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Proxima Centauri b

Coordinates: Sky map 14h 29m 42.9487s, −62° 40′ 46.141″
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Template:Planetbox begin Template:Planetbox image Template:Planetbox star Template:Planetbox character Template:Planetbox orbit Template:Planetbox discovery Template:Planetbox catalog Template:Planetbox reference Template:Planetbox end Proxima Centauri b (also called Proxima b[1][2]) is an exoplanet orbiting within the habitable zone of the red dwarf star Proxima Centauri, the closest star to the Sun.[3][4] 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. It is the closest known exoplanet to the Solar System but not one of the better candidates for hosting life.[5]

In August 2016, the European Southern Observatory announced the discovery of the planet.[6][3][7]Cite error: The <ref> tag has too many names (see the help page).[8] Researchers think that its proximity to Earth offers an opportunity for possible robotic exploration of the planet with the Starshot project[3][4] or, at least, "in the coming centuries".[4]

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 (6.6 ft) per second.[6]

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 ME, which would be the actual mass if its orbit were seen edge on from the Earth, producing the maximum Doppler shift.[6] 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 ME.[9] If the planet 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.[10] The planet has an equilibrium temperature of 234 K (−39 °C; −38 °F).[6] This puts it in the habitable zone of its parent star.

Host star

The planet orbits a (M-type) red dwarf star named Proxima Centauri. The star has a mass of 0.12 M☉ and a radius of 0.14 R☉.[6] It has a surface temperature of 3042 K [11] and is 4.85 billion years old.[12] In comparison, the Sun is 4.6 billion years old [13] and has a surface temperature of 5778 K.[14] Proxima Centauri rotates once roughly every 83 days,[15] and has a luminosity about 0.0015 L☉.[6] The star is rich in metals, 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.[16][note 1]

The star’s apparent magnitude, or how bright it appears from Earth's perspective, is 11.13.[17] Even though it is the closest star to the Sun, it is not visible to the unaided eye from Earth because of its low luminosity.

Proxima Centauri is a flare star that undergoes occasional dramatic increases in brightness and high-energy emissions because of magnetic activity[18] 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.[6] Comparatively, Mercury, the closest planet to the Sun, has a semi-major axis distance of 0.39 AU. Proxima Centauri b receives from its host star about 65% of the amount of radiative flux that the Earth receives from the Sun. However, because of its tight orbit, Proxima Centauri b receives about 400 times more X-ray flux than the Earth does.[6]

Habitability

Artist's conception of Proxima Centauri b, with Proxima Centauri and the Alpha Centauri binary system in the background
See also: Habitability of red dwarf systems

The habitability of Proxima Centauri b has not been established.[19][20] [5] Depending on the volatile reservoirs and the rotation rate of the planet, 3D global climate models and theoretical arguments can be contemplated.[20][21]

The exoplanet is predicted to be 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 with an orbital period of ∼9.1–24.5 days.[6][further explanation needed]

Proxima Centauri b is close enough to its star that it might be tidally locked.[22][23] 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 permanently dark and freezing cold.[24][25] Scientists think that some habitable regions, if they exist, would be confined to the region in between the two extreme areas, referred to as the terminator line, where the temperatures might be suitable for liquid water to exist on such a planet.[23]

Proxima Centauri b's orbital eccentricity is not known with certainty, only that it is below 0.35[26] – 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.[27] The European Southern Observatory predicts that a far more clement environment would result from such a configuration, with average temperatures similar to those on Earth.[26][better source needed] 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.[23] If it has an atmosphere, simulations suggest that the planet could have lost about 1 ocean's worth of water 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 either in an area in the hemisphere of the planet facing the star or in a tropical belt (3:2 resonance rotation).[20][21] The planet may be within reach of telescopes and techniques that could reveal more about its composition and atmosphere, if it has any. [5]

Discovery

The first indications of the exoplanet were found in 2013 by Mikko Tuomi from archival observation data.[15][28] To confirm the possible discovery, the European Southern Observatory launched the Pale Red Dot[note 2] project in January 2016.[29] On 24 August 2016 the team, led by Guillem Anglada-Escudé of Queen Mary University of London, confirmed the existence of Proxima Centauri b[12]. The discovery was reported in Nature.[6][22] 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.[6] 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.[15]

  • 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.
    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.
    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 with the Very Large Telescope Interferometer (VLTI) at the ESO Paranal Observatory. The Sun and planet Jupiter are also shown for comparison.
    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 with the Very Large Telescope Interferometer (VLTI) at the ESO Paranal Observatory. 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 is too faint to see with the unaided eye but can be found using a small telescope.
    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 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, which was discovered using the HARPS instrument on the ESO 3.6-metre 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, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.

