# Proxima Centauri b

Discovery Artist's conception of Proxima Centauri b as a rocky-like exoplanet, with Proxima Centauri and the Alpha Centauri binary system in the background. The actual appearance of the planet is unknown. Anglada-Escudé et al. European Southern Observatory 24 August 2016 Doppler spectroscopy 0.0485+0.0041−0.0051 AU 0.124+0.070−0.068 11.18427+0.00066−0.00070[1] d 310 ± 50[2] 1.38 ± 0.21[2] Proxima Centauri 1.30+1.20−0.62[3]R⊕ 1.60+0.46−0.36[3]M⊕ ~1.1 g, ~0.95 g Teq: 234 K (−39 °C; −38 °F) .mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

Proxima Centauri b (also called Proxima b[4][5] or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system.[6][7] It is approximately 4.2 light-years (4.0×1013 km) from Earth in the constellation Centaurus, making it and Proxima c the closest known exoplanets to the Solar System.

Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7,500,000 km; 4,600,000 mi) with an orbital period of approximately 11.2 Earth days, and has an estimated mass of at least 1.2 times that of Earth. It is subject to stellar wind pressures of more than 2,000 times those of Earth from the solar wind, and its habitability has not yet been definitively established.[8][9][10]

The planet's discovery was announced in August 2016.[6][2] It was found using the radial velocity method, where periodic Doppler shifts of the parent star's spectral lines suggest an orbiting object. From these readings, the parent star's radial velocity relative to the Earth is varying with an amplitude of about 1.4 metres (4.5 feet) per second.[2] According to Guillem Anglada‐Escudé, the planet's proximity to Earth offers an opportunity for robotic exploration with the Starshot project[6][7] or, at least, "in the coming centuries".[7]

Without its orbital inclination known, Proxima Centauri b's exact mass is unknown. If its orbit is nearly edge-on, it would have a mass of 1.173±0.086 M (Earth masses).[1] Statistically, there is a roughly 90% chance that its mass is less than 2.77 M.[1][11]

In May 2019, a paper presenting recent Spitzer Space Telescope data concluded that Proxima Centauri b did not transit its sun relative to Earth, and attributed previous transit detections to correlated noise.[12]

## Physical characteristics

The apparent inclination of Proxima Centauri b's orbit has not yet been measured. The minimum mass of Proxima b is 1.17 M, which would be the actual mass if its orbit were seen edge-on from the Earth.[1] Once its orbital inclination is known, the mass will be calculable. More tilted orientations imply a higher mass, with 90% of possible orientations implying a mass below 2.77 M.[1] If Proxima Centauri b's orbit is coplanar with that of the candidate exoplanet Proxima Centauri c, estimates of whose true mass were recently calculated using various combinations of its spectroscopic orbital parameters, Gaia DR2 proper motion anomaly, and astrometric measurements, then a true mass of Proxima b can be estimated. For example, a 2020 paper published by Tasker and Laneuville et al. estimates 1.60+0.46
−0.36
Earth masses.[3] Other possible values have been suggested, including another 2020 paper by Kervella et al. estimated 2.1+1.9
−0.6
Earth masses,[13] and another by Benedict et al. estimated 3.0±0.3 Earth masses[14] as true mass values for Proxima b.

The planet's exact radius is estimated to be slightly larger than that of Earth, but the exact degree is not fully known, though recent estimates suggest around 1.3 R. If it has a rocky composition and a density equal to Earth's, its radius is smaller. It could be larger if it has a lower density than Earth, or a mass higher than the minimum mass.[15] Like many super-Earth sized planets, Proxima Centauri b may have an icy composition like Neptune, with a thick enveloping hydrogen and helium atmosphere; this likelihood has been calculated to be greater than 10%. [16] However, based on recent modeled mass and radius, this seems unlikely.

The planet has an equilibrium temperature of 234 K (−39 °C; −38 °F),[2] somewhat colder than Earth’s 255 K (−18 °C; −1 °F).[17] The exact surface temperature of the planet cannot be determined currently, due to multiple influencing factors determining the temperature being unknown. Such factors would include whether it has an atmosphere or tidal heating.

