LP 890-9

LP 890-9, also known as SPECULOOS-2 or TOI-4306, is a high proper motion red dwarf star located 105 light-years (32 pc) away from the Solar System in the constellation of Eridanus. The star has 12% the mass and 15% the radius of the Sun, and a temperature of 2,871 K (2,598 °C; 4,708 °F). It is extremely faint and, with an apparent magnitude of 18, is the faintest star with exoplanets discovered by the Transiting Exoplanet Survey Satellite.^[6]

LP 890-9

Observation data Epoch J2000      Equinox J2000
Constellation	Eridanus[1]
Right ascension	04h 16m 31.16176s[2]
Declination	−28° 18′ 52.9543″[2]
Apparent magnitude (V)	18.0±0.2[3]
Characteristics
Evolutionary stage	Main sequence
Spectral type	M6V[4]
Apparent magnitude (V)	18.0±0.2[3]
Apparent magnitude (G)	15.791±0.003[2]
Apparent magnitude (J)	12.258±0.023[3]
Apparent magnitude (H)	11.692±0.025[3]
Apparent magnitude (K)	11.344±0.023[3]
Astrometry
Radial velocity (Rv)	28.84±2.84[2] km/s
Proper motion (μ)	RA: 218.569 mas/yr[2] Dec.: −251.145 mas/yr[2]
Parallax (π)	30.9326±0.0418 mas[2]
Distance	105.4 ± 0.1 ly (32.33 ± 0.04 pc)
Absolute magnitude (MV)	15.45±0.2[note 1]
Details[3]
Mass	0.118±0.002 M☉
Radius	0.1532+0.0048 −0.0024 R☉
Luminosity (bolometric)	0.001438±0.000037 L☉
Surface gravity (log g)	5.139+0.013 −0.028 cgs
Temperature	2871+32 −45 K
Metallicity [Fe/H]	−0.028±0.089 dex
Age	7.2+2.2 −3.1 Gyr
Other designations
SPECULOOS-2, LP 890-9, NLTT 12925, TOI-4306, TIC 44898913, 2MASS J04163114-2818526, WISEA J041631.33-281855.5[5]
Database references
SIMBAD	data
Exoplanet Archive	data

Planetary system

In 2022, two exoplanets were discovered in orbit around this star. The first planet, LP 890-9 b, was initially identified using TESS. Further observations using SPECULOOS confirmed this planet and discovered a second planet, LP 890-9 c. Both planets are likely terrestrial planets, somewhat larger than Earth. The outer planet LP 890-9 c orbits within the habitable zone, and is a favorable target for atmospheric characterization using JWST.^[3][7]

LP 890-9 c orbits near the inner edge of the conservative habitable zone, and models differ as to whether the planet is more likely to resemble Earth or Venus. Spectra from JWST should make it possible to distinguish between these two scenarios.^[4] The planet is tidally locked to its host, meaning it has no day-night cycle like Earth.^[8] While the planet's location in the habitable zone suggests a strong possibility of an Earth-like atmosphere and climate, the planet's large size may count against its habitability. In addition, the planet is close enough to its star that powerful radiation may reduce its habitability.^[9] Another factor that reduces habitability of LP 890-9 c is the magma ocean that would have formed during its formation which could have lasted for up to 50 million years. This could have removed eight Earth oceans of water and leave 2000 bars of Oxygen in it’s atmosphere. However if it had an initial Hydrogen envelope of 0.1 Earth masses, no water would be loss. Furthermore the circulation of the planets orbit would take about 7 billion years producing hundreds of terawatts of tidal heating.^[10]

The habitability of LP 890-9 c depends heavily on the initial volatile content and properties and is unlikely to support life.^[10]

The LP 890-9 planetary system^[3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	<13.2 M🜨	0.01875±0.00010	2.7299025+0.0000034 −0.0000040	—	89.67+0.22 −0.33°	1.320+0.053 −0.027 R🜨
c	<25.3 M🜨	0.03984±0.00022	8.457463±0.000024	—	89.287+0.026 −0.047°	1.367+0.055 −0.039 R🜨

See also

• Proxima Centauri - Closest star to the Sun, a red dwarf that hosts terrestrial planets with one inside the habitable zone
• Teegarden's Star - A nearby red dwarf with two terrestrial planets in the habitable zone, in the constellation of Aries
• TRAPPIST-1 - An ultra-cool red dwarf in the constellation of Aquarius
• Wolf 359 - A planet hosting nearby ultra-cool red dwarf in the Leo constellation

Notes

1. The absolute magnitude M_V of the star can be calculated from its apparent magnitude m_V and distance d using the following equation: ${\displaystyle \scriptstyle M_{V}=m_{V}-5\log _{10}\left({\frac {d}{10\mathrm {\ parsecs} }}\right)}$