Observations Of Saturn Research Articles

Infrared emissivity of icy surfaces

Context. Most analyses of the infrared emission of Saturn’s rings and icy satellites have considered pure water ice as the constituent of regolith and particle surfaces. Visual and near-infrared observations have shown, however, that darkening and reddening contaminants are present at a fraction level of a few percent. In the spectral domain 10–2000 cm−1, water ice becomes transparent in a few windows, which in particular causes the roll-off of emissivity of icy surfaces that is observed below 50 cm−1. Their emissivity there may be affected by these contaminants. Aims. We present a quantitative global sensitivity analysis of a hybrid Mie-Hapke model to evaluate the influence of regolith properties and contaminant fraction on the infrared emissivity of icy rings or moons over this spectral range. Methods. A hybrid Mie–Hapke model of the hemispherical emissivity ε*h(Wn) was made, including various diffraction correction and mixing types with tholins or amorphous carbon grains, or grain size distributions and some anisotropy in emission. A Sobol global sensitivity analysis provided quantitative levels of importance for these factors versus wave number wn. Results. Given the a priori uncertainties, the most important factor acting on ε*h(Wn) remains the size distribution of regolith grains and the average anisotropy factor ξ. For wn> 50 cm−1, ξ, the power-law index p and the minimum amin of the size distribution are most influential. In windows of water-ice transparency (10–50, 300–600, and 900–1300 cm−1), the emissivity is also sensitive, but to a lesser extent, to the maximum grain size amax and the fraction f of contaminants, if mixed at the molecular level. Conclusions. This model provides a self-consistent tool for interpreting multi-modal observations of the thermal emission from icy surfaces. It also offers interesting insights into recent mid-infrared observations of Saturn’s rings and Jupiter’s moon Ganymede by the JWST-MIRI instrument.

The RATT PARROT: serendipitous discovery of a peculiarly scintillating pulsar in MeerKAT imaging observations of the Great Saturn – Jupiter Conjunction of 2020. I. Dynamic imaging and data analysis

ABSTRACT We report on a radiopolarimetric observation of the Saturn–Jupiter Great Conjunction of 2020 using the MeerKAT L-band system, initially carried out for science verification purposes, which yielded a serendipitous discovery of a pulsar. The radiation belts of Jupiter are very bright and time variable: coupled with the sensitivity of MeerKAT, this necessitated development of dynamic imaging techniques, reported on in this work. We present a deep radio ‘movie’ revealing Jupiter’s rotating magnetosphere, a radio detection of Callisto, and numerous background radio galaxies. We also detect a bright radio transient in close vicinity to Saturn, lasting approximately 45 min. Follow-up deep imaging observations confirmed this as a faint compact variable radio source, and yielded detections of pulsed emission by the commensal MeerTRAP search engine, establishing the object’s nature as a radio emitting neutron star, designated PSR J2009−2026. A further observation combining deep imaging with the PTUSE pulsar backend measured detailed dynamic spectra for the object. While qualitatively consistent with scintillation, the magnitude of the magnification events and the characteristic time–scales are odd. We are tentatively designating this object a pulsar with anomalous refraction recurring on odd time-scales (PARROT). As part of this investigation, we present a pipeline for detection of variable sources in imaging data, with dynamic spectra and light curves as the products, and compare dynamic spectra obtained from visibility data with those yielded by PTUSE. We discuss MeerKAT’s capabilities and prospects for detecting more of such transients and variables.

Microwave spectra of the leading and trailing hemispheres of Iapetus

The leading hemisphere of Saturn’s synchronous moon Iapetus is covered by a low-albedo material, contrasting with its bright trailing hemisphere. This dichotomy is also apparent in radar and microwave radiometry observations, which are sensitive to the properties of the near subsurface. To better understand the regional properties of Iapetus and their variations with depth, we assemble the microwave spectra of its leading and trailing hemispheres. Pre-existing data are combined with new millimetric and centimetric observations acquired with the IRAM 30-meter dish, IRAM NOEMA interferometer, and VLA interferometer. These data, interpreted with the help of a model with vertically uniform thermal properties, reveal complex variations in structure and/or composition with depth on the leading side. Meanwhile, the trailing side emissivity is found to be especially low at all observed frequencies, indicating efficient scattering processes on subsurface structures, as observed on Saturn’s other icy moons. We also report the first observations of Saturn’s retrograde moon Phoebe at these frequencies, which has an emissivity higher than that of the trailing hemisphere of Iapetus and similar to its dark leading side, consistent with the theory that Phoebe is the source of the dark material on Iapetus.