### Host star

The planet orbits an M-type red dwarf named Proxima Centauri. The star has a mass of 0.12 M and a radius of 0.14 R.[2] It has a surface temperature of 3042 K[18] and is 4.85 billion years old.[19] In comparison, the Sun is 4.6 billion years old [20] and has a surface temperature of 5778 K.[21] Proxima Centauri rotates once roughly every 83 days,[22] and has a luminosity about 0.0015 L.[2] Like the two larger stars in the triple star system, Proxima Centauri is rich in metals compared with the Sun, something not normally found in low-mass stars like Proxima.[citation needed] Its metallicity ([Fe/H]) is 0.21, or 1.62 times the amount found in the Sun's atmosphere.[23][note 1]

Even though Proxima Centauri is the closest star to the Sun, it is not visible to the unaided eye from Earth because of its low luminosity (average apparent magnitude of 11.13[24]).

Proxima Centauri is a flare star.[25] This means that it undergoes occasional dramatic increases in brightness and high-energy emissions because of magnetic activity that would create large solar storms. On 18 March 2016, a superflare was observed with an energy of 1026.5 joules.[26] The March 2016 flare reached about 68 times usual level, thus a little brighter than the Sun.[27] The surface irradiation was estimated to be 100 times what is required to kill even UV-hardy microorganisms. Based on the rate of observed flares, total ozone depletion of an Earth-like atmosphere would occur within several hundred thousand years.[28][29]

## Habitability

Artist's conception of the surface of Proxima Centauri b. The Alpha Centauri binary system can be seen in the background, to the upper right of Proxima.

The habitability of Proxima Centauri b has not been established,[8][9] but the planet is subject to stellar wind pressures of more than 2,000 times those experienced by Earth from the solar wind.[8][32] Absent a magnetic field, this radiation and the stellar winds would likely blow any atmosphere away, leaving the subsurface as the only potentially habitable location on that planet.[29][33]

The exoplanet is orbiting within the habitable zone of Proxima Centauri, the region where, with the correct planetary conditions and atmospheric properties, liquid water may exist on the surface of the planet. The host star, with about an eighth of the mass of the Sun, has a habitable zone between ∼0.0423–0.0816 AU.[2] In October 2016, researchers at France's CNRS research institute stated that there is a considerable chance of the planet harboring surface oceans and having a thin atmosphere.[34] However, unless the planet transits in front of its star from the perspective of Earth, it is difficult to test these hypotheses.

### Tidal effects and stellar flares

Even though Proxima Centauri b is in the habitable zone, the planet's habitability has been questioned because of several potentially hazardous physical conditions. The exoplanet is close enough to its host star that it might be tidally locked.[35] In this case, it is possible that any habitable areas could be confined to the border region between the two extreme sides, generally referred to as the terminator line, since it is only here that temperatures might be suitable for liquid water to exist.[36] If the planet's orbital eccentricity is 0, this could result in synchronous rotation, with one hot side permanently facing towards the star, while the opposite side is in permanent darkness and freezing cold.[37][38] However, Proxima Centauri b's orbital eccentricity is not known with certainty, only that it is below 0.35—potentially high enough for it to have a significant chance of being captured into a 3:2 spin-orbit resonance similar to that of Mercury, where Proxima b would rotate around its axis approximately every 7.5 Earth days with about 22.4 Earth days elapsing between one sunrise and the next.[10][39][40] Resonances as high as 2:1 are also possible.[10][40] Another problem is that the flares released by Proxima Centauri could have eroded the atmosphere of the exoplanet. However, if Proxima b had a strong magnetic field, the flare activity of its parent star would not be a problem.[2]

### Climate and atmosphere possibilities

If water and an atmosphere are present, a far more hospitable environment would result. Assuming an atmospheric N2 pressure of 1 bar and ∼0.01 bar of CO2, in a world including oceans with average temperatures similar to those on Earth, a wide equatorial belt (non-synchronous rotation), or the majority of the sunlit side (synchronous rotation), would be permanently ice-free.[40][41] A large portion of the planet may be habitable if it has an atmosphere thick enough to transfer heat to the side facing away from the star.[36] If it has an atmosphere, simulations suggest that the planet could have lost about as much as the amount of water that Earth has due to the early irradiation in the first 100–200 million years after the planet's formation. Liquid water may be present only in the sunniest regions of the planet's surface in pools either in an area in the hemisphere of the planet facing the star or—if the planet is in a 3:2 resonance rotation—diurnally in the equatorial belt.[10][40] All in all, astrophysicists consider the ability of Proxima Centauri b to retain water from its formation as the most crucial point in evaluating the planet's present habitability.[42] The planet may be within reach of telescopes and techniques that could reveal more about its composition and atmosphere, if it has any.[8]

