Search

Context. Different theories have been developed to explain the origins and properties of close-in giant planets, but none of them alone can explain all of the properties of the warm Jupiters (WJs, Porb = 10–200 days). One of the most intriguing characteristics of WJs is that they have a wide range of orbital eccentricities, challenging our understanding of their formation and evolution. Aims. The investigation of these systems is crucial in order to put constraints on formation and evolution theories. TESS is providing a significant sample of transiting WJs around stars bright enough to allow spectroscopic follow-up studies. Methods. We carried out a radial velocity (RV) follow-up study of the TESS candidate TOI-4515 b with the high-resolution spectrograph HARPS-N in the context of the GAPS project, the aim of which is to characterize young giant planets, and the TRES and FEROS spectrographs. We then performed a joint analysis of the HARPS-N, TRES, FEROS, and TESS data in order to fully characterize this planetary system. Results. We find that TOI-4515 b orbits a 1.2 Gyr-old G-star, has an orbital period of Pb = 15.266446 ± 0.000013 days, a mass of Mb = 2.01 ± 0.05 MJ, and a radius of Rb = 1.09 ± 0.04 RJ. We also find an eccentricity of e = 0.46 ± 0.01, placing this planet among the WJs with highly eccentric orbits. As no additional companion has been detected, this high eccentricity might be the consequence of past violent scattering events. [ABSTRACT FROM AUTHOR]

The regular polygons of circumpolar cyclones, discovered by Juno in 2017, are one of the most puzzling features of Jupiter. Here we show new recent global pictures of the North polar cyclones' structure. These are the first simultaneous images of the whole structure since 2017, and we find that it remained almost unperturbed, just like the South one. The observation of these long‐lasting structures poses questions regarding the formation mechanism of cyclones, and on their vertical structure. Data by Juno/JIRAM infrared camera collected over the last 5 years show that cyclones migrate around what may seem like equilibrium positions, with timescales of a few months but, aside from that, the cyclones systems are very stable. Our analysis of the observations shows that the motion of cyclones around their equilibrium position is uncorrelated with their position if a barotropic approximation (β‐drift) is assumed. Thus, a different dynamical explanation than the barotropic β‐drift is needed to explain the stability of the observed features. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed lapse of time in most cases. Plain Language Summary: In 2017, Juno discovered that the poles of Jupiter are occupied by regular polygons of cyclones. Here we report 5 years of observations of these cyclones by JIRAM, the infrared imaging spectrometer on board Juno. In particular, we show the latest observations of the North Pole cyclones structure. In fact, this structure has only been partially observed since its discovery 5 years ago. One important question is how these structures of cyclones form, and if they are stable. We find that both remained almost unperturbed. Hence, we show that these cyclones may have very long lifetimes. Cyclones migrate around what may appear to be equilibrium positions. The scale time is a few months. We analyzed the movement of cyclones and compared it with a model where winds don't change with depth (a barotropic model). We found that the motion of the cyclones is not related to their position according to this model. We conclude that a different model is needed to explain some of the observed characteristics. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed time span in most cases. Key Points: For the first time after 5 years, we show a global picture of the North polar cyclones' structure, which has remained almost unperturbedEach cyclone has a peculiar morphology, which differs from the others and it is stable over the observed lapse of timeBeta‐drift is not responsible for the motion of the vortices on timescales of months [ABSTRACT FROM AUTHOR]

