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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

Like Earth, Jupiter has aurorae generated by energetic particles hitting its atmosphere. Those incoming particles can come from Jupiter's moons Io and Ganymede. Mura et al. used infrared observations from the Juno spacecraft to image the moon-generated aurorae. The pattern induced by Io showed an alternating series of spots, reminiscent of vortices, and sometimes split into two arcs. Aurorae related to Ganymede could also show a double structure. Although the cause of these unexpected features remains unknown, they may provide a way to examine how the moons produce energetic particles or how the particles propagate to Jupiter. Science , this issue p. 774 Auroral features induced on Jupiter by the moons Io and Ganymede have complex spatial structures. 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 the magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.

Visible and infrared images obtained from above each pole of Jupiter by the Juno spacecraft reveal polygonal patterns of large cyclones; it is unknown how these cyclones evolved, or how they persist without merging. Polygonal cyclones around Jupiter's poles Jupiter's colourful low-latitude weather bands turn into cyclones at high latitudes, but the polar region is not visible from Earth and was poorly characterized by previous spacecraft. Alberto Adriani and colleagues report visible and infrared observations of Jupiter's polar regions made by the Juno spacecraft, which is in a highly elliptical polar orbit. They find that the cyclones create persistent polygonal patterns. There are eight circumpolar cyclones rotating around a single cyclone in the north, while the South Polar Cyclone is circled by five such features. The authors do not know how these cyclones evolved to their current state or how they persist without merging. The familiar axisymmetric zones and belts that characterize Jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes 1 . 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 2 . The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur 3 , 4 . 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 5 , 6 , 7 , 8 , 9 . 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.

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.

Simultaneous observations of Venus by Visible and Infrared Thermal Imaging Spectrometer and Venus Monitoring Camera onboard the Venus Express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet (UV) markings. The cloud top altitude is retrieved from the depth of CO2 absorption band at 1.6 μm. In low and middle latitudes the cloud top is located at 74 ± 1 km. It decreases poleward of ±50° and reaches 63–69 km in the polar regions. This depression coincides with the eye of the planetary vortex. At the same latitude and hour angle, cloud top can experience fast variations of about 1 km in tens of hours, while larger long‐term variations of several kilometers have been observed only at high latitudes. UV markings correlate with the cloud altimetry, however, the difference between adjacent UV dark and bright regions does not exceed several hundred meters. Surprisingly, CO2 absorption bands are often weaker in the dark UV features, indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds. Ultraviolet dark spiral arms, which are often seen at about −70°, correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude. Cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in UV images. This implies that the UV optically thick polar hood is transparent in the near IR.

We report the first observation of the vertical and temporal structure of the H3+ emission at the auroral footprint of Io, as observed by Juno/JIRAM. The brightness vertical profile shows a maximum at 600 km above 1 bar, with no apparent difference between the main Alfvén wing (MAW) spot emission and the tail of the footprint. This observation better aligns with a broadband energy distribution of the precipitating electrons, instead of a monoenergetic one. The temporal profile of H3+ column density has been observed after the passage of the MAW and shows a hyperbolic decrease. A model of H3+ decay is proposed, which takes into account the second-order kinetics of dissociative recombination of H3+ ions with electrons. The model is found to be in very good agreement with Juno observations. The conversion factor from radiance to column density has been derived, as well as the half-life for H3+, which is not constant but inversely proportional to the H3+ column density. This explains the wide range of H3+ lifetimes proposed before.

Initial images of Venus's south pole by the Venus Express mission have shown the presence of a bright, highly variable vortex, similar to that at the planet's north pole. Using high-resolution infrared measurements of polar winds from the Venus Express Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument, we show the vortex to have a constantly varying internal structure, with a center of rotation displaced from the geographic south pole by ~3 degrees of latitude and that drifts around the pole with a period of 5 to 10 Earth days. This is indicative of a nonsymmetric and varying precession of the polar atmospheric circulation with respect to the planetary axis.

