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Gliese 180
Observation data; Epoch J2000 Equinox J2000
Constellation	Eridanus
Right ascension	04h 53m 49.97992s
Declination	−17° 46′ 24.3093″
Apparent magnitude (V)	10.894
Characteristics
Spectral type	M2V or M3V
U−B color index	1.155
B−V color index	1.549
V−R color index	1.018
R−I color index	1.205
J−H color index	0.553
J−K color index	0.815
Astrometry
Radial velocity (Rv)	−14.87±0.14 km/s
Proper motion (μ)	RA: 408.573±0.012 mas/yr ; Dec.: −644.457±0.013 mas/yr
Parallax (π)	83.6897 ± 0.0160 mas
Distance	38.972 ± 0.007 ly ; (11.949 ± 0.002 pc)
Absolute magnitude (MV)	10.48
Details
Mass	0.4316±0.0050 M☉
Radius	0.4229±0.0047 R☉
Luminosity	0.02427±0.00036 L☉
Surface gravity (log g)	4.73+0.05; −0.07 cgs
Temperature	3,634+57; −40 K
Metallicity [Fe/H]	−0.12±0.16 dex
Rotation	65 days
Rotational velocity (v sin i)	3.4+1.9; −0.8 km/s
Age	5.0 Gyr
Other designations
	GJ 180, HIP 22762, L 736-30, LFT 377, LHS 1712, LP 776-27, LPM 198, LTT 2116, NLTT 14144, PLX 1097, TYC 5903-680-1, 2MASS J04534995-1746235, [RHG95] 838
Database references
SIMBAD	data
Exoplanet Archive	data
ARICNS	data

Gliese 180 (often shortened to GJ 180), is a small red dwarf star in the equatorial constellation of Eridanus. It is invisible to the naked eye with an apparent visual magnitude of 10.9.^[2] The star is located at a distance of 39 light years from the Sun based on parallax,^[1] and is drifting closer with a radial velocity of −14.6 km/s.^[9] It has a high proper motion, traversing the sky at the rate of 0.765 arcseconds per year.^[10]

The stellar classification of GJ 180 is catalogued as M2V^[3] or M3V,^[4] depending on the study, which indicates this is a dim red dwarf – an M-type main-sequence star that is generating energy by core hydrogen fusion. Reiners and associates (2012) do not consider it to be an active star.^[11] It is about five^[7] billion years old and is spinning with a projected rotational velocity of ~3 km/s,^[5] giving it a rotation period of about 65 days.^[6] The star has 43% of the Sun's mass and 42% of the radius of the Sun. It is radiating just 2.4%^[3] of the luminosity of the Sun from its photosphere at an effective temperature of 3,634 K.^[5]

Planetary system

Gliese 180 is known to have at least two exoplanets, designated Gliese 180 b and Gliese 180 d, and possibly a third, Gliese 180 c; all are super-Earths or mini-Neptunes.^[12] Planets 'b' and 'c' were initially reported in 2014,^[13] and a follow-up study in 2020 confirmed planet 'b' and found a new planet 'd', but did not find the previously claimed planet 'c'.^[12] According to the 2014 study, planets 'b' and 'c' have an orbital period ratio of 7:5, which suggests a mean motion resonance that is stabilizing the orbits. The habitable zone of this star, by the criteria of Kopparapu and associates (2013), ranges from 0.12 AU out to 0.24 AU, which thus includes planet 'c'.^[13]

According to the Planetary Habitability Laboratory (PHL) in Puerto Rico, both b and c worlds in the system may be classifiable as potentially habitable planets. Planets Gliese 180 b and Gliese 180 c have minimum masses of 6.4 and 8.3 Earth masses, respectively.^[14] However, Dr Mikko Tuomi, of the UK's University of Hertfordshire, whose team identified the planets, disagreed, stating:

"The PHL adds some sort of an “extended HZ”, which I, frankly, do not know how it’s calculated, but that adds some areas of potential habitability to the inner and outer edges of the HZ as we have defined it. They included the inner companion of the GJ 180 system (planet b) that we consider too hot to be potentially habitable.”^[14]

However, as of 2022, the PHL lists only planets c and d, not b, as potentially habitable.^[15]

