TOI-270

TOI-270, also known as L 231-32, is a red dwarf star 73.3 light-years (22.5 parsecs) away in the constellation Pictor. It has about 39% the mass and 38% the radius of the Sun, and a temperature of about 3,506 K (3,233 °C; 5,851 °F). TOI-270 hosts a system of three known exoplanets.

TOI-270

Observation data Epoch J2000      Equinox J2000
Constellation	Pictor[1]
Right ascension	04h 33m 39.72001s[2]
Declination	−51° 57′ 22.4354″[2]
Apparent magnitude (V)	12.617[3]
Characteristics
Evolutionary stage	Main sequence[4]
Spectral type	M3.0V[5]
Apparent magnitude (V)	12.617±0.03[3]
Apparent magnitude (R)	12.147±0.05[3]
Apparent magnitude (G)	11.621±0.003[2]
Apparent magnitude (J)	9.099±0.032[3]
Apparent magnitude (H)	8.531±0.073[3]
Apparent magnitude (K)	8.251±0.029[3]
Astrometry
Radial velocity (Rv)	25.90±0.37[2] km/s
Proper motion (μ)	RA: +83.082 mas/yr[2] Dec.: −269.803 mas/yr[2]
Parallax (π)	44.4899±0.0147 mas[2]
Distance	73.31 ± 0.02 ly (22.477 ± 0.007 pc)
Details[4]
Mass	0.386±0.008 M☉
Radius	0.378±0.011 R☉
Luminosity (bolometric)	0.0194±0.0019 L☉
Surface gravity (log g)	4.872±0.026 cgs
Temperature	3506±70 K
Metallicity [Fe/H]	−0.20±0.12 dex
Other designations
L 231-32, PM J04336-5157, TOI-270, TIC 259377017, 2MASS J04333970-5157222[3]
Database references
SIMBAD	data
Exoplanet Archive	data

Planetary system

The three planets of TOI-270 were discovered in 2019 by the transit method with TESS.^[5] Their masses have since been measured by both Doppler spectroscopy^[4] and transit-timing variations.^[6] The innermost planet, TOI-270 b, is a rocky super-Earth, while the two outer planets are mini-Neptunes.^[4] TOI-270 b and c orbit near a 5:3 resonance, while TOI-270 c and d orbit near a 2:1 resonance.^[5]

Observations of the outermost planet, TOI-270 d, by the Hubble Space Telescope suggest a hydrogen-rich atmosphere with signs of water vapor.^[7] TOI-270 c & d are good targets for atmospheric detection with the James Webb Space Telescope.^[8]

The James Webb Space Telescope detected methane (CH₄), carbon dioxide (CO₂) and water vapor in the atmosphere of TOI-270 d.^[9] The atmosphere of this planet was also found to be metal-rich, with a mean molecular weight of 5.47+1.25
−1.14 and an atmospheric metal mass fraction (percentage of the mass of metals in the atmosphere) of 58%+8%
−12%.^[9] Possible signatures of sulfur dioxide (SO₂) and carbon disulfide (CS₂) were also found.^[9]

The TOI-270 planetary system^[4][6]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	1.48±0.18 M🜨	0.03197(22)	3.3601538(48)	0.0167(84)	89.39±0.37°	1.206±0.039 R🜨
c	6.20±0.31 M🜨	0.04526(31)	5.6605731(31)	0.0044(6)	89.36±0.24°	2.355±0.064 R🜨
d	4.20±0.16 M🜨	0.07210(50)	11.379573(13)	0.0066(20)	89.73±0.16°	2.133±0.058 R🜨

Comparison of the TOI-270 planetary system to Jupiter's moon system^[10]

Artist's impression of the three known planets in the TOI-270 system and their size comparison with Earth