The Jovian InfraRed Auroral Mapper (JIRAM) onboard the NASA Juno mission monitored the evolution of Jupiter's polar cyclones since their first observation ever in February 2017. Data acquired by JIRAM have revealed cloudy cyclones organized in a complex, yet stable geometrical pattern at both poles. Several studies have investigated the dynamics and the structure of these cyclones, to understand the physical mechanisms behind their formation and evolution. In this work, we present vorticity maps deduced from the wind fields for the region poleward of ∼−80°, which has been extensively covered over the last four years of observations. The cyclonic features related to the stable polar cyclones are embedded in a slightly, but diffused anticyclonic circulation, in which short‐living anticyclones emerge with respect to the surroundings. Although the general stability of both the cyclones and the whole system is strongly confirmed by this work, variations in the shape of the vortices, as well as changes in the local structures, have been observed. Plain Language Summary: The Jovian InfraRed Auroral Mapper is the instrument onboard the NASA Juno spacecraft that has provided observations of Jupiter's poles since February 2017. These data have shown cyclones organized in snowflake‐like structures. The Jupiter's polar cyclones are long‐lasting features, which did not disappear or merge during 4 years of observations. In general, the analysis of the winds is important in the study of the cyclones. In this work, we focus on the vorticity, a quantity derived by the winds, that gives information on the magnitude and direction of the rotation of the cyclones. We focused on the southern polar region, which has a better coverage in time, with respect to the northern counterpart. The general pattern of the southern polar cyclones is preserved along the observations. Key Points: The vorticity field of Jupiter's southern polar cyclones is evaluated for different orbitsThe temporal variability of the vorticity field of the central polar cyclone is analyzedWe found extremely long stability of the morphology of circumpolar cyclones both in terms of clouds and winds [ABSTRACT FROM AUTHOR]

Pebble accretion is an efficient mechanism that is able to build up the core of the giant planets within the lifetime of the protoplanetary disc gas-phase. The core grows via this process until the protoplanet reaches its pebble isolation mass and starts to accrete gas. During the growth, the protoplanet undergoes a rapid, large-scale, inward migration due to the interactions with the gaseous protoplanetary disc. In this work, we have investigated how this early migration would have affected the minor body populations in our solar system. In particular, we focus on the Jupiter Trojan asteroids (bodies in the coorbital resonance 1:1 with Jupiter, librating around the L4 and L5 Lagrangian points called, respectively, the leading and the trailing swarm) and the Hilda asteroids. We characterised their orbital parameter distributions after the disc dispersal and their formation location and compare them to the same populations produced in a classical in situ growth model. We find that a massive and eccentric Hilda group is captured during the migration from a region between 5 and 8 au and subsequently depleted during the late instability of the giant planets. Our simulations also show that inward migration of the giant planets always produces a Jupiter Trojans' leading swarm more populated than the trailing one, with a ratio comparable to the current observed Trojan asymmetry ratio. The in situ formation of Jupiter, on the other hand, produces symmetric swarms. The reason for the asymmetry is the relative drift between the migrating planet and the particles in the coorbital resonance. The capture happens during the growth of Jupiter's core and Trojan asteroids are afterwards carried along during the giant planet's migration to their final orbits. The asymmetry and eccentricity of the captured Trojans correspond well to observations, but their inclinations are near zero and their total mass is three to four orders of magnitude higher than the current population. Future modelling will be needed to understand whether the dynamical evolution of the Trojans over billions of years will raise the inclinations and deplete the masses to observed values. [ABSTRACT FROM AUTHOR]

Dawn space mission will provide the first, detailed data of two of the major bodies in the main asteroid belt, Vesta and Ceres. Through its connection with Howardite, Eucrite, Diogenite (HED) meteorites, Vesta is known as one of the first bodies to have accreted and differentiated in the solar nebula, predating the formation of Jupiter and surviving the violent evolution of the early Solar system. The formation time of Ceres instead is unknown, but it should not postdate that of Jupiter by far, since the perturbations of the giant planet stopped planetary accretion in the main asteroid belt. In this work we modelled the collisional histories of Vesta and Ceres at the time of the formation of Jupiter, assumed to be the first giant planet to form. In this first investigation of the evolution of the early Solar system, we did not include the presence of planetary embryos in the disc of planetesimals but concentrated on the role of the forming Jupiter and the effects of its possible inward migration due to disc-planet interactions. Our results clearly indicate that the formation of the giant planet caused an intense early bombardment in the orbital region of the main asteroid belt. We explored the effects of such bombardment on Vesta and Ceres assuming different size distributions of the primordial planetesimals. According to our results, Vesta and Ceres would not have survived the Jovian early bombardment if the disc was populated mainly by large planetesimals like those predicted to form in turbulent circumstellar discs. Discs dominated by small bodies, like those predicted to form in quiescent circumstellar discs, or with a varying fraction of the mass in the form of larger ( km) planetesimals, represent more favourable environments for the survival of the two asteroids. The abundance of planetesimals, especially the larger ones, proved a critical factor in this regard. The extent of Jupiter's radial migration due to disc-planet interactions proved itself another critical factor. In those scenarios where they survive, both asteroids had their surfaces saturated by craters as big as km and a few as big as 200-300 km. In the case of Vesta, the Jovian early bombardment would have significantly eroded (locally or globally) the crust and possibly caused effusive phenomena similar to the lunar maria, whose crystallization time would then be directly linked to the time of the formation of Jupiter. [ABSTRACT FROM AUTHOR]

