Search

The surface of Mars is cut by long linear faults with displacements of metres to kilometres, most of which are thought to have been formed by extension. The surface has also been modified by enormous floods, probably of water, which often flowed out of valleys formed by the largest of these faults. By analogy with structures on Earth, we propose here that the faults are in fact the surface expression of dykes, and not of large-scale tectonic movements. We use a numerical model to show that the intrusion of large dykes can generate structures like Valles Marineris. Such dykes can provide a heat source to melt ground ice, and so provide a source of water for the floods that have been inferred to originate in some of the large valleys.

We compare several recent Martian interior models and evaluate how these are impacted by the tidal constraints provided by the Love number k2 and the secular acceleration in longitude s of its main moon, Phobos. The expression of the latter is developed up to harmonic degree 5 to match the accuracy of the current observations. We match a number of current interior structure models to the recent measurements of the tidal parameters and derive estimations of the possible core radius, temperature profile, and attenuation in the Martian interior. Our estimation of the core radius is 1,820 ± 80 km, consistent with recent seismic measurements. The attenuation profiles in the Martian interior at the main tidal period of Phobos are similar between the considered models, giving a range for the degree‐2 bulk tidal attenuation Q2 = 93.0 ± 8.40 but diverge at seismic frequencies. At seismic frequencies, model shear attenuation Qμ ranges between 100 and 4,000 in the lower mantle, so that a measurement of seismic shear attenuation could be used as an effective means for distinguishing between the models considered. Other constraints such as elastic lithosphere thickness and Chandler Wobble period favor a thicker elastic lithosphere and models with a frequency dependence α of the shear attenuation between 0.15 and 0.4. Improved constraints on the Martian interior should be possible with additional seismic and radio observations from the InSight mission. Plain Language Summary: The largest moon of Mars, Phobos, raises tides on the red planet causing its surface to be deformed. The size of this tidal bulge depends on the elastic properties of Mars, while viscosity and anelasticity inside the planet cause the tidal bulge to be misaligned with the position of Phobos on its orbit. This misalignment between Phobos and the tidal bulge of Mars creates an acceleration in longitude for the moon, which can be measured and used with the size of the tidal bulge to constraint the interior of Mars. Both the size and orientation of the tidal bulge can be used as tidal constraints to probe the size of the core of Mars, the temperature profile in its interior, and how strong the viscous dissipation is in its mantle. Our current estimates give a wide range of possible attenuation in the Martian mantle, favoring larger core sizes with larger elastic thickness of the lithosphere, the rigid outermost layer of a solid planet. Knowledge of the Martian interior could be further improved with future seismic and radio measurements from the InSight mission. Key Points: We develop a formulation to calculate the secular acceleration of Phobos due to tidal dissipation in MarsUsing the Love number k2 and the secular acceleration s, we obtain for Mars a core size of 1,820 ± 80 km and a bulk Q of 93.0 ± 8.40We discuss several means to distinguish between Mars models using seismological, rotational, and lithospheric observations [ABSTRACT FROM AUTHOR]

Since landing on Mars, the NASA InSight lander has witnessed eight Phobos and one Deimos transits. All transits could be observed by a drop in the solar array current and the surface temperature, but more surprisingly, for several ones, a clear signature was recorded with the seismic sensors and the magnetometer. We present a preliminary interpretation of the seismometer data as temperature‐induced local deformation of the ground, supported by terrestrial analog experiments and finite‐element modeling. The magnetic signature is most likely induced by changing currents from the solar arrays. While the observations are not fully understood yet, the recording of transit‐related phenomena with high sampling rate will allow more precise measurements of the transit times, thus providing additional constraints for the orbital parameters of Phobos. The response of the seismometer can potentially also be used to constrain the thermoelastic properties of the shallow regolith at the landing site. Plain Language Summary: The geophysical lander, InSight, has been operating on the surface of Mars since November 2018. Since then, the Martian moons Phobos and Deimos have been partially blocking the Sun, as seen from the InSight landing site, multiple times. Multiple InSight instruments have been measuring the effect of those transits; this surprisingly includes the seismometer and the magnetometer. We conclude that temperature‐induced deformation and tilt are responsible for the seismic measurements. The change observed in the magnetometer measurements are most likely the result of a drop in the solar array currents. We do not observe atmospheric modulations with InSight's weather station during the transit. These observations help constrain orbital parameters of the Martian moons, and the seismometer signal might allow investigating thermoelastic properties of the shallow Martian material. Key Points: Multiple geophysical InSight instruments observe unexpected signals during Phobos transitsLocal ground deformation due to surface temperature drops explain the tilt signals seen by the seismometerThe drop in the solar array currents results in a change of the magnetic field [ABSTRACT FROM AUTHOR]

Abstract: We invert the Martian tidal response and mean mass and moment of inertia for chemical composition, thermal state, and interior structure. The inversion combines phase equilibrium computations with a laboratory‐based viscoelastic dissipation model. The rheological model, which is based on measurements of anhydrous and melt‐free olivine, is both temperature and grain size sensitive and imposes strong constraints on interior structure. The bottom of the lithosphere, defined as the location where the conductive geotherm meets the mantle adiabat, occurs deep within the upper mantle (∼200–400 km depth) resulting in apparent upper mantle low‐velocity zones. Assuming an Fe‐FeS core, our results indicate (1) a mantle with a Mg# (molar Mg/Mg+Fe) of ∼0.75 in agreement with earlier geochemical estimates based on analysis of Martian meteorites; (2) absence of bridgmanite‐ and ferropericlase‐dominated basal layer; (3) core compositions (15–18.5 wt% S), core radii (1,730–1,840 km), and core‐mantle boundary temperatures (1620–1690°C) that, together with the eutectic‐like core compositions, suggest that the core is liquid; and (4) bulk Martian compositions with a Fe/Si (weight ratio) of 1.66–1.81. We show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters. Specifically, we find that the inversion results are largely reproducible by stagnant lid convection models for a range of initial viscosities (∼1018–1020 Pa s) and radioactive element partitioning between crust and mantle around 0.01–0.1. The geodynamic models predict a mean surface heat flow between 15 and 25 mW/m2. [ABSTRACT FROM AUTHOR]

Abstract: Estimates for the martian core formation timescale based on the hafnium–tungsten (Hf–W) isotopic system have varied by almost an order of magnitude, because of uncertainties in the martian mantle Hf/W ratio. Here we argue that the Hf/W ratio is ∼4 but is uncertain by ∼25%, resulting in (instantaneous) martian core formation timescales ranging from 0 to 10 Myr; accordingly, Hf–W isotope observations currently have limited utility in distinguishing between scenarios in which Mars formed as a stranded embryo and scenarios in which Mars suffered a prolonged accretion history. [Copyright &y& Elsevier]