Spectrophotometric properties of dwarf planet Ceres from the VIR spectrometer on board the Dawn mission

We study the spectrophotometric properties of dwarf planet Ceres in the VIS-IR spectral range by means of hyper-spectral images acquired by the VIR imaging spectrometer on board the NASA Dawn mission. Disk-resolved observations with a phase angle within the $7^{\circ}<\alpha<132^{\circ}$ interval were used to characterize Ceres' phase curve in the 0.465-4.05 $\mu$m spectral range. Hapke's model was applied to perform the photometric correction of the dataset, allowing us to produce albedo and color maps of the surface. The $V$-band magnitude phase function of Ceres was fitted with both the classical linear model and H-G formalism. The single-scattering albedo and the asymmetry parameter at 0.55$\mu$m are $w=0.14\pm0.02$ and $\xi=-0.11\pm0.08$, respectively (two-lobe Henyey-Greenstein phase function); the modeled geometric albedo is $0.094\pm0.007$; the roughness parameter is $\bar{\theta}=29^{\circ}\pm6^{\circ}$. Albedo maps indicate small variability on a global scale with an average reflectance of $0.034 \pm 0.003$. Isolated areas such as the Occator bright spots, Haulani, and Oxo show an albedo much higher than average. We measure a significant spectral phase reddening, and the average spectral slope of Ceres' surface after photometric correction is $1.1\%k\AA^{-1}$ and $0.85\%k\AA^{-1}$ at VIS and IR wavelengths, respectively. Broadband color indices are $V-R=0.38\pm0.01$ and $R-I=0.33\pm0.02$. H-G modeling of the $V$-band magnitude phase curve for $\alpha<30^{\circ}$ gives $H=3.14\pm0.04$ and $G=0.10\pm0.04$, while the classical linear model provides $V(1,1,0^{\circ})=3.48\pm0.03$ and $\beta=0.036\pm0.002$. The comparison with spectrophotometric properties of other minor bodies indicates that Ceres has a less back-scattering phase function and a slightly higher albedo than comets and C-type objects. However, the latter represents the closest match in the usual asteroid taxonomy.Comment: 14 pages, 20 figures, published online on Astronomy and Astrophysics on 13 February 2017. Revised to reflect minor changes in text and figures made in proofs, updated value of V-R and R-

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

Minor Body Science with the Nancy Grace Roman Space Telescope

n/

High Thermal Inertia Zones on Ceres From Dawn Data

Thermal inertia is a key information to quantify the physical status of a planetary surface. We derive the thermal inertia of the surface of Ceres using spatially resolved data from the Dawn mission. For each location, this quantity can be constrained by comparing theoretical and observed diurnal temperature profiles from retrieved temperatures. We calculated Ceres's surface theoretical temperatures with a thermophysical model that provides temperature as a function of thermal conductivity and roughness, and we determined the values of those parameters for which the best fit with the observed data is obtained. Our results suggest that the area of crater Haulani displays thermal inertia values (up to 130-140 J·m-2·s-½·K-1) substantially higher than the very low to low values (from 1-15 to 50-60 J·m-2·s-½·K-1) derived for the overall surface of Ceres. The results are more ambiguous for the bright faculae located in the floor of crater Occator

Joint Europa Mission (JEM): a multi-scale study of Europa to characterize its habitability and search for extant life

