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.
ABSTRACT
We analyse spectra measured by the Jovian Infrared Auroral Mapper (JIRAM, a payload element of the NASA Juno mission) in the 3150–4910 cm−1 (2.0–3.2 μm) range during the perijiove passage ...of 2016 August. Despite modelling uncertainties, the quality and the relative uniformity of the data set allow us to determine several parameters characterizing the Jupiter’s upper troposphere in the latitude range of 35°S–30°N. Ammonia relative humidity at 500 millibars varies between 5 per cent to supersaturation beyond 100 per cent for about 3 per cent of the processed spectra. Ammonia appears depleted over belts and relatively enhanced over zones. Local variations of ammonia, arguably associated with local dynamics, are found to occur in several locations on the planet (Oval BA, South Equatorial Belt). Cloud altitude, defined as the level where aerosol opacity reaches unit value at 3650 cm−1 (2.74 μm), is maximum over the Great Red Spot (>20 km above the 1 bar level) and the zones (15 km), while it decreases over the belts and towards higher latitudes. The aerosol opacity scale height suggests more compact clouds over zones and more diffuse clouds over belts. The integrated opacity of clouds above the 1.3-bar pressure level is found to be minimum in regions where thermal emission of the deeper atmosphere is maximum. The opacity of tropospheric haze above the 200-mbar level also increases over zones. Our results are consistent with a Hadley-type circulation scheme previously proposed in literature for belts and zones, with clear hemisphere asymmetries in cloud and haze.
ABSTRACT
The ESA mission Comet Interceptor will target an Oort or interstellar comet during its first approach to the Sun. Meanwhile, the Vera Rubin LSST Survey will observe hundreds of active comets ...per month beyond 4 au from the Sun, where water vapour pressure is expected to be too low to eject dust. We discuss observations of dust tails at heliocentric distances larger than 4 au in order to retrieve the physical parameters driving cometary activity beyond Jupiter by means of a probabilistic tail model, which is consistent with the activity model defining the gas coma parameters due to the sublimation of carbon monoxide, molecular oxygen, methane, ethane, and carbon dioxide since the activity onset at 85 au from the Sun. We find that: (i) All the observed dust tails are consistent with the adopted activity model; (ii) The tail fits depend on three free parameters only, all correlated to the nucleus size; (iii) Tail fits are always improved by anisotropic dust ejection, suggesting activity of Oort nuclei dominated by seasons; (iv) Inbound seasons suggest cometary activity before the ejection of protocomets into the Oort cloud, as predicted by the activity model; (v) Oort nuclei larger than 1 km may be characterized by a fallout up to ≈100 m thick deposited during ≈60 yr inbound; (vi) On the other side, Oort nuclei smaller than 1 km may appear more pristine than Jupiter Family Comets when observed at 1 au from the Sun.
The Jupiter InfraRed Auroral Mapper (JIRAM) instrument on board the Juno spacecraft performed observations of two bright Jupiter hot spots around the time of the first Juno pericenter passage on 27 ...August 2016. The spectra acquired in the 4–5 µm spectral range were analyzed to infer the residual opacities of the uppermost cloud deck as well as the mean mixing ratios of water, ammonia, and phosphine at the approximate level of few bars. Our results support the current view of hot spots as regions of prevailing descending vertical motions in the atmosphere but extend this view suggesting that upwelling may occur at the southern boundaries of these structures. Comparison with the global ammonia abundance measured by Juno Microwave Radiometer suggests also that hot spots may represent sites of local enrichment of this gas. JIRAM also identifies similar spatial patterns in water and phosphine contents in the two hot spots.
Key Points
Hot spots are confirmed as very dry regions in the atmosphere of Jupiter
Consistent spatial patterns are found in the distributions of water and phosphine
Ammonia shows local enhancements in the southern parts of hot spots
•Dust particles sizes, optical depth and top altitude maps of a local dust storm.•Evidence for connections between the storm dynamics and the region topography.•Hints on the storm origins from ...thermal inertia, GCM and surface mafic features.
In this study we present the analysis of the dust properties of a local storm imaged in the Atlantis Chaos region on Mars by the OMEGA imaging spectrometer on March 2nd, 2005. We use the radiative transfer model MITRA to study the dust properties at solar wavelengths between 0.5 µm and 2.5 µm and infer the connection between the local storm dynamics and the topography.
We retrieve maps of effective grain radius (reff), optical depth at 9.3 µm (τ9.3) and top altitude (ta) of the dust layer. Our results show that large particles (reff = 1.6 µm) are gathered in the centre of the storm (lat = 33.5° S; lon = 183.5° W), where the optical depth is maximum (τ9.3 > 7.0) and the top altitude exceeds 18 km. Outside the storm, we obtain τ9.3 < 0.2, in agreement with the estimates derived from global climate models (GCM).
