Context. Studying the coma environment of comet 67P/Churyumov-Gerasimenko (67P) is one of the primary scientific goals of the VIRTIS experiment on the ESA Rosetta mission. Aims. The distribution and ...variability of water vapour and carbon dioxide in the comet’s coma are needed to estimate their production rate, abundances in the nucleus, and the spatial distribution of the active regions. Methods. Infrared emission lines from vibrational bands of water and carbon dioxide at 2.67 and 4.27 μm, respectively, were observed by the VIRTIS-M imaging channel and mapped from close to the nucleus up to ~10 km altitude with a resolution of ~40 m/px. A dataset consisting of 74 observations in the 1−5 μm spectral range acquired from 8 to 14 April 2015 when 67P was at a heliocentric distance of 1.9 AU is analysed in this work. A statistical correlation between the gas distribution and the surface’s active regions was performed. Results. The maximum H2O emission is observed within 3 km from the nucleus and is mainly concentrated above two active regions, Aten-Babi and Seth-Hapi, while the CO2 distribution appears more uniform with significant emissions coming from both the “head” and southern latitude regions. In the equatorial region, the column densities of both species decrease with altitude, although CO2 decreases more rapidly than H2O. The calculated CO2/H2O column density ratios above Aten-Babi and Seth-Hapi are 2.4 ± 0.6% and 3.0 ± 0.7%, respectively. A value equal to 3.9 ± 1.0% is observed at equatorial latitudes in the region encompassing Imothep. Conclusions. VIRTIS-M has mapped the distribution of water vapour and carbon dioxide around the nucleus of 67P with unprecedented spatial resolution. The different water and carbon dioxide outgassing above the surface, seen in the VIRTIS-M data, might be indicative of a different thermal history of the northern and southern hemispheres of 67P.
Jupiter's aurorae are produced in its upper atmosphere when incoming high-energy electrons precipitate along the planet's magnetic field lines. A northern and a southern main auroral oval are ...visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street. Well downstream of the main auroral spots the extended tail is split in two. Both of Ganymede's footprints also appear as a pair of emission features, which may provide a remote measure of Ganymede's magnetosphere. These features suggest that magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.
In this work, we present the most updated catalog of Io hot spots based on Juno/JIRAM data. We find 242 hot spots, including 23 previously undetected. Over the half of the new hot spots identified, ...are located at high northern and southern latitudes (>70°). We observe a latitudinal variability and a larger concentration of hot spots in the polar regions, in particular in the North. The comparison between JIRAM and the most recent Io hot spot catalogs listing power output (Veeder et al., 2015, https://doi.org/10.1016/j.icarus.2014.07.028; de Kleer, de Pater, et al., 2019, https://doi.org/10.3847/1538-3881/ab2380), shows JIRAM detected 63% and 88% of the total number of hot spots, respectively. Furthermore, JIRAM observed 16 of the 34 faint hot spots previously identified. JIRAM data revealed thermal emission from 5 dark pateræ inferred to be active from color ratio images, thus confirming that these are hot spots.
Plain Language Summary
We mapped the hot spot distribution on Io's surface by analyzing the images acquired by the JIRAM instrument onboard the Juno spacecraft. We identified 242 hot spots, including 23 not present in other catalogs. A large number of the new hot spots identified are in the polar regions, specifically in the northern hemisphere. The comparison between our work and the most recent and updated catalog reveals that JIRAM detected 82% of the most powerful hot spots previously identified and half of the intermediate‐power hot spots, thus showing that these are still active. JIRAM detected 16 out of the 34 faint hot spots previously reported. The resolution of JIRAM may not have been sufficient to detect these faint hot spots, or activity might have faded or stopped.
