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![Images of Uranus (top) and Neptune (bottom) showing seasons and storms. The images of Uranus labelled “HST” correspond to HST/STIS montages including a H band image on the left and a false color image on the right [82]. Amateur images from the Pic du Midi, D. Peach, and M. Lewis at visible wavelengths have been taken from the PVOL database (http://pvol2.ehu.eus/). The images of Neptune have been obtained from HST/WFPC2 in the visible [52]](publication/355786101/figure/fig1/AS:11431281125747175@1678417306896/Images-of-Uranus-top-and-Neptune-bottom-showing-seasons-and-storms-The-images-of.png)
Images of Uranus (top) and Neptune (bottom) showing seasons and storms. The images of Uranus labelled “HST” correspond to HST/STIS montages including a H band image on the left and a false color image on the right [82]. Amateur images from the Pic du Midi, D. Peach, and M. Lewis at visible wavelengths have been taken from the PVOL database (http://pvol2.ehu.eus/). The images of Neptune have been obtained from HST/WFPC2 in the visible [52]
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Uranus and Neptune are the last unexplored planets of the Solar System. I show that they hold crucial keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres. Their atmospheres are active and storms are believed to be fueled by methane condensation which is both extremely abundant and occurs at low optical dep...
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Citations
... The TBL is expected to occur at a radius of approximately 20 000 km, positioned between the inner and outer envelopes, and is considered one possible solution to explain the observed low luminosity of Uranus [15,49,50]. The sound speeds in this regime also play a pivotal role in the field of giant planet seismology, enabling us to employ Uranus quakes and ring seismology as tools to unravel the planet's internal composition [16,56,57]. ...
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Published by the American Physical Society 2024
... Ice giants also provide a unique regime to understand moist convection in giant planets Guillot 2022) and an opportunity to test the self-limited moist convection and convective inhibition proposed in this study. The vertical temperature and composition structure at the CH 4 condensation level can be constrained by radio occultation from the orbiter (Lindal et al. 1987;Lindal 1992). ...
Storms operated by moist convection and the condensation of CH 4 or H 2 S have been observed on Uranus and Neptune. However, the mechanism of cloud formation, thermal structure, and mixing efficiency of ice giant weather layers remains unclear. In this paper, we show that moist convection is limited by heat transport on giant planets, especially on ice giants where planetary heat flux is weak. Latent heat associated with condensation and evaporation can efficiently bring heat across the weather layer through precipitations. This effect was usually neglected in previous studies without a complete hydrological cycle. We first derive analytical theories and show that the upper limit of cloud density is determined by the planetary heat flux and microphysics of clouds but is independent of the atmospheric composition. The eddy diffusivity of moisture depends on the planetary heat fluxes, atmospheric composition, and surface gravity but is not directly related to cloud microphysics. We then conduct convection- and cloud-resolving simulations with SNAP to validate our analytical theory. The simulated cloud density and eddy diffusivity are smaller than the results acquired from the equilibrium cloud condensation model and mixing length theory by several orders of magnitude but consistent with our analytical solutions. Meanwhile, the mass-loading effect of CH 4 and H 2 S leads to superadiabatic and stable weather layers. Our simulations produced three cloud layers that are qualitatively similar to recent observations. This study has important implications for cloud formation and eddy mixing in giant planet atmospheres in general and observations for future space missions and ground-based telescopes.
... Possible Uranian Ar, Kr, and Xe abundances are scaled from Jupiter at a nominal enhancement of 50 times, but over a very wide range extending from the small 2.5 times Jovian amplification to an upper bound of 100 times. We have not scaled NH 3 or H 2 S from Jupiter, as neither behave simply enough at Uranian temperatures to yield trustworthy bulk abundances from remote observations (Guillot 2022). Nitrogen and sulfur will be targets for in situ measurements with the Uranus Probe. ...
