arXiv subjects

R. Hueso

Publications and source records attributed to R. Hueso.

At least 19 recordsLinked to original sources

arXiv2025

Why the Northern Hemisphere Needs a 30-40m Telescope and the Science at Stake: from Interstellar Visitors to Planetary Defence

Small Solar system Objects (SSOs) preserve the physical, chemical, and dynamical signatures of the Sun's protoplanetary disk. Upcoming surveys will discover vast numbers of new objects, yet their scientific value will depend on follow-up observations requiring far greater sensitivity and resolution than those currently available. A 30-m class telescope like the Extremely Large Telescope (ELT) will be transformative, but its Southern location will leave significant regions of the sky poorly covered or even non accessible. A Northern 30-40m telescope is therefore essential to achieve full-sky coverage and fully exploit the small body discoveries of the 2030-2050 era, in particular for targets of opportunity or unexpected discoveries, like those of interstellar objects and potentially hazardous asteroids, as well as for distant trans-Neptunian objects and space mission targets.

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arXiv2025

Martian atmospheric disturbances from orbital images and surface pressure at Jezero Crater, Mars, during Martian Year 36

We present a study of atmospheric disturbances at Jezero Crater, Mars, using ground-based measurements of surface pressure by the Perseverance rover in combination with orbital images from the Mars Express and Mars Reconnaissance Orbiter missions. The study starts at Ls $\sim$ 13.3{\deg} in MY36 (March 6th, 2021) and extends up to Ls $\sim$ 30.3{\deg} in MY37 (February 28th, 2023). We focus on the characterization of the major atmospheric phenomena at synoptic and planetary-scales. These are the thermal tides (measured up to the sixth component), long-period pressure oscillations (periods > 1 sol), the Aphelion Cloud Belt, and the occasional development of regional dust storms over Jezero. We present the seasonal evolution of the amplitudes and phases of the thermal tides and their relation with the atmospheric dust content (optical depth). Three regional dust storms and one polar storm extending over Jezero produced an increase in the diurnal and semidiurnal amplitudes but resulted in inverse responses in their phases. We show that the primary regular wave activity is due to baroclinic disturbances with periods of 2-4 sols and amplitudes $\sim$ 1-15 Pa increasing with dust content, in good agreement with theoretical predictions by model calculations. The spacecraft images show a number of arc-shaped, spiral and irregular cyclonic vortices, traced by dust and clouds at the edge of the North Polar Cap, that could be behind some of the pressure oscillations measured at Jezero.

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arXiv2024

Dynamics of Saturn's Polar Regions

We analyze data retrieved by the Imaging Science System onboard the Cassini spacecraft to study the horizontal velocity and vorticity fields of Saturn's Polar Regions (latitudes 60-90$^\circ$N in June-December 2013 and 60-90$^\circ$S in October 2006 and July-December 2008), including the Northern region where the hexagonal wave is prominent. With the aid of an automated two dimensional correlation algorithm we determine two-dimensional maps of zonal and meridional winds, and deduce vorticity maps. We extract zonal averages of zonal winds, providing wind profiles that reach latitudes as high 89.5$^\circ$ in the south and 89.9$^\circ$ in the north. Wind measurements cover the intense polar cyclonic vortices that reach similar peak velocities of 150 ms-1 at 88.5$^\circ$. The hexagonal wave lies in the core of an intense eastward jet at planetocentric latitude 75.8$^\circ$N with motions that become non-zonal at the hexagonal feature. In the south hemisphere the peak of the eastward jet is located at planetocentric latitude 70.4$^\circ$S. A large anticyclone (the South Polar Spot, SPS), similar to the North Polar Spot (NPS) observed at the Voyager times (1980-81), has been observed in images from April 2008 to January 2009 in the South Polar Region at latitude -66.1$^\circ$ close to the eastward jet. The SPS does not apparently excite a wave on the jet. We analyze the stability of the zonal jets, finding potential instabilities at the flanks of the eastward jets around 70$^\circ$ and we measure the eddy wind components, suggesting momentum transfer from eddy motion to the westward jets closer to the poles.

