Proyecto de Investigación: SCIENCE AND TECHNOLOGY FOR THE ARIEL MISSION: IAC CONTRIBUTION
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PID2021-125627OB-C32
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A transiting rocky super-Earth and a non-transiting sub-Neptune orbiting the M dwarf TOI-771
(EDP Sciences, 2025-06-20) Lacedelli, G.; Pallé, E.; Davis, Yasmin T.; Luque, R. ; Morello, G.; Tabernero, H. M.; Zapatero Osorio, María Rosa; Pozuelos, F. J.; Jankowski, Dawid; Nowak, G.; Murgas Alcaino, F.; Orell-Miquel, Jaume; Akana Murphy, Joseph M.; Barkaoui, K.; Charbonneau, D.; Dransfield, G.; Ducrot, E.; Geraldía González, Samuel; Irwin, J.; Jehin, E.; Osborne, H. L. M.; Pedersen, P. P.; Rackham, B. V. , P. P.; Scott, Madison Grace; Timmermans, M.; Triaud, A.; Van Eylen, V.; Agencia Estatal de Investigación (AEI); National Aeronautics and Space Administration (NASA); European Research Council (ERC); European Commission (EC); Science and Technology Facilities Council (STFC); Belgian National Fund for Scientific Research (FNRS); National Science Foundation (NSF)
[Context] The origin and evolution of the sub-Neptune population is a highly debated topic in the exoplanet community. With the advent of JWST, atmospheric studies can now put unprecedented constraints on the internal composition of this population. In this context, the THIRSTEE project aims to investigate the population properties of sub-Neptunes with a comprehensive and demographic approach, providing a homogeneous sample of precisely characterised sub-Neptunes across stellar spectral types.
[Aims] We present here the precise characterisation of the planetary system orbiting one of the THIRSTEE M-dwarf targets, TOI-771 (d = 25 pc, V = 14.9 mag), known to host one planet, TOI-771 b, which has been statistically validated using TESS observations.
[Methods] We use TESS, SPECULOOS, TRAPPIST, and M-Earth photometry together with 31 high-precision ESPRESSO radial velocities to derive the orbital parameters and investigate the internal composition of TOI-771 b, as well as exploring the presence of additional companions in the system.
[Results] We derived the precise mass and radius for TOI-771 b, a super-Earth with Rb = 1.36 ± 0.10 R⊕ and Mb = 2.47−0.31+0.32M⊕ orbiting every 2.3 days around its host star. Its composition is consistent with an Earth-like planet, and it adds up to the rocky population of subNeptunes lying below the density gap identified around M dwarfs. With a ∼ 13% precision in mass, a∼ 7% radius precision, and a warm equilibrium temperature of Teq =543K, TOI-771 b is a particularly interesting target for atmospheric characterisation with JWST, and it is indeed one of the targets under consideration for the Rocky World DDT programme. Additionally, we discover the presence of a second, non-transiting planet in the system, TOI-771 c, with a period of 7.61 days and a minimum mass of Mp sin i = 2.87−0.38+0.41M⊕. Even though the inclination is not directly constrained, the planet likely belongs to the temperate sub-Neptune population, with an equilibrium temperature of ∼ 365K.
Sibling sub-Neptunes around sibling M dwarfs: TOI-521 and TOI-912
(EDP Sciences, 2026-01-27) Lacedelli, G.; Pallé, E.; Luque, R.; Ikuta, Kai; Tabernero, H. M.; Zapatero Osorio, María Rosa; Almenara, J. M.; Pozuelos, F. J.; Jankowski, Dawid; Narita, N.; Fukui, A.; Nowak, G.; Hirano, T.; Ishikawa, Hiroyuki Tako; Kimura, Tadahiro; Hori, Y.; Collins, K. A.; Howell, Steve B.; Jiang, Chengzi; Murgas Alcaino, F.; Osborn, Hugh P., Hugh; Astudillo Defru, N.; Bonfils, Xavier; Charbonneau, D.; Fausnaugh, M. M.; Geraldía González, Samuel; Goździewski, Krzysztof; Guerra, P.; Hayashi, Yuya; Hodapp, K.; Horne, K.; Isogai, K.; Jafariyazani, M.; Kagetani, T.; Kawai, Y.; Kawauchi, K.; Krishnamurthy, V.; Kotani, T.; Kudo, T.; Kurokawa, Takashi; Kuzuhara, M.; Mori, M.; Nishikawa, Jun; Nugroho, Stevanus Kristianto; Omiya, M.; Schwarz, R. P.; Sefako, Ramotholo; Shporer, A.; Srdoc, G.; Teng, Huan-Yu; Watanabe, N.; Agencia Estatal de Investigación (España); National Aeronautics and Space Administration (NASA); European Research Council (ERC); Swiss National Science Foundation (SNSF); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)
Context. Sub-Neptunes are absent in the Solar System, yet they are the most common category of planets found in our Galaxy. This kind of planet challenges the internal structure models, prompts investigations into its formation and evolution, and pushes atmospheric characterisation studies to break the degeneracy in their inner composition.
