55 Cancri e

55 Cancri e / Janssen
Artist's impression of 55 Cancri e near its host star
Discovery[1]
Discovered byMcArthur et al.
Discovery siteTexas, United States
Discovery date30 August 2004
Radial velocity
Orbital characteristics
Apastron0.01617 AU (2,419,000 km)
Periastron0.01464 AU (2,190,000 km)
0.01544 ± 0.00005 AU (2,309,800 ± 7,500 km)[2]
Eccentricity0.05 ± 0.03[3]
0.73654625(15) d[4]
17.67711 h
Inclination83.59 +0.47
−0.44[3]
2,449,999.83643 ± 0.0001[5]
86.0 +30.7
−33.4[3]
Semi-amplitude6.02 +0.24
−0.23[3]
Star55 Cancri A
Physical characteristics
1.875 ± 0.029[3] R🜨
Mass7.99 +0.32
−0.33[3] ME
Mean density
6.66+0.43
−0.40[3] g cm−3
2.273 g
Temperature3,771+669
−520 K (3,498 °C; 6,328 °F, dayside)[6]
<1,649 K (1,376 °C; 2,509 °F, nightside)[6]

55 Cancri e (abbreviated 55 Cnc e, also known as Janssen /ˈdʒænsən/) is an exoplanet orbiting a Sun-like host star, 55 Cancri A. The mass of the exoplanet is about eight Earth masses and its diameter is about twice that of the Earth.[3] 55 Cancri e was discovered on 30 August 2004, thus making it the first super-Earth discovered around a main sequence star, predating Gliese 876 d by a year. It is the innermost planet in its planetary system, taking less than 18 hours to complete an orbit. However, until the 2010 observations and recalculations, this planet had been thought to take about 2.8 days to orbit the star.[5]

Due to its proximity to its star, 55 Cancri e is extremely hot, with temperatures on the day side exceeding 3,000 Kelvin.[6] The planet's thermal emission is observed to be variable, possibly as a result of volcanic activity.[7] It has been proposed that 55 Cancri e could be a carbon planet.[8]

The atmosphere of 55 Cancri e has been extensively studied, with varying results. Initial studies suggested an atmosphere rich in hydrogen and helium,[9] but later studies failed to confirm this, instead supporting an atmosphere composed of heavier molecules,[10] possibly only a thin atmosphere of vaporized rock.[11] Most recently as of 2024, JWST observations have ruled out the rock vapor atmosphere scenario and provided evidence for a substantial atmosphere rich in carbon dioxide or carbon monoxide.[12]

Name

In July 2014 the International Astronomical Union (IAU) launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[13] The process involved public nomination and voting for the new names.[14] In December 2015, the IAU announced the winning name was Janssen for this planet.[15] The winning name was submitted by the Royal Netherlands Association for Meteorology and Astronomy of the Netherlands. It honors the spectacle maker Zacharias Janssen who is sometimes associated with the invention of the telescope.[16]

Discovery

Like the majority of extrasolar planets found prior to the Kepler mission, 55 Cancri e was discovered by detecting variations in its star's radial velocity. This was achieved by making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A. At the time of its discovery, three other planets were known orbiting the star. After accounting for these planets, a signal at around 2.8 days remained, which could be explained by a planet of at least 14.2 Earth masses in a very close orbit.[1]

The same measurements were used to confirm the existence of the uncertain planet 55 Cancri c. 55 Cancri e was one of the first extrasolar planets with a mass comparable to that of Neptune to be discovered. It was announced at the same time as Gliese 436 b, another "hot Neptune" orbiting the red dwarf star Gliese 436.

Planet challenged

In 2005, the existence of planet e was questioned by Jack Wisdom in a reanalysis of the data. He suggested that the 2.8-day planet was an alias and, separately, that there was a 260-day planet in orbit around 55 Cancri. In 2008, Fischer et al. published a new analysis[5] that appeared to confirm the existence of the 2.8-day planet and the 260-day planet. However, the 2.8-day planet was shown to be an alias by Dawson and Fabrycky in 2010;[2] its true period was 0.7365 days.

