Liquid Iron Core Research Articles

Role of partial stable stratification on fluid flow and heat transfer in rotating thermal convection

The liquid iron core of the Earth undergoes vigorous convection driven by thermal and compositional buoyancy. The dynamics of convective fluid motions and heat transfer in such conditions are determined by background rotation, geometrical symmetry, and thermal interactions across the boundaries. In this study, rotating thermal convection in a horizontal fluid layer is considered to understand the fluid flow characteristics in the Earth's outer core focusing on the regions close to the rotational axis. The effects of a partial stable stratification on fluid flow and heat transfer are investigated to ascertain the physical significance of thermal core–mantle interaction on geomagnetic field generation driven by core fluid motion. It is found that even with non-linear evolution, convective instabilities retain the fundamental characteristics of linear onset modes. Mildly supercritical regimes lead to near laminar flows with the transition to turbulent convection occurring for strongly driven convection around 50–100 times enhanced buoyancy. Axial symmetry breaking and preferential damping of small-scale vortical structures are the hallmark of penetrative convection. Rapid rotation sustains small-scale helical flows in stable regions, a necessary ingredient for the sustenance of Earthlike dipolar magnetic fields. Coherent flow structures for strongly turbulent convection are obtained using reduced-order modeling. The overall total heat transfer is suppressed (up to 25%) due to the stable stratification although convective efficiency is enhanced (up to 30%) in the unstable regions favored by rapid rotation. Flow suppression is overcome under strong buoyancy forces, a relevant dynamical regime for deep-seated dynamo action in the Earth's core.

A two-phase pure slurry model for planetary cores: one-dimensional solutions and implications for Earth's F-layer

We develop and analyse a continuum model of two-phase slurry dynamics for planetary cores. Mixed solid–liquid slurry regions may be ubiquitous in the upper cores of small terrestrial bodies and have also been invoked to explain anomalous seismic structure in the F-layer at the base of Earth's liquid iron core. These layers are expected to influence the dynamics and evolution of planetary cores, including their capacity to generate global magnetic fields; however, to date, models of two-phase regions in planetary cores have largely ignored the complex fluid dynamics that arises from interactions between phases. As an initial application of our model, and to focus on fundamental fluid dynamical processes, we consider a non-rotating and non-magnetic slurry comprised of a single chemical component with a temperature that is tied to the liquidus. We study one-dimensional solutions in a configuration set up to mimic Earth's F-layer, varying gravitational strength$R$, the solid/liquid viscosity ratio$\lambda _{\mu }$and the interaction parameter$K$, which measures friction between the phases. We develop scalings describing behaviour in the limit$R \gg 1$and$\lambda _{\mu } \gg 1$, which are in excellent agreement with our numerical results. Application to Earth's core, where$R \sim 10^{28}$and$\lambda _{\mu } \sim 10^{22}$, suggests that a pure iron slurry F-layer would contain a mean solid fraction of at most 5 %.

Mechanisms of Translation of Deep-Seated Pulses into External Shells of the Modern Earth: Evidence from Late Cenozoic Global Tectonomagmatic Activation of Our Planet

It is known that the Earth’s history is characterized by periodic activation of tectonomagmatic processes, when they are intensified without visible reasons. This is obviously related to the evolution of deep-seated petrological processes, the peculiar reflect of which are events in the external shells of the modern Earth (tectonosphere), but the nature of these processes and mechanisms of their translation in tectonosphere remain weakly studied. This problem is considered by the Late Cenozoic (Neogene–Quaternary) global activation. The modern Earth represents a cooling body with solidifying liquid iron core. This process should be accompanied by several thermodynamic, physical, and physical-chemical effects, which could lead to the internal activation of our planet. We attempted to decipher these problems using available geological, petrological, geochemical, and geophysical data on the present-day activation. It is shown that main active element in the modern Earth is uninterruptedly upward moving thin crystallization zone located between completely solidified part of the core (solid inner core) and its completely liquid part (external liquid core). Diverse phase transitions in a cooling melt passing through bifurcation points are related to this zone. The phase transitions are represented by both a change of crystallizing solid phases which built up inner core and retrograde boiling with formation of drops of “core” fluids. These drops are floated in high-Fe host melt and are accumulated at the mantle base, where they are involved in the formation of mantle plumes, which are the main carriers of deep-seated pulsed into external geosphere, and finally leave the core with them. It is suggested that in one of such points the fluid solubility in cooling high-Fe liquid of external core sharply decreases. This should lead to the simultaneous intensification of retrograde boiling of this melt over the entire zone surface of zone of the core crystallization zone, i.e., on a global scale. This could provide the influx of excess “core” fluids required for large-scale generation of mantle plumes and serve as trigger for Late Cenozoic global tectonomagmatic activation of the Earth.