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arXiv2024

The long-term steady motion of Saturn's Hexagon and the stability of its enclosed jet-stream under seasonal changes

We investigate the long-term motion of Saturn's North-Pole Hexagon and the structure of its associated eastward jet, using Cassini ISS and ground-based images from 2008 to 2014. We show that both are persistent features that have survived the long polar night, the jet profile remaining essentially unchanged. During those years the hexagon vertices showed a steady rotation period of 10 hr 39 min 23.01 $\pm$ 0.01 s. Analysis of Voyager 1 and 2 (1980-1981) and HST and ground-based (1990-91) images shows a period shorter by 3.5s, due to the presence at the time of a large anticyclone. We interpret the hexagon as a manifestation of a vertically trapped Rossby wave on the polar jet and, because of their survival and unchanged properties under the strong seasonal variations in insolation, we propose that both hexagon and jet are deep-rooted atmospheric features that could reveal the true rotation of the planet Saturn.

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arXiv2024

A model of scattered thermal radiation for Venus from 3 to 5 $\mu$ m

Thermal radiation becomes a prominent feature in the continuum spectrum of Venus longwards of $\sim$3 $\mu$m. The emission is traceable to the upper cloud and haze layers in the planet's mesosphere. Venus' thermal radiation spectrum is punctuated by CO$_2$ bands of various strengths probing into different atmospheric depths. It is thus possible to invert measured spectra of thermal radiation to infer atmospheric temperature profiles and offer some insight into the cloud and haze structure. In practice, the retrieval becomes complicated by the fact that the outgoing radiation is multiply scattered by the ubiquitous aerosol particles before leaving the atmosphere. We numerically investigate the radiative transfer problem of thermal radiation from the Venus night side between 3 and 5 $\mu$m with a purpose-built model of Venus' mesosphere. Special emphasis is laid on the significance of scattering. The simulations explore the space of model parameters, which includes the atmospheric temperature, cloud opacity, and the aerosols' size and chemical composition. We confirm that aerosol scattering must be taken into account in a prospective temperature retrieval, which means an additional complication to the already ill-posed retrieval problem. We briefly touch upon the degeneracy in the spectrum's shape associated with parameterization of the Venus clouds. Reasonable perturbations in the chemical composition and size of aerosols do not significantly impact the model simulations. Although the experiments are specific to the technical characteristics of the Visual and Infrared Thermal Imaging Spectrometer on the Venus Express spacecraft, the conclusions are generally valid.

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arXiv2024

Potential Vorticity of the South Polar Vortex of Venus

Venus' atmosphere shows highly variable warm vortices over both of the planet's poles. The nature of the mechanism behind their formation and properties is still unknown. Potential vorticity is a conserved quantity when advective processes dominate over friction and diabatic heating, and is a quantity frequently used to model balanced flows. As a step toward understanding the vortices' dynamics, we present maps of Ertel's potential vorticity (EPV) at Venus' south polar region. We analyze three configurations of the South Polar Vortex at the upper cloud level ($P\sim 240 mbar$; $z\sim 58 km$), based on our previous analyses of cloud motions and thermal structure from data acquired by the VIRTIS instrument onboard Venus Express. Additionally, we tentatively estimate EPV at the lower cloud level ($P\sim 2200 mbar$; $z\sim 43 km$), based on our previous wind measurements and on static stability data from Pioneer Venus and the VIRA model. Values of EPV are on the order of $10^{-6}$ and $10^{-8} K m^2 kg^{-1} s^{-1}$ at the upper and lower cloud levels, respectively, being 3 times larger than the estimated errors. The morphology observed in EPV maps is mainly determined by the structures of the vertical component of the relative vorticity. This is in contrast to the vortex's morphology observed in 3.8 or 5 $\mu m$ images which are related to the thermal structure of the atmosphere at the cloud top. Some of the EPV maps point to a weak ringed structure in the upper cloud while a more homogenous EPV field is found in the lower cloud.

