We present the results of the first-ever visible spectroscopic survey fully dedicated to the small (absolute magnitude H ≥ 20) near-Earth asteroid (NEA) population. Observations have been performed ...at the New Technology Telescope (NTT) of the European Southern Observatory (ESO), during a 30-night Guaranteed Time Observations programme, in the framework of the European Commission financed NEOShield-2 project. The visible spectra of 147 objects have been obtained and taxonomically classified. They show a peculiar taxonomic distribution, with respect to larger NEAs. In particular, olivine-rich A-types and organic-rich D-types are more abundant than what could be expected by extrapolating the taxonomic distribution of larger NEAs. Such results have implications for the investigation of the first phases of solar system history, including the delivery of prebiotic material on the early Earth. Having been obtained over a large range of solar phase angles, our data allowed us to evidence peculiar phase reddening behaviours for asteroids belonging to different taxonomic types. Low-albedo asteroids display no or limited phase reddening, compared to moderate- and high-albedo objects. This result suggests a promising novel way to distinguish primitive asteroids in the X-complex. In agreement with previous laboratory experiments, olivine-rich surfaces are the most affected by phase reddening.
•We present a visible spectroscopic survey of the small near-Earth asteroids (NEAs).•Small NEAs present a peculiar taxonomic distribution compared to larger asteroids.•Types A (olivine-rich) and D (organic-rich) are relatively abundant at small sizes.•Different taxonomical groups correspond to peculiar solar phase reddening curves.•Phase reddening most affects moderate/high-albedo, olivine-rich surfaces.
ABSTRACT
Phobos and Deimos, the two satellites of Mars, were largely studied in the past using ground-based telescope and spacecraft data, although most of the data were obtained by opportunity ...observations performed by Mars dedicated orbiters. Despite the data available so far, the main composition of the two moons is not yet fully understood. The possible presence of hydrated minerals along with mafic minerals olivine and pyroxene seems to be the most plausible interpretation, but more investigations are needed. MIRS spectrometer on-board the future JAXA MMX sample return mission will help to unveil the open question on the composition of Phobos and Deimos. In this work, we review past spectroscopic observations of the Martian moons, both from ground observatories and spacecraft data set, aiming at better understanding the constraints in interpreting the Mars satellites composition and at identifying the best spectroscopic analogues. We also present new laboratory measurements on mineral mixing and meteorites to match the satellites spectral behaviour. New measurements were acquired at INAF-Astrophysical Observatory of Arcetri and IPAG laboratories at room conditions exploring different geometries and the results obtained set new constraints for future laboratory measurements. Our preliminary results confirm that the surface of Phobos and Deimos can be associated with samples characterized by a higher presence of dark components (e.g. amorphous carbon) or minerals produced by space weathering (e.g. Fe0 and FeS-bearing materials). Presence of dark component could also be totally responsible for the reduced hydrated band observed on the moons without invoking dehydration or OH-implantation on anhydrous surface.
ABSTRACT
Phobos is the target of the Martian Moons eXploration (MMX), the next sample return mission of the Japanese space agency (JAXA). The mission will investigate the origin of Phobos and Deimos ...– the two martian moons, using a suite of dedicated instruments. Infrared analysis of the surface composition will be performed by the MIRS spectrometer onboard MMX. Within the scientific studies performed in preparation for the mission, we developed a new laboratory spectral simulant that well reproduces the red and featureless spectrum of Phobos. Our results show that a visible and near-infrared simulant can be developed using dark, opaque materials such as anthracite and coal to reduce the reflectance and absorption features. To investigate the reliability of our proposed simulant in terms of composition and mineralogy, we discussed the similarities and differences in the mid-infrared (MIR) range between our laboratory simulant and some past observations acquired on Phobos. Spectra with different observation geometries were also acquired for our simulant, which give information about grain size and textures of the surface. The simulant developed in our study presents a better match for the Phobos spectrum in the visible and near-infrared compared to the previously proposed simulants.
