Observations Of Jupiter Research Articles

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

Alkali metal depletion in the deep Jovian atmosphere: The role of anions

The Juno Microwave Radiometer has allowed observation of Jupiter's atmosphere down to previously inaccessible depths, although the complexity of the atmospheric dynamics has complicated analysis. The longest-wavelength channel (600 MHz) is sensitive to pressure levels of hundreds of bars, and has observed opacity sources other than the known gaseous and cloud components, likely caused by thermally ionized free electrons from alkali metal vapor. We extend previous analysis of limb darkening at these wavelengths, using radiative transfer and thermal equilibrium modeling, by considering the effect of anions in the deep Jovian atmosphere, which act as a sink for free electrons and will thus decrease opacity for a given alkali metal abundance. We show that MWR observations are consistent with a sodium and potassium abundance on the order of 0.1× solar around the 1-kilobar level, higher than previously estimated but still substantially depleted compared to other heavy elements, a value that would be within the range of observed alkali metal abundances on giant exoplanets; alternatively, MWR observations may be consistent with 3× solar sodium abundance, but only if potassium is even more strongly depleted. Such depletion may be the result of either chemical processes yet deeper in the atmosphere, such as in the silicate clouds, or of a long-lived stable layer shallower than the alkali salt clouds.

Effect of the Earth’s declination variation on characteristics of Jovian decametric radio emissions

Context. The variation in the Jovicentric sub-latitude (declination, DE) of a radio observer of Jupiter has long been known to affect the observation of Jupiter’s decametric (DAM) radio emissions due to these emissions’ anisotropic nature (through cyclotron maser instability beaming cones centered on Jovian magnetic field lines). The effect of the DE variation, however, is still not clearly understood. For ground-based observations of Jupiter, the DE variation, from −4° to +4°, occurs concomitantly with the cyclic variation in the distance to Jupiter, R, and Jupiter’s elongation angle, γ, which also affect the emission observation. Those covariant effects must be removed, then, for an analysis of the pure effect of DE. Aims. The aim of this study is to investigate the pure effect of the Earth’s DE variation on the maximum frequency, duration, average Io phase, and average longitude of Io-induced DAM emissions observed with the Nançay Decameter Array (NDA). Methods. For this purpose, we selected from the NDA/Routine digital catalog Jovian DAM emissions with an intensity (distance-corrected) above or equal to 8.8 dB and a maximum frequency above or equal to 20 MHz (25 MHz) for southern (northern) emissions. Distinct maximum frequency thresholds were adopted because of the typical discrepancy in the emissions’ frequency due to the high amplitude anomaly in the Jovian magnetic field at Jupiter’s northern hemisphere. The selected emissions comprise a new “unbiased” catalog. After analyzing the tenuous variation in the characteristics of the unbiased set of Io-DAM emissions with DE, we compared them with those of matching Io-DAM simulations obtained with the Exoplanetary and Planetary Radio Emissions Simulator (ExPRES). Results. From both the NDA data and the ExPRES simulations, it is observed that the pure DE effect on the Io-DAM emissions characteristics is minor, yet a clear proportionality of the maximum frequency and duration of the northern Io-DAM emissions with DE is noticed. Conclusions. The northern Io-DAM emissions seem to be more strongly affected by the DE variation than the southern emissions. Additionally, ExPRES can predict Io-DAM emissions consistently, from which we conclude that the current understanding of emission generation and propagation is reasonable. This study may be extended for broader ranges of DE, such as Juno’s.

