Spectroscopic survey of M--type asteroids

M-type asteroids, as defined in the Tholen taxonomy (Tholen, 1984), are medium albedo bodies supposed to have a metallic composition and to be the progenitors both of differentiated iron-nickel meteorites and enstatite chondrites. We carried out a spectroscopic survey in the visible and near infrared wavelength range (0.4-2.5 micron) of 30 asteroids chosen from the population of asteroids initially classified as Tholen M -types, aiming to investigate their surface composition. The data were obtained during several observing runs during the years 2004-2007 at the TNG, NTT, and IRTF telescopes. We computed the spectral slopes in several wavelength ranges for each observed asteroid, and we searched for diagnostic spectral features. We confirm a large variety of spectral behaviors for these objects as their spectra are extended into the near-infrared, including the identification of weak absorption bands, mainly of the 0.9 micron band tentatively attributed to orthopyroxene, and of the 0.43 micron band that may be associated to chlorites and Mg-rich serpentines or pyroxene minerals such us pigeonite or augite. A comparison with previously published data indicates that the surfaces of several asteroids belonging to the M-class may vary significantly. We attempt to constrain the asteroid surface compositions of our sample by looking for meteorite spectral analogues in the RELAB database and by modelling with geographical mixtures of selected meteorites/minerals. We confirm that iron meteorites, pallasites, and enstatite chondrites are the best matches to most objects in our sample, as suggested for M-type asteroids. The presence of subtle absorption features on several asteroids confirms that not all objects defined by the Tholen M-class have a pure metallic composition.Comment: 10 figures, 6 tables; Icarus, in pres

The albedo-color diversity of transneptunian objects

We analyze albedo data obtained using the Herschel Space Observatory that reveal the existence of two distinct types of surface among midsized transneptunian objects. A color-albedo diagram shows two large clusters of objects, one redder and higher albedo and another darker and more neutrally colored. Crucially, all objects in our sample located in dynamically stable orbits within the classical Kuiper belt region and beyond are confined to the bright-red group, implying a compositional link. Those objects are believed to have formed further from the Sun than the dark-neutral bodies. This color-albedo separation is evidence for a compositional discontinuity in the young solar system.Comment: 16 pages, 4 figures, 1 table, published in ApJL (12 August 2014), The Astrophysical Journal (2014), vol. 793, L

A plausible link between the asteroid 21 Lutetia and CH carbonaceous chondrites

A crucial topic in planetology research is establishing links between primitive meteorites and their parent asteroids. In this study we investigate the feasibility of a connection between asteroids similar to 21 Lutetia, encountered by the Rosetta mission in July 2010, and the CH3 carbonaceous chondrite Pecora Escarpment 91467 (PCA 91467). Several spectra of this meteorite were acquired in the ultraviolet to near-infrared (0.3 to 2.2 {\mu}m) and in the mid-infrared to thermal infrared (2.5 to 30.0 {\mu}m or 4000 to ~333 cm^-1), and they are compared here to spectra from the asteroid 21 Lutetia. There are several similarities in absorption bands and overall spectral behavior between this CH3 meteorite and 21 Lutetia. Considering also that the bulk density of Lutetia is similar to that of CH chondrites, we suggest that this asteroid could be similar, or related to, the parent body of these meteorites, if not the parent body itself. However, the apparent surface diversity of Lutetia pointed out in previous studies indicates that it could simultaneously be related to other types of chondrites. Future discovery of additional unweathered CH chondrites could provide deeper insight in the possible connection between this family of metal-rich carbonaceous chondrites and 21 Lutetia or other featureless, possibly hydrated high-albedo asteroids.Comment: 26 pages, 7 figures and 2 tables, Meteoritics and Planetary Science, manuscript #2225 (2016

Near-IR spectroscopy of asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin, and 5480 (1989YK8), potential targets for the Rosetta mission; remote observations campaign on IRTF

In the frame of the international campaign to observe potential target asteroids for the Rosetta mission, remote observations have been carried out between Observatoire de Paris, in Meudon-France, and the NASA Infrared Telescope Facility on Mauna Kea. The SpeX instrument was used in the 0.8-2.5 microns spectral region, for two observing runs in March and June 2003. This paper presents near-IR spectra of the asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin, and 5480 (1989YK8). Near-IR spectra of the asteroids 21 Lutetia and 140 Siwa are flat and featureless. The spectrum of 89 Julia reveals absorption bands around 1 and 2 microns, which may indicate the presence of olivine and olivine-pyroxene mixtures and confirm the S-type designation. The small main-belt asteroids 2181 Fogelin and 5480 (1989YK8) are investigated spectroscopically for the first time. Near-IR spectra of these asteroids also show an absorption feature around 1 micron, which could be and indicator of igneous/metamorphic surface of the objects; new observations in visible as well as thermal albedo data are necessary to draw a reliable conclusion on the surface mineralogy of both asteroids.Comment: Sent: October 2003, Accepted: December, 200

Asteroid target selection for the new Rosetta mission baseline: 21 Lutetia and 2867 Steins

Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at http://www.aanda.org.International audienceThe new Rosetta mission baseline to the comet 67P/Churyumov-Gerasimenko includes two asteroid fly-bys. To help in target selection we studied all the candidates of all the possible scenarios. Observations have been carried out at ESO-NTT (La Silla, Chile), TNG (Canaries), and NASA-IRTF (Hawaii) telescopes, in order to determine the taxonomy of all the candidates. The asteroid targets were chosen after the spacecraft interplanetary orbit insertion manoeuvre, when the available total amount of ΔV was known. On the basis of our analysis and the available of ΔV, we recommended to the ESA ScienceWorking Group the asteroids 21 Lutetia and 2867 Steins as targets for the Rosetta mission. The nature of Lutetia is still controversial. Lutetia's spectral properties may be consistent with a composition similar to carbonaceous chondrite meteorites. The spectral properties of Steins suggest a more extensive thermal history. Steins may have a composition similar to relatively rare enstatite chondrite/achondrite meteorites

Compost application boosts soil restoration in highly disturbed hillslope vineyard

A field trial was carried out to investigate the effects of compost application on a young Cabernet sauvignon vineyard located in a hilly area in the North-East of Italy and subjected to land terracing before plantation. The use of a compost based on manure, pruning residues and pomace at a rate of 65 t ha-1 was compared to the mineral fertilization regime recommended for the vineyards in the area (NPK: 80, 50, 200 kg ha-1). A multi-factorial approach that considered soil chemical properties, microbial community structure and function, vine nutritional and vegetative indexes, yield and quality parameters was applied in the attempt of depict interrelated effects of compost on all these factors. Results of this study show that the application of compost for three consequent years greatly increased soil organic matter content and improved the mineral nutrient availability in the soil. Soil biological fertility showed a slow but significant response to compost addition as from the second year of treatment microbial growth and enzyme activity were increased compared to those of the inorganic fertilization, with special regard to enzymes involved in P cycle. A shift in the soil microbial community structure was also observed in compost-treated soil, with higher presence of copiotrophic bacteria, indicators of soil quality, and phosphorus solubilizing bacteria. A decrease of pathogenic fungal strains was also observed. Organic fertilization increased plant nutrient uptake and vegetative growth compared to those observed in chemically fertilized vines. A trend toward increased yield and improvements for some grape quality parameters such as acidity and pH were observed in the first year of production. These results provide evidence that compost can boost soil fertility restoration in vineyard disturbed by land terracing, allowing for agronomic performances comparable or even improved than those of chemically fertilized vines

