Giuseppe Morello

Context . Detecting light reflected off the dayside of an exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. Aims . We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. Methods . We introduce a new figure of merit that quantifies the favourability of different systems for a reflection study, the reflection spectroscopy metric. Applying this metric, we identify the KELT-9 system, which features a highly misaligned, rapidly rotating host star, as the target for a case study based on a spectroscopic time series obtained by CARMENES. We also perform an injection-recovery test to determine the detectability of the signal in our data and demonstrate its sensitivity to rotational line broadening. Results . The search for a genuine reflection signal in our data resulted in a non-detection. The injection-recovery test puts this finding into context by revealing the critical importance of taking rotational broadening into account when dealing with systems featuring rapidly rotating stars and large spin-orbit misalignments. Conclusions . The case study presented here underscores the need to incorporate stellar rotation and spin-orbit misalignment into assessments of a given planet’s favourability to reflection studies.

Unlocking the atmospheres of sub-Neptune planets is among the revolutionary accomplishments of JWST. However, such observations require complex data analysis methodologies, which have a strong impact on the derived conclusions. Here, we present an independent re-analysis of the JWST transmission spectrum of the temperate sub-Neptune K2-18 b, aimed at assessing the robustness of previously claimed atmospheric detections, exploring the planet’s possible parameter space, and determining the implications behind its formation. The NIRISS/SOSS and NIRSpec/G395H observations were reduced using a combination of public and customised pipelines. We produced a total of 12 different versions of the transmission spectrum by varying key steps: spectral binning, limb-darkening treatment, and the application of a novel correction for an occulted stellar spot, as well as error inflation and instrumental offsets. We performed atmospheric retrievals using TauREx 3, comparing models of varying complexity. We robustly detected CH ₄ at a >3σ significance across the majority of reduction and retrieval setups. Hints of CO ₂ appear in most configurations, but the evidence is weak and strongly model-dependent. The tentative detection of dimethyl sulphide, reported in previous studies, vanishes in our most comprehensive retrieval models. We find that correcting the stellar spot in the NIRISS transit is a critical step, introducing a uniform offset that primarily drives the inference of a lighter atmosphere characterised by a lower mean molecular weight. Furthermore, the assumed complexity of the retrieval model itself introduces significant biases; including more molecules systematically increases the retrieved CH ₄ abundance and atmospheric mean molecular weight, even for species without spectral features. The data are consistent with a hydrogen-rich (i.e. primordial) atmosphere with an elevated O abundance and an even more elevated C abundance, leading to a C/O ratio that is significantly greater than solar. We show that the physical properties of the K2-18 system planets (i.e. the innermost planet, K2-18 c, and K2-18 b) are consistent with those expected by the in situ formation theory of inside-out planet formation. Furthermore, these properties predict a temperature of K2-18 b at the time of formation of ≳500 K. This is much warmer than the current equilibrium temperature and just interior to the carbon ‘soot’ line, where an elevated C/O ratio and a correspondingly volatile-poor (dry) atmospheric composition is expected to be inherited from the protoplanetary disk, arguing against an Hycean world scenario.

Stellar rotation is closely linked to both the age and the magnetic activity of stars. Through gyrochronology, studying stellar rotation provides a means to estimate stellar ages and trace the evolution of planetary systems, and it is also a crucial means to constrain and correct stellar activity effects for robust exoplanet detection and characterisation. CARMENES is a dual-channel, high-resolution (ℛ > 80 000) spectrograph that has been highly successful in detecting exoplanets around M-dwarf stars using the radial-velocity technique, and it also enables precise measurements of the projected rotational velocity ( v sin i ) from spectral line broadening. We present an oversampled convolution method that incorporates a realistic limb-darkening model to determine v sin i from CARMENES spectra by comparing observed spectra with that of a template star. The advantages over existing methods in the literature have been assessed using high-resolution synthetic spectrat that span effective temperatures of 2500–4000 K and projected rotational velocities of up to 50 km s ⁻¹ . We applied our method to 392 M dwarfs observed with CARMENES and it yielded v sin i measurements (or upper limits at 2 km s ⁻¹ ) with a median relative uncertainty of 6.8%, which is substantially smaller than the 15.4% reported in the literature. This work provides the largest uniform catalogue of v sin i measurements for M dwarfs, including significantly updated values for several targets, along with 36 new targets.

