The Radiation Environment of Ceres and Implications for Surface Sampling.

Ceres is a large water-rich dwarf planet located within the asteroid belt. Its surface displays evidence of material sourced from a deep subsurface liquid brine layer within recent geologic time, making it a candidate ocean world with possible present-day activity. However, Ceres lacks a substantial atmosphere and likely does not possess a global magnetic field. Therefore, any material emplaced or exposed on the surface will be subject to weathering by charged particles of solar and galactic origin. We have evaluated the effect of charged particle radiation on material within the near-surface of Ceres and find that the timescale for radiation-induced modification and destruction of organics and endogenic material is ∼100 Myr to 1 Gyr within the top 10-20 cm of the surface. Furthermore, we find that the timescale for sterilization of any putative living organisms contained within material at these depths is <500 kyr. Future missions to the surface may therefore consider targeting regions with geologic ages that fall between these two timescales to avoid the risk of backward contamination while ensuring that sampled material is not heavily radiation processed.

The varied sources of faculae-forming brines in Ceres' Occator crater emplaced via hydrothermal brine effusion.

Before acquiring highest-resolution data of Ceres, questions remained about the emplacement mechanism and source of Occator crater's bright faculae. Here we report that brine effusion emplaced the faculae in a brine-limited, impact-induced hydrothermal system. Impact-derived fracturing enabled brines to reach the surface. The central faculae, Cerealia and Pasola Facula, postdate the central pit, and were primarily sourced from an impact-induced melt chamber, with some contribution from a deeper, pre-existing brine reservoir. Vinalia Faculae, in the crater floor, were sourced from the laterally extensive deep reservoir only. Vinalia Faculae are comparatively thinner and display greater ballistic emplacement than the central faculae because the deep reservoir brines took a longer path to the surface and contained more gas than the shallower impact-induced melt chamber brines. Impact-derived fractures providing conduits, and mixing of impact-induced melt with deeper endogenic brines, could also allow oceanic material to reach the surfaces of other large icy bodies.

Distribution of phyllosilicates on the surface of Ceres.

The dwarf planet Ceres is known to host phyllosilicate minerals at its surface, but their distribution and origin have not previously been determined. We used the spectrometer onboard the Dawn spacecraft to map their spatial distribution on the basis of diagnostic absorption features in the visible and near-infrared spectral range (0.25 to 5.0 micrometers). We found that magnesium- and ammonium-bearing minerals are ubiquitous across the surface. Variations in the strength of the absorption features are spatially correlated and indicate considerable variability in the relative abundance of the phyllosilicates, although their composition is fairly uniform. These data, along with the distinctive spectral properties of Ceres relative to other asteroids and carbonaceous meteorites, indicate that the phyllosilicates were formed endogenously by a globally widespread and extensive alteration process.

Cryovolcanism on Ceres.

Volcanic edifices are abundant on rocky bodies of the inner solar system. In the cold outer solar system, volcanism can occur on solid bodies with a water-ice shell, but derived cryovolcanic constructs have proved elusive. We report the discovery, using Dawn Framing Camera images, of a landform on dwarf planet Ceres that we argue represents a viscous cryovolcanic dome. Parent material of the cryomagma is a mixture of secondary minerals, including salts and water ice. Absolute model ages from impact craters reveal that extrusion of the dome has occurred recently. Ceres' evolution must have been able to sustain recent interior activity and associated surface expressions. We propose salts with low eutectic temperatures and thermal conductivities as key drivers for Ceres' long-term internal evolution.

Cratering on Ceres: Implications for its crust and evolution.

Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no impact craters. We present observations by the Dawn spacecraft that reveal a heavily cratered surface, a heterogeneous crater distribution, and an apparent absence of large craters. The morphology of some impact craters is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed craters are also present. Numerous craters exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. Crater morphology and simple-to-complex crater transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan crater, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.

Dawn arrives at Ceres: Exploration of a small, volatile-rich world.

On 6 March 2015, Dawn arrived at Ceres to find a dark, desiccated surface punctuated by small, bright areas. Parts of Ceres' surface are heavily cratered, but the largest expected craters are absent. Ceres appears gravitationally relaxed at only the longest wavelengths, implying a mechanically strong lithosphere with a weaker deep interior. Ceres' dry exterior displays hydroxylated silicates, including ammoniated clays of endogenous origin. The possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits, lobate flows of materials, and a singular mountain that appears to be an extrusive cryovolcanic dome. On one occasion, Ceres temporarily interacted with the solar wind, producing a bow shock accelerating electrons to energies of tens of kilovolts.

A partially differentiated interior for (1) Ceres deduced from its gravity field and shape.