Aims . This study aims to analyze Phobos’ photometric properties using Mars Express mission observations to support the Martian Moons exploration mission (MMX) devoted to the investigation of the ...Martian system and to the return of Phobos samples. Methods . We analyzed resolved images of Phobos acquired between 2004 and 2022 by the High Resolution Stereo Camera (HRSC) on board the Mars Express spacecraft at a resolution ranging from ~30 m px −1 to 330 m px −1 . We used data acquired with the blue, green, red, and IR filters of HRSC and the panchromatic data of the Super Resolution Channel (SRC). The SRC data are unique because they cover small phase angles (0.2–10°), permitting the investigation of the Phobos opposition effect. We simulated illumination and geometric conditions for the different observations using the Marx Express and the camera spice kernels provided by the HRSC team. We performed photometric analysis using the Hapke model for both integrated and disk-resolved data. Results . The Phobos phase function is characterized by a strong opposition effect due to shadow hiding, with an amplitude and a half-width of the opposition surge of 2.28±0.03 and 0.0573±0.0001, respectively. Overall, the surface of Phobos is dark, with a geometric albedo of 6.8% in the green filter and backscattering. Its single-scattering albedo (SSA) value (7.2% in the green filter) is much higher than what has been found for primitive asteroids and cometary nuclei and is close to the values reported in the literature for Ceres. We also found a surface porosity of 87%, indicating the presence of a thick dust mantle or of fractal aggregates on the top surface. The SSA maps revealed high reflectance variability, with the blue unit area in the northeast Stickney rim being up to 65% brighter than average, while the Stickney floor is among the darkest regions, with reflectance 10 to 20% lower than average. Photometric modeling of the regions of interest selected in the red and blue units indicates that red unit terrains have a stronger opposition effect and a smaller SSA value than the blue ones, but they have similar porosity and backscattering properties. Conclusions . The HRSC data provide a unique investigation of the Phobos phase function and opposition surge, which is valuable information for the MMX observational planning. The Phobos opposition surge, surface porosity, phase integral, and spectral slope are very similar to the values observed for the comet 67P and for Jupiter family comets in general. Based on these similarities, we formulate a hypothesis that the Mars satellites might be the results of a binary or bilobated comet captured by Mars.
Context . A number of bodies in the Solar System are characterized by dark surfaces, from carbonaceous asteroids to the enigmatic surface of Phobos and Deimos. Our understanding of the spectroscopic ...behavior of low-albedo surfaces remains incomplete. To improve the interpretation of remote sensing data, laboratory studies continue to serve as a pivotal tool for unveiling the physical state and composition of such surfaces. Aims . Several processes can be simulated in the laboratory, however, the preparation and analysis of a complex mixing of analog material is one of the most fundamental among them, while also being one of the most complex when multiple components are used. In this work, we aim to study how dark material mixed with basaltic material at different grain sizes can affect the spectroscopic features from the near- to mid- infrared (1.25–25 µm). Methods . Our sample set includes four series of basaltic mix (feldspar and pyroxene) at different grain sizes from <50 µm to 1000 µm, mixed with amorphous carbon at increasing weight percentages ranging from 1% to 50%. We analyzed several features on the spectrum of each mineral mixture. In particular, we investigated the behavior of the: (i) near-infrared slope; (ii) 2.7 µm OH-stretching band; (iii) Christiansen features; and (iv) Reststrahlen band and Transparency feature. Results . The measurements presented in this work, which take into account a large wavelength range for the first time, point toward a critical effect of dark material, but with a different outcomes for each grain size. Some of the most interesting results involve the slope trend of modification with dark material and the variant behavior of the Reststrahlen band and Transparency feature. Conclusions . This dataset will offer a key support in the interpretation of data collected on dark surfaces by past and future space missions. This knowledge will be also important in the context of linking analyses of returned samples with remote sensing data collected on planetary surfaces.
In the framework of the Near Earth Objects (NEOs) observational campaign carried out within the NEOShield-2 project, we identify nine new small D-type asteroids with estimated diameter less than 600 ...m. The link with meteorites for this class of asteroids is weak and the best fit obtained is with the Tagish Lake meteorite for seven of them. D-type asteroids are believed to contain the most pristine material of the Solar system and could have delivered the pre-biotic material to the Earth. Our results double the known sample of the D-types in the NEO population and triple the candidates of this class for a sample-return mission (at very low ΔV). Our finding increases considerably the number of targets for sample-return mission. A sample-return mission to a D-type asteroid will provide a major progress in understanding the early history of the Solar system and to investigate the origin of life on the Earth.
Results from the NASA/MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission showed that 27% of Mercury's surface is covered by smooth plains mostly produced by extensive ...effusive volcanism. The Caloris impact basin is associated with two, mostly volcanic, smooth plains, one in its interior and one surrounding the basin. Previous studies have shown that it is difficult to estimate the relative ages of the interior and exterior plains and to explain their spectral and compositional differences. We perform an exhaustive spectral analysis of the basin based on data obtained by the Mercury Atmospheric and Surface Composition Spectrometer spectrometer onboard MESSENGER between 300 and 1,450 nm with a 5 nm resolution. Unlike previous results based on crater counts, we found that the exterior plains were emplaced before the interior plains although both postdate the formation of the basin. We propose a decrease in the partial melting degree and/or partial melting depth over time to explain the spectral and compositional differences. The study highlights spectrally heterogeneous exterior plains associated with a compositional heterogeneity and the presence of low reflectance material (LRM) deposits. This heterogeneity in the exterior plains could be related to the formation of the basin and asymmetry of the ejecta deposits or to a heterogeneous distribution of LRM present at depths before the formation of the basin.
