Proxima Centauri b

Proxima Centauri b
Exoplanet List of exoplanets

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.
Parent star
Star Proxima Centauri
Constellation Centaurus
Right ascension (α) 14h 29m 42.94853s
Declination (δ) −62° 40′ 46.1631″
Apparent magnitude (mV) 11.13
Distance4.224 ly
(1.295[1] pc)
Spectral type M6Ve[2]
Mass (m) 0.123 (± 0.006)[3] M☉
Radius (r) 0.141 (± 0.007)[4] R☉
Temperature (T) 3042 (± 117)[3] K
Metallicity [Fe/H] 0.21[5]
Age 4.85[6] Gyr
Physical characteristics
Minimum mass(m sin i)1.27+0.19
−0.17[1] M⊕
Radius(r)≥1.1 (± 0.3)[7] R⊕
Stellar flux(F⊙)0.65[1] ⊕
Temperature (T) 234 K (−39 °C; −38 °F)
Orbital elements
Semi-major axis(a) 0.0485+0.0041
−0.0051[1] AU
Eccentricity (e) <0.35[1]
Orbital period(P) 11.186+0.001
−0.002[1] d
Argument of
periastron		 (ω) 310 (± 50)[1]°
Semi-amplitude (K) 1.38 (± 0.21)[1] m/s
Discovery information
Discovery date 24 August 2016
Discoverer(s) Anglada-Escudé (ca) et al.
Discovery method Doppler spectroscopy
Discovery site European Southern Observatory
Discovery status Confirmed
Other designations
Alpha Centauri Cb, Proxima b, GL 551 b, HIP 70890 b
Database references
Extrasolar Planets
Encyclopaedia		data
SIMBADdata
Exoplanet Archivedata
Open Exoplanet Cataloguedata

Proxima Centauri b (also called Proxima b[8][9]) is an exoplanet orbiting within the habitable zone of the red dwarf star Proxima Centauri, the closest star to the Sun.[10][11] It is located about 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) from Earth in the constellation of Centaurus, making it the closest known exoplanet to the Solar System. It is unlikely to be habitable, as the planet is subject to stellar wind pressures of more than 2,000 times those experienced by Earth from the solar wind. More information about the planet's physical characteristics is needed for a proper evaluation.[12][13][14]

In August 2016, the European Southern Observatory announced the discovery of the planet.[1][10][15][16][17] The planet was found using the radial velocity method, where periodic Doppler shifts of spectral lines of the host star suggest an orbiting object. From these readings, the radial velocity of the parent star relative to the Earth is varying with an amplitude of about 2 metres (7 feet) per second.[1]

Researchers think that its proximity to Earth offers an opportunity for robotic exploration of the planet with the Starshot project[10][11] or, at least, "in the coming centuries".[11]

Characteristics

Mass, radius and temperature

The apparent inclination of Proxima Centauri b's orbit has not yet been measured. The minimum mass of Proxima b is 1.27 M⊕, which would be the actual mass if its orbit were seen edge on from the Earth, producing the maximum Doppler shift.[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 3 M⊕.[18] The planet's exact radius is unknown. If it has a rocky composition and a density equal to that of the Earth, then its radius is at least 1.1 R⊕. It could be larger if it has a lower density than the Earth, or a mass higher than the minimum mass.[7] The planet has an equilibrium temperature of 234 K (−39 °C; −38 °F).[1]

Host star

The planet orbits a (M-type) red dwarf named Proxima Centauri. The star has a mass of 0.12 M☉ and a radius of 0.14 R☉.[1] It has a surface temperature of 3042 K [3] 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☉.[1] Like the two larger stars in the triple star system, Proxima Centauri is rich in metals, relative to the Sun, something not normally found in low-mass stars like Proxima. Its metallicity ([Fe/H]) is 0.21, or 1.62 times the amount found in the Sun's atmosphere.[5][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 (apparent magnitude of 11.13[23]).

Proxima Centauri is a flare star that undergoes occasional dramatic increases in brightness and high-energy emissions because of magnetic activity[24] that would create large solar storms, possibly irradiating the surface of the exoplanet if it does not possess a strong magnetic field or a protective atmosphere.