The obliquity of Mercury: Models and interpretation

AbstractMercury is locked in an unusual 3:2 spin-orbit resonance and as such is expected to be in a state of equilibrium called Cassini state. In that state, the angle between the spin axis and orbit normal, called obliquity, remains almost constant while the spin axis remains almost in the plane, also called Cassini plane, defined by the normal to the Laplace plane and the normal to the orbital plane. The spin axis and the orbit normal precess together with a period of about 300 kyr. The orientation of the spin axis of Mercury has been estimated using different approaches: (i) Earth-based radar observations, (ii) Messenger images and altimeter data, and (iii) Messenger radio tracking data. The different estimates all tend to confirm that Mercury occupies the Cassini state. The observed obliquity is small and close to 2 arcmin. It indicates a normalized polar moment of inertia of about 0.34. This information, combined with the existence of a liquid iron core, as evidenced by the librations, allows to constrain the interior structure of Mercury. However, the different estimates of the orientation of the spin axis locate the spin axis somewhat behind or ahead of the Cassini plane, and it is difficult to reconcile and interpret them coherently in terms of detailed interior properties. We review recent models for the obliquity and spin orientation of Mercury, which include the effects of complex orbital dynamics, tidal deformations and associated dissipation, and internal couplings related to the presence of fluid and solid cores. We discuss some implications regarding the interpretations of the orientation estimates in term of interior properties.

Thermal Evolution and Magnetic History of Rocky Planets

We present a thermal evolution model coupled with a Henyey solver to study the circumstances under which a rocky planet could potentially host a dynamo in its liquid iron core and/or magma ocean. We calculate the evolution of planet thermal profiles by solving the energy-balance equations for both the mantle and the core. We use a modified mixing length theory to model the convective heat flow in both the magma ocean and solid mantle. In addition, by including the Henyey solver, we self-consistently account for adjustments in the interior structure and heating (cooling) due to planet contraction (expansion). We evaluate whether a dynamo can operate using the critical magnetic Reynolds number. We run simulations to explore how the planet mass (M pl), core mass fraction (CMF), and equilibrium temperature (T eq) affect the evolution and lifetime of possible dynamo sources. We find that the T eq determines the solidification regime of the magma ocean, and only layers with melt fraction greater than a critical value of 0.4 may contribute to the dynamo source region in the magma ocean. We find that the mantle mass, determined by M pl and CMF, controls the thermal isolating effect on the iron core. In addition, we show that the liquid core lasts longer with increasing planet mass. For a core thermal conductivity of 40 Wm−1 K−1, the lifetime of the dynamo in the iron core is limited by the lifetime of the liquid core for 1 M ⊕ planets and by the lack of thermal convection for 3 M ⊕ planets.

