Shallow water simulations of Saturn's giant storms at different latitudes

Shallow water simulations are used to present a unified study of three major storms on Saturn (nicknamed as Great White Spots, GWS) at different latitudes, polar (1960), equatorial (1990), and mid-latitude (2010) (Sánchez-Lavega, 2004; Sánchez-Lavega et al., 2011). In our model, the three GWS are initiated by introducing a Gaussian function pulse at the latitude of the observed phenomena with controlled horizontal size and amplitude. This function represents the convective source that has been observed to trigger the storm. A growing disturbance forms when the pulse reacts to ambient winds, expanding zonally along the latitude band of the considered domain. We then compare the modeled potential vorticity with the cloud field, adjusting the model parameters to visually get the closest aspect between simulations and observations. Simulations of the 2010 GWS (planetographic latitude ~+40º, zonal velocity of the source ~-30 m s-1) indicate that the Coriolis forces and the wind profile structure shape the disturbance generating, as observed, a long region to the east of the convective source with a high speed peripheral anticyclonic circulation, and a long-lived anticyclonic compact vortex accompanied by strong zonal advection on the southern part of the storm forming a turbulent region. Simulations of the equatorial 1990 GWS (planetographic latitude +12º-+5º, zonal velocity of the source 365-400 m s-1) show a different behavior because of the intense eastward jet, meridional shear at the equatorial region, and low latitude dynamics. A round shaped source forms as observed, with the rapid growth of a Kelvin-Helmholtz instability on the north side of the source due to advection and to the strong meridional wind shear, whereas at the storm latitude the disturbance grows and propagates eastward. The storm nucleus is the manifestation of a Rossby wave, while the eastward propagating planetary-scale disturbance is a gravity-Rossby wave trapped around the equator. The simulated 1960 GWS disturbance (planetographic latitude +56º, zonal velocity 4 m s-1) formed a chain of periodic oval spots that mimic the few available observations of the phenomenon. For the mid and high latitude storms, simulations predict a strong injection of negative relative vorticity due to divergence of the upwelling storm material, which may produce large anticyclones on the anticyclonic side of the zonal profile, and a quick turbulent expansion on the background cyclonic regions. In general, simulations indicate that negative relative vorticity injected by storms determines the natural reaction to zonal winds at latitudes where Coriolis forces are dominant.Peer ReviewedPostprint (published version

XO-7 b: A Transiting Hot Jupiter with a Massive Companion on a Wide Orbit

Transiting planets orbiting bright stars are the most favorable targets for follow-up and characterization. We report the discovery of the transiting hot Jupiter XO-7 b and of a second, massive companion on a wide orbit around a circumpolar, bright, and metal rich G0 dwarf (V = 10.52, Teff = 6250±100 K, [Fe/H] = 0.432 ± 0.057 dex). We conducted photometric and radial velocity follow-up with a team of amateur and professional astronomers. XO-7 b has a period of 2.8641424±0.0000043 days, a mass of 0.709±0.034 MJ, a radius of 1.373±0.026 RJ, a density of 0.340±0.027 g cm-3 , and an equilibrium temperature of 1743 ± 23 K. Its large atmospheric scale height and the brightness of the host star make it well suited to atmospheric characterization. The wide orbit companion is detected as a linear trend in radial velocities with an amplitude of ~ 100 m s-1 over two years, yielding a minimum mass of 4 MJ; it could be a planet, a brown dwarf, or a low mass star. The hot Jupiter orbital parameters and the presence of the wide orbit companion point towards a high eccentricity migration for the hot Jupiter. Overall, this system will be valuable to understand the atmospheric properties and migration mechanisms of hot Jupiters and will help constrain the formation and evolution models of gas giant exoplanets.The XO project is supported by NASA grant NNX10AG30G. I.R., F.V. and E.H. acknowledge support by the Spanish Ministry for Science, Innovation and Universities (MCIU) and the Fondo Europeo de Desarrollo Regional (FEDER) through grant ESP2016- 80435-C2-1-R, as well as the support of the Generalitat de Catalunya/CERCA programme. The Joan Oró Telescope (TJO) of the Montsec Astronomical Observatory (OAdM) is owned by the Generalitat de Catalunya and operated by the Institute for Space Studies of Catalonia (IEEC). NCS was supported by FCT - Funda c~ao para a Ci^encia e a Tecnologia through national funds and by FEDER - Fundo Europeu de Desenvolvimento Regional through COMPETE2020 - Programa Operacional Competitividade e Internacionalizaçao by these grants: UID/FIS/04434/2019; PTDC/FISAST/ 28953/2017 & POCI-01-0145-FEDER-028953 and PTDC/FIS-AST/32113/2017 & POCI-01-0145- FEDER-032113. HPO acknowledges support from Centre National d'Etudes Spatiales (CNES) grant 131425- PLATO. This research made use of Photutils, an Astropy package for detection and photometry of astronomical sources (Bradley et al. 2019). This research has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org, the Extrasolar Planets Encyclopaedia at exoplanet.eu, and the SIMBAD and VizieR databases at simbad.ustrasbg. fr/simbad/ and http://vizier.u-strasbg.fr/vizbin/ VizieR.Peer ReviewedPostprint (author's final draft

