Amir Khan

Concerted exploration and a ten‐fold increase in Martian meteorites reveal a mostly ancient (>4 Ga), lithologically diverse mafic crust (igneous SiO ₂ ranging from ∼40%–70%), commonly exhibiting alkaline affinities and with felsic compositions restricted to ancient crust. Most crustal growth (∼80%) took place during the pre‐Noachian, resulting from magma ocean processes. Later crustal additions continued at diminishing rates to the latest Amazonian (2 = 48%, K ₂ O = 0.5%, La _N /Yb _N ∼ 1.8) that becomes less incompatible element‐enriched over geological time. The petrological nature of the crust likely varies in a complex way with depth that may explain the intracrustal seismic discontinuity. The crust contains ∼45 10% of the most incompatible elements in the primitive mantle and this composition is consistent with a mass balance model among crust, MSL, “depleted” mantle and primitive mantle. A geodynamic model for Mars can be constructed that is consistent with geophysical and geochemical constraints currently available.

Electromagnetic sounding coupled with experimental measurements of electrical conductivity (EC) can provide valuable constraints on the thermochemical state of Earth's lower mantle. Here, we report a new set of experimentally determined EC values of pyrolite, a candidate composition of the lower mantle, between 25 and 80 GPa at room temperature and high temperature between 1,200 and 2,300 K using a laser‐heated diamond anvil cell combined with impedance spectroscopy. To maintain and better constrain the geometry of the experimental assembly, we used focused ion beam‐cut discs of a pre‐synthesized pyrolitic sample. Our results reveal a monotonic increase in EC with pressure, in contrast to earlier measurements that suggested a spin‐transition‐induced conductivity drop in the mid‐lower mantle. We also identify intrinsic voltage‐ and pressure‐related time‐dependent behavior that are likely expressions of nonlinear grain‐boundary conduction and stress‐driven relaxation processes, respectively. To our knowledge, this is the first report of such behavior in geological materials and may represent a previously unrecognized source of uncertainty in earlier high‐pressure EC data sets. Finally, we compare predictions based on our experimental findings against the radial EC structure derived from analysis of 10 years of satellite magnetic data from the ESA Swarm mission, with improved resolution in the lower mantle down to 2,200 km. We find that the measured EC of pyrolite is consistent with the geophysically inferred conductivity structure.

The dwarf planet Pluto and its largest moon Charon represent a fully tidally evolved system: their orbital eccentricity is almost zero and their respective rotational periods are equal to the mutual orbital period. According to a widely accepted hypothesis, Charon as well as other Pluto moons originated in a giant oblique impact (e.g., Canup et al., 2005; Arakawa et al., 2019), forming on a tight orbit above the synchronous radius, and evolved by tidal recession from the primary, which was endowed with a large angular momentum and thus fast rotation. A recent, alternative scenario proposes formation by collisional capture (Denton et al., 2025), resulting in Charon’s emplacement on an initially circular close-in orbit and a primordial synchronisation at high spin rate.A tidally evolving binary is subjected to surface stresses that are strongly dependent on the mutual distance and, for small orbital separations, may lead to the formation of tidally-oriented fractures in the ice shell similar to those on Enceladus or Europa. The orientation of fractures identified on images from the New Horizons mission is, however, not correlated with expected tidal stresses and has instead been attributed to ocean freezing, which would have postdated the full orbital evolution (Rhoden et al., 2020). Moreover, an initially quickly rotating Pluto (and Charon) consistent with the giant impact scenarios would lead to a considerable rotational bulge that would only be able to relax before present in the case of a thin lithosphere and a weak ice shell above a subsurface ocean (McKinnon et al., 2025).Here, we present a model of the Pluto-Charon synchronisation that predicts lower tidal stresses and does not require initial fast rotation of the partners, thus potentially alleviating some of the challenges posed by the standard tidal recession scenario. We propose that the binary was formed by a capture of a highly inclined retrograde minor planet (proto-Charon) by a prograde-rotating Pluto and subsequently evolved by tidal approach. Following this line, we perform numerical simulations of the binary’s orbital evolution, studying the effect of various initial spin rates, eccentricities, and interior properties. During the evolution, Pluto acquires its present-day retrograde rotation and, depending on ice viscosity, Charon may experience episodes of higher spin-orbit resonances (such as 3:2 or 2:1). Since the evolution of a planet with a retrograde moon proceeds at distances greater than the present-day semi-major axis, both Pluto and Charon experience tidal heating and stresses two orders of magnitude lower than in the tidal recession scenario.

It is usually taken for granted that mutual synchronization of a tidal two-body system is attained through tidal recession, assuming the reduced Hill sphere is not reached. However, synchronization can be achieved also via tidal approach, provided the Roche limit is not crossed. For each of the two scenarios, we derive the condition under which the evolving synchronicity radius catches up with the tidally evolving orbit. We consider the two scenarios for the Pluto–Charon system and examine the impact-origin hypothesis of Charon’s formation against capture. Based on geophysical evidence, we propose that capture appears more likely. Motivated by this conclusion, we investigate both analytically and numerically the capture scenario, wherein the orbital evolution of Charon starts at a higher altitude than present and undergoes tidal descent. We also consider the possibility that Pluto’s initial prograde spin underwent a reversal by a tidally approaching retrograde Charon. Depending on the initial conditions, we observe temporary locking of Charon into higher spin-orbit resonances (3:2 to 7:2) during the first 0.5 Myr of the system’s evolution. Owing to a greater initial separation between the partners, the power dissipated in each of them turns out to be much lower than in the case of tidal recession of bodies of the same internal structure. The greater initial separation also results in lower tidal stress, which may explain the absence of tidally generated fracture patterns.

