Gliese 180

Gliese 180

A star chart of the constellation of Eridanus showing the position of Gliese 180
Observation data Epoch J2000      Equinox J2000
Constellation	Eridanus
Right ascension	04h 53m 49.9798s[1]
Declination	−17° 46′ 24.294″[1]
Apparent magnitude (V)	10.894[2]
Characteristics
Spectral type	M2V[3] or M3V[4]
U−B color index	1.155[2]
B−V color index	1.549[2]
V−R color index	1.018[2]
R−I color index	1.205[2]
J−H color index	0.553[2]
J−K color index	0.815[2]
Astrometry
Radial velocity (Rv)	−14.55±0.24[5] km/s
Proper motion (μ)	RA: 408.571[1] mas/yr Dec.: −644.464[1] mas/yr
Parallax (π)	83.7182 ± 0.0313[1] mas
Distance	38.96 ± 0.01 ly (11.945 ± 0.004 pc)
Absolute magnitude (MV)	10.48[2]
Details
Mass	0.4316±0.0050[3] M☉
Radius	0.4229±0.0047[3] R☉
Luminosity	0.02427±0.00036[3] L☉
Surface gravity (log g)	4.73+0.05 −0.07[6] cgs
Temperature	3,634+57 −40[6] K
Metallicity [Fe/H]	−0.12±0.16[3] dex
Rotation	65 days[7]
Rotational velocity (v sin i)	3.4+1.9 −0.8[6] km/s
Age	5.0[8] 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,[9] [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.^[5] 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 active star.^[11] It is about five^[8] billion years old and is spinning with a projected rotational velocity of ~3 km/s,^[6] giving it a rotation period of about 65 days.^[7] 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.^[6]

Planetary system[]

Gliese 180 is known to have three exoplanets designated Gliese 180 b, Gliese 180 c and Gliese 180 d,^[9] by order of distance from the star. The components 'b' anc 'c' are super Earths with 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 object 'c'.^[12]

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. Planet Gliese 180 b and Gliese 180 c have masses of 6.4 and 8.3 Earth masses, respectively.^[13] 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.”^[13]