During the first orbit around Jupiter of the NASA/Juno mission, the Jovian Auroral Infrared Mapper (JIRAM) instrument observed the auroral regions with a large number of measurements. The measured ...spectra show both the emission of the
H3+ ion and of methane in the 3–4 μm spectral region. In this paper we describe the analysis method developed to retrieve temperature and column density (CD) of the
H3+ ion from JIRAM spectra in the northern auroral region. The high spatial resolution of JIRAM shows an asymmetric aurora, with CD and temperature ovals not superimposed and not exactly located where models and previous observations suggested. On the main oval averaged
H3+ CDs span between 1.8 × 1012 cm−2 and 2.8 × 1012 cm−2, while the retrieved temperatures show values between 800 and 950 K. JIRAM indicates a complex relationship among
H3+ CDs and temperatures on the Jupiter northern aurora.
Key Points
First global maps of
H3+ intensity, column density, and temperature for the Jupiter northern aurora with high spatial resolution
One side of the auroral oval shows higher
H3+ column density and lower temperatures in comparison with the other side
Column densities main oval and temperature main oval do not superimpose
Global and local stressors are causing the worldwide loss of coral cover and structural complexity at an unprecedented pace on reefs. In consequence the habitat of coral reef fish has suffered a ...profound degradation affecting the abundance, biodiversity and species composition of this taxonomic group. Thus, understanding the link between coral reef fish assemblages and their habitats is paramount to predict their responses to increasing human threats. Herein, we implemented Structure from Motion (SfM) techniques and digital mosaics to characterize the habitat of reef fish in terms of structural complexity and cover of benthic organisms, and we examined the relationships between these metrics and the variation in fish assemblages among sites using a multivariate approach. We found that fish assemblage attributes varied across reef sites in Los Roques, depending on the highly specific features of the benthic habitat. Results indicate that 69% of the variation in species-specific abundance of fish (i.e., reef fish assemblage structure) was explained by cover of massive coral and turf algae, the number and sizes of holes, and the site. Furthermore, when fish biomass per species was utilized as a response variable, 64% of the variation in assemblage structures was explained by a model that included: cover of crustose coralline algae (CCA), variation and the maximum height of reef structures along the transect, the number of holes and the site. All these variables together also explained > 60% of variation of total abundance, biomass and species richness. When data were sorted by trophic groups, CCA cover explained 70% of the variation in forager biomass, whereas the number of holes explained up to 60% of variation in carnivore biomass. These results suggest that each trophic group relates differently to the benthic habitat. We conclude that variation in fish assemblages among sites can be explained by features of the benthic habitat, but more importantly the absence of specific attributes may impact fish trophic groups differently.
In 2017, the Jupiter InfraRed Auroral Mapper (JIRAM), on board the NASA-ASI Juno mission, observed a wide longitude region (50° W-80° E in System III) that was perturbed by a wave pattern centered at ...15° N in the Jupiter's North Equatorial Belt (NEB). We analyzed JIRAM data acquired on 2017 July 10 using the M-channel and on 2017 February 2 with the spectrometer. The two observations occurred at different times and at slightly different latitudes. The waves appear as clouds blocking the deeper thermal emission. The wave crests are oriented north-south, and the typical wave packet contains 10 crests and 10 troughs. We used Fourier analysis to rigorously determine the wavenumbers associated with the observed patterns at a confidence level of 90%. Wavelet analysis was also used to constrain the spatial localization of the largest energies involved in the process and determine the wavelengths carrying the major contribution. We found wavelengths ranging from 1400 to 1900 km, and generally decreasing toward the west. Where possible, we also computed a vertical location of the cloud pressure levels from the inversion of the spectral radiances measured by the JIRAM spectrometer. The waves were detected at pressure levels consistent with the NH3 as well as NH4SH clouds. Phase velocities could not be determined with sufficient confidence to discriminate whether the alternating crests and troughs are a propagating wave or a manifestation of a fluid dynamical instability.