We speculate that a low thermal inertia region at the western border of Atlantis Chaos is a possible source of the dust storm. Moreover, we find evidence that topography plays a role in confining the local storm in Atlantis Chaos. The vertical wind component from the GCM does not provide any hint for the triggering of dust lifting. On the other hand, the combination of the horizontal and vertical wind profiles suggests that the dust, once lifted, is pushed eastward and then downward and gets confined within the north-east ridge of Atlantis Chaos.
From our results, the thickness of the dust layer collapsed on the surface ranges from about 1 µm at the storm boundaries up to more than 100 µm at its centre. We verify that a layer of dust thicker than 1 µm, deposited on the surface, can prevent the detection of mafic absorption features. However, such features are still present in OMEGA data of Atlantis Chaos registered after the storm. Hence, we deduce that, once the storm is over, the dust deposited on an area larger than the one where it has been observed.
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
We compare Jupiter observations made around 27 August 2016 by Juno's JunoCam, Jovian Infrared Auroral Mapper (JIRAM), MicroWave Radiometer (MWR) instruments, and NASA's Infrared Telescope Facility. ...Visibly dark regions are highly correlated with bright areas at 5 µm, a wavelength sensitive to gaseous NH3 gas and particulate opacity at p ≤5 bars. A general correlation between 5‐µm and microwave radiances arises from a similar dependence on NH3 opacity. Significant exceptions are present and probably arise from additional particulate opacity at 5 µm. JIRAM spectroscopy and the MWR derive consistent 5‐bar NH3 abundances that are within the lower bounds of Galileo measurement uncertainties. Vigorous upward vertical transport near the equator is likely responsible for high NH3 abundances and with enhanced abundances of some disequilibrium species used as indirect indicators of vertical motions.
Key Points
A high correlation between visibly dark clouds and 5‐micron radiation extends only partially to microwave radiation
Five‐micron spectroscopy and microwave radiometry yield a 5‐bar NH3 abundance not inconsistent with Galileo results
Meridional dependence of deep atmospheric opacity is dynamically consistent with most other vertical‐motion tracers
Plain Language Summary
Comparison of observations of Jupiter by different Juno and ground‐based instruments verified some long‐standing relationships, such as those between visibly dark regions and clear, dry parts of the atmosphere. But Juno saw significant exceptions. Different instrument results for the abundance of ammonia gas, a condensate similar to water in the Earth's atmosphere, at 5 bars of pressure were self‐consistent and within the uncertainty of Galileo results. The substantial upwelling of ammonia detected by the Microwave Radiometer from great depth near the equator is consistent with other indirect tracers of vertical winds.
In this paper we report the mapping of H3+, C2H2, and CH4 as derived by an unexploited Galileo/Near‐Infrared Mapping Spectrometer (NIMS) data set. As previously observed, hydrocarbons emissions ...appear to be located in the internal part of the auroral main oval, where CH4 3 µm vibrational band intensity ratios suggest that nonthermal excitation mechanisms, such as auroral particle precipitation and/or Joule heating, are responsible for the observed emissions. Temperature estimation are in good agreement for the CH4‐emitting region on the hot spot, while the values obtained for H3+ are lower in comparison with Cassini/visual and infrared mapping spectrometer and ground‐based data. C2H2 emission overlaps the CH4 one only at higher latitudes >75°N, indicating that different energetic particles are at work inside the main oval polar ward. CH4 is also found on the northern section of the main oval (135°< longitude <190°, 60°< latitude <90°N). The present investigation results have implications on the Juno/Jovian InfraRed Auroral Mapper observation planning as well as on the codes that will be used to retrieve temperatures and densities of all the emitting species involved in the Jupiter auroral processes.
Key Points
Maps of H3+, C2H2, and CH4 as derived by unexploited Galileo/NIMS data
H3+ and CH4 temperatures and column densities derived for specific mean spectra. H3+ temperatures lower than previously reported
Hydrocarbons emissions overlap only for latitudes >75°N indicating different energies of impacting particles polar ward
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
Plagioclase feldspars are among the most prevalent minerals in the solar system, and are present in many chondritic and achondritic meteorite families. Nevertheless, spectral features of plagioclases ...have never been unambiguously and directly observed in remote observations of asteroids. We report here the detection of an absorption band at 12.2 m on Vesta spectra provided by ground-based spectral observations at the Subaru Telescope. This signature represents the first direct evidence of a widespread presence of crystalline Ca-rich plagioclase on Vesta and reveals that its regolith is comminuted to a very fine grain size, smaller than a few tens of microns, indicating that the mechanical brecciation process has been very effective. The crystalline nature of plagioclase strongly suggests that impacts alone cannot be the sole mechanism for regolith formation on Vesta and a milder process, such as thermal fatigue, should be invoked as an important and concomitant process Thermal fatigue should be considered a very effective process in regolith production and rejuvenation not only for near-Earth asteroids but even for large asteroids located in the main belt.
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