Jupiter's Hotspots as observed by JIRAM-Juno: limb darkening in thermal infrared

ABSTRACT The Jupiter InfraRed Auroral Mapper (JIRAM) instrument onboard the Juno spacecraft performed repeated observations of Jupiter's North Equatorial Belt (NEB) around the time of 12th Juno pericenter passage on 2018 April 1. The data consist of thermal infrared images and show, among other atmospheric features, two bright Hotspots on the boundary between the NEB and the Equatorial Zone. Night-time images of the same areas at different emission angles were used to constrain the trend of the limb-darkening function. Comparison with simulated observations, computed for different emission angles, total opacities, single scattering albedo ω0, and asymmetry parameter g suggests that ω0 ∼ 0.90 ± 0.05 and g ∼ 0.37 ± 0.15 provide best match with data. Subsequently, we computed the ω0 and g resulting from different size distributions, taking into account the complex refractive indices of ammonium hydrosulfide (NH4SH) by Howett et al. [2007] and Ferraro et al. [1980]. Only the former data set is marginally consistent with JIRAM observations. Similarly, ammonia and hydrazine barely reproduce the experimental data. Tholin, although not usually considered a realistic component for Jupiter's aerosols, provides a better match for particle radii between 0.7 and 1 μm, both as a pure material as well as a thick coating over NH4SH cores. Notably, this radius range is consistent with the mean radius of aerosols as estimated by Ragent et al. [1998] on the basis of Galileo entry probe data. Comparison with literature suggests that similar results can be achieved by a large variety of contaminants bearing C–N bounds.

Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over ∼75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale CMB polarization to constrain the tensor-to-scalar ratio and the optical depth to last scattering. This paper presents the optical characterization of the 90 GHz telescope. Observations of the Moon establish the pointing while dedicated observations of Jupiter are used for beam calibration. The standard deviations of the pointing error in azimuth, elevation, and boresight angle are 1.′3, 2.′1, and 2.′0, respectively, over the first 3 yr of observations. This corresponds to a pointing uncertainty ∼7% of the beam’s full width at half-maximum (FWHM). The effective azimuthally symmetrized instrument 1D beam estimated at 90 GHz has an FWHM of 0.°620 ± 0.°003 and a solid angle of 138.7 ± 0.6(stats.) ± 1.1(sys.) μsr integrated to a radius of 4°. The corresponding beam window function drops to bℓ2=0.93,0.71,0.14 at ℓ = 30, 100, 300, respectively. Far-sidelobes are studied using detector-centered intensity maps of the Moon and measured to be at a level of 10−3 or below relative to the peak. The polarization angle of Tau A estimated from preliminary survey maps is 149°.6 ± 0°.2(stats.) in equatorial coordinates. The instrumental temperature-to-polarization (T → P) leakage fraction, inferred from per-detector demodulated Jupiter scan data, has a monopole component at the level of 1.7 × 10−3, a dipole component with an amplitude of 4.3 × 10−3, with no evidence of quadrupolar leakage.

Ionospheric irregularities at Jupiter observed by JWST

Jupiter’s upper atmosphere is composed of a neutral thermosphere and charged ionosphere. In the latter, the dominant molecular ion H3+ emits in the near-infrared, allowing for the remote exploration of the physical properties of the upper atmosphere. However, the Jovian low-latitude ionosphere remains largely unexplored because H3+ emissions from this region are faint and spectrally entangled with bright neutral species, such as CH4. Here, we present James Webb Space Telescope H3+ observations of Jupiter’s low-latitude ionosphere in the region of the Great Red Spot, showing unexpected small-scale intensity features such as arcs, bands and spots. Our observations may imply that the low-latitude ionosphere of Jupiter is strongly coupled to the lower atmosphere via gravity waves that superimpose to produce this complex and intricate morphology.

Examination of Magnetic Field Signatures and Local Plasma Distribution Variations in Jupiter's Magnetosphere

AbstractSpinning disk of plasma results in deformation of Jupiter's magnetic field from a dipole to a magnetodisc configuration with significant radial and azimuthal components. Polar orbit of the Juno spacecraft enables a comprehensive in situ observation of Jupiter's plasmadisc at different latitudes. Observations from magnetometer and plasma distribution instruments on Juno mission were used to examine interaction of magnetic field and heavy ions in Jupiter's nightside magnetosphere. Power spectrum analysis was used to evaluate magnetic fluctuations inside and outside of the plasmadisc. Extensive radial maps of magnetic activity in Jupiter's nightside magnetosphere are presented. Comprehensive examination of magnetic fluctuations enable to identify local plasma density variations that correlate with plasma distribution count rate fluctuations. Observations of magnetic signatures together with examination of plasma distribution are used to detect features that point to plasma transport inside and outside of Jupiter's plasmadisc. This work shows that plasma in Jupiter's magnetosphere is contained near centrifugal equator and is not a subject to curvature drift that could generate ring currents. Signatures described as current sheet crossings were investigated. On close inspection these signatures show attributes that belong to stand alone formations rather than a single current sheet structure. This work shows that current flow is not an adequate mechanism to explain deformation of Jupiter's magnetic field.