Noble gases provide tracers of cosmic provenance that are accessible to a future Uranus atmospheric probe. Argon and krypton are expected to be well mixed on Uranus with respect to H 2 and He, although condensation at the winter pole may be possible. The Ar/H 2 and Ar/Kr ratios address whether the materials accreted by Uranus resembled the extremely cold materials accreted by Jupiter’s atmosphere, whether they were warmer, like comet 67P/Churyumov–Gerasimenko (67P/C-G), or whether Uranus is like neither. Xenon condenses as an ice, probably on methane ice, in Uranus’s upper troposphere. Condensation may complicate the interpretation of Xe/H 2 , but it also presents an opportunity to collect concentrated xenon samples suitable for measuring isotopes. Solar system Xe tracks three distinct nucleosynthetic xenon reservoirs, one evident in the Sun and in chondritic meteorites, a second in refractory presolar grains, and a third evident in comet 67P/C-G and in Earth’s air. The first and third reservoirs appear to have been captured from different clouds of gas. The two gases do not appear to have been well mixed; moreover, the high ¹²⁹ Xe/ ¹³² Xe ratio in 67P/C-G implies that the gas was captured before the initial nucleosynthetic complement of ¹²⁹ I (15.7 Myr half-life) had decayed. Xenon’s isotopic peculiarities, if seen in Uranus, could usefully upset our understanding of planetary origins. Krypton’s isotopic anomalies are more subtle and may prove hard to measure. There is a slight chance that neon and helium fractionations can be used to constrain how Uranus acquired its nebular envelope.
... A notable exception is Uranus, whose intrinsic heat luminosity is about 5 to 10 times lower than the other three giant planets and compatible with zero (Pearl and Conrath 1991). Several hypotheses have been put forward (see Helled and Fortney 2020), but the recent 30% upward revision of Jupiter's intrinsic luminosity (Li et al. 2018) calls for a reanalysis of available data, and ultimately, in situ measurements at Uranus (e.g., Fletcher et al. 2020;Guillot 2022). ...
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... Yet, the current measurements of Uranus and Neptune are poor, and consequently, the observations cannot distinguish between the suggested models, and there is a great degeneracy in terms of the shape of the composition gradients and their content. As of today, more observations are needed in order to achieve further progress in understanding the interiors of the two planets [136][137][138]. ...
The giant planets were the first to form and hold the key to unveiling the solar system's formation history in their interiors and atmospheres. Furthermore, the unique conditions present in the interiors of the giant planets make them natural laboratories for exploring different elements under extreme conditions. We are at a unique time to study these planets. The missions Juno to Jupiter and Cassini to Saturn have provided invaluable information to reveal their interiors like never before, including extremely accurate gravity data, atmospheric abundances and magnetic field measurements that revolutionised our knowledge of their interior structures. At the same time, new laboratory experiments and modelling efforts also improved, and statistical analysis of these planets is now possible to explore all the different conditions that shape their interiors. We review the interior structure of Jupiter, Saturn, Uranus and Neptune, including the need for inhomogeneous structures to explain the data, the problems unsolved and the effect that advances in our understanding of their internal structure have on their formation and evolution.
... Yet, the current measurements of Uranus and Neptune are poor, and consequently, the observations cannot distinguish between the suggested models, and there is a great degeneracy in terms of the shape of the composition gradients and their content. As of today, more observations are needed in order to achieve further progress in understanding the interiors of the two planets [136][137][138]. ...
The giant planets were the first to form and hold the key to unveiling the solar system’s formation history in their interiors and atmospheres. Furthermore, the unique conditions present in the interiors of the giant planets make them natural laboratories for exploring different elements under extreme conditions. We are at a unique time to study these planets. The missions Juno to Jupiter and Cassini to Saturn have provided invaluable information to reveal their interiors like never before, including extremely accurate gravity data, atmospheric abundances and magnetic field measurements that revolutionised our knowledge of their interior structures. At the same time, new laboratory experiments and modelling efforts also improved, and statistical analysis of these planets is now possible to explore all the different conditions that shape their interiors. We review the interior structure of Jupiter, Saturn, Uranus and Neptune, including the need for inhomogeneous structures to explain the data, the problems unsolved and the effect that advances in our understanding of their internal structure have on their formation and evolution.
... Within the Solar System itself, Uranus also holds a crucial role in studying its origin and evolution. [5,7]. ...
