The star hosts two planets discovered by the transit method. They were initially observed in TESS data from Sector 13 (June and July 2019) and Sector 27 (July 2020) and were validated with ground based observations with LCO telescope network during 2021, with a study published in 2023.[2] Spectroscopic measurements of the star for the purposes of radial velocity measurements to determine the planets' masses were performed by ESPRESSO between April 2022 and March 2023, as well as NIRPS at the ESO 3.6 m Telescope between August and October 2023.[6] The planets are orbiting close to a 2:1 mean-motion resonance.
Both planets are sub-Neptunes, similar in size, expected to have atmospheres with a significant fraction of hydrogen and helium. Based on the calculated insolation, the planets are expected to have equilibrium temperatures of 633.6+6.2 −6.3K and 508.9+5.0 −5.0K respectively.[2]
While the planets have very similar radii, their masses are measured to be significantly different. The densities calculated from the measured values for radius and mass are 3.18+0.70 −0.63g⋅cm−3 for the planet b and 2.01+0.65 −0.60g⋅cm−3 for the planet c. There are different possible interpretations for their compositions based on those density values. TOI-4342 b could be an ocean world with an Earth-like core surrounded by a ~50% mass fraction steam atmosphere, or it could have a much less massive hydrogen-rich atmosphere instead. The lower inferred density together with a lower equilibrium temperature of TOI-4342 c is not compatible with the water-dominated envelope models, instead pointing at a higher abundance of hydrogen and helium.[6]
Radial velocity measurements also point at existence of an additional planet candidate orbiting on a ~48-day orbit with a minimum mass of 17.8±3.0M🜨, which however hasn't been detected in TESS transits. This is likely due to a larger orbital inclination, in which case transits are not visible from Earth, but it is possible transits were missed due to the limited time span of available observations as of January2026[update]. TESS is scheduled to observe the star again for three months during 2026, during which time transits, if occurring, should be detected.[6]
Due to orbiting within 5% of the 2:1 mean-motion resonance, the system is expected to show transit-timing variations due to mutual perturbations. Observation of the amplitudes of this perturbation could additionally help constrain planet masses. However, the limited observations available by the time of the discovery paper were only adequate to rule out deviations by more than 5min from linear ephemerides.[2] The observed low value of perturbation also confirms a low orbital eccentricity for the planets.[2] The follow-up study published in 2026 also failed to observe any transit-timing variations, noting that the signal-to-noise ratio of TESS and ground-based transit data is too small for clear detection of the predicted amplitudes based on the masses determined from radial velocity measurements.[6]
See also
TOI-270 – another M-type main sequence star with two sub-Neptunes
123Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
12345Parc, Léna; etal. (2026-01-29). "Densities of small planets around the M dwarfs TOI-4336 A and TOI-4342 with ESPRESSO: Three sub-Neptunes, one super-Earth, and a Neptune-mass candidate". arXiv:2601.22115 [astro-ph].