The Simons Observatory: Beam Characterization for the Small Aperture Telescopes

We use time-domain simulations of Jupiter observations to test and develop a beam reconstruction pipeline for the Simons Observatory Small Aperture Telescopes. The method relies on a mapmaker that estimates and subtracts correlated atmospheric noise and a beam fitting code designed to compensate for the bias caused by the mapmaker. We test our reconstruction performance for four different frequency bands against various algorithmic parameters, atmospheric conditions, and input beams. We additionally show the reconstruction quality as a function of the number of available observations and investigate how different calibration strategies affect the beam uncertainty. For all of the cases considered, we find good agreement between the fitted results and the input beam model within an ∼1.5% error for a multipole range ℓ = 30–700 and an ∼0.5% error for a multipole range ℓ = 50–200. We conclude by using a harmonic-domain component separation algorithm to verify that the beam reconstruction errors and biases observed in our analysis do not significantly bias the Simons Observatory r-measurement

Long Exposure Chandra X‐Ray Observation of Jupiter's Auroral Emissions During Juno Plasmasheet Encounters in September 2021

AbstractOn 15 September 2021, Chandra carried out a 40‐hr (∼4 jovian rotations) observation as part of its longest planetary campaign to study the drivers of jovian X‐ray aurora that may be linked to ultra‐low frequency (ULF) wave activity. During this time, Juno's orbit had taken the spacecraft into Jupiter's dusk magnetosphere. Here is believed to be the most probable location of ULF waves propagating along jovian magnetic field lines that drive the X‐ray auroral emissions. This is the first time that this region has been observed by an orbiter since Galileo >20 years ago, and never before has there been contemporaneous in situ and X‐ray observations. A 1D solar wind propagation model identifies a compression event near the midpoint of the 40‐hr observation window. The influence of a compression is confirmed when comparing the measured magnetic field in the dusk lobes of the magnetotail from Juno MAG data against a baseline lobe field model. Data from the Juno Waves instrument also show activation of broadband kilometric (bKOM) emissions during the arrival of the shock, a feature that has previously been observed during compression events. Therefore this is the first time we can fully analyze the morphological variability during the evolution of a shock. Wavelet transforms and Rayleigh testing are used to search for statistically significant quasi‐periodic pulsations (QPPs) of the X‐ray emissions in the data set, and find significant QPPs with periods of 25–26 min for the northern auroral X‐rays.

Asymmetric Ionospheric Jets in Jupiter's Aurora

AbstractSimultaneous infrared observations of and H2 emissions from Jupiter's northern aurora using the Near Infrared Spectrograph at Keck Observatory were used to measure the ionospheric and thermospheric wind velocities. ions supercorotate near the dawn auroral oval and subcorotate across the dusk sector and in the dawn polar region relative to the planetary rotation rate, broadly in agreement with past observations and models. An anticyclonic vortex is discovered in H2 flows, closely matching the mean magnetospheric subcorotation when the observed magnetospheric flows are averaged azimuthally. In comparing ion and neutral winds, we measure the line‐of‐sight effective ion drift in the neutral reference frame for the first time, revealing two blue‐shifted sunward flows of ∼2 km/s. Observed and H2 emissions overlap with predictions of the Pedersen conductivity layer, suggesting two different regions of the ionosphere: (a) a deep layer, where neutral forces dominate the thermosphere and symmetric breakdown‐in‐corotation currents can close, and (b) a higher layer, where the observed effective ion drift allows dawn‐to‐dusk Pedersen currents within the upper atmosphere, in turn closing asymmetric currents within the magnetosphere. This ionospheric structure aligns well with recent Juno observations of Jupiter's aurora. The detected thermospheric vortex implies the driving of neutral flows by the momentum from the magnetosphere within the thermosphere and deeper in the atmosphere to potentially 20 mbar. Jovian neutral thermosphere might bridge the gap between current observations and modelings and perhaps be significant to the dynamics of aurora on Earth and other outer planets.

