Urs Schroffenegger

The radii of small exoplanets form two populations, super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This feature could be produced by the removal of atmospheres by stellar or internal heating or by the lack of an initial envelope. We used transit photometry and radial velocity measurements to detect and characterize four exoplanets orbiting LHS 1903, a red dwarf star in the Milky Way’s thick disk. These four planets have orbital periods ranging from 2.2 to 29.3 days and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, whereas LHS 1903 c and LHS 1903 d have extended atmospheres. The most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating that it formed from gas-depleted material.

Sub-Neptune-sized exoplanets are the most common class discovered by transit surveys, yet their detailed exploration has just begun. Their demographics have inspired models of planetary formation and evolution, though the sample is naturally biased toward the predominance of M-dwarf systems, which provide more favourable observing conditions. We aim to validate the planetary nature of four candidates identified by the Transiting Exoplanet Survey Satellite (TESS) orbiting K-dwarf stars: TOI-2133.01, TOI-5734.01, TOI-5938.01, and TOI-7009.01. We used photometric, spectroscopic, and high-resolution imaging data from the TESS Follow-up Observing Programme with well-established and cutting-edge tools for validating the planetary nature of the candidates. We validate all four candidates and determine their system parameters. TOI-2133 b and TOI-5734 b lie near the upper edge of the radius valley, while TOI-5938 b and TOI-7009 b are at the boundary of the Neptune desert, making them rare additions to the known sub-Neptune population. The planets are suitable for precise mass measurements and atmospheric characterization with current facilities, making them benchmark targets for testing formation and evolution models around K-dwarf hosts, a population less accessible than the typical M-dwarf systems.

Earth-sized planets transiting M dwarf stars present one of the best opportunities with current facilities for studying the atmospheric and bulk compositions of terrestrial worlds. Here, we statistically validate five new transiting Earth and super-Earth sized planets orbiting M dwarf stars using a combination of light curves from the Transiting Exoplanet Survey Satellite, multicolor observations from Palomar and Las Cumbres Observatory, high-resolution imaging, and stellar spectroscopy. The sample includes TOI-5716 b, an Earth-sized planet ( R _p = 0.96 ± 0.05 R _⊕ ) with a 6.766 day orbit around a metal-poor thin-disk star ([Fe/H] = −0.54 ± 0.10); TOI-5728 b, a super-Earth ( R _p = 1.31 ± 0.05 R _⊕ ) on an 11.497 day orbit; and TOI-5736 b, a larger planet ( R _p = 1.56 ± 0.07 R _⊕ ) with an ultrashort period of just 0.649 days. We also statistically validate a multiplanet system, TOI-5489, hosting two similarly sized super-Earths: TOI-5489 b ( R _p = 1.40 ± 0.05 R _⊕ ) and TOI-5489 c ( R _p = 1.28 ± 0.07 R _⊕ ) with orbital periods of 3.152 and 4.921 days, respectively. Due to their longer orbital periods, TOI-5716 b and TOI-5728 b both have equilibrium temperatures ≤ 400 K, making them useful test cases for studies of atmospheric mass loss. If TOI-5728 b is confirmed to have an Earth-like bulk composition, it would join the very small sample of rocky planets orbiting mid-to-late M dwarfs that lie below the cosmic shoreline and therefore may have retained high mean molecular weight atmospheres.

We report the discovery of two warm exoplanets orbiting the cool binary system TOI-2267, composed of the M5 (TOI-2267A) and M6 (TOI-2267B) stars, whose angular separation is 0.384 arcsec, corresponding to a projected distance of only about 8 au at 22 pc from the Solar System. To confirm the planetary nature of these objects, we combined photometry from the Transiting Exoplanet Survey Satellite ( TESS ) and ground-based facilities together with high-resolution images, archival data, and statistical validation in our analyses. From the current data set, we cannot unambiguously determine which star of the binary the planets orbit. These planets are Earth-sized with radii of 1.00±0.11 and 1.14±0.13 R _⊕ for TOI-2267 b (P = 2.28 d) and TOI-2267 c (P = 3.49 d), respectively, when orbiting TOI-2267A, whereas the radii are of 1.22±0.29 and 1.36±0.33 R _⊕ when orbiting TOI-2267B. In addition to the signals attributed to TOI-2267 b and c, the TESS data reveal a third strong signal with a periodicity of 2.03 d (TOI-2267.02). Although statistical analyses support its planetary nature, ground-based follow-up observations did not detect this signal. Its status therefore remains that of a planetary candidate, with an Earth-size of 0.95±0.12 R _⊕ or 1.13±0.30 R _⊕ when orbiting TOI-2267A or B, respectively. If this candidate is confirmed, dynamical analyses indicate that all three planets cannot orbit the same star. The most plausible configurations are b–c or .02–c orbiting the same star, while the .02–b case is unlikely due to strong instabilities. The proximity of b and c to a first-order 3:2 mean motion resonance suggests they likely orbit the same star, with .02 orbiting the other component. This scenario would make TOI-2267 the most compact binary system known to host planets, with both components harbouring transiting worlds, and offer a unique benchmark for studying planet formation and evolution in compact binary environments.

We present the discovery by the TESS mission of one transiting Neptune-sized planet, TOI-6223 b, and two transiting super-Earths, TOI-1743 b and TOI-5799 b. We validate these planets using a statistical validation method, multi-color light curves, and other ancillary observations. We combined TESS and ground-based photometric data to constrain the physical properties of the planets. TOI-6223 b is slightly larger than Neptune R_p = 5.12_−0.25^+0.24 R_⊕) orbiting an early M dwarf in 3.86 days, and it has an equilibrium temperature of T_eq = 714 ± 14 K. TOI-1743 b orbits its mid-dwarf star every 4.27 days. It has a radius of R_p = 1.83_−0.10^+0.11 R_⊕ and an equilibrium temperature of T_eq = 485₋₁₃⁺¹⁴. TOI-5799 b has a radius of R_p = 1.733_−0.090^+0.096 R_⊕ and an equilibrium temperature of T_eq = 505 ± 16 K. It orbit around an M2 dwarf in 4.17 days. We also present the discovery of an additional transiting planet, TOI-5799 c, which we identified in the TESS data and validated using the SHERLOCK pipeline. TOI-5799 c is a super-Earth with a radius of R_p = 1.76_−0.10^+0.11 R_⊕. Its orbital period and its equilibrium temperature are 14.01 days and T_eq = 337 ± 11 K, respectively, which place it near the inner edge of the habitable zone of its star. We show that these planets are suitable for both radial velocity follow-up and atmospheric characterization. They orbit bright (K_mag) early M dwarfs, making them accessible for precise mass measurements. The combination of the planet sizes and stellar brightness of their host stars also make them suitable targets for atmospheric exploration with the JWST. Such studies may provide insights into planet formation and evolution, as TOI-1743 b, TOI-5799 b, and TOI-5799 c lie within what is known as the radius valley, while TOI-6223 b is located on the Neptunian ridge in the period-radius plane.