Uranus is a unique solar system body with its extreme rotational axis, low luminosity, asymmetrical internal magnetic field and magnetosphere, and questionable internal structure. Yet unlike the other Solar System planets, Uranus is the least understood and least visited planet that was only be attained once by Voyager 2 flyby mission in 1986. However, with the development of observation techniques and instruments both in space and ground, some advanced telescopes presently observe Uranus routinely. Moreover, most of the exoplanets detected so far have similarities with the ice giant type. Atacama Large Millimeter/submillimeter Array (ALMA) is one high-end radio interferometer that frequently observes Uranus since it is often chosen as a calibrator. With the abundance of ALMA data, this study is aimed to reconstruct the Uranus images and build the Uranus continuum model from the distribution of flux density over several frequencies on ALMA wide-range bands. Common Astronomy Software Application (CASA) data processing tool with a Python interface is used to achieve these goals. The ALMA data used in this research was Uranus observational data from 2012 to 2018 at bands 3, 4, 6, 7, and 8. After careful data selection and calibration, we obtained 110 observational data points. Due to the high angular resolution that can be achieved by ALMA, some well-resolved radio continuum images of Uranus were also obtained. Furthermore, the deconvolution result of the combined 78-point continuum data is sufficiently representative to build the continuum model, showing the higher the frequency the higher the flux density.KeywordsUranus continuumMillimeter/submillimeter wavelengthALMA dataFlux densityBrightness temperature
... Although Uranus and Neptune are more distant from us, research about them is also of great significance. Guillot's research shows that Uranus and Neptune are the key to understanding planets with hydrogen atmospheres [18]. Voosen et al. [19] said that Uranus should be the primary goal of NASA. ...
With the development of aerospace science and technology, more and more probes are expected to be deployed around extraterrestrial planets. In this paper, some special orbits around Jupiter, Saturn, Uranus, and Neptune are discussed and analyzed. The design methods of some special orbits are sorted out, considering the actual motion parameters and main perturbation forces of these four planets. The characteristics of sun-synchronous orbits, repeating ground track orbits, and synchronous planet orbits surrounding these plants are analyzed and compared. The analysis results show that Uranus does not have sun-synchronous orbits in the general sense. This paper also preliminarily calculates the orbital parameters of some special orbits around these planets, including the relationship between the semi-major axis, the eccentricity and the orbital inclination of the sun-synchronous orbits, the range of the regression coefficient of the sun-synchronous repeating ground track orbits, and the orbital parameters of synchronous planet orbits, laying a foundation for more accurate orbit design of future planetary probes.
... In hydrogen-helium atmospheres, condensables are heavier than dry air, imposing a fundamentally different dynamic regime to non-hydrogen based atmospheres [14]. In the Gas and Ice Giants, above a critical abundance of the condensing species, moist convection is inhibited by the weight of the condensables rather than favored by latent heat release [14,15,16,17]. This inhibition requires a sufficiently high abundance of condensables, which might be close to the water abundance in Jupiter [18] and might be found in the deep water cloud in Saturn, thus providing a way to explain the observations of episodic storms on this planet [19]. ...
... In order to get a simplified grasp of the inhibition of convection we will calculate a few numbers that will help us to show the regions of the atmosphere where convective inhibition plays a role and we extend this discussion to the deep clouds that determine the vertical structure of the atmosphere. We closely follow [17] in this discussion, and ignore the negative buoyancy effect of the weight of condensates, assuming precipitation is efficient. There are a number of quantities important to examine the potential to drive moist convection. ...
... The third quantity is the moist convection inhibition factor ξ i [14,15,17], which predicts that moist convection for condensable i is not possible when ξ i > 1. This inhibition factor is defined as: Table 1: Convective parameters for different condensables for models of Uranus and Neptune for 20 times solar abundances (1; left columns) and 80 times solar abundances (2; right columns). ...
The Ice Giants Uranus and Neptune have hydrogen-based atmospheres with several constituents that condense in their cold upper atmospheres. A small number of bright cloud systems observed in both planets are good candidates for moist convective storms, but their observed properties (size, temporal scales and cycles of activity) differ from moist convective storms in the Gas Giants. These clouds and storms are possibly due to methane condensation and observations also suggest deeper clouds of hydrogen sulfide (H$_2$S) at depths of a few bars. Even deeper, thermochemical models predict clouds of ammonia hydrosulfide (NH$_4$SH) and water at pressures of tens to hundreds of bars, forming extended deep weather layers. Because of hydrogen's small molecular weight and the high abundance of volatiles, their condensation imposes a strongly stabilizing vertical gradient of molecular weight larger than the equivalent one in Jupiter and Saturn. The resulting inhibition of vertical motions should lead to a moist convective regime that differs significantly from the one occurring on nitrogen-based atmospheres like those of Earth or Titan. As a consequence, the thermal structure of the deep atmospheres of Uranus and Neptune is not well understood. Similar processes might occur at the deep water cloud of Jupiter in Saturn, but the Ice Giants offer the possibility to study these physical aspects in the upper methane cloud layer. A combination of orbital and in situ data will be required to understand convection and its role in atmospheric dynamics in the Ice Giants, and by extension, in hydrogen atmospheres including Jupiter, Saturn and giant exoplanets.
