K2-72 - Wikipedia

Star in the constellation Aquarius K2-72

Observation dataEpoch J2000      Equinox J2000
Constellation	Aquarius[1]
Right ascension	22h 18m 29.25485s[2]
Declination	−09° 36′ 44.3811″[2]
Apparent magnitude (V)	15.37[3]
Characteristics
Evolutionary stage	main sequence[3]
Spectral type	M2V[4]
Astrometry
Radial velocity (Rv)	−42.92±3.35[2] km/s
Proper motion (μ)	RA: 195.834 mas/yr[2] Dec.: 74.259 mas/yr[2]
Parallax (π)	15.0346±0.0277 mas[2]
Distance	216.9 ± 0.4 ly (66.5 ± 0.1 pc)
Details
Mass	0.27+0.08−0.09[5] M☉
Radius	0.33±0.03[5] R☉
Luminosity	0.0134[4] L☉
Surface gravity (log g)	4.83±0.14[6] cgs
Temperature	3360+87−86[5] K
Rotational velocity (v sin i)	6.07[6] km/s
Age	1.0[7] Gyr
Other designations
EPIC 206209135, 2MASS J22182923-0936444
Database references
SIMBAD	data
Exoplanet Archive	data

K2-72 (also designated EPIC 206209135) is a cool red dwarf star of spectral class M2V located about 217 light-years (67 parsecs) away from the Earth in the constellation of Aquarius. It is known to host four planets, all similar in size to Earth, with one of them residing within the habitable zone.

Nomenclature and history

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K2-72 also has the 2MASS catalogue number J22182923-0936444. Its EPIC (Ecliptic Plane Input Catalog) number is 206209135.

The star's planetary companions were discovered by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of Earth. The name K2-72 derives directly from the fact that the star is the catalogued 72nd star discovered by the K2 mission to have confirmed planets.

The designation b, c, d, and e derives from the order of discovery. The designation of b is given to the first planet orbiting a given star, and e to the last.[8] In the case of K2-72, there were four planets, so only letters b to e are used. At first the planets were all thought to be smaller than Earth. However, in 2017, new analysis by Martinez et al. and Courtney Dressing found that K2-72 was significantly larger than previous estimates, and found that the planets were all larger than Earth, although all are still expected to be rocky.

Stellar characteristics

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K2-72 is a M-type star that is approximately 27% the mass of and 33% the radius of the Sun, according to the analysis done by Dressing et al. The results found by Martinez et al. suggest a larger star, with about 36% the radius and mass of the Sun. Both give a luminosity estimate between 0.013 and 0.015 solar luminosities. It has a surface temperature of between 3360 and 3370 K and its age is unknown. In comparison, the Sun is about 4.6 billion years old[9] and has a surface temperature of 5778 K.[10]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 15.309. Therefore, it is too dim to be seen with the naked eye and can only be observed with a telescope.

Planetary system

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The star is known to host four planets, all likely to be rocky. Only one (K2-72e) is currently known to reside inside the habitable zone, although K2-72c may straddle the inner edge.

The K2-72 planetary system[5]

Companion(in order from star)	Mass	Semimajor axis(AU)	Orbital period(days)	Eccentricity	Inclination	Radius
b	—	0.040+0.004−0.005	5.577212+0.000417−0.000419	0.110000+0.196982−0.087659	89.15+0.59−0.86°	1.08±0.11 R🜨
d	—	0.050+0.004−0.006	7.760178±0.001496	0.110000+0.207832−0.092330	89.26+0.50−0.69°	1.16±0.13 R🜨
c	—	0.078+0.007−0.01	15.189034+0.003128−0.003149	0.110000+0.201970−0.091536	89.54+0.32−0.44°	1.01±0.12 R🜨
e	—	0.106+0.009−0.013	24.158868+0.003726−0.003850	0.110000+0.198676−0.086832	89.68+0.22−0.32°	1.29+0.14−0.13 R🜨