The Jovian InfraRed Auroral Mapper, JIRAM, is an image-spectrometer onboard the NASA Juno spacecraft flying to Jupiter. The instrument has been designed to study the aurora and the atmosphere of the ...planet in the spectral range 2–5 μm. The very first scientific observation taken with the instrument was at the Moon just before Juno’s Earth fly-by occurred on October 9, 2013. The purpose was to check the instrument regular operation modes and to optimize the instrumental performances. The testing activity will be completed with pointing and a radiometric/spectral calibrations shortly after Jupiter Orbit Insertion. Then the reconstruction of some Moon infrared images, together with co-located spectra used to retrieve the lunar surface temperature, is a fundamental step in the instrument operation tuning. The main scope of this article is to serve as a reference to future users of the JIRAM datasets after public release with the NASA Planetary Data System.
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•Modeling of Titan visible and NIR surface spectrum.•Spectra of Titan terrains in visible are shifted depending on the humidity.•Spectral shift and brightness appears correlated.
...Titan is an icy satellite of Saturn with a dense atmosphere and covered by a global photochemical organic haze. Ground based observations and the Huygens descent probe allowed to retrieve the main spectral signature of the water ice (Griffith, C.A. et al. 2003. Science 300(5619), 628–630; Coustenis, A. et al. 2005. Icarus 177, 89–105) at the surface, possibly covered by a layer of sedimented organic material (Tomasko, M.G. et al. 2005. Nature 438(7069), 765–778). However, the spectrum of the surface is not yet understood. In this study, we find that the surface reflectivity at the Huygens Landing Site (HLS) is well modeled by a layer of water ice grains overlaid by a moist layer of weakly compacted photochemical aggregated aerosols. Moist soils have spectra shifted toward short wavelengths relatively to spectra of dry soils. Cassini observations of Shangri-La region from orbit also show a very dark surface with a reflectivity peak shifted toward short wavelengths in respect to the reflectivity peak of bright surfaces, revealing a dichotomy between terrains based to their spectra in visible.
Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the ...acquired images and spectra confirmed a significant presence of methane (CH4) near both poles through its 3.3 μm emission overlapping the H3+ auroral feature at 3.31 μm. Neither acetylene (C2H2) nor ethane (C2H6) have been observed so far. The analysis method, developed for the retrieval of H3+ temperature and abundances and applied to the JIRAM‐measured spectra, has enabled an estimate of the effective temperature for methane peak emission and the distribution of its spectral contribution in the polar regions. The enhanced methane inside the auroral oval regions in the two hemispheres at different longitude suggests an excitation mechanism driven by energized particle precipitation from the magnetosphere.
Key Points
Evidence of diffuse CH4 emission inside the northern and southern Jupiter auroral ovals
Detailed maps of the distribution of the CH4 emission are obtained for both poles
Estimated rotational temperatures of the CH4 emission are about 500 K for the north pole and 650 K for the south pole
We investigate the variability of the power emission of Io’s hotspots by using recent Juno/JIRAM infrared observations. The Jovian Infrared Auroral Mapper (JIRAM) is an imaging spectrometer which ...began observing Jupiter in August 2016. Although observing Jupiter’s moons is not its primary objective, JIRAM can use the frequent opportunities to observe Io (up to once per orbit) to gather infrared images and spectra of its surface. The present study uses the data acquired by JIRAM during the last 2 years, including the location and morphology of Io’s hotspots, and the temporal variability of the total output. A new photometric model for the hotspots and the dayside surface has been developed, which permits us to disentangle the temporal variability from the changes in the observation geometry. While the latitudinal dependence of the power output is not well constrained, low-latitude hotspots show a significantly more intense temporal variability and greater temperature.