Transit

The planet's transit of its host star was announced on 27 April 2011, based on two weeks of nearly continuous photometric monitoring with the MOST space telescope.[17] The transits occur with the period (0.74 days) and phase that had been predicted by Dawson and Fabrycky. This is one of the few planetary transits to be confirmed around a well-known star, and allowed investigations into the planet's composition.

Orbit and rotation

55 Cancri e orbits very close to its parent star; with average orbital distance of 0.01544 ± 0.00005 AU, it takes only 18 hours to complete an orbit. Analysis of its transits reveal that its orbital inclination is about 83.6°,[3] and appears to be close to being aligned with the rotation of its parent star, with obliquity of 23 +14°
−12°, favouring dynamically gentle inward migration scenarios for this planet.[18] 55 Cancri e may also be coplanar with the next planet in the system, 55 Cancri b.[19]

Due to its old age and proximity to the star, the planet is extremely likely to be tidally locked, meaning that one hemisphere, referred to as dayside, permanently faces the star, while the other, the nightside, always faces away from it.[20]

Characteristics

Artist's impression of 55 Cancri e as a lava planet
Artist's impression of 55 Cancri e with a thick atmosphere
NASA "Exoplanet Travel Bureau" poster for 55 Cancri e

55 Cancri e receives more radiation than Gliese 436 b.[21] The side of the planet facing its star has temperatures more than 2,000 Kelvin (approximately 1,700 degrees Celsius or 3,100 Fahrenheit), hot enough to melt iron.[22] Infrared mapping with the Spitzer Space Telescope indicated an average day-side temperature of 2,700 K (2,430 °C; 4,400 °F) and an average night-side temperature of around 1,380 K (1,110 °C; 2,020 °F).[23] Reanalysis of the Spitzer data in 2022 found a hotter day-side temperature of 3,770 K (3,500 °C; 6,330 °F) and set an upper limit of 1,650 K (1,380 °C; 2,510 °F) on the night-side temperature.[6]

It was initially unknown whether 55 Cancri e was a small gas giant like Neptune or a large rocky terrestrial planet. In 2011, a transit of the planet was confirmed, allowing scientists to calculate its density. At first it was suspected to be a water planet.[17][24] As initial observations showed no hydrogen in its Lyman-alpha signature during transit,[19] Ehrenreich speculated that its volatile materials might be carbon dioxide instead of water or hydrogen.[19]

An alternative possibility is that 55 Cancri e is a solid planet made of carbon-rich material rather than the oxygen-rich material that makes up the terrestrial planets in the Solar System.[25] In this case, roughly a third of the planet's mass would be carbon, much of which may be in the form of diamond as a result of the temperatures and pressures in the planet's interior. Further observations are necessary to confirm the nature of the planet.[26][8]

A third argument is that the tidal forces, together with the orbital and rotational centrifugal forces, can partially confine a hydrogen-rich atmosphere on the nightside.[27] Assuming an atmosphere dominated by volcanic species and a large hydrogen component, the heavier molecules could be confined within latitudes < 80° while the volatile hydrogen is not. Because of this disparity, the hydrogen would have to slowly diffuse out into the dayside where X-ray and ultraviolet irradiation would destroy it. In order for this mechanism to have taken effect, it is necessary for 55 Cancri e to have become tidally locked before losing the totality of its hydrogen envelope. This model is consistent with spectroscopic measurements claiming to have discovered the presence of hydrogen[28][29] and with other studies which were unable to discover a significant hydrogen-destruction rate.[19][30]