... Guillot, 1995;Leconte et al., 2017;Friedson and Gonzales, 2017). The ways in which these effects can shape the energy transport and P -T profiles in H 2 -rich atmospheres are not yet fully understood, though future missions to Uranus or Neptune may help to elucidate this Guillot (2019). ...
Observations of exoplanet atmospheres have flourished in recent years, revealing a remarkable diversity of thermal, chemical and dynamical conditions. In particular, thermal emission observations of such atmospheres provide unique insights into their temperature profiles, chemistry and energy transport mechanisms. In this thesis, I explore the radiative and thermal conditions in exoplanets across a wide range of masses and irradiation conditions, from isolated brown dwarfs to rocky exoplanets. I begin by investigating important considerations for the atmospheric retrieval of isolated brown dwarfs. These objects provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-SNR observations of exoplanets. I introduce novel retrieval methods for isolated brown dwarfs, including a new temperature profile parameterisation and a method for including model uncertainty. I demonstrate this retrieval framework on both simulated and real data, showing that excellent precisions can be achieved on the inferred chemical abundances. I further investigate the temperature profiles and thermal emission spectra of hot Jupiters, including thermal inversions in their dayside atmospheres. In particular, TiO has long been proposed to cause thermal inversions in hot Jupiters and its spectral features in the optical and near-infrared have been detected. I investigate how TiO detections can depend on the molecular line list used to interpret the data, and how this sensitivity varies across different types of atmospheric observations. I also explore the occurrence of thermal inversions due to TiO and assess the performance of photometric metrics used to quantify them over a range in chemical composition, irradiation, gravity and stellar type. Recent optical observations of hot Jupiters in secondary eclipse are providing new constraints on their albedos and cloud/haze scattering. I investigate this for three hot Jupiters spanning a range of temperatures and gravities: KELT-1 b, WASP-18 b and WASP- 43 b. Using self-consistent atmospheric models, I interpret the optical to infrared spectra of these three targets and find that they can be explained by pure thermal emission, without the need for optical scattering by clouds or hazes. Furthermore, I find that inefficient day-night energy redistribution is needed to explain the high infrared fluxes from the daysides of these planets, consistent with previous works. I then explore the atmospheric conditions in mini-Neptunes, whose observations are beginning to provide constraints on their chemical and thermal properties, while also providing clues about their interiors and potential surfaces. With their relatively large scale heights and large planet-star contrasts, mini-Neptunes are currently ideal targets towards the goal of characterising temperate low-mass exoplanets. I explore the effects of irradiation, internal flux, metallicity, clouds and hazes on the atmospheric temperature profiles and thermal emission spectra of temperate mini-Neptunes. Building on recent suggestions of habitability of the mini-Neptune K2-18 b, I find a range of physically-motivated atmospheric conditions that allow for liquid water under the H2-rich atmospheres of such planets. I find that observations of thermal emission with the James Webb Space Telescope (JWST) can place useful constraints on the habitability of temperate mini-Neptunes such as K2-18 b. These results underpin the potential of temperate mini-Neptunes such as K2-18 b as promising candidates in the search for habitable exoplanets. Finally, I explore the characterisation of rocky exoplanet atmospheres across a wide temperature range. JWST will allow unprecedented characterisation of the atmospheres of small, rocky exoplanets. In particular, emission spectroscopy is an ideal technique to observe the secondary atmospheres of rocky exoplanets as such observations are not limited by the small scale height of high-mean-molecular-weight atmospheres. I develop a new retrieval framework tailored for rocky exoplanet atmospheres with unknown atmospheric constituents, and use this to assess the observability of promising, known rocky exoplanet targets. I find that the atmospheres of several known rocky exoplanets across a range of temperatures can be characterised using JWST.
