TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star

The hot Neptune desert is a region hosting a small number of short-period Neptunes in the radius-instellation diagram. Highly irradiated planets are usually either small (R ≲ 2 R⊕) and rocky or they are gas giants with radii of ≳1 RJ. Here, we report on the intermediate-sized planet TOI-2196 b (TIC 372172128.01) on a 1.2 day orbit around a G-type star (V = 12.0, [Fe/H] = 0.14 dex) discovered by the Transiting Exoplanet Survey Satellite in sector 27. We collected 41 radial velocity measurements with the HARPS spectrograph to confirm the planetary nature of the transit signal and to determine the mass. The radius of TOI-2196 b is 3.51 ± 0.15 R⊕, which, combined with the mass of 26.0 ± 1.3 M⊕, results in a bulk density of 3.31−0.43+0.51 g cm−3. Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. A significant trend in the HARPS radial velocity measurements points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 MJ, respectively, assuming zero eccentricity. The short period of planet b implies a high equilibrium temperature of 1860 ± 20 K, for zero albedo and isotropic emission. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of ≳1800 K: a hot sub-Neptune desert devoid of planets with radii of ≈ 1.8−3 R⊕ and a sub-Jovian desert for radii of ≈5−12 R⊕. More planets in this parameter space are needed to further investigate this finding. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4% and 3%, with a mean value of 0.7% on top of a rocky interior. We estimated the amount of mass this planet might have lost at a young age and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet and it remains one at present

TOI-2196 b : Rare planet in the hot Neptune desert transiting a G-type star

Funding: C.M.P., M.F., I.G., and J.K. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18, 177/19, 2020-00104). L.M.S and D.G. gratefully acknowledge financial support from the CRT foundation under Grant No. 2018.2323 “Gaseous or rocky? Unveiling the nature of small worlds”. P.K. acknowledges support from grant LTT-20015. E.G. acknowledge the support of the Thüringer Ministerium für Wirtschaft, Wissenschaft und Digitale Gesellschaft. J.S.J. gratefully acknowledges support by FONDECYT grant 1201371 and from the ANID BASAL projects ACE210002 and FB210003. H.J.D. acknowledges support from the Spanish Research Agency of the Ministry of Science and Innovation (AEI-MICINN) under grant PID2019-107061GBC66, DOI: 10.13039/501100011033. D.D. acknowledges support from the TESS Guest Investigator Program grants 80NSSC21K0108 and 80NSSC22K0185. M.E. acknowledges the support of the DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (HA 3279/12-1). K.W.F.L. was supported by Deutsche Forschungsgemeinschaft grants RA714/14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. N.N. acknowledges support from JSPS KAKENHI Grant Number JP18H05439, JST CREST Grant Number JPMJCR1761. M.S.I.P. is funded by NSF.The hot Neptune desert is a region hosting a small number of short-period Neptunes in the radius-instellation diagram. Highly irradiated planets are usually either small (R ≲ 2 R⊕) and rocky or they are gas giants with radii of ≳1 RJ. Here, we report on the intermediate-sized planet TOI-2196 b (TIC 372172128.01) on a 1.2 day orbit around a G-type star (V = 12.0, [Fe/H] = 0.14 dex) discovered by the Transiting Exoplanet Survey Satellite in sector 27. We collected 41 radial velocity measurements with the HARPS spectrograph to confirm the planetary nature of the transit signal and to determine the mass. The radius of TOI-2196 b is 3.51 ± 0.15 R⊕, which, combined with the mass of 26.0 ± 1.3 M⊕, results in a bulk density of 3.31−0.43+0.51 g cm−3. Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. A significant trend in the HARPS radial velocity measurements points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 MJ, respectively, assuming zero eccentricity. The short period of planet b implies a high equilibrium temperature of 1860 ± 20 K, for zero albedo and isotropic emission. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of ≳1800 K: a hot sub-Neptune desert devoid of planets with radii of ≈ 1.8−3 R⊕ and a sub-Jovian desert for radii of ≈5−12 R⊕. More planets in this parameter space are needed to further investigate this finding. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4% and 3%, with a mean value of 0.7% on top of a rocky interior. We estimated the amount of mass this planet might have lost at a young age and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet and it remains one at present.Publisher PDFPeer reviewe

Retracing the fate of volatile compounds : from circumstellar disks to planetary interiors

Les composés volatils constituent non seulement une part considérable des briques élémentaires pour la formation des planètes, mais sont également indispensables à la naissance de la vie. Les travaux effectués dans cette thèse cherchent à retracer le parcours des composés volatils dans le système solaire ainsi que dans les intérieurs planétaires, via la modélisation numérique des processus physiques qui sont importants pour la formation planétaire et la structure des planètes. D'une part, ces travaux ont mené au développement d'un modèle qui décrit l'évolution de la nébuleuse protosolaire, correspondant à l'état de notre système solaire qui précède la formation des planètes. Ce modèle calcule la distribution radiale des volatils dans la nébuleuse protosolaire, qui est ensuite confrontée aux mesures des abondances dans les planètes pour contraindre leurs conditions de formation. D'autre part, des implémentations ont été faites sur un modèle de structure interne de planètes pré-existants pour étendre le domaine d'application du modèle. Ce modèle de structure interne permet de caractériser les intérieurs des exoplanètes, dont les propriétés sont extraites des observations depuis la Terre ou l'espace.Volatile compounds are a part of the elementary blocks in planet formation, and are also essentials for the formation of life. The work done in this thesis aims at tracing the path of volatile compounds in the solar system and in planetary interiors, through the modeling of physical processes that are at play at the planetary scale. First, this work led to the development of a model describing the evolution of the protosolar nebula, which corresponds the state of our solar system preceding the formation of planets. This model computes the radial distribution of volatile species in the protosolar nebula, which is then confronted to measurements of abundances in planets to constrain their formation conditions. Second, some implementations were added to an already existing planet interior structure model to extends its working range. This interior model is used to characterize the interior of exoplanets, the properties of which are derived from ground-based and space-borne observatories