The Gliese 180 planetary system^[13]^[12]
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥6.49±0.68 $M$ _🜨	0.092±0.003	17.133±0.003	0.07±0.04	—	—
с (unconfirmed)	≥6.4+3.7 −4.1 M_🜨	0.129+0.007 −0.017	24.329+0.052 −0.066	0.09+0.20 −0.09	—	—
d	≥7.56±1.07 $M$ _🜨	0.309±0.010	106.300±0.129	0.14±0.04	—	—

References

^ ^a ^b ^c ^d ^e ^f 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.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Koen, C.; et al. (April 21, 2010), "UBV(RI)_CJHK observations of Hipparcos-selected nearby stars", Monthly Notices of the Royal Astronomical Society, 403 (4): 1949–1968, Bibcode:2010MNRAS.403.1949K, doi:10.1111/j.1365-2966.2009.16182.x.
^ ^a ^b ^c ^d ^e ^f ^g Schweitzer, A.; et al. (May 2019). "The CARMENES search for exoplanets around M dwarfs. Different roads to radii and masses of the target stars". Astronomy & Astrophysics. 625: 16. arXiv:1904.03231. Bibcode:2019A&A...625A..68S. doi:10.1051/0004-6361/201834965. S2CID 102351979. A68.
^ ^a ^b Stephenson, C. B. (July 1986), "Dwarf K and M stars of high proper motion found in a hemispheric survey", The Astronomical Journal, 92: 139–165, Bibcode:1986AJ.....92..139S, doi:10.1086/114146.
^ ^a ^b ^c ^d ^e Passegger, V. M.; et al. (October 2020), "The CARMENES search for exoplanets around M dwarfs. A deep learning approach to determine fundamental parameters of target stars", Astronomy & Astrophysics, 642: 16, arXiv:2008.01186, Bibcode:2020A&A...642A..22P, doi:10.1051/0004-6361/202038787, A22.
^ ^a ^b Astudillo-Defru, N.; et al. (April 2017), "Magnetic activity in the HARPS M dwarf sample. The rotation-activity relationship for very low-mass stars through R'_HK", Astronomy & Astrophysics, 600: 15, arXiv:1610.09007, Bibcode:2017A&A...600A..13A, doi:10.1051/0004-6361/201527078, S2CID 119237202, A13
^ ^a ^b Miles, Brittany E.; Shkolnik, Evgenya L. (2017), "HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive", The Astronomical Journal, 154 (2), American Astronomical Society: 67, arXiv:1705.03583, Bibcode:2017AJ....154...67M, doi:10.3847/1538-3881/aa71ab, ISSN 1538-3881, S2CID 119385780.
^ "L 736-30". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-15.
^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ Luyten, Willem J. (1979), LHS catalogue. A catalogue of stars with proper motions exceeding 0".5 annually (2nd ed.), Minneapolis: University of Minnesota, Bibcode:1979lccs.book.....L.
^ Reiners, Ansgar; et al. (April 2012), "A Catalog of Rotation and Activity in Early-M Stars", The Astronomical Journal, 143 (4): 15, arXiv:1201.5774, Bibcode:2012AJ....143...93R, doi:10.1088/0004-6256/143/4/93, S2CID 118425326, 93.
^ ^a ^b ^c Feng, Fabo; et al. (2020), "Search for Nearby Earth Analogs. II. Detection of Five New Planets, Eight Planet Candidates, and Confirmation of Three Planets around Nine Nearby M Dwarfs", The Astrophysical Journal Supplement Series, 246 (1): 11, arXiv:2001.02577, Bibcode:2020ApJS..246...11F, doi:10.3847/1538-4365/ab5e7c, S2CID 210064560.
^ ^a ^b ^c Tuomi, Mikko; et al. (2014), "Bayesian search for low-mass planets around nearby M dwarfs – estimates for occurrence rate based on global detectability statistics", Monthly Notices of the Royal Astronomical Society, 441 (2): 1545–1569, arXiv:1403.0430, Bibcode:2014MNRAS.441.1545T, doi:10.1093/mnras/stu358, S2CID 32965505.
^ ^a ^b Sutherland, Paul (March 5, 2014). "Habitable planets common around red dwarf stars". Sen. Sen Corporation Ltd. Archived from the original on November 12, 2020. Retrieved November 2, 2014.
^ "The Habitable Exoplanets Catalog". Planetary Habitability Laboratory. University of Puerto Rico at Arecibo. Archived from the original on 1 December 2017. Retrieved 4 December 2022.