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arXiv2024

Instantaneous Three-dimensional Thermal Structure of the South Polar Vortex of Venus

The Venus thermal radiation spectrum exhibits the signature of $CO_2$ absorption bands. By means of inversion techniques, those bands enable the retrieval of atmospheric temperature profiles. We have analyzed VIRTIS-M-IR night-side data obtaining high-resolution thermal maps of Venus south polar region between 55 and 85 km altitudes for three dynamical configurations of the vortex. The cold collar is clearly distinguishable at $\sim 62$ km altitude level, and it is more than 15 K colder than the pole on average. The South Polar Vortex appears as a vertically extended hot region close to the pole and squeezed by the cold collar between altitudes 55 and 67 km but spreading equatorward at about 74 km. Both the instantaneous temperature maps and their zonal averages show that the top altitude limit of the thermal signature of the vortex is at $\sim 80$ km altitude, at least on the night-side of the planet. The upper part of the atmosphere (67 - 85 km) is more homogeneous and has long-scale horizontal temperature differences of about 25 K over horizontal distances of $\sim 2,000$ km. The lower part (55 - 67 km) shows more fine-scale structure, creating the vortex' morphology, with thermal differences of up to about 50 K over $\sim 500$ km horizontal distances. We also study the vertical stability of different atmospheric layers within the 55 - 85 km altitude range for the three vortex configurations. It is always positive, but the cold collar is the most vertically stable structure at polar latitudes, while the vortex and sub-polar latitudes show lower stability values. Furthermore, the hot filaments present within the vortex exhibit lower stability values than their surroundings. The layer between 62 and 67 km resulted to be the most stable. These results are in good agreement with conclusions from previous radio occultation analyses.

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arXiv2024

An Enduring Rapidly Moving Storm as a Guide to Saturn's Equatorial Jet's Complex Structure

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn's equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms-1 not measured since 1980-81 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10\degree N to 10\degree S) suffers intense vertical shears reaching +2.5 ms-1 km-1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.

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arXiv2024

A chaotic long-lived vortex at Venus southern pole

Polar vortices are common in the atmospheres of rapidly rotating planets [1-4]. On Earth and Mars they are tied to the surface and their existence follows the seasonal insolation cycle [1-3]. Venus is a slowly rotating planet but it is also known to have vortices at both poles at the edge of a superrotating atmosphere [5-8]. However, their nature and long-term properties have not been constrained so far impeding precise modeling. Here we report cloud motions at two altitude levels (about 42 km and 63 km above the surface) using infrared images from the VIRTIS instrument onboard Venus Express that show that the south polar vortex is a permanent but erratic and unpredictable feature. We find that the centers of rotation of the vortex at these levels rarely coincide and both wander erratically around the pole with speeds of up to 16 m s-1. The cloud morphology and vorticity patches are uncorrelated and change continuously developing transient areas of small vertical motions. Venus south polar vortex is a continuously evolving structure immersed in a baroclinic environment laying at altitude levels that have variable vertical and meridional wind shears, extending at least 20 km in height through a quasi-convective turbulent region.

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arXiv2024

Multilayer hazes over Saturn's hexagon from Cassini ISS limb images

In June 2015, Cassini high-resolution images of Saturn's limb southwards of the planet's hexagonal wave revealed a system of at least six stacked haze layers above the upper cloud deck. Here, we characterize those haze layers and discuss their nature. Vertical thickness of layers ranged from 7 to 18 km, and they extended in altitude approx 130 km, from pressure level 0.5 bar to 0.01 bar. Above them, a thin but extended aerosol layer reached altitude approx 340 km (0.4 mbar). Radiative transfer modeling of spectral reflectivity shows that haze properties are consistent with particles of diameter 0.07- 1.4 \{mu}m and number density 100 - 500 cm -3. The nature of the hazes is compatible with their formation by condensation of hydrocarbon ices, including acetylene and benzene at higher altitudes. Their vertical distribution could be due to upward propagating gravity waves generated by dynamical forcing by the hexagon and its associated eastward jet.