If an atmosphere is present, longer-wavelength radiation from the red dwarf parent star means that weather will be affected. Cloud formation on the day side of the planet will be inhibited compared to Earth (or Venus), resulting in clearer skies.[43]

## View from Proxima Centauri b

Looking towards the sky around Orion from Alpha Centauri with Sirius near Betelgeuse, Procyon in Gemini, and the Sun between Perseus and Cassiopeia generated by Celestia

Viewed from near the Alpha Centauri system, the sky would appear much as it does for an observer on Earth, except that Centaurus would be missing its brightest star. The Sun would be a yellow star of an apparent magnitude of +0.5 in eastern Cassiopeia, at the antipodal point of Alpha Centauri's current right ascension and declination, at 02h 39m 35s +60° 50′ (2000). This place is close to the 3.4-magnitude star ε Cassiopeiae. Because of the placement of the Sun, an interstellar or alien observer would find the \/\/ of Cassiopeia had become a /\/\/ shape[note 3] nearly in front of the Heart Nebula in Cassiopeia. Sirius lies less than a degree from Betelgeuse in the otherwise unmodified Orion and with a magnitude of −1.2 is a little fainter than from Earth but still the brightest star in the Alpha Centauri sky. Procyon is also displaced into the middle of Gemini, outshining Pollux, whereas both Vega and Altair are shifted northwestward relative to Deneb (which barely moves, due to its great distance), giving the Summer Triangle a more equilateral appearance.

From Proxima Centauri b, Alpha Centauri AB would appear like two close bright stars with the combined apparent magnitude of −6.8. Depending on the binary's orbital position, the bright stars would appear noticeably divisible to the naked eye, or occasionally, but briefly, as a single unresolved star. Based on the calculated absolute magnitudes, the apparent magnitudes of Alpha Centauri A and B would be −6.5 and −5.2, respectively.[note 4]

## Formation

It is unlikely that Proxima Centauri b originally formed in its current orbit since disk models for small stars like Proxima Centauri would contain less than one Earth mass M of matter within the central one AU at the time of their formation. This implies that either Proxima Centauri b was formed elsewhere in a manner still to be determined, or the current disc models for stellar formation are in need of revision.[2]

## Discovery

Velocity of Proxima Centauri towards and away from the Earth as measured with the HARPS spectrograph during the first three months of 2016. The red symbols with black error bars represent data points, and the blue curve is a fit of the data. The amplitude and period of the motion were used to estimate the planet's minimum mass.

The first indications of the exoplanet were found in 2013 by Mikko Tuomi of the University of Hertfordshire from archival observation data.[22][44] To confirm the possible discovery, a team of astronomers launched the Pale Red Dot[note 5] project in January 2016.[45] On 24 August 2016, the team of 31 scientists from all around the world,[46] led by Guillem Anglada-Escudé of Queen Mary University of London, confirmed the existence of Proxima Centauri b[19] through their research, published in a peer-reviewed article in Nature.[47][2][35][48][49][50]

The measurements were done using two spectrographs, HARPS on the ESO 3.6 m Telescope at La Silla Observatory and UVES on the 8-metre Very Large Telescope.[2] The peak radial velocity of the host star combined with the orbital period allowed for the minimum mass of the exoplanet to be calculated. The chance of a false positive detection is less than one in ten million.[22]

Observational complications of the star tend to indicate additional, not insignificant size, orbiting planets. Another super-Earth was noted on discovery of this planet as possible; its presence would not destabilize the orbit of Proxima Centauri b.[2] One very large super-Earth was discovered in 2019, known as Proxima Centauri c – it orbits at 1.5 AU away, too far to tug on the other planet at all significantly.

