Wikipedia

51 Pegasi b

"Dimidium" redirects here. For the value, seehalf.For C. dimidium, seeCaladenia dimidia.

51 Pegasi b,officially namedDimidium/dɪˈmɪdiəm/,is anextrasolar planetapproximately 50light-years(15parsecs) away in theconstellationofPegasus.It was the firstexoplanetto be discoveredorbitingamain-sequencestar,[3]theSun-like51 Pegasi,and marked a breakthrough in astronomical research. It is theprototypefor a class of planets calledhot Jupiters.[4]

Dimidium/51 Pegasi b
An artist's impression of 51 Pegasi b (center) and its star (right).
Discovery
Discovered byMichel Mayorand
Didier Queloz
Discovery siteOHP,France
Discovery date6 October 1995;29 years ago(6 October 1995)
Radial velocity(ELODIE)
Designations
Dimidium
Orbital characteristics
Aphelion0.0534 AU (7,990,000 km)
Perihelion0.0520 AU (7,780,000 km)
0.0527 ± 0.0030 AU (7,880,000 ± 450,000 km)
Eccentricity0.013 ± 0.012
4.230785 ± 0.000036d
101.5388h
136km/s
Star51 Pegasi
Physical characteristics
1.2±0.1RJ[1]
Mass0.46±0.02MJ[2]
Temperature1,250K[2]

In 2017, traces of water were discovered in the planet'satmosphere.[5]In 2019, theNobel Prize in Physicswas awarded in part for the discovery of 51 Pegasi b.[6]

Name

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51 Pegasiis theFlamsteed designationof the host star. The planet was originally designated 51 Pegasi b byMichel MayorandDidier Queloz,who discovered the planet in 1995. The following year it was unofficially dubbed "Bellerophon"/bɛˈlɛrəfɒn/by astronomerGeoffrey Marcy,who followed theconventionof naming planets afterGreekandRoman mythological figures(Bellerophonis a figure from Greek mythology who rode the winged horsePegasus).[7]

In July 2014, theInternational Astronomical UnionlaunchedNameExoWorlds,a process for giving proper names to certainexoplanetsand their host stars.[8]The process involved public nomination and voting for the new names.[9]In December 2015, theIAUannounced the winning name for thisplanetwas Dimidium.[10]The name was submitted by theAstronomische Gesellschaft Luzern(Germanfor 'Astronomical Society of Lucerne'),Switzerland.'Dimidium' isLatinfor 'half', referring to the planet'smassof approximately half the mass ofJupiter.[11]

Discovery

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The location of51 PegasiinPegasus

Theexoplanet's discovery was announced on October 6, 1995, byMichel MayorandDidier Quelozof theUniversity of Genevain the journalNature.[12]They used theradial velocity methodwith theELODIE spectrographon theObservatoire de Haute-Provencetelescope in France and made world headlines with their announcement. For this discovery, they were awarded the 2019Nobel Prize in Physics.[6]

The planet was discovered using a sensitivespectroscopethat could detect the slight and regularvelocitychanges in the star'sspectral linesof around 70 metres per second. These changes are caused by the planet'sgravitationaleffects from just 7 million kilometres' distance from the star.

Within a week of the announcement, the planet was confirmed by another team using theLick ObservatoryinCalifornia.[13]

Physical characteristics

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Profile of planet 51 Pegasi b by NASA
Promotional "Exoplanet Travel Bureau" poster from NASA

After its discovery, many teams confirmed the planet's existence and obtained more observations of its properties. It was discovered that the planet orbits the star in around four days. It is much closer to it thanMercuryis to the Sun,[3]moves at anorbital speedof 136 km/s (300,000 mph), yet has a minimum mass about half that of Jupiter (about 150 times that of theEarth). At the time, the presence of a huge world so close to its star was not compatible with theories ofplanet formationand was considered an anomaly. However, since then, numerous other "hot Jupiters" have been discovered[3](such as55 Cancriandτ Boötis), and astronomers are revising their theories of planet formation to account for them by studyingorbital migration.[4]

Assuming the planet is perfectly grey with no greenhouse or tidal effects, and aBond albedoof 0.1, the temperature would be 1,265 K (992 °C; 1,817 °F). This is between the predicted temperatures ofHD 189733 bandHD 209458 b(1,180 K (910 °C; 1,660 °F)–1,392 K (1,119 °C; 2,046 °F)), before they were measured.[14]

In the report of the discovery, it was initially speculated that 51 Pegasi b was the stripped core of a brown dwarf of a decomposed star and was therefore composed of heavy elements, but it is now believed to be agas giant.It is sufficiently massive that its thick atmosphere is not blown away by the star'ssolar wind.

