International audienc

No abstract

Abstract.Two end-member models of Mars' present interior structure are presented: the first model is optimized to satisfy the geochemical data derived from the SNC meteorites in terms of the bulk chondritic ratio Fe/Si-1. lithosphere is estimated to be about 500 km thick and to be subdivided into a 300-km-thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection. Given the core sulfur content of 14 wt% as derived from SNC meteorites, the Martian core is found to be entirely molten, implying the nonoperation of a self-sustained dynamo due to the absence of sufficiently vigorous convection.

No abstract

No abstract

Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. The oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. Here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. We further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 Earth masses. We show that outgassing of reduced systems is dominated by strongly reduced gases such as $$\text {H}_{2}$$H2, with only smaller fractions of moderately reduced/oxidised gases ($$\text {CO}$$CO, $$\text {H}_{2}\text {O}$$H2O). Overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. Atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states.

[1] Interior models of a differentiated Titan with an internal ammonia-water ocean and chondritic radiogenic heat production in an undifferentiated rock + iron core have been calculated. We assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice I layer on top of the ocean as well as the moment of inertia factor and the tidal Love numbers for comparison with Cassini gravity data. The Love numbers are linearly dependent on the thickness of the ice I shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean. Ice shell thicknesses are between 90 and 105 km for models with 5 wt.% ammonia and for core densities between 3500 and 4500 kg m À3 . For 15 wt.% ammonia, the shell is 65 to 70 km thick. We use a strongly temperature-dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice I shell. Tidal heating in the warm convective sublayer is of minor importance. The internal ocean is several hundred kilometers thick, and its thickness decreases with increasing thickness of the ice shell. Core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0.30 ± 0.01.

[1] Most recent Martian interior structure models are based on the planet's polar moment of inertia C, although the mean moment of inertia I is required for constructing spherically symmetric models of planetary interiors. Using the improved value of C/M p R p 2 recently obtained from a combined reanalysis of the entire set of radio science data collected during the last three decades and accounting for the rotationally and topographically induced shape of the planet's gravitational field, we find a mean moment-of-inertia factor of I/M p R p 2 = 0.3635 ± 0.0012. The new lower value suggests a core radius several tens of kilometers larger if other parameters like core density, crust density, and crust thickness are fixed. It further implies that the Martian crust is several tens of kilometers thicker than previously thought if crust and mantle densities and core size are given. Moreover, the Martian mantle may be less dense, about several tens of kg m À3 , with a smaller iron content than previously thought if crust thickness and core size are specified. The mantle density of Mars is relatively well determined by the planet's moment of inertia factor if crust thickness and density are specified.