163 research outputs found
Uranus and Neptune
The two icy giant planets, Uranus and Neptune, offer a wide population of icy moons and rings of great interest for the planetary geologist. Among moons, Miranda has a very rough surface, peculiar for such a small moon. Triton is characterized by the presence of active geysers on the south polar region and by a tenuous atmosphere made of nitrogen and methane. All moons show the presence of very volatile ices (nitrogen, ammonia, methane, water) thanks to their low surface temperatures
The SSDC contribution to the improvement of knowledge by means of 3D data projections of minor bodies
The latest developments of planetary exploration missions devoted to minor
bodies required new solutions to correctly visualize and analyse data acquired
over irregularly shaped bodies. ASI Space Science Data Center (SSDC-ASI,
formerly ASDC-ASI Science Data Center) worked on this task since early 2013,
when started developing the web tool MATISSE (Multi-purpose Advanced Tool for
the Instruments of the Solar System Exploration) mainly focused on the
Rosetta/ESA space mission data. In order to visualize very high-resolution
shape models, MATISSE uses a Python module (vtpMaker), which can also be
launched as a stand-alone command-line software. MATISSE and vtpMaker are part
of the SSDC contribution to the new challenges imposed by the "orbital
exploration" of minor bodies: 1) MATISSE allows to search for specific
observations inside datasets and then analyse them in parallel, providing
high-level outputs; 2) the 3D capabilities of both tools are critical in
inferring information otherwise difficult to retrieve for non-spherical targets
and, as in the case for the GIADA instrument onboard Rosetta, to visualize data
related to the coma. New tasks and features adding valuable capabilities to the
minor bodies SSDC tools are planned for the near future thanks to new
collaborations
VNIR spectroscopy of rock forming minerals mixtures: a tool to interpret planetary igneous compositions
Visible and Near Infrared (VNIR) spectroscopy is a powerful technique to investigate and map the mineralogical composition of a Solar System body. Laboratory activities, measuring and analyzing minerals and their mixtures, rock powders and slabs, varying the particle and grain sizes, permit to improve the confidence on the spectra.s interpretation. Here we summarized a set of activity on spectral mixtures between plagioclases and mafic materials at 63-125 and 125-250 µm: illustrating the spectral variations due to the different intensity of the plagioclase absorption varying it Fe2+ content once mixed with orthopyroxene - clinopyroxene, orthopyroxene - olivine poor and - olivine rich materials (Serventi et al., 2013); an IMSA (Hapke, 1993) application to retrieve the endmember.s optical constants and to model the relative mineral abundances in intimate mixtures (Ciarniello et al., 2011) highlighting the influence of the mineral distributions (Carli et al., 2014); a spectra deconvolution with Modified Gaussians (MGM, Sunshine et al., 1990) to define spectral parameters (Band Center, Depth and Width) trends respect to the mineralogical composition of endmembers (mineral chemistry) and mixtures (mineral abundances). Also discussing the influence of the sizes (Serventi et al., 2015)
Ceres' opposition effect observed by the Dawn framing camera
The surface reflectance of planetary regoliths may increase dramatically
towards zero phase angle, a phenomenon known as the opposition effect (OE). Two
physical processes that are thought to be the dominant contributors to the
brightness surge are shadow hiding (SH) and coherent backscatter (CB). The
occurrence of shadow hiding in planetary regoliths is self-evident, but it has
proved difficult to unambiguously demonstrate CB from remote sensing
observations. One prediction of CB theory is the wavelength dependence of the
OE angular width. The Dawn spacecraft observed the OE on the surface of dwarf
planet Ceres. We characterize the OE over the resolved surface, including the
bright Cerealia Facula, and to find evidence for SH and/or CB. We analyze
images of the Dawn framing camera by means of photometric modeling of the phase
curve. We find that the OE of most of the investigated surface has very similar
characteristics, with an enhancement factor of 1.4 and a FWHM of 3{\deg} (broad
OE). A notable exception are the fresh ejecta of the Azacca crater, which
display a very narrow brightness enhancement that is restricted to phase angles
{\deg} (narrow OE); suggestively, this is in the range in which CB is
thought to dominate. We do not find a wavelength dependence for the width of
the broad OE, and lack the data to investigate the dependence for the narrow
OE. The prediction of a wavelength-dependent CB width is rather ambiguous. The
zero-phase observations allow us to determine Ceres' visible geometric albedo
as . A comparison with other asteroids suggests that
Ceres' broad OE is typical for an asteroid of its spectral type, with
characteristics that are primarily linked to surface albedo. Our analysis
suggests that CB may occur on the dark surface of Ceres in a highly localized
fashion.Comment: Credit: Schr\"oder et al, A&A in press, 2018, reproduced with
permission, \copyright ES
Spectrophotometric Modeling and Mapping of Ceres
We report a comprehensive analysis of the global spectrophotometric
properties of Ceres using Dawn Framing Camera images collected from April to
June 2015 during the RC3 and Survey mission phases. The single-scattering
albedo of Ceres at 555 nm is 0.140.04, the geometric albedo is
0.0960.006, and the Bond albedo is 0.0370.002. The asymmetry factors
calculated from the best-fit two-term Henyey-Greenstein (HG) single-particle
phase function (SPPF) show a wavelength dependence, suggesting that the phase
reddening of Ceres is dominated by single-particle scattering rather than
multiple scattering or small-scale surface roughness. The Hapke roughness
parameter of Ceres is derived to be 206 with no wavelength
dependence. The phase function of Ceres shows appreciably strong scattering
around 90 phase angle that cannot be fitted with a single-term HG SPPF,
suggesting possible stronger forward scattering than other asteroids previously
analyzed with spacecraft data. We speculate that such a scattering
characteristic of Ceres might be related to its unique surface composition. We
grouped the reflectance data into a 1 latitude-longitude grid and
fitted each grid independently to study the spatial variations of photometric
properties. The albedo and color maps are consistent with previous studies. The
SPPF over the surface of Ceres shows stronger backscattering associated with
lower albedo and vice versa, consistent with the general trend among asteroids.