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arXiv2024

Mars 2020 Perseverance rover studies of the Martian atmosphere over Jezero from pressure measurements

The pressure sensors on Mars rover Perseverance measure the pressure field in the Jezero crater on regular hourly basis starting in sol 15 after landing. The present study extends up to sol 460 encompassing the range of solar longitudes from Ls 13{\deg} - 241{\deg} (Martian Year (MY) 36). The data show the changing daily pressure cycle, the sol-to-sol seasonal evolution of the mean pressure field driven by the CO2 sublimation and deposition cycle at the poles, the characterization of up to six components of the atmospheric tides and their relationship to dust content in the atmosphere. They also show the presence of wave disturbances with periods 2-5 sols, exploring their baroclinic nature, short period oscillations (mainly at night-time) in the range 8-24 minutes that we interpret as internal gravity waves, transient pressure drops with duration 1-150 s produced by vortices, and rapid turbulent fluctuations. We also analyze the effects on pressure measurements produced by a regional dust storm over Jezero at Ls 155{\deg}.

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arXiv2022

Constraints on the structure and seasonal variations of Triton's atmosphere from the 5 October 2017 stellar occultation and previous observations

A stellar occultation by Neptune's main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. We aimed at constraining Triton's atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range $\sim$8 km to $\sim$190 km, corresponding to pressure levels from 9 μbar down to a few nanobars. Results. (i) A pressure of 1.18$\pm$0.03 μbar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 μbar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude.

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arXiv2021

Convective storms and atmospheric vertical structure in Uranus and Neptune

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.

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arXiv2021

A long term study of Mars mesospheric clouds seen at twilight based on Mars Express VMC images

We present the first systematic study of clouds observed during twilight on Mars. We analyze images obtained by the Visual Monitoring Camera (VMC) on Mars Express between 2007 and 2020. Using an automated retrieval algorithm we found 407 cases of clouds observed at twilight, in which the geometry of the observations allows to derive the minimum altitude, revealing that many of these clouds are in the mesosphere (above 40km and up to 90km). The majority of these mesospheric clouds were detected in mid-latitudes at local autumn and winter, a new trend only hinted at by previous studies. In particular, we find a massive concentration of clouds in the southern mid-latitudes between Terra Cimmeria and Aonia, a region where high altitude events have been previously observed. We propose that there is an unknown mechanism in these regions that enhances the probability to host high altitude clouds around the southern winter solstice.

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arXiv2021

Jupiter's third largest and longest-lived oval: Color changes and dynamics

The transition region between the North Equatorial Band (NEBn) and North Tropical Zone (NTrZ) in Jupiter is home to convective storms, systems of cyclones and anticyclones and atmospheric waves. A large anticyclone formed in the year 2006 at planetographic latitude 19N and persists since then after a complex dynamic history, being possibly the third longest-lived oval in the planet after Jupiter's Great Red Spot and oval BA. This anticyclone has experienced close interactions with other ovals, merging with another oval in February 2013; it has also experienced color changes, from white to red (September 2013). The oval survived the effects of the closely located North Temperate Belt Disturbance, which occurred in October 2016 and fully covered the oval, rendering it unobservable for a short time. When it became visible again at its expected longitude from its previous longitudinal track, it reappeared as a white large oval keeping this color and the same morphology since 2017 at least until the onset of the new convective disturbance in Jupiter's North Temperate Belt in August 2020. Here we describe the historic evolution of the properties of this oval. We use JunoCam and Hubble Space Telescope (HST) images to measure its size and its internal rotation. We also used HST and PlanetCam-UPV/EHU multi-wavelength observations to characterize its color changes and Junocam images to unveil its detailed structure. The color and the altitude-opacity indices show that the oval is higher and has redder clouds than its environment but has lower cloud tops than other large ovals like the GRS, and it is less red than the GRS and oval BA. We show that in spite of the dramatic environmental changes suffered by the oval during all these years, its main characteristics are stable in time and therefore must be related with the atmospheric dynamics below the observable cloud decks.