Remote observations of the asteroid (1) Ceres from ground- and space-based telescopes have provided its approximate density and shape, leading to a range of models for the interior of Ceres, from homogeneous to fully differentiated. A previously missing parameter that can place a strong constraint on the interior of Ceres is its moment of inertia, which requires the measurement of its gravitational variation together with either precession rate or a validated assumption of hydrostatic equilibrium. However, Earth-based remote observations cannot measure gravity variations and the magnitude of the precession rate is too small to be detected. Here we report gravity and shape measurements of Ceres obtained from the Dawn spacecraft, showing that it is in hydrostatic equilibrium with its inferred normalized mean moment of inertia of 0.37. These data show that Ceres is a partially differentiated body, with a rocky core overlaid by a volatile-rich shell, as predicted in some studies. Furthermore, we show that the gravity signal is strongly suppressed compared to that predicted by the topographic variation. This indicates that Ceres is isostatically compensated, such that topographic highs are supported by displacement of a denser interior. In contrast to the asteroid (4) Vesta, this strong compensation points to the presence of a lower-viscosity layer at depth, probably reflecting a thermal rather than compositional gradient. To further investigate the interior structure, we assume a two-layer model for the interior of Ceres with a core density of 2,460-2,900 kilograms per cubic metre (that is, composed of CI and CM chondrites), which yields an outer-shell thickness of 70-190 kilometres. The density of this outer shell is 1,680-1,950 kilograms per cubic metre, indicating a mixture of volatiles and denser materials such as silicates and salts. Although the gravity and shape data confirm that the interior of Ceres evolved thermally, its partially differentiated interior indicates an evolution more complex than has been envisioned for mid-sized (less than 1,000 kilometres across) ice-rich rocky bodies.

Bright carbonate deposits as evidence of aqueous alteration on (1) Ceres.

The typically dark surface of the dwarf planet Ceres is punctuated by areas of much higher albedo, most prominently in the Occator crater. These small bright areas have been tentatively interpreted as containing a large amount of hydrated magnesium sulfate, in contrast to the average surface, which is a mixture of low-albedo materials and magnesium phyllosilicates, ammoniated phyllosilicates and carbonates. Here we report high spatial and spectral resolution near-infrared observations of the bright areas in the Occator crater on Ceres. Spectra of these bright areas are consistent with a large amount of sodium carbonate, constituting the most concentrated known extraterrestrial occurrence of carbonate on kilometre-wide scales in the Solar System. The carbonates are mixed with a dark component and small amounts of phyllosilicates, as well as ammonium carbonate or ammonium chloride. Some of these compounds have also been detected in the plume of Saturn's sixth-largest moon Enceladus. The compounds are endogenous and we propose that they are the solid residue of crystallization of brines and entrained altered solids that reached the surface from below. The heat source may have been transient (triggered by impact heating). Alternatively, internal temperatures may be above the eutectic temperature of subsurface brines, in which case fluids may exist at depth on Ceres today.

8-Methoxypsoralen potentiates the photocytotoxic effect of Photofrin II towards EMT-6 murine tumor cells.

Pretreatment of EMT-6 murine tumor cells for 24 h with 10(-4) M 8-methoxypsoralen (8-MOP) increased the photocytotoxicity of Photofrin II (P2) after cell exposure to low doses (1-1.5 J/cm2) of UVA by two- to three-fold. 8-MOP alone had no cytotoxic action under these experimental conditions and did not significantly change the amount of P2 recovered in cells. 8-MOP enhanced the lipid peroxidation end product formation measured as thiobarbituric acid reactive substances (TBARS) during cell photosensitization by P2. The psoralen alone also slightly increased the TBARS level after UVA exposure. These results suggest that 8-MOP, albeit non-photocytotoxic by itself under our experimental conditions, could enhance the efficiency of P2 by increasing cellular lipid peroxidation following light exposure.

Different responses of free and peptide-bound cross-links to vitamin D and calcium supplementation in elderly women with vitamin D insufficiency.