We observed the evolution of Jupiter's polar cyclonic structures over two years between February 2017 and February 2019, using polar observations by the Jovian InfraRed Auroral Mapper, JIRAM, on the ...Juno mission. Images and spectra were collected by the instrument in the 5‐μm wavelength range. The images were used to monitor the development of the cyclonic and anticyclonic structures at latitudes higher than 80° both in the northern and the southern hemispheres. Spectroscopic measurements were then used to monitor the abundances of the minor atmospheric constituents water vapor, ammonia, phosphine, and germane in the polar regions, where the atmospheric optical depth is less than 1. Finally, we performed a comparative analysis with oceanic cyclones on Earth in an attempt to explain the spectral characteristics of the cyclonic structures we observe in Jupiter's polar atmosphere.
Plain Language Summary
The Jovian InfraRed Auroral Mapper (JIRAM) is an instrument on‐board the Juno NASA spacecraft. It consists of an infrared camera, for mapping both Jupiter's auroras and atmosphere, and a spectrometer. In February 2017, the complex cyclonic structures that characterize the Jupiter's polar atmospheres were discovered. Here, we report the evolution of those cyclonic structures during the 2 years following the discovery. We use for this purpose infrared maps built by the JIRAM camera images collected at wavelengths around 5 μm. The cyclones have thick clouds that obstruct most of the view of the deeper atmosphere. However, some areas, near the cyclones, are only covered by thin clouds allowing the spectrometer to see deeper in the atmosphere. In those areas, the instrument was able to detect spectral signatures that permitted estimation of abundances of water vapor, ammonia, phosphine, and germane. Those gases are minor but significant constituents of the atmosphere. Finally, the dynamics of the Jupiter's polar atmosphere are not well understood and are still under study. Here, to suggest possible mechanisms that governs the polar dynamics, we attempted a comparative analysis with some Earth oceanic cyclones that show similarities with the Jupiter ones.
Key Points
The Jupiter's polar cyclonic structures did not change much in two years of observations from February 2017 to February 2019
Abundances of some atmospheric minor constituents measured in the hottest spots of the polar regions, higher values registered in the south
Earth oceanic cyclones analogies suggest a well‐mixed upper boundary layer on Jupiter's Poles
The Jovian InfraRed Auroral Mapper (JIRAM) on board the NASA Juno spacecraft is a dual‐band imager and spectrometer in the 2–5 μm range with 9‐nm spectral sampling, primarily designed to study the ...Jovian atmosphere and aurorae. In addition to these goals, JIRAM is used to obtain images and spectra of the Galilean satellites, every time the spacecraft attitude is favorable. Here we present JIRAM images and spectra of Ganymede obtained during the first 4 years of the mission. In particular, on 26 December 2019, during a relatively close passage of Juno with the moon, a dedicated reorientation of the spacecraft was performed to achieve optimized observations of Ganymede by Juno's remote sensing instruments, including JIRAM. In the outbound phase of the flyby, observing the northern polar regions of Ganymede at a distance of roughly 100,000 km, JIRAM collected infrared images and spectra of the surface at a spatial resolution as high as 23 km per pixel, covering high northern latitudes that were scarcely mapped previously. A photometric model of Ganymede reflectance is produced, which diverges from the Lambert model. The spatial distribution of the obtained spectra complements the available coverage of the surface, with particular regard to the 2.0‐µm water ice absorption band and, to a lesser extent, to the 4.26‐µm spectral feature diagnostic of CO2 trapped in water ice. The water ice distribution is compatible with sputtered‐induced water ice grain enrichment at high latitude (>45°). Several minor species (hydrated salts, trapped H2, CO2, and acids) are also identified in the measured spectra.