References

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1. ^ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
2. ^ a b c d e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
3. ^ a b Suissa, Gabrielle; Mandell, Avi M.; Wolf, Eric T.; Villanueva, Geronimo L.; Fauchez, Thomas; Kopparapu, Ravi Kumar (2020). "Dim Prospects for Transmission Spectra of Ocean Earths around M Stars". The Astrophysical Journal. 891 (1): 58. arXiv:1912.08235. Bibcode:2020ApJ...891...58S. doi:10.3847/1538-4357/ab72f9.
4. ^ a b Dressing, Courtney D.; et al. (2017). "Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7". The Astrophysical Journal. 836 (2) 167. arXiv:1701.00586. Bibcode:2017ApJ...836..167D. doi:10.3847/1538-4357/836/2/167.
5. ^ a b c d "NASA Exoplanet Archive". NASA Exoplanet Science Institute. 14 October 2020. Retrieved 2020-10-13.
6. ^ a b Jönsson, Henrik; Holtzman, Jon A.; Allende Prieto, Carlos; Cunha, Katia; García-Hernández, D. A.; Hasselquist, Sten; Masseron, Thomas; Osorio, Yeisson; Shetrone, Matthew; Smith, Verne; Stringfellow, Guy S.; Bizyaev, Dmitry; Edvardsson, Bengt; Majewski, Steven R.; Mészáros, Szabolcs; Souto, Diogo; Zamora, Olga; Beaton, Rachael L.; Bovy, Jo; Donor, John; Pinsonneault, Marc H.; Poovelil, Vijith Jacob; Sobeck, Jennifer (2020). "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South". The Astronomical Journal. 160 (3): 120. arXiv:2007.05537. Bibcode:2020AJ....160..120J. doi:10.3847/1538-3881/aba592.
7. ^ McIntyre, Sarah R. N.; Lineweaver, Charles H.; Ireland, Michael J. (2019). "Planetary magnetism as a parameter in exoplanet habitability". Monthly Notices of the Royal Astronomical Society. 485 (3): 3999. arXiv:1903.03123. Bibcode:2019MNRAS.485.3999M. doi:10.1093/mnras/stz667.
8. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
9. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
10. ^ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.

v t e Constellation of Aquarius
Aquarius in Chinese astronomy Aquarius Stream List of stars in Aquarius
Stars	Bayer α (Sadalmelik) β (Sadalsuud) γ (Sadachbia) δ (Skat) ε (Albali) ζ η θ (Ancha) ι κ (Situla) λ (Shatabhisha) μ ν ξ (Bunda) ο π ρ σ τ1 τ2 υ φ χ ψ1 ψ2 ψ3 ω1 ω2 Flamsteed 1 3 (k) 4 5 7 8 9 10 11 12 14 15 16 17 18 19 20 21 24 25 (d) 26 28 29 30 32 35 36 37 38 (e) 39 40 41 42 44 45 47 49 50 51 53 (f) 54 56 58 60 61 64 65 66 (g1) 67 68 (g2) 70 72 74 75 77 78 81 82 83 (h) 84 85 86 (c1) 87 88 (c2, Safina) 89 (c3) 94 96 97 98 (b1) 99 (b2) 100 101 (b3) 103 (A1) 104 (A2) 106 (i1) 107 (i2) 108 (i3) Variable R U AE DV EP EW EZ FK FL FO HK HU IL IZ LL LP HR 8017 8056 8121 8263 8363 8453 8500 8507 8581 8612 8629 8645 8716 8783 8836 8856 8879 8924 9014 HD 206610 (Bosona) 210277 212771 (Lionrock) 215152 219617 220466 220689 222093 222582 224018 Other 2MASS J21392676+0220226 BD−22 5866 Fomalhaut C GALEX J2339−0424 Gliese 849 K2-21 K2-28 K2-58 K2-72 K2-138 LS IV-14 116 PHL 5038 Sneden's Star TRAPPIST-1 WASP-6 (Márohu) WASP-47 WASP-69 (Wouri) WASP-75
Exoplanets ψ1 Aquarii b Gliese 849 b Gliese 876 b c d e HD 206610 b (Naron) HD 210277 b HD 212771 b (Victoriapeak) HD 221416 b HD 222582 b K2-66b K2-72b c d e K2-138b TRAPPIST-1b c d e f g h WASP-6b (Boinayel)
Star clusters Messier 2 Messier 72 Messier 73
Nebulae Helix Nebula Lyman-alpha blob 1 Saturn Nebula
Galaxies	NGC 6962 6975 7001 7010 7047 7051 7065 7069 7077 7081 7171 7184 7222 7252 7257 7300 7301 7302 7364 7393 7492 7585 7592 7600 7606 7721 7723 7727 7759 Other 3C 446 Aquarius Dwarf ESO 603-G21 MACS 2129-1 MR 2251−178 PGC 1228197 PHL 293B PJ352–15 PKS 2131−021 PKS 2134+004 PKS 2215+020 SDSS J211852.96−073227.5 SMM J2135−0102 South America Galaxy WISE J224607.57−052635.0 J2345−0449
Galaxy clusters Abell 2597 RXC J2211.7−0350 SSA22 Protocluster XMMXCS 2215−1738
Astronomical events SN 2213−1745
Category