Key Points
We produced a new Io hot spot map based on Juno/JIRAM data
We identified 242 hot spots, including 23 previously undetected
The latitudinal hot spot distribution is uneven with a larger concentration at the poles
The familiar axisymmetric zones and belts that characterize Jupiter's weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. Two-dimensional turbulence in ...combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows. The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur. Simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. Jovian polar regions are not visible from Earth owing to Jupiter's low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter's equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn's polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown.
Context. Since its rendezvous with comet 67P/Churyumov-Gerasimenko (67P), the Rosetta spacecraft has provided invaluable information contributing to our understanding of the cometary environment. On ...board, the VIRTIS and ROSINA instruments can both measure gas parameters in the rarefied cometary atmosphere, the so-called coma, and provide complementary results with remote sensing and in situ measurement techniques, respectively. The data from both ROSINA and VIRTIS instruments suggest that the source regions of H2O and CO2 are not uniformly distributed over the surface of the nucleus even after accounting for the changing solar illumination of the irregularly shaped rotating nucleus. The source regions of H2O and CO2 are also relatively different from one another. Aims. The use of a combination of a formal numerical data inversion method with a fully kinetic coma model is a way to correlate and interpret the information provided by these two instruments to fully understand the volatile environment and activity of comet 67P. Methods. In this work, the nonuniformity of the outgassing activity at the surface of the nucleus is described by spherical harmonics and constrained by ROSINA-DFMS data. This activity distribution is coupled with the local illumination to describe the inner boundary conditions of a 3D direct simulation Monte-Carlo (DSMC) approach using the Adaptive Mesh Particle Simulator (AMPS) code applied to the H2O and CO2 coma of comet 67P. Results. We obtain activity distribution of H2O and CO2 showing a dominant source of H2O in the Hapi region, while more CO2 is produced in the southern hemisphere. The resulting model outputs are analyzed and compared with VIRTIS-M/-H and ROSINA-DFMS measurements, showing much better agreement between model and data than a simpler model assuming a uniform surface activity. The evolution of the H2O and CO2 production rates with heliocentric distance are derived accurately from the coma model showing agreement between the observations from the different instruments and ground-based observations. Conclusions. We derive the activity distributions for H2O and CO2 at the surface of the nucleus described in spherical harmonics, which we couple to the local solar illumination to constitute the boundary conditions of our coma model. The model presented reproduces the coma observations made by the ROSINA and VIRTIS instruments on board the Rosetta spacecraft showing our understanding of the physics of 67P’s coma. This model can be used for further data analyses, such as dust modeling, in a future work.
The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the ...H3+ infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. The extended Io “tail” persists for ~3 h after the passage of the satellite flux tube. Multi‐arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3+ emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions.
Key Points
Detailed observation of a very long tail of the Io magnetic footprint
Identification of thin multiple arc structures in the northern and southern ovals, and of bright spots and depletion in the south pole
Filamentation of alternatively upward and downward current in the 0°–90° SIII sector in the north
Aeronomy of the Venus Upper Atmosphere Gérard, J.-C.; Bougher, S. W.; López-Valverde, M. A. ...
Space science reviews,
11/2017, Letnik:
212, Številka:
3-4
Journal Article, Web Resource
Recenzirano
Odprti dostop
We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on ...VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus’ upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O
2
nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons.
The paper is devoted to the investigation of Venus mesosphere circulation at 90–110 km altitudes, where tracking of the O2(a1Δg) 1.27 μm nightglow is practically the only method of studying the ...circulation. The images of the nightglow were obtained by VIRTIS‐M on Venus Express over the course of more than 2 years. The resulting global mean velocity vector field covers the nightside between latitudes 75°S–20°N and local time 19–5 h. The main observed mode of circulation is two opposite flows from terminators to midnight; however, the wind speed in the eastward direction from the morning side exceeds the westward (evening) by 20–30 m/s, and the streams “meet” at 22.5 ± 0.5 h. The influence of underlying topography was suggested in some cases: Above mountain regions, flows behave as if they encounter an “obstacle” and “wrap around” highlands. Instances of circular motion were discovered, encompassing areas of 1,500–4,000 km.
