Astronomy:TOI-270

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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.[1] Their masses have since been measured by both Doppler spectroscopy[2] and transit-timing variations.[3] The innermost planet, TOI-270 b, is a volatile-rich super-Earth[4], while the two outer planets are mini-Neptunes.[2] TOI-270 b and c orbit near a 5:3 resonance, while TOI-270 c and d orbit near a 2:1 resonance.[1]

Observations of the outermost planet, TOI-270 d, by the Hubble Space Telescope suggest a hydrogen-rich atmosphere with signs of water vapor.[5] TOI-270 c & d are good targets for atmospheric detection with the James Webb Space Telescope (JWST).[6]

The JWST detected methane (CH4), carbon dioxide (CO2) and water vapor in the atmosphere of TOI-270 d.[7] 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%.[7] Possible signatures of sulfur dioxide (SO2) and carbon disulfide (CS2) were also found.[7] 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.[4]

The TOI-270 planetary system[2][3][4]
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) 89.41±0.43° 1.306±0.028 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[8]
Artist's impression of the three known planets in the TOI-270 system and their size comparison with Earth

References

  1. ↑ 1.0 1.1 Günther, Maximilian N. et al. (July 2019). "A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270". Nature Astronomy 3 (12): 1099–1108. doi:10.1038/s41550-019-0845-5. Bibcode: 2019NatAs...3.1099G. 
  2. ↑ 2.0 2.1 2.2 Van Eylen, V. et al. (October 2021). "Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley". Monthly Notices of the Royal Astronomical Society 507 (2): 2154–2173. doi:10.1093/mnras/stab2143. Bibcode: 2021MNRAS.507.2154V. 
  3. ↑ 3.0 3.1 Kaye, Laurel et al. (March 2022). "Transit Timing Variations in the three-planet system: TOI-270". Monthly Notices of the Royal Astronomical Society 510 (4): 5464–5485. doi:10.1093/mnras/stab3483. Bibcode: 2022MNRAS.510.5464K. 
  4. ↑ 4.0 4.1 4.2 Coulombe, Louis-Philippe; Benneke, Björn; Krissansen-Totton, Joshua; l'Heureux, Alexandrine; Piaulet-Ghorayeb, Caroline; Radica, Michael; Roy, Pierre-Alexis; Ahrer, Eva-Maria et al. (2025). "Possible Evidence for the Presence of Volatiles on the Warm Super-Earth TOI-270 B". The Astronomical Journal 170 (4): 226. doi:10.3847/1538-3881/adfc6a. 
  5. ↑ Mikal-Evans, Thomas et al. (March 2023). "Hubble Space Telescope Transmission Spectroscopy for the Temperate Sub-Neptune TOI-270 d: A Possible Hydrogen-rich Atmosphere Containing Water Vapor". The Astronomical Journal 165 (3): 84. doi:10.3847/1538-3881/aca90b. Bibcode: 2023AJ....165...84M. 
  6. ↑ Chouqar, J. et al. (June 2020). "Properties of sub-Neptune atmospheres: TOI-270 system". Monthly Notices of the Royal Astronomical Society 495 (1): 962–970. doi:10.1093/mnras/staa1198. Bibcode: 2020MNRAS.495..962C. 
  7. ↑ 7.0 7.1 7.2 Benneke, Björn; Roy, Pierre-Alexis; Coulombe, Louis-Philippe; Radica, Michael; Piaulet, Caroline; Ahrer, Eva-Maria; Pierrehumbert, Raymond; Krissansen-Totton, Joshua et al. (2024-03-05), JWST Reveals CH$_4$, CO$_2$, and H$_2$O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet 
  8. ↑ Reddy, Francis (29 July 2019). "NASA's TESS Mission Scores 'Hat Trick' With 3 New Worlds". NASA. https://www.nasa.gov/universe/nasas-tess-mission-scores-hat-trick-with-3-new-worlds/. 

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