Charles-Edouard Boukaré, PhD

 Authors: C.-E. Boukaré, N. Cowan, D. Lemasquerier, L. Dang, M. Herath., H. Samuel, J. Badro, S. Charnoz. Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting that orbit so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such “lava planets” harbors a rock-vapor atmosphere that flows quickly toward the airless nightside—this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat toward the nightside. As a result, the surface temperature of the magma ocean may range from 3000 K near the substellar point down to 1500 K near the day–night terminator.  We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the substellar point. Our principa...

 Authors: K. Moore, N. Cowan, C.-E. Boukaré, C. Goldblatt Earth-like planets orbiting M-dwarf stars, M-Earths, are likely the best targets to search for signatures of life in the foreseeable future. Life as we know it requires liquid surface water. The habitability of M-Earths is jeopardized by the loss of water to space: high bolometric and extreme ultraviolet flux from young M dwarfs can drive the loss of 1--10 Earth Oceans.  To investigate the fate of surface water on M-Earths, we develop a 0-D "box model" for Earth-mass terrestrial exoplanets tracking water loss to space and exchange between reservoirs during an early global magma ocean phase, and during the longer deep-water cycling phase, for planets orbiting different host stars at various distances within the habitable zone. In our coupled simulations including a magma ocean, deep-water cycling, and water loss to space, a key feature is the relative duration of the magma ocean and runaway greenhouse. These timescale...

Authors: Ch.-Ed. Boukaré, J. Badro The composition of the Earth’s core in light elements such as Si, Mg, O or S, remains largely controversial. Conditions under which liquid metal saturates in these elements offer strong constrains on core composition. For instance, MgO can dissolve in the metallic phase at high temperature [1][2] and then precipitates upon core cooling. Similarly, ex-solution of SiO2 can occur if the liquid core start over saturated in Si and O and reach the saturation limit during secular cooling [3]. The issue of light elements ex-solution/precipitation is crucial as it is a powerful source to drive the Earth’s dynamo prior to inner-core growth.  We present a self-consistent thermodynamics approach that aims to determine the saturation conditions of liquid iron alloys in the Fe-Si-O system. The model is based on global Gibbs free energy minimization   inspired from [4][5]. The Gibbs free energy of end-members are taken from [6] for Fe-liquid, Fe-...

Authors: Ch.-Ed. Boukaré, Marc Parmentier and Steve Parman At the end of planetary accretion, magma ocean (MO) evolution is thought to set the initial conditions for the long-term evolution of terrestrial planets. Most aspects of MO dynamics are derived from the lunar MO based on data of the Apollo mission obtained more than forty years ago. However, crucial aspects of MO evolution are still highly debated. One of the key aspects of MO ocean evolution are the time of MO solidification, the degree of silicate differentiation and the initial degree of mantle mixing. If interpreted as the first solid lunar surface, the relative young age of the lunar anorthosite must be reconciled with a relative fast MO solidification suggested by the canonical thermal models. The fractional solidification and the overturn hypothesis, while only an ideal limiting case, can explain important geochemical features of both the Moon and Mars. However, the actual geodynamic evolution of the lunar mantl...

Authors: Ch.-Ed. Boukaré, Steve Parman and Marc Parmentier To explain the high sulfur content and low FeO content of the Mercury’s surface lavas, it has been proposed that Mercury is deprived of oxygen compared to the Earth, Moon and Mars. Such reducing conditions would lead to significant differences between the evolution of the Mercury magma ocean (MMO) and the canonical Lunar magma ocean. Here, we investigate the formation of sulfide layering produced by the solidification of a global magma ocean in Mercury. We use experimentally determined sulfur solubility in silicate melts to predict the depth at which sulfides precipitate in the case of ideal fractional solidification. The model produces primordial sulfide layers whose thickness and locations depend upon the oxygen fugacity and initial sulfur content of the Mercurian magma ocean. A geodynamic model is then used to test under which conditions the initial mineralogical layering can be preserved during the...

Authors: Ch.-Ed. Boukaré, Marc Parmentier, Yanick Ricard and Steve Parman Observations of present day magnetic field on small planetary bodies such as Ganymede or Mercury challenges our understanding of planetary dynamo. Several mechanisms have been proposed to explain the origin of magnetic fields. Among the proposed scenarios, one family of models relies on snow regime. Snow regime is supported by experimental studies showing that melting curves can first intersect adiabats in regions where the solidifying phase is not gravitationaly stable. First solids should thus remelt during their ascent or descent. The effect of the snow zone on magnetic field generation remains an open question. Could magnetic field be generated in the snow zone? If not, what is the depth extent of the snow zone? How remelting in the snow zone drive compositional convection in the liquid layer? Several authors have tackled this question with 1D-spherical models. Zhang and Schubert, 2012 mode...