Orbit

Proxima Centauri b orbits its host star every 11.186 days at a semi-major axis distance of approximately 0.05 astronomical units (7,000,000 km; 5,000,000 mi), which means the distance from the exoplanet to its host star is one-twentieth of the distance from the Earth to its own host star, the Sun.[1] Comparatively, Mercury, the closest planet to the Sun, has a semi-major axis distance of 0.39 AU. Proxima Centauri b receives about 65% of the amount of radiative flux from its host star that the Earth receives from the Sun. Most of the radiative flux from Proxima Centauri is in the infrared spectrum. In the visible spectrum, the exoplanet only receives 2% of the light Earth does, so it would never get brighter than twilight anywhere on Proxima Centauri b's surface.[note 2] However, because of its tight orbit, Proxima Centauri b receives about 400 times more X-ray radiation than the Earth does.[1]

Habitability

Artist's conception of Proxima Centauri b, with Proxima Centauri and the Alpha Centauri binary system in the background

It is unlikely that Proxima Centauri b is habitable, as the planet is subject to stellar wind pressures of more than 2,000 times those experienced by Earth from the solar wind.[12][25] This radiation and the stellar winds would likely blow any atmosphere away, leaving the undersurface as the only vaguely habitable location on that planet.[26] But the habitability of Proxima Centauri b has not been established.[12][13] Depending on the volatile reservoirs and the rotation rate of the planet, 3D global climate models and theoretical arguments can be contemplated.

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 red dwarf host star, with about an eighth of the mass of the Sun, has a habitable zone between ∼0.0423–0.0816 AU.[1]

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.[27][28] If the planet's orbital eccentricity is 0, this could result in synchronous rotation, with one blazing hot side permanently facing towards the star, while the opposite side is in permanent darkness and freezing cold.[29][30] In this case, scientists think that any habitable areas on the planet, if they exist, would be confined to the border region between the two extreme sides, generally referred to as the terminator line. Only here, temperatures might be suitable for liquid water to exist.[28] However, Proxima Centauri b's orbital eccentricity is not known with certainty, only that it is below 0.35[31] – 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 a Proxima b day would be roughly equivalent to that of 7.5 Earth days.[14][32][33] Resonances as high as 2:1 are possible and an initial inclination of the planetary orbit to the plane of the ecliptic could contribute to this.[14][33]

The European Southern Observatory estimates that if water and an atmosphere are present, a far more clement environment would result from such a configuration. In a world including oceans, with average temperatures similar to those on Earth, assuming an atmospheric N2 pressure of 1 bar and ∼0.01 bar of CO2, a wide equatorial belt (non-synchronous rotation), or the majority of the sunlit side (synchronous rotation), would be permanently ice-free.[31][33] 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.[28] 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 diurnally in the equatorial belt (3:2 resonance rotation).[14][33] 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.[34] The planet may be within reach of telescopes and techniques that could reveal more about its composition and atmosphere, if it has any.[12]

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.[35] However, unless the planet transits, it is difficult to confirm these hypotheses.

Formation

It seems implausible that Proxima Centauri b originally formed in its current orbit since disk models for small stars like Proxima Centauri would contain less than one M⊕ within the central one AU. This implies that Proxima Centauri b was either formed elsewhere in a way still to be determined or that the current disk models for stellar formation have to be revised.[1]

Discovery

The first indications of the exoplanet were found in 2013 by Mikko Tuomi of the University of Hertfordshire from archival observation data.[22][36] To confirm the possible discovery, the European Southern Observatory launched the Pale Red Dot[note 3] project in January 2016.[37] On 24 August 2016 the team of 31 scientists from all around the world,[38] led by Guillem Anglada-Escudé of Queen Mary University of London, confirmed the existence of Proxima Centauri b[19] through a peer-reviewed article published by Nature.[1][27] 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.[1] 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 odds of a false positive detection is less than one in ten million.[22]

Observational complications of the system still leave theoretical room for additional large planets to orbit Proxima Centauri. Calculations suggest that another super-Earth planet around the star cannot be ruled out and that its presence would not destabilize the orbit of Proxima Centauri b.[1] A second signal in the range of 60 to 500 days was also detected, but its nature is still unclear due to stellar activity.[1]

Observations

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.[39] The JWST may be able to characterize the atmosphere of Proxima Centauri b[40] and 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.[41] The planet might be in the reach of telescopes and other techniques.[12] Although no current technology allows a detailed observation of Proxima b, the potential habitability of the planet prompts the development of mechanisms and techniques to achieve new discoveries. Future telescopes (the European Extremely Large Telescope, the Giant Magellan Telescope, and the Thirty Meter Telescope) could have the capability to characterize Proxima Centauri b.

