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.

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 volatile-rich super-Earth, while the two outer planets are mini-Neptunes. TOI-270 b and c orbit near a 5:3 resonance, while TOI-270 c and 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 (JWST).

The JWST 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 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%. Possible signatures of sulfur dioxide (SO2) and carbon disulfide (CS2) were also found. It was found that TOI-270 b possibly has an atmosphere rich in water vapor based on the revised density value and JWST transmission spectroscopy result.