A whirling vortex has been observed in the atmosphere at the south pole of Venus. Cloud motions tracked by the Venus Express spacecraft suggest that the south polar vortex is long-lived, erratic and baroclinic in character. Polar vortices are common in the atmospheres of rapidly rotating planets 1 , 2 , 3 , 4 . On Earth and Mars, vortices are generated by surface temperature gradients and their strength is modulated by the seasonal insolation cycle 1 , 2 , 3 . Slowly rotating Venus lacks pronounced seasonal forcing, but vortices are known to occur at both poles, in an atmosphere that rotates faster than the planet itself 5 , 6 , 7 , 8 . Here we report observations of cloud motions at altitudes of 42 and 63 km above Venus’s south pole using infrared images from the VIRTIS instrument onboard the Venus Express spacecraft. We find that the south polar vortex is a long-lived but unpredictable feature. Within the two cloud layers sampled, the centres of rotation of the vortex are rarely aligned vertically and both wander erratically around the pole with velocities of up to 16 m s −1 . At the two horizontal levels, the observed cloud morphologies do not correlate with the vorticity of the wind field and change continuously, and vertical and meridional wind shears are also highly variable. We conclude that Venus’s south polar vortex is a continuously evolving structure that is at least 20 km high, extending through a quasi-convective turbulent region.

We present observations of both the (0–0) and (0–1) bands at 1.27 and 1.58 μm of the O2(a1Δg − X3Σg−) nightglow made with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument aboard Venus Express. The observations were conducted in both nadir and limb viewing modes, the latter constituting the first systematic investigation into the vertical distribution of the volume emission rate of the infrared oxygen nightglow in Venus' upper atmosphere. Limb measurements from 42 orbits covering the latitude range 7°S to 77°N are analyzed. The peak altitude of the volume emission rate occurs typically between 95 and 100 km, with a mean of 97.4 ± 2.5 km. The vertical profile is broader near the equator, with a full width at half maximum of 11 km, a factor 2 larger than at middle latitudes. A double peak is frequently observed, with the lower and upper peaks occurring near 96–98 km and 103–105 km, respectively. On average, the nightglow appears brightest in the vicinity of the antisolar point. This conclusion is consistent with past ground‐based observations and nadir measurements by VIRTIS. We mapped the global mean O2 nightglow intensity from VIRTIS data collected during 880 orbits. Patchy features of the nightglow intensity observed in nadir view are correlated with the thermal brightness at 4.23–4.28 μm. The observed positive correlation is consistent with downwelling (upwelling) of oxygen atoms accompanying compressional heating (expansion cooling) or with modulation by gravity waves. Finally, from simultaneous measurements of the 1.27 and 1.58 μm bands, we have estimated the ratio of the transition probabilities A00/A01 to be 63 ± 8.

The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)–X(v″) progression more than 3 decades ago. We search for its emission at 400 nm–700 nm in spectra obtained with the VIRTIS instrument on Venus Express. Despite the weakness of the signal, integration over a few hours of limb observations of the planet's upper atmosphere reveals the unambiguous pattern of the progression. The selected data sample mainly the northern latitudes within a few hours of local midnight. The emission is ubiquitous on the nightside of Venus and can be discerned at tangent altitudes from 80 km to 110 km. The average emission vertical profiles of the c(0)–X(v″) progression and the O2a(0)–X(0) band, the latter from simultaneous near‐infrared spectra, are quite similar, with their respective peaks occurring within ±1 km of each other. We conclude that the net yield for production of the c(0) state is low, ∼1%–2% of the oxygen recombination rate, and that O(3P) and CO2 are the two likely quenchers of the Herzberg II nightglow, although CO cannot be ruled out. We also derive a value of 2.45 × 10−16 cm3 s−1 for the rate constant at which CO2 collisionally quenches the c(0) state. Our VIRTIS spectra show hints of O2A′(0)–a(v″) emission but no traces of the O (1S–1D) green line at 557.7 nm.