Thermal state of earth's mantle during accretion

We investigate the thermal evolution of the Earth's mantle during accretion, assuming that the initial proto-Earth grows by accreting 25 Moon to Mars-sized planetary embryos in 100 Myr. The initial proto-Earth is a differentiated planetary embryo with a liquid iron core of 1670 km radius overlain by a silicate mantle of 3430 km radius. Each embryo is assumed to impact vertically with a modified escape velocity and completely merges to the proto-Earth. The impact heating creates a large partially molten magma pond in the mantle beneath the impact site that directly interacts with the core. The iron content of the embryo sinks through the pond and merges to the core, while the partially molten buoyant silicate with temperatures higher than the stiff magma temperature pours out and spreads on the proto-Earth, forming a superheated global magma ocean. The ocean cools to the atmosphere by convection until it behaves like solid, and then cools by thermal conduction. The successive embryo impacts result in overlapping high temperature solidified magma oceans with thicknesses of 70–135 km, which hamper the creation of global mantle convection. We examine the effects of a few key physical parameters; the kinetic viscosity of the magma ocean, the total accretion time, the impact velocities of the embryos, the atmospheric temperature, and the impact time intervals using 12 thermal evolution models. The high temperature solid surface layers are the main characteristics of all of the models. It takes about 150 Myr after the accretion for the mantle to create a global convection.

Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo

Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth's Hadean liquid iron core.

Data-driven modelling of the Van Allen Belts: The 5DRBM model for trapped electrons

The magnetosphere sustained by the rotation of the Earth’s liquid iron core traps charged particles, mostly electrons and protons, into structures referred to as the Van Allen Belts. These radiation belts, in which the density of charged energetic particles can be very destructive for sensitive instrumentation, have to be crossed on every orbit of satellites traveling in elliptical orbits around the Earth, as is the case for ESA’s INTEGRAL and XMM-Newton missions. This paper presents the first working version of the 5DRBM-e model, a global, data-driven model of the radiation belts for trapped electrons. The model is based on in situ measurements of electrons by the radiation monitors on board the INTEGRAL and XMM-Newton satellites along their long elliptical orbits for respectively 16 and 19 years of operations. This model, in its present form, features the integral flux for trapped electrons within energies ranging from 0.7 to 1.75 MeV. Cross-validation of the 5DRBM-e with the well-known AE8min/max and AE9mean models for a low eccentricity GPS orbit shows excellent agreement, and demonstrates that the new model can be used to provide reliable predictions along widely different orbits around Earth for the purpose of designing, planning, and operating satellites with more accurate instrument safety margins. Future work will include extending the model based on electrons of different energies and proton radiation measurement data.

Anelastic torsional oscillations in Jupiter's metallic hydrogen region

We consider torsional Alfvén waves which may be excited in Jupiter's metallic hydrogen region. These axisymmetric zonal flow fluctuations have previously been examined for incompressible fluids in the context of Earth's liquid iron core. Theoretical models of the deep-seated Jovian dynamo, implementing radial changes of density and electrical conductivity in the equilibrium model, have reproduced its strong, dipolar magnetic field. Analysing such models, we find anelastic torsional waves travelling perpendicular to the rotation axis in the metallic region on timescales of at least several years. Being excited by the more vigorous convection in the outer part of the dynamo region, they can propagate both inwards and outwards. When being reflected at a magnetic tangent cylinder at the transition to the molecular region, they can form standing waves. Identifying such reflections in observational data could determine the depth at which the metallic region effectively begins. Also, this may distinguish Jovian torsional waves from those in Earth's core, where observational evidence has suggested waves mainly travelling outwards from the rotation axis. These waves can transport angular momentum and possibly give rise to variations in Jupiter's rotation period of magnitude no greater than tens of milliseconds. In addition these internal disturbances could give rise to a 10% change over time in the zonal flows at a depth of 3000 km below the surface.

Scale separated low viscosity dynamos and dissipation within the Earth\u2019s core

The mechanism by which the Earth’s magnetic field is generated is thought to be thermal convection in the metallic liquid iron core. Here we present results of a suite of self-consistent spherical shell computations with ultra-low viscosities that replicate this mechanism, but using diffusivities of momentum and magnetic field that are notably dissimilar from one another. This leads to significant scale separation between magnetic and velocity fields, the latter being dominated by small scales. We show a zeroth order balance between the azimuthally-averaged parts of the Coriolis and Lorentz forces at large scales, which occurs when the diffusivities of magnetic field and momentum differ so much, as in our model. Outside boundary layers, viscous forces have a magnitude that is about one thousandth of the Lorentz force. In this dynamo dissipation is almost exclusively Ohmic, as in the Earth, with convection inside the so-called tangent cylinder playing a crucial role; it is also in the “strong field” regime, with significantly more magnetic energy than kinetic energy (as in the Earth). We finally show a robust empirical scaling law between magnetic dissipation and magnetic energy.