Spherical harmonic decomposition and interpretation of the shapes of the small Saturnian inner moons

Context. The Cassini-Huygens space mission made a series of observations of Saturn’s small satellites during its grand finale stage. These measurements were performed in order to study the shape, geology, and surface composition of the small satellites as well as to study the impact of the environment, in particular the rings, on these small bodies. Aims. The purpose of this study is to focus on the shape analysis of the small Saturnian satellites in order to describe their global figure and large-scale topography, as well as to deduce fundamental quantities, gravity field, and amplitude of the diurnal libration by assuming that the bodies are homogeneous. Methods. We used two approaches in this study. On the one hand, we directly exploited the Cassini images of the small satellites by performing limb measurements and deducing a confidence interval on the shape measurements. On the other hand, we used previously published shape models which combine limb measurements and control points. These shape models were then decomposed and described in spherical harmonics. Results. We found that the shape of the small satellites can be described with a confidence interval between 50 and 150 m. The low degree in spherical harmonics (degree 2) indicated that Telesto, Pandora, Pan, Janus, and Helene have a degree 2 shape close to the Omega sequence, which was defined recently, where the potential is constant along a meridian perpendicular to the longest axis. The degree 2 shape of Epimetheus, on the other hand, is close to the Roche sequence. In contrast, Prometheus, Calypso, and Atlas are in the Low-Brown region. The root mean square spectrum and spherical harmonic maps then allowed us to describe the topography of the satellites, and in particular to highlight equatorial ridges for some satellites including Daphnis. Finally, our estimates of the libration amplitude in the homogeneous case provide values in agreement with previously published librational measurements for Epimetheus while highlighting the proximity of the resonance for Epimetheus, Pandora, and Prometheus. Conclusions. The high resolution images of the internal satellites have allowed us to describe the geology and the geophysics of these bodies. Future comparison of these amplitudes with new librational measurements deduced, for example, by the astrometric method, will allow us to obtain information on the internal structure of these bodies. Similar studies could be carried out on the internal satellites of Jupiter using images from the Europa Clipper (NASA) or JUICE (ESA) missions.

First absolute wind measurements in Saturn’s stratosphere from ALMA observations

Context. Past observations of Saturn with ground-based and space telescopes have enabled the monitoring of tropospheric wind speeds using cloud-tracking techniques. The most remarkable feature is a broad and fast prograde jet at the equator that reaches speeds of ~400 m s−1. Saturn’s stratospheric dynamics are less well-known. At low latitudes, they are characterized by the thermal signature of an equatorial oscillation; the observed thermal structure implies that there is a strong oscillating vertical shear of the zonal winds throughout the stratosphere. However, wind speeds in this region cannot be measured by cloud-tracking techniques and remain unknown. Aims. The objective of this study is to measure directly and for the first time the zonal winds in Saturn’s stratosphere using the ALMA interferometer. Methods. We observed the spectral lines of CO at 345.796 GHz and HCN at 354.505 GHz with the high spatial (~0.6″ × 0.5″) and spectral resolutions enabled by ALMA, and measured the Doppler shift induced by the winds on the lines at the planet limb where the emission is the strongest. After subtracting the beam-convolved planet rotation, we derived the zonal wind speeds as a function of latitude. Results. We measured the zonal winds from ~20°S to the northern polar latitudes. Latitudes between 20°S and 45°S were obscured by the rings and were inaccessible southward of 45°S. The zonal wind profiles obtained on the eastern and western limbs are consistent within the error bars and probe from the 0.01 to the 20 mbar level. We most noticeably detect a broad super-rotating prograde jet that spreads from 20°S to 25°N with an average speed of 290 ± 30 m s−1. This jet is asymmetrical with respect to the equator, a possible seasonal effect. We tentatively detect the signature of the Saturn semi-annual oscillation (SSAO) at the equator, in the form of a ~−50 ± 30 m s−1 peak at the equator which lies on top of the super-rotating jet. We also detect a broad retrograde wind (−45 ± 20 m s−1) of about 50 m s−1 in the mid-northern latitudes. Finally, in the northern polar latitudes, we observe a possible auroral effect in the form of a ~200 m s−1 jet localized on the average position of the northern main auroral oval and in couter-rotation, like the Jovian auroral jets. Conclusions. Repeated observations are now required to monitor the temporal evolution of the winds and quantify the variability of the SSAO jet, to test the seasonality of the asymmetry observed in the broad super-rotating jet, and to verify the presence of auroral jets in the southern polar region of Saturn.