Data of ESPRESSO excludes extra companions with masses above 0.6 M at periods shorter than 50 days.[1] A potential companion, Proxima Centauri d, at 0.29 M, was found to have an orbit around 5.15 days.[1] It requires further study, to confirm its existence and identify its orbital properties.

## Future observations

The Very Large Telescope and the star system Alpha Centauri.[51]

A team of scientists think they can image Proxima Centauri b and probe the planet's atmosphere for signs of oxygen, water vapor, and methane, combining ESPRESSO and SPHERE on the VLT.[52] The James Webb Space Telescope may be able to characterize the atmosphere of Proxima Centauri b,[53] but there is no conclusive evidence for transits combining MOST and HATSouth photometry, giving it less than a 1 percent chance of being a transiting planet.[54] Future telescopes (the Extremely Large Telescope, the Giant Magellan Telescope, and the Thirty Meter Telescope) could have the capability to characterize Proxima Centauri b.[citation needed]

The discovery of Proxima b was significant to Breakthrough Starshot, a proof of concept project aiming to send a fleet of miniature probes to the Alpha Centauri system.[55] The project is led by research company Breakthrough Initiatives, and plans to develop and launch a fleet of miniature unmanned spacecraft called StarChips,[56] which could travel at up to 20% of the speed of light,[57][58] arriving at the system in roughly 20 years with notification reaching Earth a little over 4 years later.[6]

### 2069 Alpha Centauri mission

In 2017, Breakthrough Initiatives and the European Southern Observatory (ESO) entered a collaboration to enable and implement a search for habitable planets in the nearby star system, Alpha Centauri. The agreement involves Breakthrough Initiatives providing funding for an upgrade to the VISIR (VLT Imager and Spectrometer for mid-Infrared) instrument on ESO's Very Large Telescope (VLT) in Chile.[51]

## Notes

1. ^ Taken from 100.21, which gives 1.62 times the metallicity of the Sun
2. ^ From knowing the absolute visual magnitude of Proxima Centauri, ${\displaystyle \scriptstyle M_{V_{\ast }}=15.6}$, and the absolute visual magnitude of the Sun, ${\displaystyle \scriptstyle M_{V_{\odot }}=4.83}$, the visual luminosity of Proxima Centauri can be calculated: ${\displaystyle \scriptstyle {\frac {L_{V_{\ast }}}{L_{V_{\odot }}}}=10^{0.4\left(M_{V_{\odot }}-M_{V_{\ast }}\right)}}$ = 4.92×10−5. Proxima Centauri b orbits at 0.0485 AU and so therefore, through use of the inverse-square law, the visual luminosity—intensity at the planet's distance—can be calculated: ${\displaystyle \scriptstyle 4.92*10^{-5}\ *\ \scriptstyle {\left({\frac {1}{0.0485}}\right)^{2}}\ =\ 0.0209}$
3. ^ The coordinates of the Sun would be diametrically opposite Alpha Centauri AB, at α=02h 39m 36.4951s, δ=+60° 50′ 02.308″
4. ^ Computed; using in solar terms: 1.1 M and 0.92 M, luminosities 1.57 and 0.51 L*/L, Sun magnitude −26.73(v), 11.2 to 35.6 AU orbit. The minimum luminosity adds the planet's orbital radius to the A–B distance (max) (conjunction). The maximum luminosity subtracts the planet's orbital radius to the A–B distance (min) (opposition).
5. ^ Pale Red Dot is a reference to Pale Blue Dot—a distant photo of Earth taken by Voyager 1.