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arXiv2021

An Extremely Elongated Cloud over Arsia Mons Volcano on Mars: I. Life Cycle

We report a previously unnoticed annually repeating phenomenon consisting of the daily formation of an extremely elongated cloud extending as far as 1800 km westward from Arsia Mons. It takes place in the Solar Longitude (Ls) range of ~220-320, around the Southern solstice. We study this Arsia Mons Elongated Cloud (AMEC) using images from different orbiters, including ESA Mars Express, NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the AMEC in detail in Martian Year (MY) 34 in terms of Local Time and Ls and find that it exhibits a very rapid daily cycle: the cloud growth starts before sunrise on the western slope of the volcano, followed by a westward expansion that lasts 2.5 hours with a velocity of around 170 m/s in the mesosphere (~45 km over the areoid). The cloud formation then ceases, it detaches from its formation point, and continues moving westward until it evaporates before the afternoon, when most sun-synchronous orbiters observe. Moreover we comparatively study observations from different years (i.e. MYs 29-34) in search of interannual variations and find that in MY33 the cloud exhibits lower activity, whilst in MY34 the beginning of its formation was delayed compared to other years, most likely due to the Global Dust Storm. This phenomenon takes place in a season known for the general lack of clouds on Mars. In this paper we focus on observations, and a theoretical interpretation will be the subject of a separate paper.

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arXiv2021

The 2018 Martian Global Dust Storm over the South Polar Region studied with MEx/VMC

We study the 2018 Martian Global DustStorm (GDS 2018) over the Southern Polar Region using images obtained by the Visual Monitoring Camera (VMC) on board Mars Express during June and July 2018. Dust penetrated into the polar cap region but never covered the cap completely, and its spatial distribution was nonhomogeneous and rapidly changing. However, we detected long but narrow aerosol curved arcs with a length of 2,000-3,000 km traversing part of the cap and crossing the terminator into the night side. Tracking discrete dust clouds allowed measurements of their motions that were towards the terminator with velocities up to 100 m/s. The images of the dust projected into the Martian limb show maximum altitudes of around 70 km but with large spatial and temporal variations. We discuss these results in the context of the predictions of a numerical model for dust storm scenario.

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arXiv2020

The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation

Among the four known transneptunian dwarf planets, Haumea is an exotic, very elongated, and fast rotating body. In contrast to the other dwarf planets, its size, shape, albedo, and density are not well constrained. Here we report results of a multi-chord stellar occultation, observed on 2017 January 21. Secondary events observed around the main body are consistent with the presence of a ring of opacity 0.5, width 70 km, and radius 2,287$_{-45}^{+75}$ km. The Centaur Chariklo was the first body other than a giant planet to show a ring system and the Centaur Chiron was later found to possess something similar to Chariklo's rings. Haumea is the first body outside the Centaur population with a ring. The ring is coplanar with both Haumea's equator and the orbit of its satellite Hi'iaka. Its radius places close to the 3:1 mean motion resonance with Haumea's spin period. The occultation by the main body provides an instantaneous elliptical limb with axes 1,704 $\pm$ 4 km x 1,138 $\pm$ 26 km. Combined with rotational light-curves, it constrains Haumea's 3D orientation and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea's largest axis is at least 2,322 $\pm$ 60 km, larger than thought before. This implies an upper limit of 1,885 $\pm$ 80 kg m$^{-3}$ for Haumea's density, smaller and less puzzling than previous estimations, and a geometric albedo of 0.51 $\pm$ 0.02, also smaller than previous estimations. No global N$_2$ or CH$_4$ atmosphere with pressures larger than 15 and 50 nbar (3-$σ$ limits), respectively, is detected.

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