Exploration

The discovery of Proxima b was significant to Breakthrough Starshot, a recent project aiming to send a fleet of miniature probes to the Alpha Centauri system. The project, led by Breakthrough Initiatives, a research company funded by Russian entrepreneur Yuri Milner, plans to develop and launch a fleet of miniature unmanned spacecraft called StarChips,[42] which could travel at up to 20% of the speed of light,[43][44][45][46] arriving at the system in 20 years with notification reaching Earth 4 years later.[10]

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.
 
An angular size comparison of how Proxima will appear in the sky seen from Proxima b, compared to how the Sun appears in our sky on Earth. Proxima is much smaller than the Sun, but Proxima b lies very close to its star.
 
The relative sizes of a number of objects, including the three stars of the Alpha Centauri triple system and some other stars for which the angular sizes have also been measured. The Sun and planet Jupiter are also shown for comparison.
 
This chart shows the large southern constellation of Centaurus (the Centaur) and shows most of the stars visible with the naked eye on a clear dark night. The location of the closest star to the Solar System, Proxima Centauri, is marked with a red circle. Proxima Centauri is too faint to see with the unaided eye but can be found using a small telescope.
 
This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b.
 

Videos

A numerical simulation of possible surface temperatures on Proxima b performed with the Laboratoire de Météorologie Dynamique's Planetary Global Climate Model. Here it is hypothesised that the planet possesses an Earth-like atmosphere and that it is covered by an ocean (the dashed line is the frontier between the liquid and icy oceanic surface). Two models were produced for the planet's rotation. Here the planet is in a so-called 3:2 resonance (a natural frequency for the orbit), and is seen as a distant observer would do during one full orbit.
 
A numerical simulation of possible surface temperatures. Here it is hypothesised that the planet possesses an Earth-like atmosphere and that it is covered by an ocean (the dashed line is the frontier between the liquid and icy oceanic surface). Here the planet is in synchronous rotation (like the Moon around the Earth), and is seen as a distant observer would do during one full orbit.
 