## References

1. Suárez Mascareño, A.; Faria, J. P.; Figueira, P.; Lovis, C.; Damasso, M.; González Hernández, J. I.; Rebolo, R.; Cristiano, S.; Pepe, F.; Santos, N. C.; Zapatero Osorio, M. R.; Adibekyan, V.; Hojjatpanah, S.; Sozzetti, A.; Murgas, F.; Abreo, M.; Affolter, M.; Alibert, Y.; Aliverti, M.; Allart, R.; Allende Prieto, C.; Alves, D.; Amate, M.; Avila, G.; Baldini, V.; Bandi, T.; Barros, S. C. C.; Bianco, A.; Benz, W.; et al. (2020). "Revisiting Proxima with ESPRESSO". arXiv:2005.12114 [astro-ph.EP].
2. Anglada-Escudé G, Amado PJ, Barnes J, Berdiñas ZM, Butler RP, Coleman GA, de la Cueva I, Dreizler S, Endl M, Giesers B, Jeffers SV, Jenkins JS, Jones HR, Kiraga M, Kürster M, López-González MJ, Marvin CJ, Morales N, Morin J, Nelson RP, Ortiz JL, Ofir A, Paardekooper S, Reiners A, Rodríguez E, Rodriguez-López C, Sarmiento LF, Strachan JP, Tsapras Y, Tuomi M, Zechmeister M (25 August 2016). "A terrestrial planet candidate in a temperate orbit around Proxima Centauri" (PDF). Nature. 536 (7617): 437–440. arXiv:1609.03449. Bibcode:2016Natur.536..437A. doi:10.1038/nature19106. ISSN 0028-0836. PMID 27558064.
3. ^ a b c Tasker, Elizabeth J.; Laneuville, Matthieu; Guttenberg, Nicholas (7 January 2020). "Estimating Planetary Mass with Deep Learning". The Astronomical Journal. 159 (2): 41. arXiv:1911.11035. Bibcode:2020AJ....159...41T. doi:10.3847/1538-3881/ab5b9e. ISSN 1538-3881.
4. ^ "Earth-like planet discovered orbiting sun's neighbor". CNN. 24 August 2016. Retrieved 24 August 2016. A planet named Proxima b has been discovered orbiting the closest star to our sun.
5. ^ Davis, Nicola (24 August 2016). "Discovery of potentially Earth-like planet Proxima b raises hopes for life". The Guardian. Archived from the original on 14 April 2019. Retrieved 24 August 2016.
6. ^ a b c d Chang, Kenneth (24 August 2016). "One Star Over, a Planet That Might Be Another Earth". The New York Times. Archived from the original on 26 June 2019. Retrieved 24 August 2016.
7. ^ a b c Strickland, Ashley (24 August 2016). "Closest potentially habitable planet to our solar system found". CNN. Archived from the original on 30 August 2016. Retrieved 25 August 2016.
8. ^ a b c d Clery, Daniel (26 August 2016). "The exoplanet next door". Science. 353 (6302): 857. Bibcode:2016Sci...353..857C. doi:10.1126/science.353.6302.857. PMID 27563079. Researchers have already found hundreds of similarly sized planets, and many appear to be far better candidates for hosting life than the one around Proxima Centauri, called Proxima b.
9. ^ a b Amos, Jonathan (24 August 2016). "Neighbouring star Proxima Centauri has Earth-sized planet". BBC News. Archived from the original on 24 August 2016. Retrieved 25 August 2016. Just how "habitable" this particular planet really is, one has to say is pure speculation for the time being.
10. ^ a b c d Ribas, Ignasi; Bolmont, Emeline; Selsis, Franck; Reiners, Ansgar; et al. (25 August 2016). "The habitability of Proxima Centauri b: I. Irradiation, rotation and volatile inventory from formation to the present" (PDF). Astronomy & Astrophysics. 596: A111. arXiv:1608.06813. Bibcode:2016A&A...596A.111R. doi:10.1051/0004-6361/201629576. Archived (PDF) from the original on 2 May 2019.
11. ^ Marchis, Franck (24 August 2016). "Proxima Centauri b: Have we just found Earth's cousin right on our doorstep?". The Planetary Society. Archived from the original on 7 June 2019. Retrieved 24 August 2016.