51 Pegasi b probably has a greaterradiusthan that of Jupiter despite its lower mass. This is because its superheated atmosphere must be puffed up into a thick but tenuous layer surrounding it. Beneath this, the gases that make up the planet would be so hot that the planet would glow red. Clouds ofsilicatesmay exist in the atmosphere.

The planet istidally lockedto its star, always presenting the same face to it.

The planet (withUpsilon Andromedae b) was deemed a candidate for aperturepolarimetrybyPlanetpol.[15]It is also a candidate for "near-infrared characterisation.... with theVLTISpectro-Imager ".[14]

Claims of direct detection of visible light

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A 2015 study alleged the detection of 51 Pegasi b in thevisible light spectrumusing the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the European Southern Observatory'sLa Silla Observatoryin Chile.[16]This detection, if confirmed, would allow the inference of a true mass of 0.46 Jupiter masses. The findings also could suggest a high albedo for the planet, hence a large radius up to1.9±0.3Jupiter radii,which could suggest 51 Pegasi b is an inflatedhot Jupiter.[17]The optical detection could not be replicated in 2020, implying the planet has analbedobelow 0.15.[18]Measurements in 2021 have marginally detected a polarized reflected light signal, which, while they cannot place limits on the albedo without assumptions made about the scattering mechanisms, could suggest a high albedo.[19]

More recent studies found no evidence of reflected light, ruling out the previous radii and albedo estimates from previous studies. Instead, 51 Pegasi b is likely a low-albedo planet with a radius around1.2±0.1RJ.[1][20]