Aims. We report here the discovery and characterisation of new sub-Neptunes orbiting two similar M dwarfs, TOI-521 (Teff = 3544 ± 100 K, V = 14.7 mag) and TOI-912 (Teff = 3572 ± 100 K, V = 12.7 mag). Each star hosts a transiting planetary candidate identified by TESS and is part of the THIRSTEE follow-up programme, which aims to understand the sub-Neptune population through in-depth and precise characterisation studies on a population level.
Methods. We analysed TESS light curves, ground-based photometry, and high-precision ESPRESSO, HARPS, and IRD radial velocities to confirm the planetary nature of both candidates, infer the precise orbital and physical parameters of the planets, and investigate the presence of additional planets in the systems.
Results. The two stars host nearly identical planets in terms of mass and radius. TOI-521 hosts a transiting sub-Neptune in a 1.5-day orbit with radius and mass of Rb = 1.98 ± 0.14 R⊕ and Mb = 5.3 ± 1.0 M⊕, respectively. Moreover, we identified an additional candidate at 20.3 days, with a minimum mass of Mp sin i = 10.7−2.4+2.5 M⊕, currently not detected as transiting in our photometric dataset. Similarly, the planet orbiting TOI-912 is a 4.7-d sub-Neptune with Rb = 1.93 ± 0.13 R⊕ and Mb = 5.1 ± 0.5 M⊕. Interestingly, TOI-912 b likely possesses an unusually high eccentricity (e = 0.58 ± 0.02) and is probably undergoing strong tidal dissipation. If such eccentricity were confirmed, it would make TOI-912 b one of the most eccentric sub-Neptunes known to date. TOI-521 b and TOI-912 b have very similar densities (~4 g cm−3), and they lie in the degenerate region of the mass-radius diagram where different compositions are plausible, including a volatile-rich composition, or a rocky core surrounded by a H-He envelope. When compared to the other THIRSTEE M-dwarf targets, our sample supports the division of sub-Neptunes into two distinct populations divided by a density gap. Both planets are interesting targets for atmospheric follow-up in the context of understanding the temperature-atmospheric feature trend that starts to emerge thanks to JWST observations.
Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
(EDP Sciences, 2025-07-22) Castro-González, Amadeo; Bouchy, F.; Correia, A. C. M.; Sozzetti, A.; Lillo Box, J.; Figueira, P.; Lavie, B.; Lovis, C.; Hobson, Melissa J.; Sousa, S. G.; Adibekyan, Vardan; Standing, Matthew R.; Hara, Nathan C.; Barrado, David; Silva, André; Bourrier, V.; Korth, J.; Santos, Nuno C.; Damasso, M.; Zapatero Osorio, María Rosa; Rodrigues, José; Alibert, Yann; Barros, S. C. C.; Cristiani, S.; Marcantonio, Paolo Di; González Hernández, J. I.; Lo Curto, G.; Martins, C. J. A. P.; Nunes, Nelson J.; Pallé, E.; Pepe, Francesco; Suárez Mascareño, A.; Tabernero, H. M.; Fundacao para a Ciencia e a Tecnologia (FCT); European Commission (EC); Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFÍSICA DE CANARIAS (IAC), SEV-2015-0548
[Context] The formation and evolution of ultra-short-period (USP) rocky planets is poorly understood. However, it is widely thought that these planets could not have formed at their present-day close-in orbits, but instead migrated inwards through interactions with outer neighbours.
[Aims] We aim to confirm and characterise the USP Earth-sized validated planet K2-157 b (Porb = 8.8 h) and constrain the presence of additional companions in the system through radial velocity (RV) measurements.
[Methods] We measured 49 RVs with the ESPRESSO spectrograph and tested different planetary and non-planetary configurations to infer the model that best represents our data set. We derived the orbital and physical properties of the system through a global RV and transit model.
[Results] We detected two additional super-Neptune-mass planets located within the warm Neptunian savanna, K2-157 c (Porb,c = 25.942−0.044+0.045d, Mp,c sin i = 30.8 ± 1.9 M⊕) and K2-157 d (Porb,d = 66.50−0.59+0.71d, Mp,d sin i = 23.3 ± 2.5 M⊕). The joint analysis constrains the mass of K2-157 b at the 2.7σ level, Mp,b = 1.14−0.42+0.41 M⊕ (< 2.4 M⊕ at 3σ), which, together with the inferred radius, Rp,b = 0.935 ± 0.090 R⊕, make the planet compatible with a rocky composition with a likely (68% confidence) higher iron-to-silicate mass fraction than Earth. K2 data discard non-grazing transit configurations for K2-157 c (ic < 88.4° at 3σ), and ESPRESSO data constrain the eccentricities of K2-157 c and K2-157 d to ec < 0.2 and ed < 0.5 at 3σ. Our dynamical analysis indicates that the system is stable for eccentricities up to ec, ed ~ 0.3 and mutual inclinations up to ~60°. At a population level, we find that the trend that the closest USP planets tend to orbit late-type stars does not hold when scaling the orbital separation to the Roche limit, which suggests that the orbital distribution of the closest planets across spectral types is primarily determined by tidal disruption.
[Conclusions] The orbital architecture of K2-157 is unusual in the known exoplanet plethora, with only one similar case reported to date: 55 Cnc. The USP planets of these systems, being accompanied by massive, long-period, relatively spaced, and possibly misaligned neighbours, could have migrated inwards through eccentricity-based mechanisms triggered by secular interactions.