12. ^ Jenkins, James S.; Harrington, Joseph; Challener, Ryan C.; Kurtovic, Nicolás T.; et al. (11 May 2019). "Proxima Centauri b is not a transiting exoplanet". Monthly Notices of the Royal Astronomical Society. 487 (1): 268–274. arXiv:1905.01336. Bibcode:2019MNRAS.487..268J. doi:10.1093/mnras/stz1268.
13. ^ Kervella, Pierre; et al. (2020). "Orbital inclination and mass of the exoplanet candidate Proxima c". Astronomy & Astrophysics. 635: L14. arXiv:2003.13106. Bibcode:2020A&A...635L..14K. doi:10.1051/0004-6361/202037551. ISSN 0004-6361. If we assume the coplanarity of the orbits of the planets Proxima b and c, the de-projected mass of the close-in planet is mb = 2.1+1.9
−0.6
M (adopting mb sin i = 1.0±0.1 M from Damasso et al. 2020).
14. ^ Benedict, G. Fritz; et al. (2020). "A Preliminary Mass for Proxima Centauri C". Research Notes of the AAS. 4 (4): 46. Bibcode:2020RNAAS...4...46B. doi:10.3847/2515-5172/ab84f3. ISSN 2515-5172. Assuming a coplanar system, Proxima b would have Mb = 3 ± 0.3 M
15. ^ Mendez, Abel (17 August 2016). "A Potentially Habitable World in Our Nearest Star". Planetary Habitability Laboratory (Press release). University of Puerto Rico at Arecibo. Archived from the original on 2 May 2019.
16. ^ Bixel, A.; Apai, D. (21 February 2017). "Probabilistic Constraints on the Mass and Composition of Proxima b". The Astrophysical Journal Letters. 836 (2): L31. arXiv:1702.02542. Bibcode:2017ApJ...836L..31W. doi:10.3847/2041-8213/aa5f51. ISSN 2041-8205.
17. ^ "Equilibrium Temperatures of Planets". burro.astr.cwru.edu. Retrieved 1 August 2013.
18. ^ Ségransan, D.; Kervella, P.; Forveille, T.; Queloz, D. (2003). "First radius measurements of very low mass stars with the VLTI". Astronomy and Astrophysics. 397 (3): L5–L8. arXiv:astro-ph/0211647. Bibcode:2003A&A...397L...5S. doi:10.1051/0004-6361:20021714.
19. ^ a b Mathewson, Samantha (24 August 2016). "Proxima b By the Numbers: Possibly Earth-Like World at the Next Star Over". Space.com. Archived from the original on 16 November 2018. Retrieved 25 August 2016.
20. ^ Cain, Fraser (16 September 2008). "How Old is the Sun?". Universe Today. Archived from the original on 18 August 2010. Retrieved 19 February 2011.
21. ^ Cain, Fraser (15 September 2008). "Temperature of the Sun". Universe Today. Archived from the original on 29 August 2010. Retrieved 19 February 2011.
22. ^ a b c "Proxima b is our neighbor… better get used to it!". Pale Red Dot. 24 August 2016. Archived from the original on 31 March 2019. Retrieved 24 August 2016.
23. ^ Schlaufman, Kevin C.; Laughlin, Gregory (September 2010). "A physically-motivated photometric calibration of M dwarf metallicity". Astronomy and Astrophysics. 519: A105. arXiv:1006.2850. Bibcode:2010A&A...519A.105S. doi:10.1051/0004-6361/201015016.
24. ^ Jao, Wei-Chun; Henry, Todd J.; Subasavage, John P.; Winters, Jennifer G.; et al. (January 2014). "The Solar Neighborhood. XXXI. Discovery of an Unusual Red+White Dwarf Binary at ~25 pc via Astrometry and UV Imaging". The Astronomical Journal. 147 (1): 21. arXiv:1310.4746. Bibcode:2014AJ....147...21J. doi:10.1088/0004-6256/147/1/21. ISSN 0004-6256.
25. ^ Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S.; Dupuis, J.; Keenan, F. P. (2004). "A Detailed Study of Opacity in the Upper Atmosphere of Proxima Centauri" (PDF). The Astrophysical Journal. 612 (2): 1140–1146. Bibcode:2004ApJ...612.1140C. doi:10.1086/422803. hdl:10211.3/172067. Archived (PDF) from the original on 10 July 2019.
26. ^ Williams, Matt (10 April 2018). "Proxima Centauri Just Released a Flare so Powerful it was Visible to the Unaided Eye. Planets There Would Get Scorched". Universe Today. Archived from the original on 31 March 2019. Retrieved 17 January 2019.