Solar occultation observations of Saturn's rings with Cassini UVIS

The Ultraviolet Imaging Spectrograph (UVIS) instrument onboard the Cassini spacecraft observed 41 solar occultations by Saturn's rings through its extreme ultraviolet (56–118 nm) spectrographic channel. These solar occultations complement the set of stellar occultations measured by the broadband UVIS High Speed Photometer in the far ultraviolet (110–190 nm). We provide a uniform calibration of all of the UVIS solar occultation data across the full ring system. We have compiled complete catalogs of these occultations as high-level data products delivered to the Planetary Data System (PDS) Ring Moon Systems Node. This manuscript serves as a guide to this dataset and the corresponding high-level data products outlining their value for analysis of Saturn's rings. These products include light curves and optical depth profiles as functions of ring radius. In addition to providing key parameters of interest obtained through each of these occultations, we show that the optical depths of various ring regions derived from solar occultations are consistent with those from stellar occultations. We also demonstrate that fits to self-gravity wake parameters are similar for solar and stellar occultations. Lastly, we identify a variety of potential spectral trends at various ring locations that future investigations may further explore to address key questions pertaining to the properties of Saturn's rings.

Joint evolution of equatorial oscillation and interhemispheric circulation in Saturn’s stratosphere

Planetary stratospheres are characterized by a subtle interplay between dynamics, radiation and chemistry. Observations of Saturn’s stratosphere have revealed a semi-annual equatorial oscillation of temperature and hinted at an interhemispheric circulation of hydrocarbon species. Both the forcing mechanisms of the former and the existence of the latter have remained debated. Here we use a new troposphere-to-stratosphere Saturn global climate model to argue that those two open questions are intimately connected. Our Saturn climate model reproduces a stratospheric oscillation exhibiting the observed semi-annual period, amplitude and downward propagation. In the same Saturn simulation, a prominent stratospheric summer-to-winter hemispheric circulation develops at the solstices, controlled by both the seasonal radiative gradients and Rossby-wave pumping in the winter-subsiding branch, analogous to Earth’s Brewer–Dobson circulation. Furthermore, we show that Saturn’s equatorial oscillation is driven by the seasonal variability of both the resolved planetary-scale wave activity and the interhemispheric circulation, akin to Earth’s Semi-Annual oscillation. A high-resolution three-dimensional global climate model of Saturn captures the small-scale dynamics of its stratosphere. It is able to reproduce the observed semi-annual equatorial oscillation and finds evidence of an interhemispheric meridional circulation that can explain the periodicity of its equatorial oscillation and the seasonal behaviour of hydrocarbon abundances.

The Atacama Cosmology Telescope: measurement and analysis of 1D beams for DR4

We describe the measurement and treatment of the telescope beams for the Atacama Cosmology Telescope's fourth data release, DR4. Observations of Uranus are used to measure the central portion (<12') of the beams to roughly -40 dB of the peak. Such planet maps in intensity are used to construct azimuthally averaged beam profiles, which are fit with a physically motivated model before being transformed into Fourier space. We investigate and quantify a number of percent-level corrections to the beams, all of which are important for precision cosmology. Uranus maps in polarization are used to measure the temperature-to-polarization leakage in the main part of the beams, which is ≲ 1% (2.5%) at 150 GHz (98 GHz). The beams also have polarized sidelobes, which are measured with observations of Saturn and deprojected from the ACT time-ordered data. Notable changes relative to past ACT beam analyses include an improved subtraction of the atmospheric effects from Uranus calibration maps, incorporation of a scattering term in the beam profile model, and refinements to the beam model uncertainties and the main temperature-to-polarization leakage terms in the ACT power spectrum analysis.

Searching for Saturn’s X-rays during a rare Jupiter Magnetotail crossing using Chandra

