A race against the clock: Constraining the timing of cometary bombardment relative to Earth's growth

Comets are considered a potential source of inner solar system volatiles, but the timing of this delivery relative to that of Earth's accretion is still poorly understood. Measurements of xenon isotopes in comet 67P/Churyumov-Gerasimenko revealed that comets partly contributed to the Earth's atmosphere. However, there is no conclusive evidence of a significant cometary component in the Earth's mantle. These geochemical constraints would favour a contribution of comets mainly occurring after the last stages of Earth's formation. Here, we evaluate whether dynamical simulations satisfy these constraints in the context of an Early Instability model. We perform dynamical simulations of the solar system, calculate the probability of collision between comets and Earth analogs component embryos through time and estimate the total cometary mass accreted in Earth analogs as a function of time. While our results are in excellent agreement with geochemical constraints, we also demonstrate that the contribution of comets on Earth might have been delayed with respect to the timing of the instability, due to a stochastic component of the bombardment. More importantly, we show that it is possible that enough cometary mass has been brought to Earth after it had finished forming so that the xenon constraint is not necessarily in conflict with an Early Instability scenario. However, it appears very likely that a few comets were delivered to Earth early in its accretion history, thus contributing to the mantle's budget. Finally, we compare the delivery of cometary material on Earth to Venus and Mars. These results emphasize the stochastic nature of the cometary bombardment in the inner solar system.Comment: 26 pages, 12 figure

Local electrochemical investigation of copper patina

The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.CAPESSpanish Education Ministr

Étude de l’effet d’un polyacrylate et d’un polyphosphate sur la morphologie et la minéralogie du sulfate de calcium

The retarding influence of polyacrylate and polyphosphate on the nucleation of calcium sulphate was investigated. SEM analyses show that these inhibitors didn’t only influence the nucleation kinetics but also the precipitate morphology by adsorption onto crystal growth sites. The influence of different concentrations of the additives on the mineralogy of solid precipitated was also examined. Spectroscopy Raman analyses showed that the calcium sulphate can precipitate under different phases, gypsum (CaSO$_4$.2H$_2$O), hemihydrate (CaSO$_4$.1/2H$_2$O) and / or anhydride (CaSO$_4$), as function of inhibitors concentrations

Nucleation-growth process of scale electrodeposition – influence of the magnesium ions

International audienceElectrodeposition of CaCO3 was studied under the influence of magnesium ions present in a carbonically pure water. The investigation was performed using electrochemical, gravimetric and optical methods. The chronoamperometric measurements confirmed the inhibiting property of Mg2+ when its concentration is higher than 120 mg L−1 in a solution containing 160 mg L−1 of Ca2+. The optical technique led the nucleation-growth process to be accessed by means of an optical microscope positioned behind a transparent electrode. The increase of Mg2+ concentration changed drastically the calcite morphology. At 360 mg L−1 of Mg2+, the calcite morphology was optically amorphous but the Raman spectrum confirmed its structure. The crystal growth was recorded in situ and the image analysis software characterised the nucleation process as well as the growth rate of the crystals. It allowed the influence of the Mg2+ ions on the crystallisation process of CaCO3 to be quantified