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.

See also

Notes

  1. ^ Taken from 100.21, which gives 1.62 times the metallicity of the Sun
  2. ^ Pale Red Dot is a reference to Pale Blue Dot – a distant photo of Earth taken by Voyager 1.

References

  1. ^ "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.
  2. ^ Davis, Nicola (24 August 2016). "Discovery of potentially Earth-like planet Proxima b raises hopes for life". The Guardian. Retrieved 24 August 2016.
  3. ^ a b c Chang, Kenneth (24 August 2016). "One Star Over, a Planet That Might Be Another Earth". New York Times. Retrieved 24 August 2016.
  4. ^ a b c Strickland, Ashley (24 August 2016). "Closest potentially habitable planet to our solar system found". CNN Health. Retrieved 25 August 2016.
  5. ^ a b c 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.
  6. ^ a b c d e f g h i j k 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. doi:10.1038/nature19106. ISSN 0028-0836.
  7. ^ "Planet Found in Habitable Zone Around Nearest Star". European Southern Observatory. 24 August 2016. {{cite web}}: |archive-date= requires |archive-url= (help); Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  8. ^ 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.
  9. ^ 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. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  10. ^ A Potentially Habitable World in Our Nearest Star. Planetary Habitability Laboratory. 24 August 2016.
  11. ^ 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.
  12. ^ a b 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.
  13. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  14. ^ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  15. ^ a b c "Proxima b is our neighbor… better get used to it!". Pale Red Dot. 24 August 2016. Retrieved 24 August 2016.
  16. ^ Cite error: The named reference aaa519_A105 was invoked but never defined (see the help page).
  17. ^ 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:1310.4746. Bibcode:2014AJ....147...21J. doi:10.1088/0004-6256/147/1/21. ISSN 0004-6256.
  18. ^ 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.
  19. ^ 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.
  20. ^ a b c 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" (PDF). Astronomy & Astrophysics. Retrieved 28 August 2016. {{cite journal}}: Explicit use of et al. in: |last4= (help)
  21. ^ a b The habitability of Proxima Centauri b - II. Possible climates and observability. Retrieved 25 August 2016.
  22. ^ a b 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.
  23. ^ a b c Singal, Ashok K. (2014). "Life on a tidally-locked planet". Planex Newsletter, Vol. , Issue , 8 (01). 4 (2): arXiv:1405.1025. arXiv:1405.1025. Bibcode:2014arXiv1405.1025S.
  24. ^ Barnes, Rory, ed. (2010), Formation and Evolution of Exoplanets, John Wiley & Sons, p. 248, ISBN 3527408967.
  25. ^ Heller, R.; Leconte, J.; Barnes, R. (April 2011). "Tidal obliquity evolution of potentially habitable planets". Astronomy & Astrophysics. 528: 16. arXiv:1101.2156. Bibcode:2011A&A...528A..27H. doi:10.1051/0004-6361/201015809. A27.{{cite journal}}: CS1 maint: postscript (link)
  26. ^ a b "Numerical simulation of possible surface temperatures on Proxima b (synchronous rotation)". ESO. 2016. Retrieved 24 August 2016.
  27. ^ Makarov, Valeri V. (June 2012), "Conditions of Passage and Entrapment of Terrestrial Planets in Spin-orbit Resonances", The Astrophysical Journal, 752 (1): 8, arXiv:1110.2658, Bibcode:2012ApJ...752...73M, doi:10.1088/0004-637X/752/1/73, 73.
  28. ^ Aron, Jacob. 24 August 2016. Proxima b: Closest Earth-like planet discovered right next door. New Scientist. Retrieved 24 August 2016.
  29. ^ "Follow a Live Planet Hunt!". European Southern Observatory. 15 January 2016. Retrieved 24 August 2016.
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