In February 2016, it was announced that NASA's Hubble Space Telescope had detected hydrogen cyanide, but no water vapor, in the atmosphere of 55 Cancri e, which is only possible if the atmosphere is predominantly hydrogen or helium. This is the first time the atmosphere of a super-Earth exoplanet was analyzed successfully.[31][32] In November 2017, it was announced that infrared observations with the Spitzer Space Telescope indicated the presence of a global lava ocean obscured by an atmosphere with a pressure of about 1.4 bar, slightly thicker than that of Earth. The atmosphere may contain similar chemicals in Earth's atmosphere, such as nitrogen and possibly oxygen, in order to cause the infrared data observed by Spitzer.[33][34] In contradiction to the February 2016 findings, a spectroscopic study in 2012 failed to detect escaping hydrogen from the atmosphere,[19] and a spectroscopic study in 2020 failed to detect escaping helium, indicating that the planet probably has no primordial atmosphere.[10] Atmospheres made of heavier molecules such as oxygen and nitrogen are not ruled out by these data.

A study published in May 2024 used observations from the James Webb Space Telescope's Near-InfraRed Camera and Mid-Infrared Instrument to produce a thermal emission spectrum of 55 Cancri e within the range of 4 to 12 μm. These measurements ruled out the hypothesis that the planet is a lava world covered by a "tenuous atmosphere made of vaporized rock", as previously proposed, and indicated a "bona fide volatile atmosphere likely rich in CO2 or CO". The authors stated that 55 Cancri e's magma ocean could be outgassing and sustaining this atmosphere.[12][35][36]

Volcanism

Large surface-temperature variations on 55 Cancri e have been attributed to possible volcanic activity releasing large clouds of dust which blanket the planet and block thermal emissions.[7][37] By 2022, the observation had shown a large variability in the planetary transit depths, which can be attributed to large-scale volcanism, or to the presence of a variable gas torus co-orbital with the planet.[38]

Search for Radio Emissions

Since 55 Cancri e orbits less than 0.1 AU from its host star, some scientists hypothesized that it may cause stellar flaring synchronized to the orbital period of the exoplanet. A 2011 search for these magnetic star-planet interactions that would result in coronal radio emissions resulted in no detected signal.[39]