Here we illustrate the use of parameterized models to address fundamental questions about Earth's mantle and core structure. For this, we invert a large set of normal‐mode center frequencies and quality (attenuation) factors, along with astronomic‐geodetic data, for the radial anelastic seismic structure of the Earth. We consider two distinct parameterizations that rely on physically and polynomially parameterized models. In the first approach mantle models are constructed using petrologic phase equilibria in combination with a laboratory‐based viscoelastic model connecting dissipation from seismic to tidal periods (100 s–20 years), whereas seismic properties for a homogeneous and adiabatic core are computed using equations‐of‐state. The polynomially parameterized models follow the Preliminary Reference Earth Model (PREM) and rely on a polynomial representation of density, P‐ and S‐wave velocity, attenuation, and anisotropy. To quantify uncertainty estimates on the derived structure—a feature absent from radial seismic reference models—we employ a stochastic sampling‐based approach in solving the inverse problem. To further constrain mantle and outer‐core seismic wave velocity structure, we also inverted globally‐averaged P‐ and S‐wave and multiple core‐mantle boundary underside‐reflected S‐wave travel times, respectively. The results indicate considerable deviations from PREM, including a denser outer core and less dense inner core, and thus a diminished density contrast across the inner‐core boundary. Also, outer‐core stratification, associated with the layer, appears not to be required to match data. Finally, and of general interest to the wider community, uncertainty measures on all inverted properties are provided with the models presented here.

A basal magma ocean (BMO) has been suggested to form as a consequence of cumulate overturn following crystallization of an initial global magma ocean. As a consequence of enrichment in iron and heat‐producing elements (HPE), the BMO stabilizes gravitationally at the base of the planetary mantle, affecting the efficiency of mantle convection and crustal production. Seismic data collected during the recent Mars InSight mission provide compelling evidence for the presence of a molten silicate layer at the bottom of the Martian mantle. Here, we study the role of a BMO on the long‐term evolution of Mars's interior using two‐dimensional geodynamic models in spherical annulus geometry. We compare our model predictions with available observational constraints, including crustal HPE enrichment, seismically constrained present‐day crustal and lithospheric thicknesses, and mantle temperatures. Among the parameters explored, we find that the interstitial porosity, which controls the initial HPE distribution between the BMO and the mantle, plays an important role on mantle thermal structure throughout Mars's evolution. Models with an intermediate interstitial porosity (20%–60%), and with a reference mantle viscosity of Pas (at ) provide the best match to the most observational constraints. This suggests that HPE partitioning between mantle and BMO has not been controlled by end‐member fractional crystallization of the initial magma ocean, and that chemical re‐equilibration must have occurred to some extent during cumulate overturn. Crustal growth constraints nevertheless remain difficult to reconcile independent of HPE enrichment of the BMO. Better understanding of the earliest stages of Martian differentiation is required.

A basal magma ocean (BMO) has been suggested to form as a consequence of cumulate overturn following crystallisation of an initial global magma ocean. As a consequence of enrichment in iron and heat-producing elements (HPE), the BMO stabilises gravitationally at the base of the planetary mantle, affecting the efficiency of mantle convection and crustal production. Seismic data collected during the recent Mars InSight mission provide compelling evidence for the presence of a molten silicate layer at the bottom of the Martian mantle. Here, we study the role of a BMO on the long-term evolution of Mars’s interior using two-dimensional geodynamic models in spherical annulus geometry. We compare our model predictions with available observational constraints, including crustal HPE enrichment, seismically-constrained present-day crustal and lithospheric thicknesses, and mantle temperatures. Among the parameters explored, we find that the interstitial porosity, which controls the initial HPE distribution between the BMO and the mantle, plays an important role on mantle thermal structure throughout Mars’s evolution. Models with an intermediate interstitial porosity (∼20–60%), and with a reference mantle viscosity of 1020 Pa·s (at P=0GPa, T=1600K) provide the best match to the most observational constraints. This suggests that HPE partitioning between mantle and BMO has not been controlled by end-member fractional crystallisation of the initial magma ocean, and that chemical re-equilibration must have occurred to some extent during cumulate overturn. Crustal growth constraints nevertheless remain difficult to reconcile independent of HPE enrichment of the BMO. Better understanding of the earliest stages of Martian differentiation is required.

The structure and nature of Earth’s transition zone, which is delineated by the transformation of olivine to its higher-pressure polymorphs, exerts a strong influence on material transfer between upper and lower mantle. Mars, however, because of its relatively large core, is only expected to exhibit the equivalent of Earth’s uppermost transition zone seismic discontinuity. We searched the InSight seismic data for marsquakes and impacts located in an epicentral distance range favorable for detection of seismic phases that have interacted with Mars’s olivine transition (midmantle) discontinuity. Through application of careful data selection criteria and processing schemes, we found 13 events in the distance range in which body waves are expected to refract through the midmantle of Mars. Although triplicated body waves are potentially present in seven events, the distance distribution is insufficient to allow for unambiguous detection of the triplicated waveform pattern associated with the midmantle discontinuity. Comparison of travel times of the observed waveforms with predictions from recent Mars models indicates the possible presence of a midmantle discontinuity located between 987 and 1052 km or 1075 and 1122 km depth, in which the uncertainty comes from our inability to reliably distinguish first from secondary arrivals.