Proxima b 

See also

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, , and the absolute visual magnitude of the Sun, , the visual luminosity of Proxima Centauri can be calculated: = 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:
  3. ↑ Pale Red Dot is a reference to Pale Blue Dot – a distant photo of Earth taken by Voyager 1.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Anglada-Escudé, G.; Amado, P. J.; Barnes, J.; Berdiñas, Z. M.; Butler, R. P.; Coleman, G. A. L.; de la Cueva, I.; Dreizler, S.; Endl, M.; Giesers, B.; Jeffers, S. V.; Jenkins, J. S.; Jones, H. R. A.; Kiraga, M.; Kürster, M.; López-González, M. J.; Marvin, C. J.; Morales, N.; Morin, J.; Nelson, R. P.; Ortiz, J. L.; Ofir, A.; Paardekooper, S.-J.; Reiners, A.; Rodríguez, E.; Rodrίguez-López, C.; Sarmiento, L. F.; Strachan, J. P.; 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. Bibcode:2016Natur.536..437A. doi:10.1038/nature19106. ISSN 0028-0836.
  2. ↑ Torres, C. A. O.; Quast, G. R.; Da Silva, L.; De La Reza, R.; Melo, C. H. F.; Sterzik, M. (December 2006). "Search for associations containing young stars (SACY). I. Sample and searching method". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258Freely accessible. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602.
  3. 1 2 3 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/0211647Freely accessible. Bibcode:2003A&A...397L...5S. doi:10.1051/0004-6361:20021714.
  4. ↑ Demory, B.-O.; Ségransan, D.; Forveille, T.; Queloz, D.; Beuzit, J.-L.; Delfosse, X.; Di Folco, E.; Kervella, P.; Le Bouquin, J.-B. (October 2009). "Mass-radius relation of low and very low-mass stars revisited with the VLTI". Astronomy and Astrophysics. 505 (1): 205–215. arXiv:0906.0602Freely accessible. Bibcode:2009A&A...505..205D. doi:10.1051/0004-6361/200911976.
  5. 1 2 Schlaufman, K. C.; Laughlin, G. (September 2010). "A physically-motivated photometric calibration of M dwarf metallicity". Astronomy and Astrophysics. 519: A105. arXiv:1006.2850Freely accessible. Bibcode:2010A&A...519A.105S. doi:10.1051/0004-6361/201015016.
  6. ↑ Kervella, Pierre; Thevenin, Frederic (15 March 2003). "A family portrait of the Alpha Centauri system: VLT interferometer studies the nearest stars". ESO. Retrieved 5 September 2016.
  7. 1 2 A Potentially Habitable World in Our Nearest Star. Planetary Habitability Laboratory. 24 August 2016.
  8. ↑ "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.
  9. ↑ Davis, Nicola (24 August 2016). "Discovery of potentially Earth-like planet Proxima b raises hopes for life". The Guardian. Retrieved 24 August 2016.
  10. 1 2 3 4 Chang, Kenneth (24 August 2016). "One Star Over, a Planet That Might Be Another Earth". New York Times. Retrieved 24 August 2016.
  11. 1 2 3 Strickland, Ashley (24 August 2016). "Closest potentially habitable planet to our solar system found". CNN Health. Retrieved 25 August 2016.
  12. 1 2 3 4 5 Clery, Daniel (26 August 2016). "The exoplanet next door". Science News. Retrieved 28 August 2016. 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.
  13. 1 2 Amos, Jonathan (24 August 2016). "Neighbouring star Proxima Centauri has Earth-sized planet". BBC News. Retrieved 25 August 2016. Just how "habitable" this particular planet really is, one has to say is pure speculation for the time being.
  14. 1 2 3 4 Ribas, Ignasi; Bolmont, Emeline; Selsis, Franck; et al. (25 August 2016). "The habitability of Proxima Centauri b: I. Irradiation, rotation and volatile inventory from formation to the present". arXiv:1608.06813Freely accessible [astro-ph.EP].
  15. ↑ "Planet Found in Habitable Zone Around Nearest Star". European Southern Observatory. 24 August 2016.
  16. ↑ ""Found! Potentially Earth-Like Planet at Proxima Centauri Is Closest Ever "". Space.com. 24 August 2016.
  17. ↑ 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. Telegraph Media Group. Retrieved 24 August 2016.
  18. ↑ Marchis, Franck (24 August 2016). "Proxima Centauri b: Have we just found Earth's cousin right on our doorstep?". The Planetary Society. Retrieved 24 August 2016.
  19. 1 2 Mathewson, Samantha (24 August 2016). "Proxima b By the Numbers: Possibly Earth-Like World at the Next Star Over". Space.com. Retrieved 25 August 2016.
  20. ↑ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  21. ↑ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  22. 1 2 3 "Proxima b is our neighbor ... better get used to it!". Pale Red Dot. 24 August 2016. Retrieved 24 August 2016.
