Rafael Luque

Context . Despite precise characterization measurements, the nature of planets with radii between 2 and 4 Earth radii – sub-Neptunes – remains unknown due to degeneracies in interior models. Nevertheless, the field has compiled an impressive ensemble of small planets with measured masses and radii orbiting different stars. Aims . This dataset can be used to test the prediction of large water reservoirs on sub-Neptunes, as proposed by planet formation theory with orbital migration. We aim to determine whether this water reservoir is included in photoevaporative winds and how much of it can partition into the rocky and metallic interior. Methods . We coupled the results of a planetary formation model with planetesimal and gas accretion as well as orbital migration with evolution models that assume either perfect mixing of water with H/He in the envelope or complete segregation. For the mixed envelopes, we also included an analytic treatment of fractionation during photoevaporative mass loss. Furthermore, we studied the effect of equilibrium dissolution of water into an assumed magma ocean and metallic core for the first time in coupled formation-evolution models. Results . Out of the tested scenarios, the mass–radius relation of exoplanets is relatively well matched by all scenarios where the atmosphere is of mixed composition. The agreement depends on mass, with better consistency for the model without dissolution below 3 Earth masses and hints of the opposite at higher masses. Fractionation is not found to significantly alter the properties of the planets for our initial conditions due to initially massive envelopes on all planets. For all scenarios, we quantified the radius valley location and its scaling with stellar mass. Conclusions . The mass–radius relations for water-rich sub-Neptunes are broadly consistent with observations. However, statistical surveys in both mass and radius are required to distinguish between the scenarios. The mixed-composition loss of different volatiles, their dissolution into the planetary interior, and the solidification of the magma ocean are natural next steps toward a comprehensive atmosphere-interior evolution model.

Radial velocity (RV) observations are reaching increasingly high precision, enabling the targeting of low-amplitude signals. Assessing results obtained at the limits of our capabilities requires understanding the relationship between data, models and inference. Leave-one-out cross validation (LOO-CV) has become an increasingly popular tool for interpretable model criticism in astronomical data analysis. In this work, we demonstrate how LOO-CV can provide insight into the RV analysis of exoplanetary systems through three case studies. We first investigate the anomalously high mass of HD 119130 b inferred from CARMENES RVs, later revised significantly downward after follow-up observations with other instruments. We show that this high mass was strongly driven by two individual measurements, whose removal significantly reduces the tension between data sets. Next, we use LOO-CV as a model selection tool for the GJ 4276 system. Here, LOO-CV prefers an eccentric single-planet model over a two-planet model, and identifies the orbital phases at which follow-up observations would best discriminate between them. Finally, we extend LOO-CV to models with correlated noise, applying it to the GJ 357 system, whose RVs are modeled with a Gaussian process. We find no predictive support for a fourth planetary signal that is moderately favored by the Bayesian evidence, strengthening the interpretation of a three-planet architecture previously reported in the literature. We provide practical guidance for implementing LOO-CV in RV analysis, together with an online tutorial. Such methods will become ever more important as future RV surveys push the limits of planet detection and characterization.

An open question in exoplanet science is whether rocky exoplanets extremely close in to their host stars, “lava worlds,” can retain significant atmospheres. Thermal emission observations via secondary eclipse can be used to determine whether a rocky exoplanet possesses an atmosphere. It is expected that an atmosphere could increase the planet’s albedo and/or redistribute heat away from the dayside, reducing the secondary eclipse depth measured. Recent eclipse observations of lava planets, rocky planets hot enough to have liquid magma surfaces, have suggested the presence of atmospheres. Here, we present a single JWST MIRI/LRS partial secondary eclipse of the lava planet TOI-431b. We measure an eclipse depth of 81 ± 16 ppm, which corresponds to a brightness temperature of 196 7 − 253 + 237 K and a brightness temperature ratio R = 0.81 ± 0.10, being 1.2 σ higher than the value reported by Spitzer. The observed brightness temperature ratio is 1.8 σ below that of a zero-albedo, zero heat redistribution bare rock ( R = 1). Given that magma pools are expected to have low albedos, we find that our results are best explained by the presence of an atmosphere. Future work to measure the exact composition of TOI-431b’s atmosphere and improve models of lava planet atmospheres would better constrain the nature and evolution of lava planets.

“Lava worlds”, Earth-sized planets hot enough ( T _eq ≳ 1100 K) to melt their dayside silicate surfaces, have emerged as promising candidates for atmospheric detection and characterization. Thermal emission observations show an apparent dichotomy: The hottest lava worlds have colder daysides than the temperature of a maximally emitting bare rock, indicating the likely presence of thick and/or reflective atmospheres, while the coldest ones do not. However, where in instellation flux this potential bifurcation occurs is uncertain. We present a JWST/MIRI Low Resolution Spectrometer eclipse of the ultra-short-period (USP) lava world HD 3167 b ( T _eq = 1786 K, R = 1.6 R _⊕ , P = 0.96 day) that helps bridge this gap. We measure the white-light eclipse depth to be 38 ± 11 ppm, more than 5 σ lower than the expected eclipse depth of a dark, maximally hot bare rock. We use this to derive a dayside brightness temperature that is best explained by the presence of an atmosphere that cools the dayside by reflecting incoming starlight and/or efficiently redistributing heat to the planet’s nightside. An atmosphere is further compatible with the planet’s slight underdensity compared to an Earth-like composition. The corresponding dayside emission spectrum is not precise enough to constrain atmospheric composition, motivating follow-up spectroscopic observations with JWST/NIRSpec. Lastly, we use our observation and existing data to refine key planetary parameters of the HD 3167 system. HD 3167 b is currently the least irradiated USP super-Earth with evidence for an atmosphere.