Recent findings have shown that bisphosphonates had different effects on the urinary excretion of free and peptide-bound cross-links. Because of this discrepancy, we investigated the effects of another antiresorptive therapy, i.e. vitamin D (vitD) and calcium (Ca) supplementation (800 IU vit D3 and 1 g elemental calcium daily for 6 months) in elderly women (n = 21, age: 83.5 +/- 1.5 yr) with vitD insufficiency and secondary hyperparathyroidism (mean level 25 hydroxy vitamin D = 3.17 +/- 1.2 ng/mL, mean level of intact parathormone = 45.3 +/- 22.7 pg/mL) on the urinary excretion of free and peptide-bound cross-links. A group of free-living, healthy elderly women (n = 25, age: 76.6 +/- 3.1 yr) with a normal vitD status (mean level of 25 OH D = 23.4 +/- 8.9 ng/mL, intact parathormone = 30.2 +/- 11.2 pg/mL) was simultaneously studied. Bone resorption was assessed by total (T), free (F), peptidyl (P) hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) measured with high performance liquid chromatography, by F-LP determined with enzyme linked immunosorbent assay (iF-LP) and by the N- and C-terminal telopeptides of type I collagen (NTX and Cross-laps) before and after (3 and 6 months) therapy. Comparison of the two groups of elderly women at baseline showed that the urinary excretion of pyridinoline cross-links (T, F, and peptide-bound forms) and of telopeptide fragment of type I collagen were all increased in patients with a low vitD status. Highly significant differences were seen principally for T-HP, F-HP, and F-LP (P < 0.001). Correlation studies between each marker showed that the values of pyridinoline cross-links (T and peptide-bound forms) and of the telopeptide fragments of type I collagen correlated well, but the correlation was slightly less pronounced between free pyridinolines and the other markers. After treatment, the response to therapy was greatest for peptide-bound cross-links assessed by high performance liquid chromatography and for telopeptide fragments of type I collagen (percent change at 6 months: -21% for P-HP P < 0.05, -26% for P-LP P < 0.05, -31% for NTX P < 0.01, and -51% for CLaps P < 0.001). In contrast, free pyridinolines excretion (F-HP and F-LP) assessed by high performance liquid chromatography as well as by immunoassay remained unchanged at 3 and 6 months. Because marked and significant changes were seen with peptide-bound cross-links only and not with free forms, we conclude that vitD and Ca therapy has the same effects as bisphosphonates on the urinary excretion of free and peptide-bound cross-links. So far, no rational mechanism can be given to explain this discrepancy, and further studies are needed before routine application of these bone collagen degradation products as bone resorption markers.

Effects of arginine butyrate and tributyrylxylitol on cultured human sarcoma cells.

The effects of arginine butyrate and tributyrylxylitol were studied comparatively in a human sarcoma cell line. Both induced important structural and functional modifications suggestive of cell differentiation, as shown by the dose-dependent increase of alkaline phosphatase activity and total protein content, at concentrations ranging from 1mM to 5 mM expressed in butyrate equivalents. hCG beta-subunit present in the culture medium increased with differentiation. Our results show that most of the differentiation changes previously reported for sodium butyrate in cancer cell lines are also produced by both drugs. Tributyrylxylitol appears to be the more potent and effective inducer of differentiation but its use is limited << in vitro >> on account of its relative toxicity at concentrations above 3 mM butyrate equivalents.

[Medical treatment of idiopathic calcium lithiasis (I)]. / Traitement médical de la lithiase calcique idiopathique (I).

Calcium stones is responsible for 80 per cent of the stones in the upper track. It is a frequent and particularly recurrent disease and for this reason it is important to prevent its recurrence by medical treatment, dissolution of calcium stones being impossible. In the first part of this review, we have presented the theoretical basis and the clinical studies concerning conservative therapy involving high fluid intake and dietary advice on calcium and oxalate intake. Then, for the various drugs proposed for recurrence prevention we have reviewed their mechanisms of action and the controlled clinical trials concerning these drugs. Finally, the practical therapeutical choices for the management of these patients are presented according to the results of the previous metabolic evaluation.

Swine liver L-leucine aminopeptidase: improved purification procedure.

An L-leucine aminopeptidase, having a specificity toward the substrate L-leucine amide, was purified 1084-fold from swine liver with a yield of 50.7 per cent. Purification procedure was carried out using successively centrifugation at 105 000 X g, fractionation by ammonium sulfate, DEAE Sephacel chromatography and zonal ultracentrifugation. Enzyme homogeneity and purity studies were carried out by analytical ultracentrifugation and polyacrylamide gel electrophoresis. In SDS-gel polyacrylamide, a single band was observed. It corresponded to a 55 000 molecular weight protein.

Guine pig liver L-asparaginase. Separation, purification, and intracellular localisation of two distinct enzymatic activities.

Two distinct L-asparaginase (EC 3.5.1.1) activities were detected in guinea pig liver: Asparaginase 1 and Asparaginase 2. Asparaginase 1 has been purified 272 fold from the crude homogenate; its molecular weight was evaluated by gel filtration to be about 150 000. The purified preparation was shown to be homogeneous by cellulose acetate strip and polyacrylamide disc-gel electrophoresis. Asparaginase 2 has been purified 63.5 fold from the crude homogenate. Its molecular weight was evaluated by gel filtration to be about 21 500. Cellulose acetate strip electrophoresis demonstrated two bands, one of which corresponded to Asparaginase 1 and the other to Asparaginase 2. Cellular fractionation in the ultracentrifuge, showed Asparaginase 1 to be present only in the cytosol fraction. Asparaginase 2 which was unstable at 105 000 X g seemed mostly localized in the mitochondria and secondarily in the cytoplasmic fraction.