Evolutionary scenarios for the major satellites of Jupiter, Saturn, Neptune, and Pluto-Charon are discussed. In the Jovian system the challenge is to understand how the present Laplace resonance of Io, Europa, and Ganymede was established and to determine whether the heat being radiated by Io is in balance with the present tidal dissipation in the moon. In the Saturnian system, Enceladus and Titan are the centers of attention. Tidal heating is the likely source of activity at the south pole of Enceladus, although the details of how the heating occurs are not understood. An evolutionary scenario based on accretion and internal differentiation is presented for Titan, whose present substantial orbital eccentricity is not associated with any dynamical resonance. The source and maintenance of methane in Titan's present atmosphere remain uncertain. Though most attention on the Saturnian moons focuses on Titan and Enceladus, the mid-size satellites Iapetus, Rhea, Tethys, and the irregular satellite Phoebe also draw our interest. An evolutionary scenario for Iapetus is presented in which spin down from an early rapidly rotating state is called upon to explain the satellite's present oblate shape. The prominent equatorial ridge on Iapetus is unexplained by the spin down scenario. A buckling instability provides another possible explanation for the oblateness and equatorial ridge of Iapetus. Rhea is the only medium-size Saturnian satellite for which there are gravity data at present. The interpretation of these data are uncertain, however, since it is not known if Rhea is in hydrostatic equilibrium. Pluto and Charon are representative of the icy dwarf planets of the Kuiper belt. Did they differentiate as they evolved, and do either of them have a subsurface liquid water ocean? New Horizons might provide some answers when it arrives at these bodies. [ABSTRACT FROM AUTHOR]

In this paper, we detail the retrieval methods developed for the analysis of the spectral data from the JIRAM experiment on board of the Juno NASA mission [1], operating in orbit around Jupiter since July 2016. Our focus is on the analysis of the thermal radiation in the 5 µm transparency window in regions of lesser cloud opacity (namely, hot-spots). Moving from the preliminary analysis presented in [2], a retrieval scheme has been developed and implemented as a complete end-to-end processing software. Performances in terms of fit quality and retrieval errors are discussed from tests on simulated spectra, while some example and issue from usage on actual Jupiter data are also discussed. Following the suggestion originally presented in [3] for the analysis of the data from the Near Infrared Mapping Spectrometer (NIMS) on board of the NASA Galileo spacecraft, the state vector to be retrieved has been drastically simplified on physically sounding basis, aiming mostly to distinguish between the 'deep' content of minor gaseous components (H 2 O, NH 3 , PH 3 ) and their relative humidity or fractional scale height in the upper troposphere. The retrieval code is based on a Bayesian scheme [4], complemented by simulated annealing method for most problematic cases. The key parameters retrievable from JIRAM individual spectra are the NH 3 and PH 3 deep contents, the H 2 O vapor relative humidity as well as the total aerosol opacity. Limitations related to the approximations of forward model methods are also assessed quantitatively. [ABSTRACT FROM AUTHOR]