very preliminary reference moon model abstract the deep structure of the moon is a missing piece to understand the formation and evolution of the earth moon system despite the great amount of information brought by the apollo passive seismic experiment alsep the lunar structure below deep moonquakes which occur around 900 km depth remains largely unknown we construct a reference moon model which incorporates physical constraints and fits both geodesic lunar mass and polar moment of inertia and love numbers and seismological body wave arrivals measured by apollo network data in this model the core radius is constrained by the detection of s waves reflected from the core in a first step for each core radius a radial model of the lunar interior including p and s wave velocities and density is inverted from seismic and geodesic data in a second step the core radius is determined from the detection of shear waves reflected on the lunar core by waveform stacking of deep moonquake apollo records this detection has been made possible by careful data selection and processing including a correction of the gain of horizontal sensors based on the principle of energy equipartition inside the coda of lunar seismic records and a precise alignment of sh waveforms by a non linear inversion method the very preliminary reference moon model vpremoon obtained here has a core radius of 380 40 km and an average core mass density of 5200 1000 kg m 3 the large error bars on these estimates are due to the poorly constrained s wave velocity profile at the base of the mantle and to mislocation errors of deep moonquakes the detection of horizontally polarized s waves reflected from the core and the absence of detection of vertically polarized s waves favour a liquid state in the outermost part of the core all these results are consistent within their error bars with previous estimates based on lunar rotation dissipation williams et al 2001 and on lunar induced magnetic moment hood et al 1999

seismic detection of the lunar core despite recent insight regarding the history and current state of the moon from satellite sensing and analyses of limited apollo era seismic data deficiencies remain in our understanding of the deep lunar interior we reanalyzed apollo lunar seismograms using array processing methods to search for the presence of reflected and converted seismic energy from the core our results suggest the presence of a solid inner and fluid outer core overlain by a partially molten boundary layer the relative sizes of the inner and outer core suggest that the core is 60 liquid by volume based on phase diagrams of iron alloys and the presence of partial melt the core probably contains less than 6 weight of lighter alloying components which is consistent with a volatile depleted interior

magnetic study of large apollo samples possible evidence for an ancient centered dipolar field on the moon abstract we present new rock magnetic and paleomagnetic results obtained from seventeen apollo samples measurements of the magnetic properties of the samples confirm that the magnetic properties of lunar rocks are dominated by about 0 1 wt of multidomain feni grains the ferromagnetic mineral assemblage is to the first order the same in all lunar lithologies with higher concentration in basalts than in anorthosites some of which are diamagnetic impact processing leads to an increase of the ferromagnetic content out of the seventeen samples eleven show at least one stable component of natural remanent magnetization in some cases this magnetization may be a magnetic contamination however five basalt samples have a component of magnetization that may have recorded a lunar paleofield acquired on the moon for these samples plus two similar samples from a previous study using the rock magnetic fabric as a paleohorizontal proxy paleoinclinations can be estimated from the paleomagnetic data these paleoinclinations are best explained with a dipolar field and a magnetic paleopole located at 75 n therefore our results suggest the existence on the moon at least between 3 8 and 3 3 ga of a dipolar field whose axis is close to the present day rotation axis of the moon the estimated surface field intensities of several tens of t support previous result that the moon had a dynamo field in the past and the proposed paleofield geometry suggests that this dynamo was centered on the lunar present day rotation axis

global spherical harmonic models of the internal magnetic field of the moon based on sequential and coestimation approaches 1 three new models of the global internal magnetic field of the moon based on lunar prospector lp fluxgate magnetometer observations are developed for use in understanding the origin of the moon s crustal magnetic field and for modeling its interaction with the solar wind the models are at spherical harmonic degree 170 corresponding to 64 km wavelength resolution from 30 km mean altitude lp observations coverage is complete except for a few areas near each pole original signal amplitudes are best preserved in the sequential approach map whereas feature recognition is superior in the coestimation and harmonic wave number correlation maps spherical harmonic degrees less than 15 corresponding to 666 km wavelength are largely absent from the moon s internal magnetic field we interpret this bound in terms of the moon s impact history a derived magnetization map suggests magnetizations may locally exceed 0 2 a m in the lunar crust at the survey resolution if the magnetic crust is as thick as 40 km