ABSTRACT Every 19 yr, Saturn passes through Jupiter’s ‘flapping’ magnetotail. Here, we report Chandra X-ray observations of Saturn planned to coincide with this rare planetary alignment and to analyse Saturn’s magnetospheric response when transitioning to this unique parameter space. We analyse three Director’s Discretionary Time (DDT) observations from the High Resolution Camera (HRC-I) on-board Chandra, taken on 2020 November 19, 21, and 23 with the aim to find auroral and/or disc emissions. We infer the conditions in the kronian system by looking at coincident soft X-ray solar flux data from the Geostationary Operational Environmental Satellite (GOES) and Hubble Space Telescope (HST) observations of Saturn’s ultraviolet (UV) auroral emissions. The large Saturn–Sun–Earth angle during this time would mean that most flares from the Earth-facing side of the Sun would not have impacted Saturn. We find no significant detection of Saturn’s disc or auroral emissions in any of our observations. We calculate the 3σ upper band energy flux of Saturn during this time to be 0.9–3.04 × 10−14 erg cm−2 s−1 which agrees with fluxes found from previous modelled spectra of the disc emissions. We conclude by discussing the implications of this non-detection and how it is imperative that the next fleet of X-ray telescope (such as Athena and the Lynx mission concept) continue to observe Saturn with their improved spatial and spectral resolution and very enhanced sensitivity to help us finally solve the mysteries behind Saturn’s apparently elusive X-ray aurora.

A Complete Data Set of Equatorial Projections of Saturn's Energetic Neutral Atom Emissions Observed by Cassini‐INCA

AbstractObservations of energetic neutral atoms (ENAs) are a useful tool for analyzing ion and neutral abundances in planetary magnetospheres. They are created when hot plasma, originating for example from magnetic reconnection sites, charge‐exchanges with the ambient neutral population surrounding the planet. The motion of ENAs is not governed by the magnetic field, allowing remote imaging. During the Cassini mission, the Ion and Neutral CAmera (INCA) of the Magnetosphere Imaging Instrument (MIMI) collected vast amounts of hydrogen and oxygen ENA observations of Saturn's magnetosphere from a variety of different viewing geometries. To enable investigations of the morphology and dynamics of Saturn's ring current, it is useful to re‐bin and re‐project the camera‐like views from the spacecraft‐based perspective into a common reference frame. We developed an algorithm projecting INCA's ENA observations into a regular grid in Saturn's equatorial plane. With most neutrals and ions being confined into an equatorial rotating disc, this projection is quite accurate in both spatial location and preservation of ENA intensity, provided the spacecraft is located at large enough elevations. Such projections were performed for all INCA ENA data from the Cassini Saturn tour; the data are available for download together with a Python routine flagging contaminated data and returning detailed spacecraft geometry information. The resulting data set is a good foundation for investigating for example the statistical properties of Saturn's ring current and its complicated dynamics in relation to other remote and in situ observations of, for example, auroral emissions and magnetotail reconnection events.

Recipe for a Saturn‐Like Dynamo

AbstractThe Cassini Grand Finale orbits provided detailed observations of Saturn’s internal magnetic field. Unique characteristics of the observed field, such as its axisymmetry and power spectrum, provide constraints on dynamo processes deep in Saturn’s interior. Here, we use numerical dynamo simulations to explore what ingredients are necessary in a dynamo in order to produce the unique “Saturn‐like” surface magnetic field. We find that characteristics of Saturn’s magnetic field can be sensitive to properties of a stably stratified helium rain‐out layer and thermal perturbations at the top of the layer. Our best models suggest that a relatively thick stably stratified helium rain‐out layer may extend out to 70% of Saturn’s radius, likely imprinted with weak heat flux out of the equatorial region and strong heat flux out of high latitudes. These results may provide new constraints on stable stratification inside Saturn and its thermal evolution.

Towards a solution to the energy crisis

The upper atmospheres of all the giant planets are hotter than models predict. Analysis of Cassini Grand Finale observations of Saturn provide evidence that heat generated by the aurora is responsible.

Ganymede's Far‐Ultraviolet Reflectance: Constraining Impurities in the Surface Ice

AbstractWe present reflectance spectra of Ganymede's leading and trailing hemispheres in the wavelength range 138–215 nm, obtained by the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) in 2014. The most notable feature of both spectra is the absence of a sharp water absorption edge at ~165 nm, seen in laboratory measurements of ice reflectivity and in previous observations of Saturn's icy moons and rings. Rather than displaying a sharp change in the reflectivity at the wavelength of the water ice absorption edge, Ganymede's reflectance gradually increases with wavelength at λ &gt; 165 nm. We show that the observed shape of Ganymede's UV reflectance is inconsistent with intimate mixture models of pure ice with UV‐dark materials including tholins, amorphous carbon, graphite, and silicates. However, we find that intraparticle models, in which a small proportion of a UV‐absorbing contaminant is trapped as inclusions within the ice matrix, are able to suppress the 165 nm feature at contaminant concentrations of &lt;1%. We show that models of ice with inclusions of silicates, Triton‐type tholin, or H2O2 are able to produce the observed gradual increase in reflectivity at λ &gt; 165 nm, but additional absorbing surface materials are required to produce a good fit to Ganymede's previously observed near‐UV and visible reflectance.