Constraints from material properties on the dynamics and evolution of Earth’s core

The Earth’s magnetic field is powered by energy supplied by the slow cooling and freezing of the liquid iron core. Efforts to determine the thermal and chemical history of the core have been hindered by poor knowledge of the properties of liquid iron alloys at the extreme pressures and temperatures that exist in the core. This obstacle is now being overcome by high-pressure experiments and advanced mineral physics computations. Using these approaches, updated transport properties for Fe–Si–O mixtures have been determined at core conditions, including electrical and thermal conductivities that are higher than previous estimates by a factor of two to three. Models of core evolution with these high conductivities suggest that the core is cooling much faster than previously thought. This implies that the solid inner core formed relatively recently (around half a billion years ago), and that early core temperatures were high enough to cause partial melting of the lowermost mantle. Estimates of core–mantle boundary heat flow suggest that the uppermost core is thermally stratified at the present day.

Geomagnetism under scrutiny

New calculations show that the electrical resistance of Earth's liquid-iron core is lower than had been thought. The results prompt a reassessment of how the planet's magnetic field has been generated and maintained over time. See Letter p.355 The thermal and electrical properties of iron are important for understanding the thermal evolution of the deep Earth and the power available to drive the dynamo that generates Earth's magnetic field. These parameters have previously been estimated by extrapolating results from conditions with lower pressure or temperature, but Monica Pozzo and colleagues now present a calculation from first principles of these parameters at the pressure and temperature of Earth's outer core. Both conductivities are found to be two to three times higher than earlier estimates, prompting a re-evaluation of power estimates for the dynamo. The results greatly restrict models for powering the geodynamo, and indicate that the top of the core must be thermally stratified.

Thermal and electrical conductivity of iron at Earth’s core conditions

The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection; the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.

Life of the Martian dynamo

When the core dynamo of Mars initiated and when and why it ceased is not well understood. Attempt is made in this study to constrain the active period of the core dynamo, assuming that it was powered by vigorous thermal convection in the liquid iron core. Two distinct periods of the planet are investigated: the latest stage of accretion when the growing Mars embryo likely experienced high-velocity embryo–embryo collisions, and during the late bombardment at ∼4Ga that created 20 giant basins on Mars. The impact heating of Mars embryo by a large embryo, 1000 or 1500km diameter, results in thermal stratification of the core where temperature increases with radius. The thermally stratified core requires 50–120Myr to cool and regain vigorous convection, powering a strong core dynamo. The almost non-magnetic extended area of the primordial crust in the southern hemisphere supports this likely scenario. The impact heating of Mars by the seven largest of the 20 impacts is studied in detail. The collective battering the core dynamo by the impacts probably kills the dynamo. A strong core dynamo existed for ∼350Myr, until Ares and the following Amazonis impacts introduced substantial perturbations to the core temperature and constrained the core convection to the upper ∼200km for ∼28Myr, during which no strong core dynamo was generated in this part of the core. However, it is possible that the strong dynamo that existed deep in the core prior to Ares impact retained its strength while the condition gradually changed from supercritical to subcritical until Acidalia impact which likely killed the dynamo.

Melting of the Earth’s inner core

The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection. Mantle convection extracts heat from the core at a rate that has enormous lateral variations. Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary. This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre or convection with temperature equal to the solidus but with composition varying from the outer to the inner core. The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered.

Geodynamo History Preserved in Single Silicate Crystals: Origins and Long-Term Mantle Control

The long-term history of the geodynamo provides insight into how Earth's innermost and outermost parts formed. The magnetic field is generated in the liquid-iron core as a result of convection driven by heat carried across the core-mantle boundary and freezing of the solid inner core. Earth's magnetic field acts as a shield against energetic solar radiation, and therefore the geodynamo played an important role in the development and retention of our atmosphere, ultimately setting the stage for the evolution of life. A new analytical approach, using single silicate crystals that host minute magnetic particles, can reveal heretofore hidden aspects of Earth's magnetic history. This method is being used to address some of the outstanding questions regarding the long-term behavior of the geodynamo.

