TOI-4342 b
A sub-Neptune exoplanet with a possible steam atmosphere or hydrogen-rich envelope.
TOI-4342 b is a transiting sub-Neptune exoplanet orbiting the early red dwarf star TOI-4342, located 201 light-years away in the constellation Octans. It is notable as one of two planets in the system considered good targets for transmission spectroscopy to determine atmospheric composition, and for its proximity to a 2:1 mean-motion resonance with its sibling planet TOI-4342 c.
- Discovery method
- transit method
- Stellar host
- TOI-4342 (M0V red dwarf)
- Distance
- 201 light-years
- Planet type
- sub-Neptune
- Radius
- similar to TOI-4342 c
- Mass
- significantly different from TOI-4342 c
- Density
- higher than TOI-4342 c
Lore & Background
TOI-4342 b was discovered via the transit method using TESS data from Sector 13 (June and July 2019) and Sector 27 (July 2020), and validated with ground-based observations from the LCO telescope network during 2021, with a study published in 2023. Radial velocity measurements to determine its mass were performed by ESPRESSO between April 2022 and March 2023, and by NIRPS at the ESO 3.6 m Telescope between August and October 2023. The planet orbits close to a 2:1 mean-motion resonance with TOI-4342 c, leading to expected transit-timing variations due to mutual perturbations, though observations available by the discovery paper only ruled out deviations greater than a certain threshold from linear ephemerides, and a follow-up study in 2026 also failed to detect such variations due to insufficient signal-to-noise ratio.
Reader's Guide
TOI-4342 b is significant as a target for transmission spectroscopy, which could reveal the composition of its atmosphere, expected to contain a significant fraction of hydrogen and helium. Its density, calculated from measured radius and mass, allows for different compositional interpretations: it could be an ocean world with an Earth-like core surrounded by a steam atmosphere with about 50% mass fraction, or it could have a much less massive hydrogen-rich atmosphere. The planet's mass is significantly different from that of TOI-4342 c despite their similar radii, and its higher density compared to TOI-4342 c is a key constraint for models. The system's proximity to a 2:1 mean-motion resonance makes it valuable for studying orbital dynamics, though transit-timing variations have not yet been clearly detected. The radial velocity data also hint at an additional planet candidate on a ~48-day orbit, which may or may not transit; TESS is scheduled to observe the star again for three months during 2026, which could confirm or rule out transits of that candidate.
Did You Know?
- TOI-4342 b orbits an early red dwarf of spectral class M0V.
- Radial velocity measurements for TOI-4342 b were obtained with ESPRESSO and NIRPS instruments.
- The planet's density is higher than that of its sibling TOI-4342 c.
More in Transiting Exoplanets, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced