TOI-270

TOI-270, also known as L 231-32, is a red dwarf star 73.3 ly away in the constellation Pictor. It has about 39% the mass and 38% the radius of the Sun, and a temperature of about 3506 K. TOI-270 hosts a system of three known exoplanets.

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

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

The James Webb Space Telescope detected methane (CH4), carbon dioxide (CO2) and water vapor in the atmosphere of TOI-270 d. The atmosphere of this planet was also found to be metal-rich, with a mean molecular weight of $12.617$ and an atmospheric metal mass fraction (percentage of the mass of metals in the atmosphere) of $12.147$. Possible signatures of sulfur dioxide (SO2) and carbon disulfide (CS2) were also found.