Europa is the closest and probably the most promising target to search for extant life in the Solar System, based on complementary evidence that it may fulfil the key criteria for habitability: the Galileo discovery of a sub-surface ocean; the many indications that the ice shell is active and may be partly permeable to transfer of chemical species, biomolecules and elementary forms of life; the identification of candidate thermal and chemical energy sources necessary to drive a metabolic activity near the ocean floor. In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious and exciting planetary mission, which we call the Joint Europa Mission (JEM), to reach two objectives: perform a full characterization of Europa's habitability with the capabilities of a Europa orbiter, and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere) by the combination of an orbiter and a lander. JEM can build on the advanced understanding of this system which the missions preceding JEM will provide: Juno, JUICE and Europa Clipper, and on the Europa lander concept currently designed by NASA (Maize, report to OPAG, 2019). We propose the following overarching goals for our Joint Europa Mission (JEM): Understand Europa as a complex system responding to Jupiter system forcing, characterize the habitability of its potential biosphere, and search for life at its surface and in its sub-surface and exosphere. We address these goals by a combination of five Priority Scientific Objectives, each with focused measurement objectives providing detailed constraints on the science payloads and on the platforms used by the mission. The JEM observation strategy will combine three types of scientific measurement sequences: measurements on a high-latitude, low-altitude Europan orbit; in-situ measurements to be performed at the surface, using a soft lander; and measurements during the final descent to Europa's surface. The implementation of these three observation sequences will rest on the combination of two science platforms: a soft lander to perform all scientific measurements at the surface and sub-surface at a selected landing site, and an orbiter to perform the orbital survey and descent sequences. We describe a science payload for the lander and orbiter that will meet our science objectives. We propose an innovative distribution of roles for NASA and ESA; while NASA would provide an SLS launcher, the lander stack and most of the mission operations, ESA would provide the carrier-orbiter-relay platform and a stand-alone astrobiology module for the characterization of life at Europa's surface: the Astrobiology Wet Laboratory (AWL). Following this approach, JEM will be a major exciting joint venture to the outer Solar System of NASA and ESA, working together toward one of the most exciting scientific endeavours of the 21st century: to search for life beyond our own planet

Thermal inertia of Occator's faculae on Ceres

Thermal inertia is a key information to quantify the physical status of a planetary surface; it can be retrieved by comparison between theoretical and observed temperature diurnal profiles. We have calculated the surface temperature for a set of locations on Ceres' surface with a thermophysical model that provides temperature as a function of thermal conductivity and roughness, and we have determined the values of those parameters for which the best fit with the observed data is obtained. The observed temperatures have been retrieved form spatially-resolved data from the Dawn mission. In our previous work [Rognini et al., 2019], we have found that the average thermal inertia for the overall surface of Ceres is low (from 1 to 15 to 60 J m^-2 s^1⁄2 K^-1), as expected according to the general trend observed in the Solar System for atmosphere-less bodies, while the thermal inertia of the very bright faculae found in the floor of the Occator crater could not be well defined. Using more recently acquired VIR high resolution data we find that the central part of the Cerealia facula displays a thermal anomaly (~ 10 K above the average) compatible with a higher thermal inertia with respect to the surrounding regions, while the Vinalia facula does not display any consequently could have a grain size comparable with the Ceres’ surface average

A Neutralizing RNA Aptamer against EGFR Causes Selective Apoptotic Cell Death

Nucleic acid aptamers have been developed as high-affinity ligands that may act as antagonists of disease-associated proteins. Aptamers are non immunogenic and characterised by high specificity and low toxicity thus representing a valid alternative to antibodies or soluble ligand receptor traps/decoys to target specific cancer cell surface proteins in clinical diagnosis and therapy. The epidermal growth factor receptor (EGFR) has been implicated in the development of a wide range of human cancers including breast, glioma and lung. The observation that its inhibition can interfere with the growth of such tumors has led to the design of new drugs including monoclonal antibodies and tyrosine kinase inhibitors currently used in clinic. However, some of these molecules can result in toxicity and acquired resistance, hence the need to develop novel kinds of EGFR-targeting drugs with high specificity and low toxicity. Here we generated, by a cell-Systematic Evolution of Ligands by EXponential enrichment (SELEX) approach, a nuclease resistant RNA-aptamer that specifically binds to EGFR with a binding constant of 10 nM. When applied to EGFR-expressing cancer cells the aptamer inhibits EGFR-mediated signal pathways causing selective cell death. Furthermore, at low doses it induces apoptosis even of cells that are resistant to the most frequently used EGFR-inhibitors, such as gefitinib and cetuximab, and inhibits tumor growth in a mouse xenograft model of human non-small-cell lung cancer (NSCLC). Interestingly, combined treatment with cetuximab and the aptamer shows clear synergy in inducing apoptosis in vitro and in vivo. In conclusion, we demonstrate that this neutralizing RNA-aptamer is a promising bio-molecule that can be developed as a more effective alternative to the repertoire of already existing EGFR-inhibitors