Evolution of the reservoir of volatiles in the protosolar nebula

International audienceHow volatiles were incorporated in the building blocks of planets and small bodies in the protosolar nebula remains an outstanding question. Some scenarios invoke the formation of planetesimals from a mixture of refractory material and amorphous ice in the outer nebula while others argue that volatiles have been incorporated in clathrate or pure condensate forms in these solids. Here we study the fate of volatiles (H2O, CO, CO2, CH4, H2S, N2, NH3, Ar, Kr, Xe, and PH3) initially delivered in the forms of amorphous ice or pure condensates to the protosolar nebula. We investigate the radial distribution of these volatiles via a transport module coupled with an accretion disk model. In this model, multiple icelines are considered, including the condensation fronts of pure condensates, as well as those of clathrates when enough crystalline water is available at given time and location. Our simulations show that a significant fraction of volatiles can be trapped in clathrates only if they have been initially delivered in pure condensate forms to the disk. Under specific circumstances, volatiles can be essentially trapped in clathrates but, in many cases, the clathrate of a given species coexists with its pure condensate form. Those findings have implications for the compositions of giant planets and comets

Mass–Radius Relationships for Irradiated Ocean Planets

International audienceMassive and water-rich planets should be ubiquitous in the universe. Many of these worlds are expected to be subject to important irradiation from their host star, and display supercritical water layers surrounded by extended steam atmospheres. Irradiated ocean planets with such inflated hydrospheres have been recently shown to be good candidates for matching the mass–radius distribution of sub-Neptunes. Here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (EOS) for water, and an atmospheric model that takes into account radiative transfer. We find that the use of inappropriate EOSs can lead to the overestimation of the planetary radius by up to ~10%, depending on the planet size and composition. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- or Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction (WMF) of ~20% ± 10%. We also provide fits for the mass–radius relationships, allowing one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. Our calculations finally suggest that highly irradiated planets lost their H/He content through atmospheric loss processes, and that the leftover material led to either super-Earths or sub-Neptunes, depending on the WMF

Mass-Radius relationships of small, highly irradiated exoplanets with small water mass fractions

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Tracing the Origins of the Ice Giants through Noble Gas Isotopic Composition

;The current composition of giant planet atmospheres provides information on how such planets formed, and on the origin of the solid building blocks that contributed to their formation. Noble gas abundances and their isotope ratios are among the most valuable pieces of evidence for tracing the origin of the materials from which the giant planets formed. In this review we first outline the current state of knowledge for heavy element abundances in the giant planets and explain what is currently understood about the reservoirs of icy building blocks that could have contributed to the formation of the Ice Giants. We then outline how noble gas isotope ratios have provided details on the original sources of noble gases in various materials throughout the solar system. We follow this with a discussion on how noble gases are trapped in ice and rock that later became the building blocks for the giant planets and how the heavy element abundances could have been locally enriched in the protosolar nebula. We then provide a review of the current state of knowledge of noble gas abundances and isotope ratios in various solar system reservoirs, and discuss measurements needed to understand the origin of the ice giants. Finally, we outline how formation and interior evolution will influence the noble gas abundances and isotope ratios observed in the ice giants today. Measurements that a future atmospheric probe will need to make include (1) the <sup>3</sup>He/<sup>4</sup>He isotope ratio to help constrain the protosolar D/H and <sup>3</sup>He/<sup>4</sup>He; (2) the <sup>20</sup>Ne/<sup>22</sup>Ne and <sup>21</sup>Ne/<sup>22</sup>Ne to separate primordial noble gas reservoirs similar to the approach used in studying meteorites; (3) the Kr/Ar and Xe/Ar to determine if the building blocks were Jupiter-like or similar to 67P/C-G and Chondrites; (4) the krypton isotope ratios for the first giant planet observations of these isotopes; and (5) the xenon isotopes for comparison with the wide range of values represented by solar system reservoirs.</p><p>Mandt, K. E., Mousis, O., Lunine, J., Marty, B., Smith, T., Luspay-Kuti, A., & Aguichine, A. (2020). Tracing the origins of the ice giants through noble gas isotopic composition. Space Science Reviews, 216(5), 1-37.</p&gt

Characterisation of the interior structures and atmospheres of multiplanetary systems

International audienceThe increasing number of well characterised low-mass planets, combined with the valuable informations from stellar and planetary spectroscopy, opens the way to the modeling of planetary structures and compositions, which can be obtained with theoretical and numerical works. This approach gives a valuable insight to understand the formation of planetary systems in the low-mass range. We present a 1D planetary model where the interior is coupled with the atmosphere in radiative-convective equilibirum within a Bayesian retrieval scheme. In addition to a Fe core and a silicate mantle, we take into account water in all its possible phases, including steam and supercritical phases, which is necessary for systems with a wide range of stellar irradiations. Our interior-atmosphere model calculates the compositional and atmospheric parameters, such as Fe and water content, surface pressures, scale heights and albedos. We analyse five multiplanetary systems: K2-138, TOI-178, Kepler-11, Kepler-102 and Kepler-80. From the individual composition of their planets, we derive a similar trend for these systems: a global increase on the water content with increasing distance from the star in the inner region of the systems, while the planets in the outer region present a constant water mass fraction. This trend reveals the possible effects of migration type, formation in the vicinity of the ice line and XUV atmospheric mass loss during their formation history. Slight deviations from this trend can be explained case by case with H/He atmospheres, Jeans atmospheric escape and high-CMF processes, such as mantle evaporation or formation in the vicinity of rocklines