27. ^ Howard, Ward S.; Tilley, Matt A.; Corbett, Hank; Youngblood, Allison; et al. (25 June 2018). "The First Naked-eye Superflare Detected from Proxima Centauri". The Astrophysical Journal Letters. 860 (2): L30. arXiv:1804.02001. Bibcode:2018ApJ...860L..30H. doi:10.3847/2041-8213/aacaf3.
28. ^ Airapetian, Vladimir S.; Glocer, Alex; et al. (2017). "How Hospitable Are Space Weather Affected Habitable Zones? The Role of Ion Escape". The Astrophysical Journal. 836 (1): L3. Bibcode:2017ApJ...836L...3A. doi:10.3847/2041-8213/836/1/L3.
29. ^ a b Rodriguez-Mozos, J. M.; Moya, A. (August 2019). "Erosion of an exoplanetary atmosphere caused by stellar winds". Astronomy & Astrophysics. 630. Table A.4. arXiv:1908.06695. Bibcode:2019A&A...630A..52R. doi:10.1051/0004-6361/201935543.
30. ^ Ritchie, Raymond J.; Larkum, Anthony W. D.; Ribas, Ignasi (April 2018). "Could photosynthesis function on Proxima Centauri b?". International Journal of Astrobiology. 17 (2): 147–176. Bibcode:2018IJAsB..17..147R. doi:10.1017/S1473550417000167. Retrieved 10 September 2018.
31. ^ Schlyter, Paul (5 March 2017). "Radiometry and photometry in astronomy". stjarnhimlen.se. Stockholm, Sweden. 10: How bright are natural light sources?. Retrieved 21 June 2017.
32. ^ Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer (28 September 2016). "The Space Weather of Proxima Centauri b". The Astrophysical Journal Letters. 833 (1): L4. arXiv:1609.09076. Bibcode:2016ApJ...833L...4G. doi:10.3847/2041-8205/833/1/L4.
33. ^ O'Neill, Ian (7 October 2016). "Eyeballing Proxima b: Probably Not a Second Earth". Space.com. Archived from the original on 10 July 2019. Retrieved 10 October 2016.
34. ^ "Planet in star system nearest our Sun 'may have oceans'". Phys.org. AFP. 6 October 2016. Archived from the original on 17 April 2019. Retrieved 6 October 2016.
35. ^ a b Witze, Alexandra (24 August 2016). "Earth-sized planet around nearby star is astronomy dream come true" (PDF). Nature. 536 (7617): 381–382. Bibcode:2016Natur.536..381W. doi:10.1038/nature.2016.20445. PMID 27558041. Retrieved 24 August 2016.
36. ^ a b Singal, Ashok K. (2014). "Life on a tidally-locked planet". Planex Newsletter. 4 (2): 8. arXiv:1405.1025. Bibcode:2014arXiv1405.1025S.
37. ^ Barnes, Rory, ed. (2010). Formation and Evolution of Exoplanets. John Wiley & Sons. p. 248. ISBN 978-3527408962.
38. ^ Heller, R.; Leconte, J.; Barnes, R. (April 2011). "Tidal obliquity evolution of potentially habitable planets". Astronomy & Astrophysics. 528: A27. arXiv:1101.2156. Bibcode:2011A&A...528A..27H. doi:10.1051/0004-6361/201015809.
39. ^ Makarov, Valeri V. (25 May 2012). "Conditions of Passage and Entrapment of Terrestrial Planets in Spin-orbit Resonances". The Astrophysical Journal. 752 (1): 73. arXiv:1110.2658. Bibcode:2012ApJ...752...73M. doi:10.1088/0004-637X/752/1/73.
40. ^ a b c d Turbet, Martin; Leconte, Jeremy; Selsis, Franck; Bolmont, Emeline; et al. (28 September 2016). "The habitability of Proxima Centauri b II. Possible climates and observability" (PDF). Astronomy & Astrophysics. 596: A112. arXiv:1608.06827. Bibcode:2016A&A...596A.112T. doi:10.1051/0004-6361/201629577. Retrieved 25 August 2016.
41. ^ Turbet, M.; Ribas, I. (24 August 2016). "Numerical simulation of possible surface temperatures on Proxima b (synchronous rotation)". European Southern Observatory. Retrieved 24 August 2016.