Plain Language Summary
Recent developments in the studies of Venus atmosphere reveal an intriguing phenomenon of stationary gravity waves, which emerge from the surface, interacting with the cloud layer up to ~70 km. In this paper, analysis of the oxygen nightglow on the nightside of Venus using data from VIRTIS instrument (Venus Express spacecraft) delivers clues that the atmosphere at 90–110 km altitude can as well be influenced by such mechanisms. The horizontal motion, obtained from tracking the displacements of the bright features of the nightglow, appears to hold disturbances, the positions of which in some cases coincide with highlands directly below or shifted by several degrees. The nightglow itself, known to manifest an extremely irregular behavior, sometimes repeats the shapes of the mountain ranges below. As another major result, the mean horizontal circulation, calculated for the nightside southern hemisphere, does represent neither superrotation, nor subsolar‐to‐antisolar circulation, nor a superposition of the two. Both the zonal and the meridional components of the motion have different magnitudes and direction before and after midnight. The results of this research further our knowledge on the upper atmosphere of Venus and pose a challenge for the global circulation models.
Key Points
The horizontal wind velocity in Venus atmosphere at 90–110 km was obtained from the O2(a1Δg) nightglow tracking
Average zonal component from the morning side exceeds its opposite from the evening side by 20–30 m/s; they “meet” at 22–23 h local time
The influence of the underlying topography on the wind direction was suggested in some cases
•Radiative forcing of Venus’ atmosphere is studied based on VEX data.•Cooling strongly responds to atmospheric parameter changes, heating is less sensitive.•Atmospheric net heating dominates the low ...and mid latitudes above 80km.•Atmospheric net cooling prevails at high latitudes at all mesospheric altitudes.•Venus’ atmosphere at 0–90km is not far away from radiative equilibrium.
The distribution of sources and sinks of radiative energy forces the atmospheric dynamics. The radiative transfer simulation model described by Haus et al. (2015b) is applied to calculate fluxes and temperature change rates in the middle and lower atmosphere of Venus (0–100km) covering the energetic significant spectral range 0.125–1000µm. The calculations rely on improved models of atmospheric parameters (temperature profiles, cloud parameters, trace gas abundances) retrieved from Venus Express (VEX) data (mainly VIRTIS-M-IR, but also VeRa and SPICAV/SOIR with respect to temperature results). The earlier observed pronounced sensitivity of the radiative energy balance of Venus to atmospheric parameter variations is confirmed, but present detailed comparative analyses of possible influence quantities ensure unprecedented insights into radiative forcing on Venus by contrast with former studies.
Thermal radiation induced atmospheric cooling rates strongly depend on temperature structure and cloud composition, while heating rates are mainly sensitive to insolation conditions and UV absorber distribution. Cooling and heating rate responses to trace gas variations and cloud mode 1 abundance changes are small, but observed variations of cloud mode 2 abundances and altitude profiles reduce cooling at altitudes 65–80km poleward of 50°S by up to 30% compared to the neglect of cloud parameter changes. Cooling rate variations with local time below 80km are in the same order of magnitude.
Radiative effects of the unknown UV absorber are modeled considering a proxy that is based on a suitable parameterization of optical properties, not on a specific chemical composition, and that is independent of the used cloud model. The UV absorber doubles equatorial heating near 68km. Global average radiative equilibrium at the top of atmosphere (TOA) is characterized by the net flux balance of 156W/m2, the Bond albedo of 0.76, and the effective planetary emission temperature of 228.5K in accordance with earlier results. TOA radiative equilibrium can be achieved by slight adjustments of either UV absorber or cloud mode abundances. Ratios of synthetic spectral albedo values at 0.36µm calculated for different abundance factors of the UV absorber are suggested to provide a possible tool to interpret observed VMC/VEX brightness variations with respect to actual absorber abundances.