See also

References

  1. ^ a b McArthur, Barbara E.; et al. (10 October 2004). "Detection of a Neptune-Mass Planet in the ρ1 Cancri System Using the Hobby-Eberly Telescope". The Astrophysical Journal Letters. 614 (1): L81. arXiv:astro-ph/0408585. Bibcode:2004ApJ...614L..81M. doi:10.1086/425561. S2CID 119085463.
  2. ^ a b Dawson, Rebekah I.; Fabrycky, Daniel C. (10 October 2010) [21 May 2010 (v1)]. "Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e". The Astrophysical Journal. 722 (1): 937–953. arXiv:1005.4050. Bibcode:2010ApJ...722..937D. doi:10.1088/0004-637X/722/1/937. S2CID 118592734.
  3. ^ a b c d e f g h i Bourrier, V.; Dumusque, X.; Dorn, C.; Henry, G. W.; Astudillo-Defru, N.; Rey, J.; Benneke, B.; Hébrard, G.; Lovis, C.; Demory, B. O.; Moutou, C.; Ehrenreich, D. (2018). "The 55 Cancri system reassessed". Astronomy & Astrophysics. 619: A1. arXiv:1807.04301. Bibcode:2018A&A...619A...1B. doi:10.1051/0004-6361/201833154. S2CID 209888143.
  4. ^ Kokori, A.; et al. (14 February 2023). "ExoClock Project. III. 450 New Exoplanet Ephemerides from Ground and Space Observations". The Astrophysical Journal Supplement Series. 265 (1) 4. arXiv:2209.09673. Bibcode:2023ApJS..265....4K. doi:10.3847/1538-4365/ac9da4. Vizier catalog entry
  5. ^ a b c Fischer, Debra A.; Marcy, Geoffrey W.; Butler, R. Paul; Vogt, Steven S.; Laughlin, Greg; Henry, Gregory W.; Abouav, David; Peek, Kathryn M. G.; Wright, Jason T.; Johnson, John A.; McCarthy, Chris; Isaacson, Howard (1 March 2008) [23 December 2007 (v1)]. "Five Planets Orbiting 55 Cancri". The Astrophysical Journal. 675 (1): 790–801. arXiv:0712.3917. Bibcode:2008ApJ...675..790F. doi:10.1086/525512. S2CID 55779685.
  6. ^ a b c d Mercier, Samson J.; Dang, Lisa; et al. (November 2022). "Revisiting the Iconic Spitzer Phase Curve of 55 Cancri e: Hotter Dayside, Cooler Nightside, and Smaller Phase Offset". The Astronomical Journal. 164 (5): 204. arXiv:2209.02090. Bibcode:2022AJ....164..204M. doi:10.3847/1538-3881/ac8f22.
  7. ^ a b Demory, Brice-Olivier; Gillon, Michael; Madhusudhan, Nikku; Queloz, Didier (2016). "Variability in the super-Earth 55 Cnc e". Monthly Notices of the Royal Astronomical Society. 455 (2): 2018–2027. arXiv:1505.00269. Bibcode:2016MNRAS.455.2018D. doi:10.1093/mnras/stv2239. S2CID 53662519.
  8. ^ a b Madhusudhan, Nikku; Lee, Kanani K. M.; Mousis, Olivier (10 November 2012) [9 October 2012 (v1)]. "A Possible Carbon-rich Interior in Super-Earth 55 Cancri e". The Astrophysical Journal Letters. 759 (2): L40. arXiv:1210.2720. Bibcode:2012ApJ...759L..40M. doi:10.1088/2041-8205/759/2/L40. S2CID 119303024.
  9. ^ Tsiaras, A.; Rocchetto, M.; et al. (April 2016). "Detection of an Atmosphere Around the Super-Earth 55 Cancri e". The Astrophysical Journal. 820 (2): 99. arXiv:1511.08901. Bibcode:2016ApJ...820...99T. doi:10.3847/0004-637X/820/2/99.
  10. ^ a b Zhang, Michael; Knutson, Heather A.; Wang, Lile; Dai, Fei; Oklopcic, Antonija; Hu, Renyu (2021), "No Escaping Helium from 55 Cnc e", The Astronomical Journal, 161 (4): 181, arXiv:2012.02198, Bibcode:2021AJ....161..181Z, doi:10.3847/1538-3881/abe382, S2CID 245880700
  11. ^ Rasmussen, Kaitlin C.; Currie, Miles H.; et al. (October 2023). "A Nondetection of Iron in the First High-resolution Emission Study of the Lava Planet 55 Cnc e". The Astronomical Journal. 166 (4): 155. arXiv:2308.10378. Bibcode:2023AJ....166..155R. doi:10.3847/1538-3881/acf28e.