Plain Language Summary
Results from the NASA/MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission highlighted several geological units at the surface of Mercury. The volcanic plains are defined as a sparsely cratered unit with several embayments of other landforms. Most of these plains formed by effusive volcanism before 3.5 Ga. Caloris, the largest well‐preserved impact basin, is associated with two plains, mostly volcanic, one filling the basin and one surrounding the basin, which have different spectral and compositional properties. Previous studies have shown that it is difficult to estimate the relative ages of the interior and exterior plains. In this work, we perform an exhaustive spectral analysis of Caloris based on MESSENGER data. Unlike previous results, we found that the exterior plains are older and were emplaced before the interior plains although both postdate Caloris formation. We propose an evolution of the volcanic source conditions over time to explain the spectral and compositional differences between the exterior and interior plains. A decrease in the partial melting degree and/or partial melting depth over time leads to modifications of magma properties and different compositional and spectral properties of lava. This study highlights heterogeneous exterior plains with east‐west asymmetry.
Key Points
The exterior volcanic plains of Caloris were emplaced in and around the basin followed by the interior plains within the basin only
The melting degree and/or melting depth decrease over time between the formation of the exterior and interior plains
Spectral and compositional data show heterogeneous exterior plains with east‐west asymmetry
Context. The study of the surface properties of Centaurs and trans-Neptunian objects (TNOs) provides essential information about the early conditions and evolution of the outer Solar System. Due to ...the faintness of most of these distant and icy bodies, photometry currently constitutes the best technique to survey a statistically significant number of them. Aims. Our aim is to investigate color properties of a large sample of minor bodies of the outer Solar System, and set their taxonomic classification. Methods. We carried out visible and near-infrared photometry of Centaurs and TNOs, making use, respectively, of the FORS2 and ISAAC instruments at the Very Large Telescope (European Southern Observatory). Using G-mode analysis, we derived taxonomic classifications according to the Barucci et al. (CITEa, AJ, 130, 1291) system. Results. We report photometric observations of 31 objects, 10 of them have their colors reported for the first time ever. 28 Centaurs and TNOs have been assigned to a taxon. Conclusions. We combined the entire sample of 38 objects taxonomically classified in the framework of our programme (28 objects from this work; 10 objects from DeMeo et al. CITE, A&A, 493, 283) with previously classified TNOs and Centaurs, looking for correlations between taxonomy and dynamics. We compared our photometric results to literature data, finding hints of heterogeneity for the surfaces of 4 objects.
Olivine-rich asteroids in the near-Earth space Popescu, Marcel; Perna, D; Barucci, M A ...
Monthly notices of the Royal Astronomical Society,
06/2018, Letnik:
477, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In the framework of a 30-night spectroscopic survey of small near-Earth asteroids (NEAs), we present new results regarding the identification of olivine-rich objects. The following NEAs were ...classified as A-type using visible spectra obtained with 3.6-m New Technology Telescope: (293726) 2007 RQ17, (444584) 2006 UK, 2012 NP, 2014 YS34, 2015 HB117, 2015 LH, 2015 TB179, 2015 TW144. We determined a relative abundance of 5.4 per cent (8 out of 147 observed targets) A-types at a 100-m size range of NEA population. The ratio is at least five times larger compared with the previously known A-types, which represent less than ∼1 per cent of NEAs taxonomically classified. By taking into account that part of our targets may not be confirmed as olivine-rich asteroids by their near-infrared spectra, or they can have a nebular origin, our result provides an upper-limit estimation of mantle fragments at size ranges below 300 m. Our findings are compared with the ‘battered-to-bits’ scenario, claiming that at small sizes the olivine-rich objects should be more abundant when compared with basaltic and iron ones.
Context. Gravitationally bound multiple systems provide an opportunity to estimate the mean bulk density of the objects, whereas this characteristic is not available for single objects. Being a ...primitive population of the outer solar system, binary and multiple trans-Neptunian objects (TNOs) provide unique information about bulk density and internal structure, improving our understanding of their formation and evolution. Aims. The goal of this work is to analyse parameters of multiple trans-Neptunian systems, observed with Herschel and Spitzer space telescopes. Particularly, statistical analysis is done for radiometric size and geometric albedo, obtained from photometric observations, and for estimated bulk density. Methods. We use Monte Carlo simulation to estimate the real size distribution of TNOs. For this purpose, we expand the dataset of diameters by adopting the Minor Planet Center database list with available values of the absolute magnitude therein, and the albedo distribution derived from Herschel radiometric measurements. We use the 2-sample Anderson–Darling non-parametric statistical method for testing whether two samples of diameters, for binary and single TNOs, come from the same distribution. Additionally, we use the Spearman’s coefficient as a measure of rank correlations between parameters. Uncertainties of estimated parameters together with lack of data are taken into account. Conclusions about correlations between parameters are based on statistical hypothesis testing. Results. We have found that the difference in size distributions of multiple and single TNOs is biased by small objects. The test on correlations between parameters shows that the effective diameter of binary TNOs strongly correlates with heliocentric orbital inclination and with magnitude difference between components of binary system. The correlation between diameter and magnitude difference implies that small and large binaries are formed by different mechanisms. Furthermore, the statistical test indicates, although not significant with the sample size, that a moderately strong correlation exists between diameter and bulk density.
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