Jovian Magnetospheric Injections Observed by the Hubble Space Telescope and Juno

AbstractWe compare Hubble Space Telescope observations of Jupiter's FUV auroras with contemporaneous conjugate Juno in situ observations in the equatorial middle magnetosphere of Jupiter. We show that bright patches on and equatorward of the main emission are associated with hot plasma injections driven by ongoing active magnetospheric convection. During the interval that Juno crossed the magnetic field lines threading the complex of auroral patches, a series of energetic particle injection signatures were observed, and immediately prior, the plasma data exhibited flux tube interchange events indicating ongoing convection. This presents the first direct evidence that auroral morphology previously termed “strong injections” is indeed a manifestation of magnetospheric injections, and that this morphology indicates that Jupiter's magnetosphere is undergoing an interval of active iogenic plasma outflow.

An intense narrow equatorial jet in Jupiter’s lower stratosphere observed by JWST

The atmosphere of Jupiter has east–west zonal jets that alternate as a function of latitude as tracked by cloud motions at tropospheric levels. Above and below the cold tropopause at ~100 mbar, the equatorial atmosphere is covered by hazes at levels where thermal infrared observations used to characterize the dynamics of the stratosphere lose part of their sensitivity. James Webb Space Telescope observations of Jupiter in July 2022 show these hazes in higher detail than ever before and reveal the presence of an intense (140 m s−1) equatorial jet at 100–200 mbar (70 m s−1 faster than the zonal winds at the cloud level) that is confined to ±3° of the equator and is located below stratospheric thermal oscillations that extend at least from 0.1 to 40 mbar and repeat in multiyear cycles. This suggests that the new jet is a deep part of Jupiter’s Equatorial Stratospheric Oscillation and may therefore vary in strength over time.

Drifting discrete Jovian radio bursts reveal acceleration processes related to Ganymede and the main aurora

Radio detection at high time-frequency resolutions is a powerful means of remotely studying electron acceleration processes. Radio bursts have characteristics (polarization, drift, periodicity) making them easier to detect than slowly variable emissions. They are not uncommon in solar system planetary magnetospheres, the powerful Jovian “short bursts (S-bursts)" induced by the Io-Jupiter interaction being especially well-documented. Here we present a detection method of drifting radio bursts in terabytes of high resolution time-frequency data, applied to one month of ground-based Jupiter observations. Beyond the expected Io-Jupiter S-bursts, we find decameter S-bursts related to the Ganymede-Jupiter interaction and the main Jovian aurora, revealing ubiquitous Alfvénic electron acceleration in Jupiter’s high-latitude regions. Our observations show accelerated electron energies are distributed in two populations, kilo-electron-Volts and hundreds of electron-Volts. This detection technique may help characterizing inaccessible astrophysical sources such as exoplanets.

Uncovering Ganymede's past: Tectonics at Nippur/Philus Sulci

Observations of Jupiter's largest moon Ganymede by Voyager and Galileo revealed fractures and evidence of strike-slip faulting, leading to studies for the mechanisms of these structures focused on extensional tectonism and gravitational tidal stresses. In this analysis, we investigate the geologic history of Ganymede in the area of Nippur/Philus Sulci (175°E, 36.9°N) by examining Galileo high-resolution data available for this region (∼100 m/pixel) and conducting a tidal stress investigation of Ganymede's past. Several crosscutting bands of light terrain in the Nippur/Philus Sulci site show varying degrees of tectonic deformation, ranging from smooth and less distorted bands to highly grooved and deformed terrain. The chronology of tectonic activity implied by mapped crosscutting relationships reveals three eras of distinct geologic activity: 1. Ancient, 2. Intermediate and 3. Youngest. Indicators of shear deformation are found throughout all ages of terrain, but mapped early-stage indicators of strike-slip features are exclusively located in intermediate and youngest terrain. An investigated offset feature in intermediate-aged terrain corresponds in slip direction to the predictions from modeling stresses of a higher past eccentricity. However, the en echelon structures found in a younger geologic unit do not align in slip direction with typical first-order R Riedel shears. This suggests that these features might have formed through another process and the observed en echelon folds could be passive structures, which can be created through relatively rapid large displacement on a fault. Through modeling of Ganymede's past tidal stresses, we can conclude that a past higher eccentricity (e > 0.02) could have distorted the Nippur/Philus Sulci region in its second, intermediate phase of main deformation, yielding a stress field conducive to shear failure of the icy upper crust. New data from NASA's Juno mission, as well as future observations by ESA's Jupiter Icy Moons Explorer (JUICE) mission and NASA's Europa Clipper mission, will further aid our understanding of the tectonic history of Ganymede and improve the resolution of tectonic feature analysis.

