In the history of Mars exploration its atmosphere and planetary climatology aroused particular interest. In the study of the minor gases abundance in the Martian atmosphere, water vapour became ...especially important, both because it is the most variable trace gas, and because it is involved in several processes characterizing the planetary atmosphere. The water vapour photolysis regulates the Martian atmosphere photochemistry, and so it is strictly related to carbon monoxide. The CO study is very important for the so-called “atmosphere stability problem”, solved by the theoretical modelling involving photochemical reactions in which the H
2O and the CO gases are main characters.
The Planetary Fourier Spectrometer (PFS) on board the ESA Mars Express (MEX) mission can probe the Mars atmosphere in the infrared spectral range between 200 and 2000
cm
−1 (5–50
μm) with the Long Wavelength Channel (LWC) and between 1700 and 8000
cm
−1 (1.2–5.8
μm) with the Short Wavelength Channel (SWC). Although there are several H
2O and CO absorption bands in the spectral range covered by PFS, we used the 3845
cm
−1 (2.6
μm) and the 4235
cm
−1 (2.36
μm) bands for the analysis of water vapour and carbon monoxide, respectively, because these ranges are less affected by instrumental problems than the other ones. The gaseous concentrations are retrieved by using an algorithm developed for this purpose.
The PFS/SW dataset used in this work covers more than two and a half Martian years from Ls=62° of MY 27 (orbit 634) to Ls=203° of MY 29 (orbit 6537). We measured a mean column density of water vapour of about 9.6
pr. μm and a mean mixing ratio of carbon monoxide of about 990
ppm, but with strong seasonal variations at high latitudes. The seasonal water vapour map reproduces very well the known seasonal water cycle. In the northern summer, water vapour and CO show a good anticorrelation most of the time. This behaviour is due to the carbon dioxide and water sublimation from the north polar ice cap, which dilutes non-condensable species including carbon monoxide. An analogous process takes place during the winter polar cap, but in this case the condensation of carbon dioxide and water vapour causes an increase of the concentration of non-condensable species. Finally, the results show the seasonal variation of the carbon monoxide mixing ratio with the surface pressure.
► The mean concentrations of H
2O and CO are about 9.6
pr. μm and 990
ppm, respectively. ► H
2O and CO concentrations show a strong seasonal variations at high latitudes. ► The seasonal water vapour map reproduces the known seasonal water cycle. ► H
2O and CO respond in opposite way to polar caps condensing/sublimating processes. ► The seasonal variation of CO concentration depends on the surface pressure.
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.
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, 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.
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
.
Frame-dragging, one of the outstanding phenomena predicted by General Relativity, is efficiently studied by means of the laser-ranged satellites LARES, LAGEOS and LAGEOS 2. The accurate analysis of ...the orbital perturbations of Earth’s solid and ocean tides has been relevant for increasing the accuracy in the test of frame-dragging using these three satellites. The Earth’s tidal perturbations acting on the LARES satellite are obtained for the 110 significant modes of corresponding Doodson number and are exhibited to enable the comparison to those of the LAGEOS and LAGEOS-2 satellites. For LARES we represent 29 perturbation modes for
l
= 2, 3, 4 for ocean tides.
The electromagnetic coupling between the Galilean satellites at Jupiter and the planetary ionosphere generates an auroral footprint, which is detected with high spatial resolution in the infrared L ...band by the Jovian InfraRed Auroral Mapper (JIRAM) onboard the Juno spacecraft. We report the JIRAM data acquired since 27 August 2016 until 23 May 2022, which are used to compute the average position of the footprint tracks of Io, Europa and Ganymede. The result of the present analysis help to test the reliability of magnetic field models, to calibrate ground‐based observations and to highlight the variability in the footprint positions, which can be used to probe the plasma environment at the orbit of the satellites. The determination of the plasma properties around the moons is particularly relevant to complement the Juno flybys of the moons during its extended mission, and to support the future Juice and Europa Clipper missions. Lastly, we report no clear evidence of the auroral footprint of Callisto, which is likely due to a combination of its low expected brightness and its position very close to the main Jovian aurora.
Plain Language Summary
The Jovian InfraRed Auroral Mapper onboard the Juno spacecraft around Jupiter has now been gathering 6 years of observations. Here, we report the position of the auroral infrared emission associated with the orbital motion of Io, Europa and Ganymede. The position of this emission ‐ called footprint ‐ carries information on the magnetic field geometry and the distribution of charged particles along the magnetic field. Therefore, the footprint tracks provided here can be used to test and constrain magnetic field models, and to improve the calibration of ground based observations of Jupiter: this can help better understand the source region of the main Jovian aurora and its variations. Lastly, by surveying the data acquired over 40 Juno orbits, we point out variations in the footprint position, which reflect the variability in the plasma conditions near the moons: this monitoring may help determine the mass loading of the magnetosphere, which affects the intensity of the main aurora. The possibility of investigating the plasma environment at the orbit of the satellites is important to complement the satellite flybys performed during the extended mission of Juno and to support the future Juice and Europa Clipper missions, which are dedicated to the Galilean moons.
Key Points
The position of the Io, Europa and Ganymede footprints based on Juno‐JIRAM observations are reported with unprecedented spatial resolution
The positions of the footprints support the Juno‐based magnetic field models and the calibration of ground‐based observation
The transversal shift of the Ganymede footprint suggests variations of the plasmadisk; the shift appears to be correlated with local time
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