Saturn's Rings as a Seismograph to Probe Saturn's Internal Structure

As it has already done for Earth, the Sun, and the stars, seismology has the potential to radically change the way the interiors of giant planets are studied. In a sequence of events foreseen by only a few, observations of Saturn's rings by the Cassini spacecraft have rapidly broken ground on giant planet seismology. Gravity directly couples the planet's normal mode oscillations to the orbits of ring particles, generating spiral waves whose frequencies encode Saturn's internal structure and rotation. These modes have revealed a stably stratified region near Saturn's center and provided a new constraint on Saturn's rotation.

Dust and Snow Cover on Saturn's Icy Moons

AbstractThe final analysis of the Cassini radar observations of Saturn's icy moons presented here shows that the exchange of material between the planet's dust rings and moons, which is specific to the Saturnian system, plays a key role in the current state of the airless satellite regolith. Far from Saturn, the vast debris ring from Phoebe progressively coats the leading side of Iapetus with optically dark material reducing its radar brightness. On the contrary, close to the planet, the extreme radar brightness of the innermost moons Mimas, Enceladus, and Tethys (that exceeds that of the Galilean satellites) is most likely related to Enceladus's geysers and the E‐ring which brings ultraclean water ice to their surfaces. The measured radar albedos and observed hemispheric dichotomies require at least a few decimeters thick “snow” cover and that the near surfaces of Saturn's innermost moons contain especially efficient backscattering structures whose nature remains an outstanding problem.

Local-time averaged maps of H3+ emission, temperature and ion winds.

We present Keck-NIRSPEC observations of Saturn's aurora taken over a period of a month, in support of the Cassini mission's ‘Grand Finale’. These observations produce two-dimensional maps of Saturn's temperature and ion winds for the first time. These maps show surprising complexity, with different morphologies seen in each night. The ion winds reveal multiple arcs of 0.5–1 km s−1 ion flows inside the main auroral emission. Although these arcs of flow occur in different locations each night, they show intricate structures, including mirrored flows on the dawn and dusk of the planet. These flows do not match with the predicted flows from models of either axisymmetric currents driven by the Solar Wind or outer magnetosphere, or the planetary periodic currents associated with Saturn's variable rotation rate. The average of the ion wind flows across all the nights reveals a single narrow and focused approximately 0.3 km s−1 flow on the dawn side and broader and more extensive 1–2 km s−1 sub-corotation, spilt into multiple arcs, on the dusk side. The temperature maps reveal sharp gradients in ionospheric temperatures, varying between 300 and 600 K across the auroral region. These temperature changes are localized, resulting in hot and cold spots across the auroral region. These appear to be somewhat stable over several nights, but change significantly over longer periods. The position of these temperature extremes is not well organized by the planetary period and there is no evidence for a thermospheric driver of the planetary period current system. Since no past magnetospheric or thermospheric models explain the rich complexity observed here, these measurements represent a fantastic new resource, revealing the complexity of the interaction between Saturn's thermosphere, ionosphere and magnetosphere.This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H3+, H5+ and beyond’.

Interpretation of shadows and antishadows on Saturn and the evidence against south polar eyewalls

Cassini spacecraft observations of Saturn in 2006 revealed south polar cloud shadows, the common interpretation of which was initiated by Dyudina et al. (2008, Science 319, 1801) who suggested they were being cast by concentric cloud walls, analogous to the physically and optically thick eyewalls of a hurricane. Here we use radiative transfer results of Sromovsky et al. (2019, Icarus, this issue), in conjunction with Monte Carlo calculations and physical models, to show that this interpretation is almost certainly wrong because (1) optically thick eyewalls should produce very bright features in the poleward direction that are not seen, while the moderately brighter features that are seen appear in the opposite direction, (2) eyewall shadows should be very dark, but the observed shadows create only 5–10% I/F variations, (3) radiation transfer modeling of clouds in this region have detected no optically thick wall clouds and no significant variation in pressures of the model cloud layers, and (4) there is an alternative explanation that is much more consistent with observations. The most plausible scenario is that the shadows near 87.9° S and 88.9° S are both cast by overlying translucent aerosol layers from edges created by step decreases in their optical depths, the first in the stratospheric layer at the 50 mbar level and the second in a putative diphosphine layer near 350 mbar, with optical depths reduced at the poleward side of each step by 0.15 and 0.12 respectively at 752 nm. These steps are sufficient to create shadows of roughly the correct size and shape, falling mainly on the underlying ammonia ice layer near 900 mbar, and to create the bright features we call antishadows.