On-Sky Performance of New 90 GHz Detectors for the Cosmology Large Angular Scale Surveyor (CLASS)

The Cosmology Large Angular Scale Surveyor (CLASS) is a polarization-sensitive telescope array located at an altitude of 5,200 m in the Chilean Atacama Desert and designed to measure the polarized Cosmic Microwave Background (CMB) over large angular scales. The CLASS array is currently observing with three telescopes covering four frequency bands: one at 40 GHz (Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (HF). During the austral winter of 2022, we upgraded the first 90 GHz telescope (W1) by replacing four of the seven focal plane modules. These new modules contain detector wafers with an updated design, aimed at improving the optical efficiency and detector stability. We present a description of the design changes and measurements of on-sky optical efficiencies derived from observations of Jupiter.

Ammonia Abundance Derived from Juno MWR and VLA Observations of Jupiter

The vertical distribution of trace gases in planetary atmospheres can be obtained with observations of the atmosphere’s thermal emission. Inverting radio observations to recover the atmospheric structure, however, is nontrivial, and the solutions are degenerate. We propose a modeling framework to prescribe a vertical distribution of trace gases that combines a thermochemical equilibrium model with a vertical temperature structure and compare these results to models where ammonia can vary between predefined pressure nodes. We compare these model to nadir brightness temperatures and limb-darkening parameters, together with their uncertainties, which we reduced from the raw Juno Microwave Radiometer (MWR) data set. We then apply this framework to MWR observations during Juno’s first years of operation (perijove passes 1–12) and to longitudinally averaged latitude scans taken with the upgraded Very Large Array. We use the model to constrain the distribution of ammonia between −60° and 60° latitude and down to 100 bars. We constrain the ammonia abundance to be ppm ( solar abundance) and find a depletion of ammonia down to a depth of ∼20 bars, which supports the existence of processes that deplete the atmosphere below the ammonia and water cloud layers. At the equator we find an increase of ammonia with altitude, while the zones and belts in the midlatitudes can be traced down to levels where the atmosphere is well mixed. The latitudinal variation in the ammonia abundance appears to be opposite to that shown at higher altitudes, which supports the existence of a stacked-cell circulation model.

Preliminary Modeling of Magnetized Sprite Streamers on Jupiter Following Juno's Observations of Possible Transient Luminous Events

AbstractThe first observation of possible transient luminous events (TLEs) on Jupiter was reported recently. Whereas initiation of elves on Jupiter has been theoretically studied before, the possibility of sprite streamer inception on Jupiter has not been investigated yet. Here we critically review the literature concerned with TLEs on Jupiter. Subsequently, we report on development of a numerical model for modeling of magnetized streamers in presence of Jupiter's strong magnetic field. The model utilizes the knowledge provided by recent observations of Jupiter's lightning and magnetic field by the Juno spacecraft. It is demonstrated that sprite streamer inception under realistic atmospheric conditions on Jupiter is possible.

A retrospective analysis of mid-infrared observations of the Comet D/Shoemaker-Levy 9 and Wesley impacts on Jupiter