Analysis of planetary spacecraft images with SPICE

Spacecraft images are an invaluable source of information in Planetary Science. However, they must be processed and the initial stage is to navigate them, i.e., determine the longitude and latitude coordinates of each pixel on the image plane. The main goal of the present work is to develop an open-source tool to do so. It will be independent of proprietary software and implemented in a widely used language (Java, Python). It will be able to analyse planetary images taken by different spacecraft, such as New Horizons, Cassini or Voyager, with minimal user intervention. Here we present the first steps of the process illustrating the techniques to navigate an image of an ellipsoidal body, obtained from mission kernels using NASA Jet Propulsion Laboratory SPICE library, considering that the attitude and position of the spacecraft are available; correct the camera attitude information; determine the image resolution for each pixel; and combine different images of a body to generate mosaics with high resolutio

A large active wave trapped in Jupiter's equator

Context. A peculiar atmospheric feature was observed in the equatorial zone (EZ) of Jupiter between September and December 2012 in ground-based and Hubble Space Telescope (HST) images. This feature consisted of two low albedo Y-shaped cloud structures (Y1 and Y2) oriented along the equator and centred on it (latitude 0.5°-1°N). Aims. We wanted to characterize these features, and also tried to find out their properties and understand their nature. Methods. We tracked these features to obtain their velocity and analyse their cloud morphology and the interaction with their surroundings. We present numerical simulations of the phenomenon based on one- and two-layer shallow water models under a Gaussian pulse excitation. Results. Each Y feature had a characteristic zonal length of ~15° (18¿000 km) and a meridional width (distance between the north-south extremes of the Y) of 5° (6000 km), and moved eastward with a speed of around 20-40 m¿s-1 relative to Jupiter’s mean flow. Their lifetime was 90 and 60 days for Y1 and Y2, respectively. In November, both Y1 and Y2 exhibited outbursts of rapidly evolving bright spots emerging from the Y vertex. The Y features were not visible at wavelengths of 255 or 890 nm, which suggests that they were vertically shallow and placed in altitude between the upper equatorial hazes and the main cloud deck. Numerical simulations of the dynamics of the Jovian equatorial region generate Kelvin and Rossby waves, which are similar to those in the Matsuno-Gill model for Earth’s equatorial dynamics, and reproduce the observed cloud morphology and the main properties the main properties of the Y features.Peer ReviewedPostprint (author's final draft

PlanetCam UPV/EHU: a two-channel lucky imaging camera for solar system studies in the spectral range 0.38-1.7 µm

This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.We present PlanetCam UPV/EHU, an astronomical camera designed fundamentally for high-resolution imaging of Solar System planets using the “lucky imaging” technique. The camera observes in a wavelength range from 380 nm to 1.7 µm and the driving science themes are atmosphere dynamics and vertical cloud structure of Solar System planets. The design comprises two configurations that include one channel (visible wavelengths) or two combined channels (visible and short wave nfrared) working simultaneously at selected wavelengths by means of a dichroic beam splitter. In this paper the camera components for the two configurations are described, as well as camera performance and the different tests done for the precise characterization of its radiometric and astrometric capabilities at high spatial resolution. Finally, some images of solar system objects are presented as well as photometric results and different scientific cases on astronomical targets.Peer ReviewedPostprint (author's final draft

A planetary-scale disturbance in a long living three vortex coupled system in Saturn's atmosphere

