 0.24 mas/yr in and 766.39 ± 0.24 mas/yr in , with a total tangential velocity of ~22 km/s, confirming its membership in the Alpha Centauri system and enabling precise orbital modeling. Multi-messenger efforts have focused on X-ray observations, with detecting a range of flares in 2004, from microflares at low levels (~10^28 erg) to giant events peaking at luminosities over 10^29 erg/s, showing two-temperature plasma (0.2–1 keV) and continuous heating between outbursts.

Future Exploration

Upcoming Telescopes

The (JWST), operational since 2022, continues to support observations of Proxima Centauri into 2025 and beyond, leveraging its (MIRI) for coronagraphic imaging aimed at direct detection of Proxima b. MIRI's blocks the intense light from the host star, enabling high-contrast observations in the mid-infrared to search for thermal emission from the planet's atmosphere. Simulations indicate that JWST/MIRI can achieve sufficient sensitivity to detect an Earth-sized planet in Proxima's , with planned 2025 observations specifically targeting potential additional Earth-sized companions beyond the known planets b, c, and d. Complementing , JWST's Near-Infrared Spectrograph (NIRSpec) is slated for studies of Proxima's system, focusing on atmospheric characterization during potential planetary transits or phase-curve observations. Although Proxima b does not transit from Earth's perspective, NIRSpec's high-resolution capabilities (R up to 2700) in the 0.6–5.3 μm range allow for spectral analysis of any transiting inner planets or future discoveries, probing molecular features like or . These observations build on JWST's proven for other exoplanets, adapting techniques for non-transiting cases via secondary eclipse or reflection . The (ELT), under construction by the (ESO) with first light expected in March 2029, will feature the High-Resolution Spectrograph (HIRES) for ultra-precise (RV) measurements targeting Proxima Centauri. HIRES aims for RV precision below 0.1 m/s (10 cm/s), enabling the detection of Earth-mass planets in the and refinement of masses for known planets like Proxima b. For Proxima b specifically, HIRES could confirm its mass in just four nights of observation at a of 8, using single-conjugate to mitigate stellar activity noise common in M-dwarfs. Also on the ELT, the Mid-infrared ELT Imager and Spectrograph (METIS) will enable direct of Proxima b in the L and M bands (3–19 μm), focusing on thermal emission for atmospheric characterization. METIS's high-contrast and integral field (resolution R ~ 100,000) are projected to detect a 1.1 Earth-radius like Proxima b with a of 0.3 in about 10 hours, achieving contrasts up to 1:500 at 2 λ/D separation. This capability extends to probing biosignatures such as or in reflected or emitted light, prioritizing nearby temperate worlds. The RISTRETTO instrument, a visible high-resolution spectrograph proposed as a visitor facility for ESO's Very Large Telescope (VLT), is planned for first light around 2028 to constrain Proxima b's atmosphere and albedo via reflected light spectroscopy. Employing extreme adaptive optics and a coronagraph, RISTRETTO achieves raw contrasts of 10^{-4} and post-processed contrasts of 10^{-7} in the visible band, enabling detection of the planet's spectral features across 7 spatial elements. Simulations demonstrate its ability to measure Proxima b's orbital parameters and atmospheric composition, distinguishing between bare-rock and volatile-rich scenarios. The PLAnetary Transits and Oscillations of stars () mission, scheduled for launch in 2026 by the , will conduct wide-field transit searches optimized for M-dwarfs like Proxima Centauri, aiming to identify additional small planets in habitable zones. 's array of 34 telescopes will monitor up to one million stars, including nearby M-dwarfs, with photometric precision sufficient to detect -sized transiting planets down to 0.3 radii. For Proxima, this could reveal inner transiting companions overlooked by prior surveys, complementing RV for system architecture studies.

Interstellar Mission Concepts

Proxima Centauri, located 4.24 light-years from , has inspired several conceptual interstellar mission designs aimed at direct exploration of the system. In the 1970s, scientists conducted early studies on interstellar probe concepts, including the use of advanced ion drive for flyby missions to Alpha Centauri, with proposed travel times of around 40 years relying on high-efficiency electric systems to achieve significant fractions of speed. These concepts emphasized nuclear-electric ion engines to provide continuous over decades, enabling a to accelerate gradually to velocities sufficient for a multi-decade journey while carrying instruments for during the flyby. The most prominent modern proposal is the initiative, launched in by the foundation. This project envisions a fleet of gram-scale nanocrafts, each equipped with a , propelled by a ground-based array of lasers to reach 20% of the , allowing arrival at Proxima Centauri in approximately 20 years after launch. Although the project is currently on indefinite hold as of 2025, with limited funding expended, the design prioritizes laser sails over traditional due to the need for extreme in a compact form factor, though nuclear options remain under consideration for larger precursor missions. Key challenges for such missions include developing reliable systems, managing the 4.24-year one-way communication delay inherent to the distance, and providing shielding against interstellar cosmic rays and Proxima's frequent stellar flares. Laser sail requires precise beam control to avoid instability, while nuclear or alternatives demand immense power sources without refueling. Communication lags necessitate autonomous operations, with data transmission relying on compact lasers capable of beaming signals back across light-years. shielding poses material hurdles, as high-speed impacts with interstellar could erode unshielded probes. Scientific objectives for a Proxima flyby focus on in-situ of planets like Proxima b to assess surface features and atmospheres, mapping the system's magnetic fields to understand stellar influences on , and analyzing the for evidence of planetary formation or collisions. These goals would provide unprecedented close-range data, complementing remote observations by revealing details invisible from Earth-based telescopes. In 2025, progress on materials advanced with experimental tests at Caltech demonstrating thin-film sails capable of withstanding laser pressures up to 1,000 times Earth's gravity, aiding and stability during acceleration phases potentially complicated by Proxima's upon arrival. Similarly, researchers from and TU developed an ultra-reflective membrane just 100 nanometers thick, optimized for high reflectivity and thermal resilience, which could enable safer passage through the flare-prone environment of the Proxima system. These developments address durability needs for flare , where sails might adjust orientation to harness or evade intense stellar activity.

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