We present a retrospective analysis of Earth-based mid-infrared observations of Jupiter capturing the aftermath of the impacts by Comet D/Shoemaker-Levy 9 (henceforth SL9) in July 1994 and the unknown object previously termed the “Wesley impactor” in July 2009. While the effects of both impacts on Jupiter’s atmosphere have been reported previously, we were motivated to re-examine both events using consistent data reduction and analysis methods to enable robust, quantitative comparisons. To study the aftermath of the SL9 impacts, we examined infrared (7.8–20.5μm) spectrophotometry of Jupiter measured by the MIRAC (Mid-Infrared Camera) on NASA’s Infrared Telescope Facility on July 20, 21 1994 and low-resolution (R = 100) N-band (7–13μm) spectroscopy measured by SpectroCam-10 on the Palomar Telescope on July 22 1994. To study the aftermath of the Wesley impact, we examined low-resolution (R = 100) N- and Q-band (R = 80, 17–25μm) spectroscopy recorded by Gemini South Telescope’s T-ReCS (Thermal-Region Camera Spectrograph). We analyzed the observations with two independent analyses: (1) a least-squares search over a grid of candidate mineral species to determine the composition of impact residue and (2) a radiative transfer analysis to derive atmospheric information. We observe that the SL9 impact sites are enhanced in stratospheric CH4 emissions at 7.9μm, due to shock heating and adiabatic compression from plume re-entry, and from 8.5–11.5μm due to stratospheric NH3 emission and non-gaseous cometary material, in agreement with previous work. In the G impact site, we derive NH3 concentrations of 5.7−2.8+4.5 ppmv at 30 mbar. In new findings, we find that the SL9 impact sites also exhibit a non-gaseous emission feature at 18–19μm. The non-gaseous emission at 8.5–11.5μm and 18–19μm emission result is best reproduced by predominantly amorphous olivine and (obsidian) silica at similar abundances. The Wesley impact site exhibits enhanced emissions from 8.8–11.5μm and 18–19μm. We found this could be reproduced by predominantly amorphous olivine and stratospheric gaseous NH3 at concentrations of 150−121+338 ppbv retrieved at 30 mbar. Stratospheric abundances of NH3 are a factor of ∼40 higher in the SL9 impacts compared to the Wesley impact, which confirms the former reached deeper, NH3-richer altitudes of Jupiter’s atmosphere compared to the latter. The absence of silicas in the Wesley impact would place an upper limit of 10 km/s on the incident angle and ∼9∘ on the entry angle of the impactor such that shock heating associated with the impact did not reach temperatures required for silicates to be converted.

Investigating temporal changes in Jupiter’s aerosol structure with rotationally-averaged 2015–2020 HST WFC3 images

Annual imaging observations of Jupiter from 2015 onward by the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) as part of the Outer Planet Atmospheres Legacy (OPAL) program (Simon et al., 2015) have provided a valuable data set from which Jupiter’s temporal variability can be characterized and modeled. Spectral samples at discrete filter bands from the UV to short near-IR wavelengths also provide an opportunity to connect temporal changes in reflectivity with temporal changes in cloud structure. To improve constraints on that cloud structure we used center-to-limb variations that were noise-reduced by rotational averaging during each annual OPAL observation sequence. Fitting observations at multiple and distinctly different observer zenith angles helps to make up for the lack of multiple methane-band filters in discerning the vertical distribution of aerosols. The short-wavelength limit of the OPAL observations also provides better constraints than ground-based observation on the properties of Jupiter’s chromophore, i.e., the compound that creates Jupiter’s variety of red colorations to clouds and hazes composed mainly of colorless condensates. We chose four latitudes to investigate with radiative transfer models based on a simple 3-layer aerosol structure consisting of a deep putative NH3 cloud layer, with a physically thin chromophore layer that has a fitted location at or near the top of the deep cloud, and an overlying stratospheric haze layer. Our chosen planetocentric latitudes were 5.5°S (Equatorial Zone South,EZS), 0° (Equatorial Zone, EZ), 10°N (North Equatorial Belt, NEB), and 21.75°N (North Temperate Belt, NTB). Two major color transformations occurred during the 2015–2020 period we analyzed. One is a dramatic dimming of the center of the Equatorial Zone at short wavelengths, especially after 2017, and a significant reddening of that region. The second is a significant reddening of part of the North Temperate Belt (near 22°N) between 2016 and 2017. Both reddening events can be modeled by doubling of the optical depth of the chromophore layer during the transitions. Comparison with prior 2017 model results for the NEB, EZ, and NTB have revealed agreement with Braude et al. (2020) on the vertical location of the chromophore layer but disagreements on cloud-top pressures and the vertical distribution of stratospheric haze particles. We identified what seems to be common tendency of models based on HST/WFC3 observations to either infer very little stratospheric haze opacity or to put that opacity at too high a pressure.