Seasonal evolution unveils the internal structure of cometary nuclei

Remote sensing data of comets 9P/Tempel 1 and 67P/Churyumov-Gerasimenko (67P hereafter) indicate the occurrence of water-ice-rich spots on the surface of cometary nuclei [1-5]. These spots are up to tens of metres in size and appear brighter and bluer than the average surface at visible wavelengths. In addition, the extensive observation campaign performed by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS, [6]) and the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [7]) during the Rosetta escort phase at 67P revealed a seasonal cycle of the nucleus colour. This is characterised by blueing of the surface while approaching perihelion followed by progressive reddening and restoral of the original colour along the outbound orbit. The temporal evolution of the colour has been interpreted in previous studies as the result of increasing exposure of water ice at smaller heliocentric distances [8, 9], however, an explanation of such seasonal cycle in the context of a quantitative cometary activity model was not yet been provided. Recently, in [10] we showed that the seasonal colour cycle observed on comet 67P is determined by the occurrence of the above-mentioned water-ice-rich spots (referred to as Blue Patches - BPs -, given their colour). This can be explained in the context of activity models [11, 12] of pebble-made cometary nuclei [13], i.e. in terms of nucleus surface erosion induced by H2O and CO2 ices sublimation, driving the cometary activity. According to the scenario proposed in [10] (Fig. 1), the presence of the BPs is due to the exposure of subsurface sub-metre-sized Water-ice-Enriched Blocks (WEBs) thanks to surface erosion triggered by CO2 sublimation ejecting decimetre-sized chunks [12]. The WEBs are composed of ice-rich pebbles (dust-to-ice mass ratio δ=2, [14]), embedded in a matrix of drier pebbles (δ>>5) forming most of the nucleus. Once exposed to illumination as BPs, the WEBs are eroded by water-ice sublimation ejecting sub-cm dust [11]. By means of dedicated spectral and thermophysical modelling, we match the nucleus colour temporal evolution measured by the VIRTIS Mapping channel in the 0.55-0.8 µm spectral range. In doing this, we take into account the competing effects of CO2- and H2O-driven erosion that expose and remove the BPs, respectively, and are seasonally modulated by the insolation conditions, primarily depending on the heliocentric distance. The new nucleus model proposed in [10], implying an uneven distribution of water ice in cometary nuclei, reconciles the compositional dishomogeneities observed on comets (the BPs) at macroscopic (up to tens of metres) scale, with a structurally homogeneous pebble-made nucleus at small (centimetre) scale, and with the processes determining the cometary activity at microscopic (sub-pebble) scales. Figure 1. 67P surface gets bluer approaching perihelion as a consequence of the progressive exposure to sunlight of subsurface WEBs (from Figure 4 in Ciarniello et al., 2022, Nature Astronomy, https://doi.org/10.1038/s41550-022-01625-y). The comet nucleus is made of two types of pebbles, both including refractories and CO2 ice, with different water ice content: pebbles with high content of H2O ice form the WEBs, while H2O-ice-poor pebbles represent the rest of the nucleus. CO2 ice is stable beneath the CO2 sublimation front at depths >0.1 m [12]. Approaching perihelion, the CO2 ice sublimation rate increases, eroding the surface by chunk ejection and exposing the WEBs. Once exposed, WEBs lose CO2 and are observable as BPs. Water-ice sublimation erodes the BPs ejecting sub-cm dust from their surface and preventing the formation of a dry crust [11]. The BPs survive until their water-ice fraction is sublimated, producing the observed surface blueing. Please refer to ref. [10] for complete details. References [1] Sunshine, J. M. et al. (2006) Science 311, 1453-1455.[2] Filacchione, G. et al. (2016) Nature 529, 368-372.[3] Raponi, A. et al. (2016) Mon. Not. R. Astron. Soc. 462, S476-S490.[4] Barucci, M. A. et al. (2016) Astron. Astrophys. 595, A102.[5] Oklay, N. et al. (2017) Mon. Not. R. Astron. Soc. 469, S582-S597.[6] Coradini, A. et al. (2007) Space Sci. Rev. 128, 529-559.[7] Keller, H. U. et al. (2007) Space Sci. Rev. 128, 433-506.[8] Fornasier, S. et al. (2016) Science 354, 1566-1570.[9] Filacchione, G. et al. (2020) Nature 578, 49-52.[10] Ciarniello, M. et al. (2022) Nat. Astron. doi:10.1038/s41550-022-01625-y.[11] Fulle, M. et al. (2020) Mon. Not. R. Astron. Soc. 493, 4039-4044.[12] Gundlach, B. et al (2020). Mon. Not. R. Astron. Soc. 493, 3690-3715.[13] Blum, J. et al. (2017) Mon. Not. R. Astron. Soc. 469, S755-S77.[14] O'Rourke, L. et al. (2020) Nature 586, 697-701. Acknowledgements We thank the Italian Space Agency (ASI, Italy; ASI-INAF agreements I/032/05/0 and I/024/12/0), Centre National d'Etudes Spatiales (CNES, France), and Deutsches Zentrum für Luft-und Raumfahrt (DLR, Germany) for supporting this work. VIRTIS was built by a consortium from Italy, France and Germany, under the scientific responsibility of IAPS, Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome, which also led the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI (Italy), with contributions from Observatoire de Meudon (France) financed by CNES and from DLR (Germany). The VIRTIS instrument industrial prime contractor was former Officine Galileo, now Leonardo Company, in Campi Bisenzio, Florence, Italy. Part of this research was supported by the ESA Express Procurement (EXPRO) RFP for IPL-PSS/JD/190.2016. D.K. acknowledges DFG-grant KA 3757/2-1. This work was supported by the International Space Science Institute (ISSI) through the ISSI International Team "Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet". This research has made use of NASA's Astrophysics Data System

Spectrophotometric Modeling and Mapping of (101955) Bennu

Using hyperspectral data collected by OVIRS, the visible and infrared spectrometer on board the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we modeled the global average spectrophotometric properties of the carbonaceous asteroid (101955) Bennu and mapped their variations. We restricted our analysis to 0.4–2.5 μm to avoid the wavelengths where thermal emission from the asteroid dominates (>2.5 μm). Bennu has global photometric properties typical of dark asteroids; we found a geometric albedo of 0.046 ± 0.007 and a linear phase slope of 0.024 ± 0.007 mag deg−1 at 0.55 μm. The average spectral slope of Bennu’s normal albedo is −0.0030 μm−1, and the phase-reddening parameter is 4.3 × 10−4 μm−1 deg−1, both over the spectral range of 0.5–2.0 μm. We produced normal albedo maps and phase slope maps at all spectral channels, from which we derived spectral slope and phase-reddening maps. Correlation analysis suggests that phase slope variations on Bennu are likely due to photometric roughness variation. A correlation between photometric and thermal roughness is evident, implying that the roughness of Bennu is self-similar on scales from tens of microns to meters. Our analysis reveals latitudinal trends in the spectral color slope and phase reddening on Bennu. The equatorial region appears to be redder than the global average, and the spectral slope decreases toward higher latitudes. Phase reddening on Bennu is relatively weak in the equatorial region and shows an asymmetry between the northern and southern hemispheres. We attributed the latitudinal trend to the geophysical conditions on Bennu that result in a global pattern of mass flow toward the equator

TNOs are cool: a survey of the transneptunian region

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well