  12. ^ a b Hu, Renyu; Bello-Arufe, Aaron; Zhang, Michael; Paragas, Kimberly; Zilinskas, Mantas; van Buchem, Christiaan; Bess, Michael; Patel, Jayshil; Ito, Yuichi; Damiano, Mario; Scheucher, Markus; Oza, Apurva V.; Knutson, Heather A.; Miguel, Yamila; Dragomir, Diana (8 May 2024). "A secondary atmosphere on the rocky Exoplanet 55 Cancri e". Nature. 630 (8017): 609–612. arXiv:2405.04744. doi:10.1038/s41586-024-07432-x. ISSN 1476-4687. PMID 38718834.
  13. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  14. ^ "NameExoWorlds The Process". Archived from the original on 15 August 2015. Retrieved 5 September 2015.
  15. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  16. ^ "NameExoWorlds The Approved Names". Archived from the original on 1 February 2018. Retrieved 27 December 2015.
  17. ^ a b Winn, Joshua N.; Matthews, Jaymie M.; Dawson, Rebekah I.; Fabrycky, Daniel; Holman, Matthew J.; Killinger, Thomas; Kuschnig, Rainer; Sasselov, Dimitar; Dragomir, Diana; Guenther, David B.; Moffat, Anthony F.J.; Rowe, Jason F.; Rucinski, Slavek; Weiss, Werner W. (10 August 2011) [27 Apr 2011 (v1)]. "A Super Earth Transiting a Naked-Eye Star". The Astrophysical Journal Letters. 737 (1): L18. arXiv:1104.5230. Bibcode:2011ApJ...737L..18W. doi:10.1088/2041-8205/737/1/L18. S2CID 16768578.
  18. ^ Zhao, Lily L.; Kunovac, Vedad; Brewer, John M.; Llama, Joe; Millholland, Sarah C.; Hedges, Christina; Szymkowiak, Andrew E.; Roettenbacher, Rachael M.; Cabot, Samuel H. C.; Weiss, Sam A.; Fischer, Debra A. (8 December 2022). "Measured spin–orbit alignment of ultra-short-period super-Earth 55 Cancri e". Nature Astronomy. 7. Springer Science and Business Media LLC: 198. arXiv:2212.03953. Bibcode:2023NatAs...7..198Z. doi:10.1038/s41550-022-01837-2. ISSN 2397-3366.
  19. ^ a b c d e Ehrenreich, David; Bourrier, Vincent; Bonfils, Xavier; Lecavelier des Étangs, Alain; Hébrard, Guillaume; Sing, David K.; Wheatley, Peter J.; Vidal-Madjar, Alfred; Delfosse, Xavier; Udry, Stéphane; Forveille, Thierry (1 November 2012). "Hint of a transiting extended atmosphere on 55 Cancri b". Astronomy & Astrophysics. 547: A18. arXiv:1210.0531. Bibcode:2012A&A...547A..18E. doi:10.1051/0004-6361/201219981. ISSN 0004-6361.
  20. ^ Meier, Tobias G.; Bower, Dan J.; Lichtenberg, Tim; Hammond, Mark; Tackley, Paul J. (29 September 2023). "Interior dynamics of super-Earth 55 Cancri e". Astronomy & Astrophysics. 678. EDP Sciences: A29. arXiv:2308.00592. Bibcode:2023A&A...678A..29M. doi:10.1051/0004-6361/202346950. ISSN 0004-6361.
  21. ^ Lucas, P. W.; Hough, J. H.; Bailey, J. A.; Tamura, M.; Hirst, E.; Harrison, D. (2007) [16 July 2008 (v1)]. "Planetpol polarimetry of the exoplanet systems 55 Cnc and τ 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. S2CID 8684361.
  22. ^ Science@NASA. "NASA Space Telescope Sees the Light from an Alien Super-Earth". NASA. Archived from the original on 10 June 2023. Retrieved 10 May 2012.
  23. ^ Demory, Brice-Olivier; Gillon, Michael; et al. (April 2016). "A map of the large day-night temperature gradient of a super-Earth exoplanet". Nature. 532 (7598): 207–209. arXiv:1604.05725. Bibcode:2016Natur.532..207D. doi:10.1038/nature17169. PMID 27027283. S2CID 205248003.
  24. ^ "Oozing Super-Earth: Images of Alien Planet 55 Cancri e". Space.com. 20 January 2012. Retrieved 21 January 2012.
