LHS 1140

LHS 1140

Artist's impression of LHS 1140 and LHS 1140b.
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cetus
Right ascension	00h 44m 59.33091s[1]
Declination	−15° 16′ 17.5428″[1]
Apparent magnitude (V)	14.18[2]
Characteristics
Evolutionary stage	Red dwarf
Spectral type	M4.5V[2]
Astrometry
Radial velocity (Rv)	−13.74±0.42[1] km/s
Proper motion (μ)	RA: 318.152 mas/yr[1] Dec.: −596.623 mas/yr[1]
Parallax (π)	66.8287 ± 0.0479 mas[1]
Distance	48.80 ± 0.03 ly (14.96 ± 0.01 pc)
Details[3]
Mass	0.1844±0.0045 M☉
Radius	0.2159±0.0030 R☉
Luminosity	0.0038±0.0003 L☉
Surface gravity (log g)	5.041±0.016 cgs
Temperature	3,096±48 K
Metallicity [Fe/H]	−0.15±0.09 dex
Rotation	131±5 d
Age	>5 Gyr
Other designations
GJ 3053, G 270-58, G 268-38, LHS 1140, NLTT 2465, TOI-256, TIC 92226327, 2MASS J00445930-1516166[4]
Database references
SIMBAD	data
ARICNS	data

LHS 1140 is a red dwarf in the constellation of Cetus. Based on stellar parallax measurement, it is 48.8 light-years (15.0 parsecs) away from the Sun.^[1] 'LHS' refers to the Luyten Half-Second Catalogue of stars with proper motions exceeding half a second of arc annually.^[5] The star is over 5 billion years old and has only about 18% the mass of the Sun and 21% of its radius.^[6] LHS 1140's rotational period is 130 days. No flares have been observed.^[7]

As of October 2023, LHS 1140 is known to have two confirmed planets orbiting it.^[3]

The first to be discovered was LHS 1140 b, discovered by the MEarth Project in 2017 using the transit method.^[2] Follow-up radial velocities were measured by the High Accuracy Radial Velocity Planet Searcher instrument to confirm the planet and measure the mass.^[7] The planet LHS 1140 b is a super-Earth in the habitable zone and transits the star every 24.7 days. This should allow its atmosphere to be studied in future: the combination of the transiting super-Earth and the relatively small and nearby host star make this system one of the most promising known for atmosphere studies, along with the TRAPPIST-1 system.^[2][8] Observations by the Hubble Space Telescope in 2020 found signs of water vapor in the planet's atmosphere, but this has not been confirmed.^[9]

LHS 1140 b was initially estimated to be about 7 times Earth's mass and about 1.4 times its radius, suggesting a dense rocky planet.^[2] Later studies in 2018 and 2020 revised the radius upwards to about 1.7 times Earth's, giving it a density of about 7.5 g/cm³, still consistent with a rocky composition.^[10][11] However, a 2023 study measuring the planet's mass and radius with greater precision found a lower mass of about 5.6 times Earth's, and a correspondingly lower density, no longer consistent with a rocky planet given the planet's size. LHS 1140 b is likely an ocean world (with 9-19% of its mass composed of water) or a dense mini-Neptune.^[3]

In July 2018, Feng et al. published a reanalysis of the radial velocity data for LHS 1140, and proposed the likely existence of two additional planets: an inner Earth-mass planet orbiting every 3.8 days and an outer Neptune-mass planet orbiting every 90 days.^[12] In August 2018, Ment et al., using the transit method of detection, confirmed the existence of the inner planet LHS 1140 c with a mass about 1.8 times Earth's and a radius 1.3 times as large, giving it a density of about 5 g/cm³,^[10] consistent with a rocky composition.^[3]

The orbital period of the outer planet candidate LHS 1140 d was refined to 78 days in 2020,^[11] but this radial velocity signal was found to originate from stellar activity rather than a planet in 2023.^[3]