Iron-Rich Post-Perovskite and the Origin of Ultralow-Velocity Zones

The boundary layer between the crystalline silicate lower mantle and the liquid iron core contains regions with ultralow seismic velocities. Such low compressional and shear wave velocities and high Poisson's ratio are also observed experimentally in post-perovskite silicate phase containing up to 40 mol% FeSiO3 endmember. The iron-rich post-perovskite silicate is stable at the pressure-temperature and chemical environment of the core-mantle boundary and can be formed by core-mantle reaction. Mantle dynamics may lead to further accumulation of this material into the ultralow-velocity patches that are observable by seismology.

Earth's core and the geodynamo

Earth's magnetic field is generated by fluid motion in the liquid iron core. Details of how this occurs are now emerging from numerical simulations that achieve a self-sustaining magnetic field. Early results predict a dominant dipole field outside the core, and some models even reproduce magnetic reversals. The simulations also show how different patterns of flow can produce similar external fields. Efforts to distinguish between the various possibilities appeal to observations of the time-dependent behavior of the field. Important constraints will come from geological records of the magnetic field in the past.

The Terrestrial Web

E arth is controlled by an integrated system of dynamic forces acting on all phases (gas, liquid, and solid) of the matter that makes up our terrestrial web. These forces and their phases are linked in an intricate, and in many ways unknown, pattern. Here we review some of the latest models and observations of five subsystems of Earth: the expansive plasma- dominated magnetosphere, the gaseous atmosphere, the fluid ocean, the solid convective mantle, and the fluid-to-solid core. The magnetosphere is dominated by Earth's magnetic field, which protects the planet from the solar wind while providing the connective conduit between the solar wind and the ionosphere, creating aurorae and geomagnetic storms. Lyon (p. [1987][1]) reviews the recent observations of a substorm that provides an improved understanding of magnetic reconnection between the solar wind's magnetic field and Earth's magnetic field. Coupled general circulation models (CGCMs) are one of the most promising approaches for understanding the complex interactions between the atmosphere and oceans. Grassl (p. [1991][2]) reviews the current state of CGCMs, including the ways in which they are tested and evaluated, how they have improved our understanding of climate variability, how well we think we can predict climate, the extent and causes of modern climate variability, and how CGCMs can be improved. El Nino and La Nina, the warm and cold phases of sea surface temperature in the equatorial Pacific Ocean, are the largest single sources of global interannual climate variability. How El Nino and La Nina have varied in the past; are varying now; and will vary in the future, perhaps in response to global warming, are questions with more than just academic importance. Fedorov and Philander (p. [1997][3]) review what we have learned recently about why they occur and whether or not they may be changing as a consequence of changing climate. They suggest that understanding El Nino and La Nina must include a better knowledge of the background state of climate within which they exist. In two News stories (pp. [1984][4] and [1986][5]), Richard Kerr reports that climate shifts on longer time scales than El Nino's 2 to 7 years are drawing the attention of researchers. On the decadal scale of 10 to 20 years, there are persistent signs that an inconstant sun may subtly affect climate. And on multidecadal time scales of 40 to 80 years, a restless North Atlantic seems to be at work, alternately countering and enhancing humankind's alterations of climate. Tackley (p. [2002][6]) considers our current understanding of the convective pattern of the mantle, which comprises the bulk of the silicate Earth squeezed between the crust and the core. He tries to reconcile plate tectonics with mantle convection and discusses models that improve the integration of chemical mixing with convective flow. Finally, in the center of Earth, Buffett (p. [2007][7]) explores the generation of the geodynamo by fluid motions in the outer liquid iron core, which produces the magnetic field. Models using different flow patterns are able to produce a self-sustained dipole field, and the challenge will be to determine which pattern represents Earth. Ultimately, the geodynamo drives the magnetic field, which dominates the magnetosphere. Finding the links within and between these subsystems remains a fundamental challenge for untangling the mysteries of the terrestrial web. To provide additional depth, the staff of Science Online has put together a special Web supplement that includes a selection of previous Science articles related to the themes of the special issue, as well as links to other online resources. To explore it, see [www.sciencemag.org/feature/data/earthdynamics/main.shl][8]. [1]: /lookup/doi/10.1126/science.288.5473.1987 [2]: /lookup/doi/10.1126/science.288.5473.1991 [3]: /lookup/doi/10.1126/science.288.5473.1997 [4]: /lookup/doi/10.1126/science.288.5473.1984 [5]: /lookup/doi/10.1126/science.288.5473.1986 [6]: /lookup/doi/10.1126/science.288.5473.2002 [7]: /lookup/doi/10.1126/science.288.5473.2007 [8]: http://www.sciencemag.org/feature/data/earthdynamics/main.shl