See also

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References

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  1. ^abSpring, E. F.; Birkby, J. L.; Pino, L.; Alonso, R.; Hoyer, S.; Young, M. E.; Coelho, P. R. T.; Nespral, D.; López-Morales, M. (2022-03-01)."Black Mirror: The impact of rotational broadening on the search for reflected light from 51 Pegasi b with high resolution spectroscopy".Astronomy & Astrophysics.659:A121.arXiv:2201.03600.doi:10.1051/0004-6361/202142314.ISSN0004-6361.
  2. ^abBrogi, M.; Snellen, I. A. G.; de Kok, R. J.; Albrecht, S.; Birkby, J. L.; de Mooij, E. J. W. (2013-04-01). "Detection of Molecular Absorption in the Dayside of Exoplanet 51 Pegasi b?".The Astrophysical Journal.767:27.arXiv:1302.6242.Bibcode:2013ApJ...767...27B.doi:10.1088/0004-637X/767/1/27.ISSN0004-637X.
  3. ^abcHow the Universe Works 3.Vol. Jupiter: Destroyer or Savior?.Discovery Channel.2014.
  4. ^abWenz, John (10 October 2019)."Lessons from scorching hot weirdo-planets".Knowable Magazine.Annual Reviews.doi:10.1146/knowable-101019-2.Retrieved4 April2022.
  5. ^"Water detected in the atmosphere of hot Jupiter exoplanet 51 Pegasi b".phys.org.February 1, 2017.
  6. ^ab"The Nobel Prize in Physics 2019".Nobel Media AB.Retrieved8 October2019.
  7. ^"01.17.96 - Discovery of two new planets -- the second and third within the last three months -- proves they aren't rare in our galaxy".newsarchive.berkeley.edu.Retrieved2024-12-31.
  8. ^NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars.IAU.org. 9 July 2014
  9. ^"NameExoWorlds The Process".Archived fromthe originalon 2015-08-15.Retrieved2015-09-05.
  10. ^Final Results of NameExoWorlds Public Vote Released,International Astronomical Union, 15 December 2015.
  11. ^"NameExoWorlds The Approved Names".Archived fromthe originalon 2018-02-01.Retrieved2015-12-21.
  12. ^Mayor, Michael; Queloz, Didier (1995). "A Jupiter-mass companion to a solar-type star".Nature.378(6555):355–359.Bibcode:1995Natur.378..355M.doi:10.1038/378355a0.S2CID4339201.
  13. ^Mayor, M.; Queloz, D.; Marcy, G.; Butler, P.; Noyes, R.; Korzennik, S.; Krockenberger, M.; Nisenson, P.; Brown, T.; Kennelly, T.; Rowland, C.; Horner, S.; Burki, G.; Burnet, M.; Kunzli, M. (1995)."51 Pegasi".IAU Circular.6251:1.Bibcode:1995IAUC.6251....1M.
  14. ^abRenard, Stéphanie; Absil, Olivier; Berger, Jean-Philippe; Bonfils, Xavier; Forveille, Thierry; Malbet, Fabien (2008)."Prospects for near-infrared characterisation of hot Jupiters with the VLTI Spectro-Imager (VSI)"(PDF).Optical and Infrared Interferometry.Vol. 7013. pp. 70132Z–70132Z–10.arXiv:0807.3014.Bibcode:2008SPIE.7013E..2ZR.doi:10.1117/12.790494.S2CID119268109.{{cite book}}:|journal=ignored (help)
  15. ^Lucas, P. W.; Hough, J. H.; Bailey, J. A.; Tamura, M.; Hirst, E.; Harrison, D. (2007)."Planetpol polarimetry of the exoplanet systems 55 Cnc and tau Boo".Monthly Notices of the Royal Astronomical Society.393(1):229–244.arXiv:0807.2568.Bibcode:2009MNRAS.393..229L.doi:10.1111/j.1365-2966.2008.14182.x.
  16. ^physicsworld.com 2015-04-22 First visible light detected directly from an exoplanet
  17. ^Martins, J. H. C.; Santos, N. C.; Figueira, P.; Faria, J. P.; Montalto, M.; Boisse, I.; Ehrenreich, D.; Lovis, C.; Mayor, M.; Melo, C.; Pepe, F.; Sousa, S. G.; Udry, S.; Cunha, D. (2015). "Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b".Astronomy & Astrophysics.576:A134.arXiv:1504.05962.Bibcode:2015A&A...576A.134M.doi:10.1051/0004-6361/201425298.S2CID119224213.
  18. ^Scandariato, G.; Borsa, F.; Sicilia, D.; Malavolta, L.; et al. (2020). "The GAPS Programme at TNG. XXIX. No detection of reflected light from 51 Peg b using optical high-resolution spectroscopy".Astronomy & Astrophysics.646:A159.arXiv:2012.10435.Bibcode:2021A&A...646A.159S.doi:10.1051/0004-6361/202039271.
  19. ^Bailey, Jeremy; Bott, Kimberly; Cotton, Daniel V.; Kedziora-Chudczer, Lucyna; Zhao, Jinglin; Evensberget, Dag; Marshall, Jonathan P.; Wright, Duncan; Lucas, P. W. (2021), "Polarization of hot Jupiter systems: A likely detection of stellar activity and a possible detection of planetary polarization",Monthly Notices of the Royal Astronomical Society,502(2):2331–2345,arXiv:2101.07411,doi:10.1093/mnras/stab172
  20. ^Scandariato, G.; Borsa, F.; Sicilia, D.; Malavolta, L.; Biazzo, K.; Bonomo, A. S.; Bruno, G.; Claudi, R.; Covino, E.; Marcantonio, P. Di; Esposito, M.; Frustagli, G.; Lanza, A. F.; Maldonado, J.; Maggio, A. (2021-02-01)."The GAPS Programme at TNG - XXIX. No detection of reflected light from 51 Peg b using optical high-resolution spectroscopy".Astronomy & Astrophysics.646:A159.arXiv:2012.10435.doi:10.1051/0004-6361/202039271.ISSN0004-6361.

Further reading

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