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

Mapping olivine abundance on asteroid (25143) Itokawa from Hayabusa/NIRS data

Olivine is one of the main abundant mineral in the Solar System, and the determination of its abundance on a surface may give fundamental information about its evolution. The study of surface distribution of olivine on asteroid (25143) Itokawa through near-Infrared reflectance spectroscopy is a difficult goal because olivine and pyroxene bands centred at 1 μm and 2 μm are not entirely included in Hayabusa/NIRS' spectral range. In this work, the retrieval of olivine abundance has been performed by applying two different methods: the first one uses some spectral indices to retrieve olivine abundance, whilst the second one consists of the application of the Hapke's theory in order to create synthetic spectra aimed at fitting a selection of NIRS' spectra. The analysis performed with the first method brought to an approximately homogeneous distribution of olivine content (60 ± 15% on average) on Itokawa's surface, with the exception of Sagamihara region, which has a slightly (up to 10%) lower olivine content. The second method brought to an average 60 ± 7.5% olivine content within 5 selected spectra, with the same reduction found in the spectrum from the Sagamihara region. All these values are in agreement with literature values on this topic, especially with the ones retrieved from particles sampled in Muses Sea by the Hayabusa probe

Visible-Infrared spectral characterization of 3200 Phaethon at its closest approach to Earth

The asteroid 3200 Phaethon is a peculiar object with a very eccentric orbit with a perihelion located at only 0.14 AU and it has been dynamically associated with the Geminid meteor stream (Gustafson 1989; Williams & Wu 1993; Jenniskens 2006, and references therein). Phaethon is a B-class asteroid and it is linked with carbonaceous species and hydrated silicates such as phyllosilicates. Good match of the Phaeton spectra are the aqueously altered CI/CM meteorites (Licandro, 2007) and the CK meteorites (Clark et al. 2010). The asteroid 3200 Phaethon is the target of the Destiny + Space mission, managed by Japanese Space Agency (Jaxa), which will perform a close rendevouz with this asteroid, with the scientific objectives of studying its surface properties and assessing its cometary activity in terms of release of dust and volatiles. The December 2017 Phaethon Earth approach have been a very important event since it was about 10 times closer than any other future approach predicted at least for the next 20 years. In that occasion, we observed the asteroid at the 3.5 mt Telescopio Nazionale Galileo in the spectral interval (0.4-2-5 μm).We obtained three spectra in the Visible from 0.4 to 0.8 μmm, with a strong fringing longward of 0.8 μmm which doesn't allow to use the data between 0.8 and 1 μmm. The spectra are featureless, however, the slope of two spectra agrees well with many previous observations of Phaeton (see e.g. Licandro et al, 2006). One spectra show, instead, a bluer behaviour, similarly to the unique previous observation by Luu and Jewitt (1993). The IR spectrum is almost featureless, with very weak features at the limit of the S/N which at present are under investigation

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

Detection of Crystalline and Fine-grained Calcic Plagioclases on Vesta

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 μm 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

Nature, formation, and distribution of carbonates on Ceres

Different carbonates have been detected on Ceres, and their abundance and spatial distribution have been mapped using a visible and infrared mapping spectrometer (VIR), the Dawn imaging spectrometer. Carbonates are abundant and ubiquitous across the surface, but variations in the strength and position of infrared spectral absorptions indicate variations in the composition and amount of these minerals. Mg-Ca carbonates are detected all over the surface, but localized areas show Na carbonates, such as natrite (Na_2CO_3) and hydrated Na carbonates (for example, Na_2CO_3·H_2O). Their geological settings and accessory NH_4-bearing phases suggest the upwelling, excavation, and exposure of salts formed from Na-CO_3-NH_4-Cl brine solutions at multiple locations across the planet. The presence of the hydrated carbonates indicates that their formation/exposure on Ceres’ surface is geologically recent and dehydration to the anhydrous form (Na_2CO_3) is ongoing, implying a still-evolving body

Lithologic variation within bright material on Vesta revealed by linear spectral unmixing

Vesta's surface is mostly composed of pyroxene-rich lithologies compatible with howardite, eucrite and diogenite (HED) meteorites (e.g., McCord et al. [1970] Science, 168, 1445-1447; Feierberg & Drake [1980] Science, 209, 805-807). Data provided by the Visible and Infrared (VIR) spectrometer, onboard the NASA Dawn spacecraft, revealed that all Vesta reflectance spectra show absorption bands at ∼0.9 and ∼1.9 μm, which are typical of iron-bearing pyroxenes (De Sanctis et al. [2012] Science, 336, 697-700). Other minerals may be present in spectrally significant concentrations; these include olivine and opaque phases like those found in carbonaceous chondrites. These additional components modify the dominant pyroxene absorptions. We apply linear spectral unmixing on bright material (BM) units of Vesta to identify HEDs and non-HED phases. We explore the limits of applicability of linear spectral unmixing, testing it on laboratory mixtures. We find that the linear method is applicable at the VIR pixel resolution and it is useful when the surface is composed of pyroxene-rich lithologies containing moderate quantities of carbonaceous chondrite, olivine, and plagioclase. We found three main groups of BM units: eucrite-rich, diogenite-rich, and olivine-rich. For the non-HED spectral endmember, we choose either olivine or a featureless component. Our work confirms that Vesta's surface contains a high content of pyroxenes mixed with a lower concentration of other phases. In many cases, the non-HED endmember that gives the best fit is the featureless phase, which causes a reduction in the strength of both bands. The anticorrelation between albedo and featureless endmember indicates that this phase is associated with low-albedo, CC-like opaque material. Large amounts of olivine have been detected in Bellicia, Arruntia and BU14 BM units. Other sites present low olivine content (<30%) mostly with a high concentration of diogenite