Plain Language Summary
The Jovian Infrared Auroral Mapper (JIRAM) is a dual‐band imager and spectrometer on the NASA Juno spacecraft. It works in the range of 2–5 μm and its spectral sampling is 9 nm. JIRAM is mainly used to study the Jovian atmosphere and aurora. JIRAM is also used to obtain images and spectra of the moons of Jupiter, every time the spacecraft has a favorable attitude. Here, we show Ganymede images and spectra obtained during the first 4 years of the mission. On 26 December 2019, during a close passage of Juno to Ganymede, JIRAM observed it at a distance of approximately 100,000 km. In this occasion, JIRAM collected infrared images and surface spectra with a spatial resolution of up to 23 km per pixel. This data covers North polar regions that were not mapped before. A photometric model of Ganymede's reflectance was produced, and it is different from the Lambert model. The spatial distribution of the obtained spectrum can supplement the available coverage of the surface, especially for the 2.0 µm water ice absorption band. At high latitudes (>45°), the distribution of water ice is compatible with the enrichment of water ice particles induced by sputtering. Several minor species (hydrated salts, trapped H2, CO2, and acids) were also identified in the measured spectra.
Key Points
Water ice distribution for previously unmapped regions
Latitudinal variability of CO2 spectral feature
New photometric model for Ganymede reflectance
In this work, we present the detection of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ emissions in the equatorial atmosphere of Jupiter as two well‐separated layers located, respectively, at tangent altitudes ...of about 200 and 500–600 km above the 1‐bar level using the observations of the Jovian InfraRed Auroral Mapper (JIRAM), on board Juno. This provides details of the vertical distribution of H3+ ${\mathrm{H}}_{3}^{+}$ retrieving its Volume Mixing Ratio (VMR), concentration, and temperature. The thermal profile obtained from H3+ ${\mathrm{H}}_{3}^{+}$ shows a peak of 600–800 K at about 550 km, with lower values than the ones reported in Seiff et al. (1998), https://doi.org/10.1029/98JE01766 above 500 km using VMR and temperature as free parameters and above 650 km when VMR is kept fixed with that model in the retrieval procedure. The observed deviations from the Galileo's profile could potentially point to significant variability in the exospheric temperature with time. We suggest that vertically propagating waves are the most likely explanation for the observed VMR and temperature variations in the JIRAM data. Other possible phenomena could explain the observed evidence, for example, dynamic activity driving chemical species from lower layers toward the upper atmosphere, like the advection‐diffusion processes, or precipitation by soft electrons, although better modeling is required to test these hypothesis. The characterization of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ species, simultaneously observed by JIRAM, offers the opportunity for better constraining atmospheric models of Jupiter at equatorial latitudes.
Plain Language Summary
The Jovian Infrared Auroral Mapper (JIRAM) is the infrared imager and spectrometer on board the Juno mission, designed to investigate Jupiter's atmosphere. A key objective of JIRAM is the investigation of the minor species, such as CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ that are very important to understanding the energy balance of the middle and upper atmosphere of Jupiter. These species have strong signatures in the 3.3–3.8 μm spectral region, well within the nominal wavelength range of the instrument. We present the analysis of recent images and spectra obtained by JIRAM, in the period December 2018–September 2020, plus additional measurements in March 2017, to study methane and H3+ ${\mathrm{H}}_{3}^{+}$ vertical distribution at equatorial latitudes. We find that CH4 is localized around 200 km above the 1‐bar level, while a distinct layer of H3+ ${\mathrm{H}}_{3}^{+}$ is observed around 500–600 km (0.04–0.016 μbar). The observed vertical distribution and intensity variation of H3+ ${\mathrm{H}}_{3}^{+}$ is likely to be the result of vertically propagating waves. However, other possible phenomena can be invoked to explain these findings, like for example, an uplifting of chemical species from lower layers toward the upper atmosphere, or soft electrons precipitation, although a rigorous modeling is needed to confirm the latter hypothesis.
Key Points
Detection of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ emissions over Jupiter's disc as two well separated layers in the equatorial region at 200 and 600 km
The H3+ ${\mathrm{H}}_{3}^{+}$ temperature profile shows a peak of 600–800 K at about 600 km with some differences with respect to the Galileo's profile
The observed features point out the presence of localized variability with altitude, perhaps indicative of wave activities
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