We extend the planetary census around massive stellar hosts through a long-term campaign of high-precision radial velocity (RV) measurements on evolved stars. We analysed data acquired with the CORALIE spectrograph covering 15-18 years on HD,125136, HD,127195, and HD,220218. The stellar parameters were derived through different methods for a comprehensive characterisation of each star. We then evaluated the presence of planetary signals in the RV time series using the Bayesian inference tool kima . Finally, we designed an observing strategy aimed at mitigating the impact of pulsations on evolved stars and tested its effectiveness on the low-luminosity red giant HD,127195. We detected signals that have been accurately modelled by Keplerian curves in the RV data of the three stars: one on HD,125136, two on HD,127195, and one on HD,220218. While the signals on the first two stars appear to be planetary in origin, the signal on the third one shows several signs of stellar activity. Therefore, we identified a planetary companion around HD,125136 with a minimum mass of Jup on an 850,d orbit. On HD,127195, we identified a system composed of planets with 0.66,M_ Jup and 0.78,M_ Jup with orbital periods of 535,d and 834,d, respectively. We detected three massive planets around two low-luminosity red giant stars in a region of the parameter space that is poorly populated in both stellar mass and planetary orbital periods. The dedicated observing campaign on HD,127195 showcases how stellar pulsations can be efficiently averaged out to below -1 in low-luminosity giant stars.

While recent JWST observations of mature super-Earths and sub-Neptunes have frequently revealed featureless transmission spectra, their inflated progenitors offer a unique window into understanding their primordial compositions. As part of the Keys to Revealing the Origin and Nature of Sub-Neptune Systems (KRONOS) JWST program, we present the Near Infrared Imager and Slitless Spectrograph Single Object Slitless Spectroscopy transmission spectrum of V1298 Tau c, an ∼23 Myr super-Earth progenitor orbiting a young solar analog. We detect H ₂ O in V1298 Tau c’s atmosphere with a log 10 volume mixing ratio of − 1.8 3 − 0.77 + 0.68 , but no additional molecules from these data alone. We find consistent results for the planetary atmospheric properties in both retrievals with and without informed priors on stellar heterogeneities based on the observed stellar spectrum. We infer an atmospheric metallicity [O/H] of 14 . 8 − 12.28 + 56.0 × the solar value. This metallicity is similar to literature measurements for other young planets, including its massive outer companion V1298 Tau b. In contrast, this measured metallicity is systematically lower than the metallicities of mature planets of similar mass and temperature. Altogether, these results provide tentative but growing evidence that the exoplanet mass–metallicity relation evolves with planetary age.

Theory predicts that a planet with a sufficiently strong magnetic field orbiting close to its host star could induce star-planet magnetic interactions. This is potentially observable as an optical or radio stellar activity signal synchronised with the planet’s orbital period. We analyze 18 years of high-resolution optical spectroscopy of GJ 436, a low mass star orbited by a Neptune-sized exoplanet on a polar eccentric orbit. Stellar activity indicators show enhancements at a period corresponding to the exoplanet orbit, modulated by stellar rotation, and the star’s 8-year magnetic cycle. We interpret this as a signal of star-planet magnetic interaction. Using a geometric model, we reproduce these periods if GJ 436 b has a magnetic field strength of 6 to 110 Gauss.

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.

Context . The structure and evolution of close-in exoplanets are shaped by atmospheric loss and migration processes, which give rise to key population features such as the hot Neptune desert, ridge, and savanna – regions of the period-radius space whose boundaries offer critical insights into planetary formation and survival. Aims . As part of the KESPRINT collaboration, we selected the TESS transiting planet candidate TOI-3862.01 for radial velocity follow-up to confirm its planetary nature and characterize its mass and bulk properties. This planet candidate is of particular interest due to its position in the middle of the hot Neptune desert, making it a valuable probe for testing theories of planet migration and atmospheric loss. Methods . We confirmed the planetary nature and determined the mass of TOI-3862.01 (hereinafter TOI-3862 b) by performing a joint fit with both transit and radial velocity data, precisely characterizing the bulk properties of this planet. Results . TOI-3862b is a super-Neptune on a 1.56-day orbit around a Sun-like star with an effective temperature of 5300±50 K. It has a mass of 53.7 _−2.9 ^+2.8 M _⊕ and a radius of 5.53 ± 0.18 R _⊕ , corresponding to a density of 1.7±0.2 g/cm ³ . This places it among the rare population of hot and dense super-Neptune desert planets. Conclusions . TOI-3862b, residing deep in the hot Neptune desert, represents a rare occurrence in an otherwise sparsely populated region, offering a valuable opportunity to probe the processes that may allow planets to survive in such environments.