  25. ^ "Nearby Super-Earth Likely a Diamond Planet". Science Daily. 11 October 2012. Retrieved 11 October 2012.
  26. ^ Wickham, Chris (21 October 2012). "A diamond bigger than Earth?". Reuters. Archived from the original on 31 July 2016. Retrieved 26 October 2012.
  27. ^ Modirrousta-Galian, Darius; Locci, Daniele; Tinetti, Giovanna; Micela, Giuseppina (13 January 2020). "Hot Super-Earths with Hydrogen Atmospheres: A Model Explaining Their Paradoxical Existence". The Astrophysical Journal. 888 (2): 87. arXiv:1912.05884. Bibcode:2020ApJ...888...87M. doi:10.3847/1538-4357/ab616b. ISSN 1538-4357. S2CID 209324096.
  28. ^ Tsiaras, A.; Rocchetto, M.; Waldmann, I. P.; Venot, O.; Varley, R.; Morello, G.; Damiano, M.; Tinetti, G.; Barton, E. J.; Yurchenko, S. N.; Tennyson, J. (24 March 2016). "Detection of an Atmosphere Around the Super-Earth 55 Cancri E". The Astrophysical Journal. 820 (2): 99. arXiv:1511.08901. Bibcode:2016ApJ...820...99T. doi:10.3847/0004-637X/820/2/99. ISSN 1538-4357. S2CID 53463756.
  29. ^ Esteves, Lisa J.; de Mooij, Ernst J. W.; Jayawardhana, Ray; Watson, Chris; de Kok, Remco (31 May 2017). "A Search for Water in a Super-Earth Atmosphere: High-resolution Optical Spectroscopy of 55Cancri e". The Astronomical Journal. 153 (6): 268. arXiv:1705.03022. Bibcode:2017AJ....153..268E. doi:10.3847/1538-3881/aa7133. ISSN 1538-3881. S2CID 56437290.
  30. ^ Bourrier, V.; Ehrenreich, D.; Etangs, A. Lecavelier des; Louden, T.; Wheatley, P. J.; Wyttenbach, A.; Vidal-Madjar, A.; Lavie, B.; Pepe, F.; Udry, S. (1 July 2018). "High-energy environment of super-Earth 55 Cancri e - I. Far-UV chromospheric variability as a possible tracer of planet-induced coronal rain". Astronomy & Astrophysics. 615: A117. arXiv:1803.10783. Bibcode:2018A&A...615A.117B. doi:10.1051/0004-6361/201832700. ISSN 0004-6361.
  31. ^ Staff (16 February 2016). "First detection of super-earth atmosphere". Phys.org. Retrieved 17 February 2016.
  32. ^ "A primeira detecção da composição atmosférica de uma super-Terra". GOASA. February 2016. Archived from the original on 25 February 2016. Retrieved 17 August 2015.
  33. ^ A Case for an Atmosphere on Super-Earth 55 Cancri e - Astrobiology
  34. ^ Lava or Not, Exoplanet 55 Cancri e Likely to have Atmosphere Elizabeth Landau. NOVEMBER 16, 2017
  35. ^ Todd, Iain (9 May 2024). "Webb discovers evidence of an atmosphere around a rocky super-Earth planet orbiting a Sun-like star". BBC Sky at Night. Retrieved 9 May 2024.
  36. ^ Dunham, Will (9 May 2024). "'Super-Earth': Astronomers finally find a rocky planet with atmosphere". The Sydney Morning Herald. Retrieved 9 May 2024.
  37. ^ Lemonick, Michael D. (6 May 2015). "Astronomers May Have Found Volcanoes 40 Light-Years From Earth". National Geographic. Archived from the original on 9 May 2015. Retrieved 8 May 2024.
  38. ^ Meier Valdés, E. A.; Morris, B. M.; Wells, R. D.; Schanche, N.; Demory, B.-O. (2022). "Weak evidence for variable occultation depth of 55 Cnc e with TESS". Astronomy & Astrophysics. 663: A95. arXiv:2205.08560. Bibcode:2022A&A...663A..95M. doi:10.1051/0004-6361/202243768. S2CID 248862923.
  39. ^ Route, Matthew; Wolszczan, Alex (1 August 2023). "ROME. III. The Arecibo Search for Star–Planet Interactions at 5 GHz". The Astrophysical Journal. 952 (2): 118. arXiv:2202.08899. Bibcode:2023ApJ...952..118R. doi:10.3847/1538-4357/acd9ad.
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