Atmospheric net heating dominates the low and mid latitudes above 82km, while net cooling prevails at high latitudes at all mesospheric altitudes (60–100km). This radiative forcing field has to be balanced by dynamical processes to maintain the observed thermal structure. A similar but much smaller meridional gradient is also observed at altitudes between 62 and 72km where the unknown UV absorber provides additional heating. At these altitudes, equatorial net heating dominates net cooling from about 07:30h until 16:30h local time. Intermediate altitudes (72–82km) are characterized by net cooling at all latitudes in case of VIRTIS temperature data. This planet-wide net cooling region is not observed when calculations are based on VeRa temperatures, and low latitudes are then characterized by small net heating. When a warm atmospheric layer as detected by SPICAV/SOIR around 100km is considered, strong global average net cooling occurs above 90km that is far away from radiative equilibrium. A weak net cooling layer (1–2K/day) exists at altitudes between 55 and 60km, while very weak net heating (0.1–0.5K/day) takes place near the cloud base (48km). Almost zero net heating prevails in the deep atmosphere below 44km. On global average, the entire atmosphere of Venus at altitudes between 0 and 90km is not far away from radiative equilibrium (usually within±2K/day).
Maximum temperature change rate deviations from mean values at each altitude and latitude are defined based on retrieved atmospheric parameter single standard deviations using VIRTIS data. This is an important prerequisite to investigate parameterization approaches for the calculation of atmospheric temperature change rates that can be used in Global Circulation Models. This will be a major topic of future studies on radiative energy balance of Venus’ atmosphere.
This work aims to give a summary of the water vapor at the cloud top of Venus atmosphere using the complete set of observations made using high spectral resolution channel (-H) of Visible and ...Infrared Thermal Imaging Spectrometer (VIRTIS), on board the ESA Venus Express orbiter, to measure the cloud top altitude and the water vapor abundance near this level. An initial analysis of these measurements by Cottini et al. (2012) was limited to data in 140 orbits in the period 2007–2008. These observations were limited to the Northern hemisphere due to observational geometry in this early part of the mission. In the present paper, the analysis is extended to a larger dataset covering the years 2006–2011, significantly improving the latitudinal coverage. Altitude of the cloud tops, corresponding to unit optical depth at a wavelength of 2.5µm, is equal to 69±1km at low latitudes, and decreases toward the pole to 62–64km. The water vapor abundance is equal to 3±1ppm in low latitudes and it increases reaching a maximum of 5±2ppm at 70–80° of latitude in both hemispheres, with a sharp drop in the polar regions. This can be explained by the specific dynamics of the atmosphere of Venus affecting the distribution of water vapor such as the transfer of water vapor in the Hadley cell and the dynamic in the polar vortex. The average height of the cloud tops and the H2O near this level are symmetric with respect to the equator. As a function of local solar time, the water vapor shows no particular dependence, and the cloud tops exhibit just a weak maximum around noon. Over 5 years of observations the average values of the cloud top altitude and the water vapor were quite stable in low and middle latitudes, while in high latitudes both quantities in 2009–2011 years are systematically higher than in 2006–2008. Short period variations increasing with latitude are observed, from approximately less than ±1km for cloud tops and ±1ppm for water vapor in low latitudes to, respectively, ±2km and ±2ppm in high latitudes. As a rule there is no correlation between variations of the cloud top altitude, the water vapor content, and the UV brightness. However, numerous examples can be found when UV dark features, with a characteristic size of a few degrees of latitude (several hundred kilometers), coincide with regions of higher cloud tops.
•Water vapor abundance at the cloud tops of Venus with high spectral resolution.•Complete VIRTIS-H / Venus Express day-side dataset analyzed.•Better coverage in latitude shows cloud top heights and H2O symmetric around equator.•No considerable dependence on local time is observed.•Long term stability of water vapor at low latitudes with some variations over 60°.
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