The zonal wind profile of Saturn has a unique structure at 60°N with a double-peaked jet that reaches maximum zonal velocities close to 100 ms−1. In this region, a singular group of vortices consisting of a cyclone surrounded by two anticyclones was active since 2012 until the time of this report. Our observation demonstrates that vortices in Saturn can be long-lived. The three-vortex system drifts at u = 69.0 ± 1.6 ms−1, similar to the speed of the local wind. Local motions reveal that the relative vorticity of the vortices comprising the system is ∼2–3 times the ambient zonal vorticity. In May 2015, a disturbance developed at the location of the triple vortex system, and expanded eastwards covering in two months a third of the latitudinal circle, but leaving the vortices essentially unchanged. At the time of the onset of the disturbance, a fourth vortex was present at 55°N, south of the three vortices and the evolution of the disturbance proved to be linked to the motion of this vortex. Measurements of local motions of the disturbed region show that cloud features moved essentially at the local wind speeds, suggesting that the disturbance consisted of passively advecting clouds generated by the interaction of the triple vortex system with the fourth vortex to the south. Nonlinear simulations are able to reproduce the stability and longevity of the triple vortex system under low vertical wind shear and high static stability in the upper troposphere of Saturn.This work was supported by the Spanish MICIIN projects AYA2015-65041-P (MINECO/FEDER, UE), Grupos Gobierno Vasco IT-765-13, and UFI11/55 from UPV/EHU. EGM is supported by the Serra Hunter Programme, Generalitat de Catalunya. A. Simon, K. Sayanagi and M.H. Wong were supported by a NASA Cassini Data Analysisgrant (NNX15AD33G and NNX15AD34G). We acknowledge the three orbits assigned by the Director Discretionary time from HST for this research (DD Program 14064, IP A. Sánchez-Lavega). We are very grateful to amateur astronomers contributing with their images to open databases such as PVOL (http://pvol2.ehu.eus/) and ALPO-Japan (http://alpo-j.asahikawa-med.ac.jp/)

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 1980-1981 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 degrees N to 10 degrees 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. Palabras claveThis work is based on observations and analysis from Hubble Space Telescope (GO/DD program 14064), Cassini ISS images (NASA pds), and Calar Alto Observatory (CAHA-MPIA). A.S.-L. and UPV/EHU team are supported by the Spanish projects AYA2012-36666 and AYA2015-65041-P with FEDER support, Grupos Gobierno Vasco IT-765-13, Universidad del Pais Vasco UPV/EHU program UFI11/55, and Diputacion Foral Bizkaia (BFA). We acknowledge the contribution of Saturn images by T. Olivetti, M. Kardasis, A. Germano, A. Wesley, P. Miles, M. Delcroix, C. Go, T. Horiuchi and P. Maxon. We also acknowledge the wind model data provided by J. Friedson

An enduring rapidly moving storm as a guide to Saturn's Equatorial jet's complex structure

This work is licensed under a Creative Commons Attribution 4.0Saturn 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 1980–1981 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 10ºN to 10º S) suffers intense vertical shears reaching þ2.5 ms-1 km-1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.Peer ReviewedPostprint (published version

AKATSUKI-IR2 reveals unexpected opacity disruption affecting Venus's lower clouds every 9 days

The images of AKATSUKI acquired with the camera IR2 at 1.74-2.3 µm report the discovery of an equatorial disruption or “front” in the opacity of the lower clouds of Venus at 50 km between 30ºN¿30ºS. This feature appears on the night every 9 terrestrial days during more than 8 months, and introduces a dramatic and abrupt increase of the cloud opacity and reducing the thermal radiance in a factor of about 1:2 from its brightest to the darkest side.Peer ReviewedPostprint (published version

A complex storm system in Saturn's north polar atmosphere in 2018

Saturn’s convective storms usually fall in two categories. One consists of mid-sized storms ~2,000¿km wide, appearing as irregular bright cloud systems that evolve rapidly, on scales of a few days. The other includes the Great White Spots, planetary-scale giant storms ten times larger than the mid-sized ones, which disturb a full latitude band, enduring several months, and have been observed only seven times since 1876. Here we report a new intermediate type, observed in 2018 in the north polar region. Four large storms with east–west lengths ~4,000–8,000¿km (the first one lasting longer than 200 days) formed sequentially in close latitudes, experiencing mutual encounters and leading to zonal disturbances affecting a full latitude band ~8,000¿km wide, during at least eight months. Dynamical simulations indicate that each storm required energies around ten times larger than mid-sized storms but ~100 times smaller than those necessary for a Great White Spot. This event occurred at about the same latitude and season as the Great White Spot in 1960, in close correspondence with the cycle of approximately 60 years hypothesized for equatorial Great White Spots.Peer ReviewedPostprint (author's final draft