The Transiting Exoplanet Survey Satellite (TESS) has delivered a large number of transiting planet candidates around nearby stars by identifying periodic decreases in stellar brightness. Establishing the planetary nature of these signals and determining their fundamental properties is a necessary step toward detailed studies of their internal structure, atmospheres, and formation pathways. In this work, we investigate the planetary nature of the TOI–1752 system (M1 V, 103.02 ± 0.34 pc), which hosts two TESS candidates: TOI–1752 b, a short-period object consistent with a lava-world scenario, and TOI–1752 c, a sub-Neptune-size planet candidate located in the optimistic habitable zone. We obtained ground-based multi-color photometric follow-up observations of TOI–1752, which we combined with TESS photometry to assess the nature of both signals. We performed a formal statistical validation using the TRICERATOPS framework, while independently vetting the candidates with the neural-network-based classifier WATSON-Net, which provides a machine-learning assessment of their planetary likelihood based on light-curve morphology, centroid diagnostics, and auxiliary vetting features. We validate TOI–1752 b as a bona fide planet with a radius of 1.69 ± 0.07R_⊕ and an orbital period of |$0.935186^{+0.000001}_{-0.000002}$| days, and TOI–1752 c with a radius of |$2.29^{+0.13}_{-0.14} R_{\oplus }$| and an orbital period of 32.7144 ± 0.0004 days. The combined analysis confirms TOI–1752 as a new planetary system, places TOI–1752 c within the optimistic habitable zone of its host star, and identifies TOI–1752 b as a promising target for atmospheric characterization, with an estimated emission spectroscopy metric (ESM) of up to ~8.

We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM J0902+7138), TOI-4529 (G 2-21), and TOI-5388 (Wolf 346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of 4.65, 5.88, and 2.59 days, and they orbit early-M dwarfs (M2.0 V, M1.5 V, and M3.0 V, respectively). We were able to precisely determine the radius of all three planets with a precision of R _⊕ , its mass is 7.7 ± 1.5 M _⊕ , and the mean density is 0.61 ± 0.15 ρ _⊕ . The radius of TOI-4529b is 1.77 _−0.08 ^+0.09 R _⊕ , the 3 σ upper mass limit is 4.9 M _⊕ , and the 3 σ upper density limit is 0.88 ρ _⊕ . The third planet, TOI-5388 b, is Earth-sized with a radius of 0.99 _−0.06 ^+0.07 R _⊕ , a 3 σ upper mass limit of 2.2 M _⊕ , and a 3 σ upper density limit of 2.2 ρ _⊕ . While TOI-5388 b is most probably rocky, given its Earth-like radius, TOI-1243 b and TOI-4529 b are located in a highly degenerate region in the mass-radius space. TOI-4529 b appears to lean toward a water-world composition. TOI-1243 b has enough mass to host a significant H-He envelope, although a water-world and pure rocky compositions are also consistent with the data. Our analysis indicates that future atmospheric observations using JWST can aid in determining their real composition. The sample of small planets around M dwarfs is widely used to understand planet formation and composition theories, and our study adds three planets to this sample.

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.

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.

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.

We propose a followup to our 2024 Ariel Data Challenge, which tackled the fundamental problem of extracting extremely faint exoplanetary signals hidden within non-linear noise. Despite attracting global participation with its realistic space mission simulation, the challenge remains unsolved, as even top solutions failed to meet the mission's strict requirements. Our 2025 competition enhances the existing data pipeline with improved simulation fidelity that better reflects actual space observations and incorporates Ariel's latest observation strategy. This challenge has two key goals: developing solutions directly applicable to the Ariel Space Telescope mission and advancing methodologies for processing spatial-temporal data. At its core, this competition promotes innovation in both denoising techniques and methods for proper uncertainty quantification. Advances made through this work will benefit numerous fields facing similar signal extraction challenges, including, but not limited to, earthquake analysis, remote sensing, Earth observation, and satellite imaging. At EPSC-DPS 2025, we would like to take this opportunity to advertise the challenge to the boarder scientific community, share our insights developed during ADC 2024 edition, and discuss the role of challenges in helping to promote open science to external communities.