v t e Exoplanets
Planet Definition IAU Planetary science
Main topics	Exoplanet Exoplanet orbital and physical parameters Methods of detecting exoplanets Planetary system Planet-hosting stars
Sizesand types	Terrestrial Carbon planet Catastrophically evaporating planet Coreless planet Desert planet Dwarf planet Hycean planet Ice planet Iron planet (Super-Mercury) Lava planet Ocean world Mega-Earth Steam world Sub-Earth Super-Earth Gaseous Cold Jupiter Eccentric Jupiter Mini-Neptune (Gas dwarf) Helium planet Hot Jupiter Hot Neptune Gas giant Ice giant Neptunian Jupiter analogue Super-Jupiter Super-Neptune Super-puff Ultra-hot Jupiter Ultra-hot Neptune Warm Jupiter Other types Blanet Brown dwarf Chthonian planet Circumbinary planet Circumtriple planet Disrupted planet Double planet Ecumenopolis Eyeball planet Giant planet Mesoplanet Planemo Planet/Brown dwarf boundary Planetesimal Protoplanet Pulsar planet Second generation planet Sub-brown dwarf Sub-Neptune Toroidal planet Ultra-cool dwarf Ultra-short period planet (USP)
Formation and evolution	Accretion Accretion disk Asteroid belt Circumplanetary disk Circumstellar disc Circumstellar envelope Cosmic dust Debris disk Detached object Disrupted planet Excretion disk Exozodiacal dust Extraterrestrial materials Extraterrestrial sample curation Giant-impact hypothesis Gravitational collapse Hills cloud Internal structure Interplanetary dust cloud Interplanetary medium Interplanetary space Interstellar cloud Interstellar dust Interstellar medium Interstellar space Kuiper belt List of interstellar and circumstellar molecules Merging stars Molecular cloud Nebular hypothesis Oort cloud Outer space Planetary migration Planetary system Planetesimal Planet formation Protoplanetary disk Radial drift Ring system Rubble pile Sample-return mission Scattered disc Star formation
Systems	Exocomet Interstellar Exomoon Tidally detached Rogue planet Jupiter-mass binary objects Orbits Retrograde Trojan Mean-motion resonances Titius–Bode law
Host stars	A B Binary star Brown dwarfs F/Yellow-white dwarfs G/Yellow dwarfs Herbig Ae/Be K/Orange dwarfs M/Red dwarfs Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giants
Detection	Astrometry Direct imaging list Microlensing list Polarimetry Timing list Radial velocity list Transit method list Transit-timing variation
Habitability	Astrobiology Astrooceanography Circumstellar habitable zone Earth analog Extraterrestrial liquid water Galactic habitable zone Habitability of binary star systems Habitability of F-type main-sequence star systems Habitability of K-type main-sequence star systems Habitability of natural satellites Habitability of neutron star systems Habitability of red dwarf systems Habitability of yellow dwarf systems Habitable zone for complex life List of potentially habitable exoplanets Tholin Superhabitable planet
Catalogues	Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database Open Exoplanet Catalogue
Lists	Exoplanetary systems Multiplanetary systems Circumstellar discs Exoplanets Discoveries Extremes Firsts Nearest Largest Heaviest Terrestrial candidates Kepler 1–500 501–1000 1001–1500 1501–2000 2001–2500 K2 Potentially habitable Proper names Discovered exoplanets by year before 2000 2000–2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026
Other	Carl Sagan Institute Exoplanet naming convention Exoplanet phase curves Exoplanetary Circumstellar Environments and Disk Explorer Extragalactic planet Extrasolar planets in fiction Geodynamics of terrestrial exoplanets Neptunian desert Nexus for Exoplanet System Science Planets in globular clusters Small planet radius gap Sudarsky's gas giant classification
Discoveries of exoplanets Search projects

The K2-72 system
Stars	K2-72
Exoplanets	b c d e

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