On the internal structure and dynamics of Titan

The purpose of this paper is to study the evolution of Titan from the primordial core overturn to the present, and to investigate the possible existence of both a deep liquid layer and an iron core, depending on the composition of chondrites and the primordial amount of volatiles included in ices. Models of Titan’s interior are constructed using theoretical models based on thermal and mechanical properties of ices and silicates. Depending on both the heat transfer efficiency in chondrites and ices, and the amount of heat present in the interior, many properties of the deep structure of the satellite are deduced. Heat transfer through the convecting shell in planets is commonly estimated using parameterized laws which relate the vigor of convection to the heat flux at the top of the convecting shell. These laws, established from studies with constant viscosity fluids have been changed in order to take into account the very large viscosity contrasts in the different layers. Models also require a good knowledge of both thermodynamic and rheological parameters of materials at high pressure. In Titan, many volatiles were probably present in the primordial liquid layer. These volatiles must decrease the freezing temperature of the liquid which is of fundamental importance for the evolution of the satellite. Recent experimental results on the system NH 3–H 2O are included in the present models. Evolution of the core — Using numerical models incorporating recent results on thermal convection for fluids with strongly temperature dependent viscosity, the thermal evolution of Titan’s core is presented for two possible compositions of the planetoids. In the first case, the chondritic part of the planetoids was possibly composed of CI chondrites and the core is simply composed of silicates, whereas in the second case, chondrites with a large amount of metallic iron (EH enstatite chondrites) were accreted during Titan’s formation. Diffusive heating increases the averaged temperature of the homogeneous chondritic core up to a critical value where marginal convection may occur about 1 Ga after the core overturn. In case 1, the onset of convection is accompanied by partial melting of the silicate core. Then, the vigor of convection keeps increasing and would still be vigorous at the present time. Partial melting of silicates below a thick thermal boundary layer at the top is very likely at present. In the other model (case 2), metallic iron starts melting before the onset of convection and implies a rapid overturn of the chondritic core into a layered structure with a dense liquid iron core surrounded by a silicate layer. In this layered core, convection in the silicate layer is not very vigorous, but probably still exists. Evolution of the icy layers — Radiogenic heating of silicates is transferred by convection through the ice shell. If convection is vigorous, the heat flux through the ice shell is larger than the heat flux from the core and crystallization in the liquid shell occurs both at the top and at the bottom. Then, two different evolutions can be expected: (i) the decrease of temperature due to thickening is small and the Rayleigh number of the ice I shell increases when the layer thickens (pure H 2O case). Freezing of the liquid layer is very rapid and Titan is presently composed of a thick icy mantle, which convects vigorously; and (ii) the freezing temperature decreases strongly when pressure increases so that the Rayleigh number does not increase when ice I thickens because viscosity increases rapidly (NH 3–H 2O case). As a consequence, the thickening of ice I is very slow. The present structure of Titan depends on the primordial composition of the liquid layer, but it is probable that a liquid layer, which could be more than 350 km thick, still exists in the interior of the satellite. Such a layer may be determined by the Cassini measurements.