  23. ↑ Jao, Wei-Chun; Henry, Todd J.; Subasavage, John P.; Winters, Jennifer G.; Gies, Douglas R.; Riedel, Adric R.; Ianna, Philip A. (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:1310.4746Freely accessible. Bibcode:2014AJ....147...21J. doi:10.1088/0004-6256/147/1/21. ISSN 0004-6256.
  24. ↑ 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". The Astrophysical Journal. 612 (2): 1140–1146. Bibcode:2004ApJ...612.1140C. doi:10.1086/422803.
  25. ↑ Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer (28 September 2016). "The Space Weather of Proxima Centauri b". arXiv:1609.09076Freely accessible [astro-ph.SR].
  26. ↑ O'Neill, Ian (7 October 2016). "Eyeballing Proxima b: Probably Not a Second Earth". Discovery News. Space.com. Retrieved 2016-10-10.
  27. 1 2 Witze, Alexandra (24 August 2016). "Earth-sized planet around nearby star is astronomy dream come true". Nature. pp. 381–382. doi:10.1038/nature.2016.20445. Retrieved 24 August 2016.
  28. 1 2 3 Singal, Ashok K. (2014). "Life on a tidally-locked planet". Planex Newsletter. 4 (2): 8. arXiv:1405.1025Freely accessible. Bibcode:2014arXiv1405.1025S.
  29. ↑ Barnes, Rory, ed. (2010), Formation and Evolution of Exoplanets, John Wiley & Sons, p. 248, ISBN 3527408967.
  30. ↑ Heller, R.; Leconte, J.; Barnes, R. (April 2011). "Tidal obliquity evolution of potentially habitable planets". Astronomy & Astrophysics. 528: 16. arXiv:1101.2156Freely accessible. Bibcode:2011A&A...528A..27H. doi:10.1051/0004-6361/201015809. A27.
  31. 1 2 "Numerical simulation of possible surface temperatures on Proxima b (synchronous rotation)". ESO. 2016. Retrieved 24 August 2016.
  32. ↑ Makarov, Valeri V. (June 2012), "Conditions of Passage and Entrapment of Terrestrial Planets in Spin-orbit Resonances", The Astrophysical Journal, 752 (1): 8, arXiv:1110.2658Freely accessible, Bibcode:2012ApJ...752...73M, doi:10.1088/0004-637X/752/1/73, 73.
  33. 1 2 3 4 The habitability of Proxima Centauri b - II. Possible climates and observability. Retrieved 25 August 2016.
  34. ↑ Barnes, Rory (24 August 2016). "The Habitability of Proxima Centauri b I: Evolutionary Scenarios". Astrobiology. 1608: 62. arXiv:1608.06919Freely accessible. Bibcode:2016arXiv160806919B.
  35. ↑ "Planet in star system nearest our Sun 'may have oceans'", Phys.org, Retrieved 6 October 2016
  36. ↑ Aron, Jacob. 24 August 2016. Proxima b: Closest Earth-like planet discovered right next door. New Scientist. Retrieved 24 August 2016.
  37. ↑ "Follow a Live Planet Hunt!". European Southern Observatory. 15 January 2016. Retrieved 24 August 2016.
  38. ↑ Feltman, Rachel (August 24, 2016). "Scientists say they've found a planet orbiting Proxima Centauri, our closest neighbor". The Washington Post – via GALE.
  39. ↑ Lovis, C.; Snellen, I.; Mouillet, D.; Pepe, F.; Wildi, F.; Astudillo-Defru, N.; Beuzit, J. -L.; Bonfils, X.; Cheetham, A.; Conod, U.; Delfosse, X.; Ehrenreich, D.; Figueira, P.; Forveille, T.; Martins, J. H. C.; Quanz, S.; Santos, N. C.; Schmid, H. -M.; Ségransan, D.; Udry, S. (2016). "Atmospheric characterization of Proxima b by coupling the SPHERE high-contrast imager to the ESPRESSO spectrograph". arXiv:1609.03082Freely accessible [astro-ph.EP]. line feed character in |title= at position 65 (help)
  40. ↑ Kreidberg, Laura; Loeb, Abraham (2016). "Prospects for Characterizing the Atmosphere of Proxima Centauri b". arXiv:1608.07345Freely accessible [astro-ph.EP].
  41. ↑ Kipping, David M.; Cameron, Chris; Hartman, Joel D.; Davenport, James R. A.; Matthews, Jaymie M.; Sasselov, Dimitar; Rowe, Jason; Siverd, Robert J.; Chen, Jingjing; Sandford, Emily; Bakos, Gáspár Á.; Jordan, Andres; Bayliss, Daniel; Henning, Thomas; Mancini, Luigi; Penev, Kaloyan; Csubry, Zoltan; Bhatti, Waqas; Joao Da Silva Bento; Guenther, David B.; Kuschnig, Rainer; Moffat, Anthony F. J.; Rucinski, Slavek M.; Weiss, Werner W. (2016). "No Conclusive Evidence for Transits of Proxima b in MOST photometry". arXiv:1609.08718Freely accessible [astro-ph.EP].
  42. ↑ Gilster, Paul (12 April 2016). "Breakthrough Starshot: Mission to Alpha Centauri". Centauri Dreams. Retrieved 14 April 2016.
  43. ↑ Staff (12 April 2016). "Breakthrough Starshot". Breakthrough Initiatives. Retrieved 12 April 2016.
  44. ↑ 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". New York Times. Retrieved 12 April 2016.
  45. ↑ Stone, Maddie (April 12, 2016). "Stephen Hawking and a Russian Billionaire Want to Build an Interstellar Starship". Gizmodo. Retrieved 12 April 2016.
  46. ↑ Staff (12 April 2016). "Breakthrough Initiatives - Breakthrough Starshot". Breakthrough Initiatives. Retrieved 14 April 2016.
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