The Hapke roughness parameter does not vary much across the surface of Ceres,
except for the ancient Vendimia Planitia region that has a slightly higher
roughness. Based on the wavelength dependence of the SPPF of Ceres, we
hypothesize that its regolith grains either contain a considerable fraction of
m-sized particles, or are strongly affected by internal
scatterers of this size.Comment: 43 pages, 3 tables, 17 figures, accepted by Icaru
Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.
The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time
Main results from the ISSI international team “characterization of 67P cometary activity”
The ESA/Rosetta mission accompanied the Jupiter Family Comet 67P/Churyumov-Gerasimenko and provided a huge amount of data which are providing important results about cometary activity mechanisms. We summarize the results obtained within the ISSI International Team Characterization of 67P cometary activity, which studied dust and gas ejection in different stages of the comet’s orbit, by means of a data fusion between instruments onboard the Rosetta orbiter, i.e., the OSIRIS camera, the VIRTIS imaging spectrometer, the GIADA dust detector, the MIDAS atomic force microscope, the COSIMA dust mass spectrometer, and the ROSINA gas mass spectrometer, supported by numerical models and experimental work. The team reconstructed the motion of the dust particles ejected from the comet surface, finding a correlation between dust ejection and solar illumination as well as larger occurrence of fluffy (pristine) particles in less processed and more pebble-rich terrains. Dust activity is larger in ice-rich terrains, indicating that water sublimation is the dominant activity process during the perihelion phase. The comparison of dust fluxes of different particle size suggests a link between dust morphology and ejection speed, generation of micrometric dust from fragmentation of millimetric dust, and homogeneity of physical properties of compact dust particles across the 67P surface. The comparison of fluxes of refractory and ice particles suggests the occurrence of a small amount of ice in fluffy particles, which is released when they are fragmented. A new model of cometary activity has been finally developed, according to which the comet nucleus includes Water-Ice-Enriched Blocks (WEBs), that, when exposed by CO2 activity, are the main sources of water sublimation and dust ejection
The composition of Saturn's rings
The origin and evolution of Saturn's rings is critical to understanding the
Saturnian system as a whole. Here, we discuss the physical and chemical
composition of the rings, as a foundation for evolutionary models described in
subsequent chapters. We review the physical characteristics of the main rings,
and summarize current constraints on their chemical composition. Radial trends
are observed in temperature and to a limited extent in particle size
distribution, with the C ring exhibiting higher temperatures and a larger
population of small particles. The C ring also shows evidence for the greatest
abundance of silicate material, perhaps indicative of formation from a rocky
body. The C ring and Cassini Division have lower optical depths than the A and
B rings, which contributes to the higher abundance of the exogenous neutral
absorber in these regions. Overall, the main ring composition is strongly
dominated by water ice, with minor silicate, UV absorber, and neutral absorber
components. Sampling of the innermost D ring during Cassini's Grand Finale
provides a new set of in situ constraints on the ring composition, and we
explore ongoing work to understand the linkages between the main rings and the
D ring. The D ring material is organic- and silicate-rich and water-poor
relative to the main rings, with a large population of small grains. This
composition may be explained in part by volatile losses in the D ring, and
current constraints suggest some degree of fractionation rather than sampling
of the bulk D ring material.Comment: Submitted to SSR for publication in the collection "New Vision of the
Saturnian System in the Context of a Highly Dissipative Saturn
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