Occultation observations of Saturn's rings with Cassini VIMS

We describe the prediction, design, execution and calibration of stellar and solar occultation observations of Saturn's rings by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini spacecraft. Particular attention is paid to the technique developed for onboard acquisition of the stellar target and to the geometric and photometric calibration of the data. Examples of both stellar and solar occultation data are presented, highlighting several aspects of the data as well as the different occultation geometries encountered during Cassini's 13-year orbital tour. Complete catalogs of ring stellar and solar occultations observed by Cassini-VIMS are presented, as a guide to the standard data sets which have been delivered to the Planetary Data System's Ring Moon Systems Node (Hedman and Nicholson, 2019b).

Jupiter's auroral-related stratospheric heating and chemistry III: Abundances of C2H4, CH3C2H, C4H2 and C6H6 from Voyager-IRIS and Cassini-CIRS

We present an analysis of Voyager-1-IRIS and Cassini-CIRS spectra of Jupiter's high latitudes acquired during the spacecrafts' respective flybys in November 1979 and January 2001. We performed a forward-model analysis in order to derive the abundances of ethylene (C2H4), methylacetylene (CH3C2H), diacetylene (C4H2) and benzene (C6H6) in Jupiter's northern and southern auroral regions. We also compared these abundances to: 1) lower-latitude abundances predicted by the Moses et al. (2005) ‘Model A’ photochemical model, henceforth ‘Moses 2005A’, and 2) abundances derived at non-auroral longitudes in the same latitude band. This paper serves as an extension of Sinclair et al. (2017b), where we retrieved the vertical profiles of temperature, C2H2 and C2H6 from similar datasets. We find that an enrichment of C2H4, CH3C2H and C6H6 with respect to lower-latitude abundances is required to fit the spectra of Jupiter's northern and southern auroral regions. For example, for CIRS 0.5 cm−1 spectra of Jupiter's southern auroral region, scale factor enrichments of 6.40−1.15+1.30 and 9.60−3.67+3.98 are required with respect to the Moses 2005A vertical profiles of C2H4 and C6H6, respectively, in order to fit the spectral emission features of these species at ∼950 and ∼674 cm−1. Similarly, in order to fit the CIRS 2.5 cm−1 spectra of Jupiter's northern auroral region, scale factor enrichments of 1.60−0.21+0.37, 3.40−1.69+1.89 and 15.00−4.02+4.01 with respect to the Moses 2005A vertical profiles of C2H4, CH3C2H and C6H6 were required, respectively. Outside of Jupiter's auroral region in the same latitude bands, only upper-limit abundances of C2H4, CH3C2H and C6H6 could be determined due to the limited sensitivity of the measurements, the weaker emission features combined with cooler stratospheric temperatures (and therefore decreased thermal emission) of these regions. Nevertheless, for a subset of the observations, derived abundances of C2H4 and C6H6 in Jupiter's auroral regions were higher (by 1 σ) with respect to upper-limit abundances derived outside the auroral region in the same latitude band. This is suggestive that the influx of energetic ions and electrons from the Jovian magnetosphere and external solar-wind environment into the neutral atmosphere in Jupiter's auroral regions drives enhanced ion-related chemistry, as has also been inferred from Cassini observations of Saturn's high latitudes (Fletcher et al., 2018; Guerlet et al., 2015; Koskinen et al., 2016). We were not able to constrain the abundance of C4H2 in either Jupiter's auroral regions or non-auroral regions due to its lower (predicted) abundance and weaker emission feature. Thus, only upper-limit abundances were derived in both locations. From CIRS 2.5 cm−1 spectra, the upper limit abundance of C4H2 corresponds to a scale factor enhancement of 45.6 and 23.8 with respect to the Moses 2005A vertical profile in Jupiter's non-auroral and auroral regions.

An Early Compilation of Saturn Observations from Babylon

In this paper, I publish and analyse a compilation of observations of the synodic phenomena of Saturn from Babylon, which can be dated to the early sixth century b.c. By comparing these observations with records found in other early compilations of planetary observations it is possible to trace the development of observational practice in Babylonia. The compilation contains references to several stars that are previously unattested in cuneiform texts. An attempt is made to identify these stars.