42. ^ Barnes, Rory; Deitrick, Russell; Luger, Rodrigo; Driscoll, Peter E.; et al. (24 August 2016). "The Habitability of Proxima Centauri b I: Evolutionary Scenarios". Astrobiology. 1608: 62. arXiv:1608.06919. Bibcode:2016arXiv160806919B.
43. ^ Eager, Jake K.; Reichelt, David J.; et al. (2020). "Implications of different stellar spectra for the climate of tidally locked Earth-like exoplanets". Astronomy & Astrophysics. 639: A99. arXiv:2005.13002. Bibcode:2020A&A...639A..99E. doi:10.1051/0004-6361/202038089.
44. ^ Aron, Jacob (24 August 2016). "Proxima b: Earth-like planet spotted just 4 light years away". New Scientist. Archived from the original on 20 September 2016. Retrieved 24 August 2016.
45. ^ "Follow a Live Planet Hunt!". European Southern Observatory. 15 January 2016. Archived from the original on 9 June 2019. Retrieved 24 August 2016.
46. ^ Feltman, Rachel (24 August 2016). "Scientists say they've found a planet orbiting Proxima Centauri, our closest neighbor". The Washington Post. Archived from the original on 7 September 2016.
47. ^ "Planet Found in Habitable Zone Around Nearest Star – Pale Red Dot campaign reveals Earth-mass world in orbit around Proxima Centauri". European Southern Observatory. 24 August 2016. Archived from the original on 21 March 2019. Retrieved 10 January 2017.
48. ^ "Planet Found in Habitable Zone Around Nearest Star". European Southern Observatory. 24 August 2016. Archived from the original on 9 July 2019.
49. ^ Wall, Mike (24 August 2016). "Found! Potentially Earth-Like Planet at Proxima Centauri Is Closest Ever". Space.com. Archived from the original on 3 July 2019.
50. ^ Knapton, Sarah (24 August 2016). "Proxima b: Alien life could exist on 'second Earth' found orbiting our nearest star in Alpha Centauri system". The Telegraph. Archived from the original on 26 August 2016. Retrieved 24 August 2016.
51. ^ a b "VLT to Search for Planets in Alpha Centauri System – ESO Signs Agreement with Breakthrough Initiatives" (Press release). ESO. Archived from the original on 27 April 2019. Retrieved 10 January 2017.
52. ^ Lovis, C.; Snellen, I.; Mouillet, D.; Pepe, F.; et al. (March 2017). "Atmospheric characterization of Proxima b by coupling the SPHERE high-contrast imager to the ESPRESSO spectrograph". Astronomy & Astrophysics. 599: A16. arXiv:1609.03082. Bibcode:2017A&A...599A..16L. doi:10.1051/0004-6361/201629682.
53. ^ Kreidberg, Laura; Loeb, Abraham (15 November 2016). "Prospects for Characterizing the Atmosphere of Proxima Centauri b". The Astrophysical Journal. 832 (1): L12. arXiv:1608.07345. Bibcode:2016ApJ...832L..12K. doi:10.3847/2041-8205/832/1/L12.
54. ^ Kipping, David M.; Cameron, Chris; Hartman, Joel D.; Davenport, James R. A.; et al. (2 February 2017). "No Conclusive Evidence for Transits of Proxima b in MOST Photometry". The Astronomical Journal. 153 (3): 93. arXiv:1609.08718. Bibcode:2017AJ....153...93K. doi:10.3847/1538-3881/153/3/93.
55. ^ "Starshot". Breakthrough Initiatives. 12 April 2016. Archived from the original on 22 May 2019. Retrieved 12 April 2016.
56. ^ Gilster, Paul (12 April 2016). "Breakthrough Starshot: Mission to Alpha Centauri". Centauri Dreams. Retrieved 14 April 2016.
57. ^ Overbye, Dennis (12 April 2016). "Reaching for the Stars, Across 4.37 Light-Years; A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away". The New York Times. Archived from the original on 15 April 2016. Retrieved 12 April 2016.
58. ^ Stone, Maddie (12 April 2016). "Stephen Hawking and a Russian Billionaire Want to Build an Interstellar Starship". Gizmodo. Archived from the original on 30 May 2019. Retrieved 12 April 2016.