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
In this study we map the methane gas in the Martian atmosphere. The main goal of this work is to show the methane behaviour across the planet seasonally. To this aim, we analyze the strongest methane ...band in the short wavelength channel of the Planetary Fourier Spectrometer (PFS) on board ESA Mars Express (MeX) spacecraft. The optical line depth is used to derive the column density of methane. The maps thus obtained show the spatial variability of this non-condensable gas and how the gas is transported in the atmosphere due to the cycle of carbon dioxide. Moreover, the increase of methane over the north polar cap during local summer, which cannot be explained by global circulation, strongly suggests that there could be methane reservoir associated with the polar cap.
The study of extrasolar planets and of the Solar System provides complementary pieces of the mosaic represented by the process of planetary formation. Exoplanets are essential to fully grasp the huge ...diversity of outcomes that planetary formation and the subsequent evolution of the planetary systems can produce. The orbital and basic physical data we currently possess for the bulk of the exoplanetary population, however, do not provide enough information to break the intrinsic degeneracy of their histories, as different evolutionary tracks can result in the same final configurations. The lessons learned from the Solar System indicate us that the solution to this problem lies in the information contained in the composition of planets. The goal of the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL), one of the three candidates as ESA M4 space mission, is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres, which should show minimal condensation and sequestration of high-Z materials and thus reveal their bulk composition across all main cosmochemical elements. In this work we will review the most outstanding open questions concerning the way planets form and the mechanisms that contribute to create habitable environments that the compositional information gathered by ARIEL will allow to tackle.
Discovery of CH4 in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH4 and its temporal ...and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH4 by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2∘) in the northern hemisphere on Mars. The high altitude of SOFIA (~13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH4 lines because it reduces the impact of telluric CH4 on Martian CH4, and allows us to use CH4 lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH4. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH4 volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH4 on Mars is sporadic and/or localized if the process is present.
We characterize the origin and evolution of a mesoscale wave pattern in Jupiter's North Equatorial Belt (NEB), detected for the first time at 5
m using a 2016-17 campaign of "lucky imaging" from the ...VISIR instrument on the Very Large Telescope and the NIRI instrument on the Gemini observatory, coupled with
-band imaging from Juno's JIRAM instrument during the first seven Juno orbits. The wave is compact, with a 1°.1-1°.4 longitude wavelength (wavelength 1300-1600 km, wavenumber 260-330) that is stable over time, with wave crests aligned largely north-south between 14°N and 17°N (planetographic). The waves were initially identified in small (10° longitude) packets immediately west of cyclones in the NEB at 16°N but extended to span wider longitude ranges over time. The waves exhibit a 7-10 K brightness temperature amplitude on top of an ∼210 K background at 5
m. The thermal structure of the NEB allows for both inertio-gravity waves and gravity waves. Despite detection at 5
m, this does not necessarily imply a deep location for the waves, and an upper tropospheric aerosol layer near 400-800 mbar could feature a gravity wave pattern modulating the visible-light reflectivity and attenuating the 5-
m radiance originating from deeper levels. Strong rifting activity appears to obliterate the pattern, which can change on timescales of weeks. The NEB underwent a new expansion and contraction episode in 2016-17 with associated cyclone-anticyclone formation, which could explain why the mesoscale wave pattern was more vivid in 2017 than ever before.
One of the auroral features of Jupiter is the emission associated with the orbital motion of its moon Io. The relative velocity between Io and the surrounding plasma trigger perturbations that ...travels as Alfvén waves along the magnetic field lines toward the Jovian ionosphere. These waves can accelerate electrons into the atmosphere and ultimately produce an auroral emission, called the Io footprint. The speed of the Alfvén waves—and hence the position of the footprint—depends on the magnetic field and on the plasma distribution along the field line passing through Io, whose SO2‐rich atmosphere is the source of a dense plasma torus around Jupiter. Since 2016, the Jovian InfraRed Auroral Mapper (JIRAM) onboard Juno has been observing the Io footprint with a spatial resolution of ∼few tens of km/pixel. JIRAM detected evidences of variability in the Io footprint position that are not dependent on the System III longitude of Io. The position of the Io footprint in the JIRAM images is compared with the position predicted by a model of the Io Plasma Torus and of the magnetic field. This is the first attempt to retrieve quantitative information on the variability of the torus by looking at the Io footprint. The results are consistent with previous observations of the density and temperature of the Io Plasma Torus. However, we found that the plasma density and temperature exhibit considerable non‐System III variability that can be due either to local time asymmetry of the torus or to its temporal variability.
Key Points
Juno‐JIRAM detected evidence of variability in the Io footprint that are not related to the System III longitude of Io
Quantitative information on the state of the Io Plasma Torus and its variability are inferred from the Io footprint position
The Io Plasma Torus electron density varies between <2,000 and ∼2,750 cm−3, while the thermal ion temperature varies between 40–100 eV
During the first perijove passage of the Juno mission, the Jovian InfraRed Auroral Mapper (JIRAM) observed a line of closely spaced oval features in Jupiter's southern hemisphere, between 30°S and ...45°S. In this work, we focused on the longitudinal region covering the three ovals having higher contrast at 5 μm, i.e., between 120°W and 60°W in System III coordinates. We used the JIRAM's full spectral capability in the range 2.4–3 μm together with a Bayesian data inversion approach to retrieve maps of column densities and altitudes for an NH3 cloud and an N2H4 haze. The deep (under the saturation level) volume mixing ratio and the relative humidity for gaseous ammonia were also retrieved. Our results suggest different vortex activity for the three ovals. Updraft and downdraft together with considerations about the ammonia condensation could explain our maps providing evidences of cyclonic and anticyclonic structures.
Key Points
JIRAM data from first Juno orbit highlighted the presence of several ovals in Jupiter's southern hemisphere
Column densities and altitudes for an NH3 cloud and an N2H4 haze have been retrieved for three ovals in the region between 60–120°W and 30–45°S
Evidences of cyclonic and anticyclonic structures inside the ovals have been found
Abstract
A stellar occultation occurs when a Solar System object passes in front of a star for an observer. This technique allows the sizes and shapes of the occulting body to be determined with ...kilometer precision. In addition, this technique constrains the occulting body’s positions, albedos, densities, and so on. In the context of the Galilean moons, these events can provide their best ground-based astrometry, with uncertainties in the order of 1 mas (∼3 km at Jupiter’s distance during opposition). We organized campaigns and successfully observed a stellar occultation by Io (JI) in 2021, one by Ganymede (JIII) in 2020, and one by Europa (JII) in 2019, with stations in North and South America. We also re-analyzed two previously published events: one by Europa in 2016 and another by Ganymede in 2017. We then fit the known 3D shape of the occulting satellite and determine its center of figure. This resulted in astrometric positions with uncertainties in the milliarcsecond level. The positions obtained from these stellar occultations can be used together with dynamical models to ensure highly accurate orbits of the Galilean moons. These orbits can help when planning future space probes aiming at the Jovian system, such as JUICE by ESA and Europa Clipper by NASA. They also allow more efficient planning of flyby maneuvers.
LARES 2 is an Italian Space Agency (ASI) satellite designed for testing with unprecedented accuracy frame-dragging, a fundamental prediction of general relativity, for other tests of fundamental ...physics and to contribute to space geodesy with a precision higher than any other satellite presently in orbit. The choice of the material for the body of LARES 2 satellite determines, along with its dimensions, the surface-to-mass ratio minimization, which is the main requirement for the satellite. The paper will report the studies conducted for the fulfillment of the above-mentioned requirement and the tests performed to qualify the materials for construction of the satellite.
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