an early lunar core dynamo driven by thermochemical mantle convection although the moon currently has no internally generated magnetic field palaeomagnetic data combined with radiometric ages of apollo samples provide evidence for such a magnetic field from 3 9 to 3 6 billion years gyr ago1 possibly owing to an ancient lunar dynamo1 2 but the presence of a lunar dynamo during this time period is difficult to explain1 2 3 4 because thermal evolution models for the moon5 yield insufficient core heat flux to power a dynamo after 4 2 gyr ago here we show that a transient increase in core heat flux after an overturn of an initially stratified lunar mantle might explain the existence and timing of an early lunar dynamo using a three dimensional spherical convection model6 we show that a dense layer enriched in radioactive elements a thermal blanket at the base of the lunar mantle can initially prevent core cooling thereby inhibiting core convection and magnetic field generation subsequent radioactive heating progressively increases the buoyancy of the thermal blanket ultimately causing it to rise back into the mantle the removal of the thermal blanket proposed to explain the eruption of thorium and titanium rich lunar mare basalts7 plausibly results in a core heat flux sufficient to power a short lived lunar dynamo

a long lived lunar dynamo driven by continuous mechanical stirring lunar rocks contain a record of an ancient magnetic field that seems to have persisted for more than 400 million years and which has been attributed to a lunar dynamo models of conventional dynamos driven by thermal or compositional convection have had difficulty reproducing the existence and apparently long duration of the lunar dynamo here we investigate an alternative mechanism of dynamo generation continuous mechanical stirring arising from the differential motion due to earth driven precession of the lunar spin axis between the solid silicate mantle and the liquid core beneath we show that the fluid motions and the power required to drive a dynamo operating continuously for more than one billion years and generating a magnetic field that had an intensity of more than one microtesla 4 2 billion years ago3 are readily obtained by mechanical stirring the magnetic field is predicted to decrease with time and to shut off naturally when the moon recedes far enough from earth that the dissipated power is insufficient to drive a dynamo in our nominal model this occurred at about 48 earth radii 2 7 billion years ago thus lunar palaeomagnetic measurements may be able to constrain the poorly known early orbital evolution of the moon this mechanism may also be applicable to dynamos in other bodies such as large asteroids

collisionless encounters and the origin of the lunar inclination the moon is generally thought to have formed from the debris ejected by the impact of a planet sized object with the proto earth towards the end of planetary accretion models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the moon in a near equatorial orbit forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value a long standing discrepancy known as the lunar inclination problem here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with earth crossing planetesimals that were not yet accreted at the time of the moon forming event the currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass corresponding to 0 0075 0 015 earth masses eventually accreted to the earth carried by a few bodies consistent with the constraints and models of late accretion although the encounter process has a stochastic element the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters the excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the earth moon system with strong dissipation of tidal energy on the early earth this mechanism obviates the need for previously proposed but idealized excitation mechanisms places the moon forming event in the context of the formation of earth and constrains the pristineness of the dynamical state of the earth moon system

magnetic field generation in the lunar core the role of inner core growth abstract the source of the magnetic field recorded in the lunar crust remains an unresolved problem the field was most likely produced by a self sustaining dynamo in the moon s electrically conducting metal core but heat flux across the core mantle boundary was probably insufficient to power a dynamo for the field s currently known duration from 4 2 to 3 56 ga since seismic measurements indicate the existence of a solid iron inner core in addition to a still liquid iron alloy outer core inner core solidification and its associated thermochemically driven convection in the outer core could have been responsible for extending the dynamo s lifetime even in the absence of superadiabatic heat flux here we present a coupled mantle core thermal evolution model of the moon and show that core solidification could explain the onset and shutoff of the lunar dynamo consistent with the global magnetic field inferred from the paleomagnetic record

the lunar dynamo background it is unknown whether the moon has a fully differentiated and melted structure with a metallic core or retains a partially primordial unmelted interior the differentiation history of the moon is manifested by its record of past magnetism paleomagnetism although the moon today does not have a global magnetic field the discovery of remanent magnetization in lunar rocks and in the lunar crust demonstrated that there was a substantial lunar surface field billions of years ago however the origin intensity and lifetime of this field have been uncertain as a result it has been unclear whether this magnetization was produced by a dynamo in the moon s advecting metallic core or by fields generated externally to the moon establishing whether the moon formed a core dynamo would have major implications for understanding its interior structure thermal history and mechanism of formation as well for our understanding of the physics of planetary magnetic field generation the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas advances a new generation of laboratory magnetic studies of lunar rocks and spacecraft measurements of lunar crustal magnetic fields have produced major advances in our understanding of the evolution of ancient magnetic fields on the moon it has now been established that a dynamo magnetic field likely existed on the moon from at least 4 5 billion to 3 56 billion years ago with an intensity similar to that at the surface of earth today the field then declined by at least an order of magnitude by 3 3 billion years ago the early epoch of high field intensities may require an exceptionally energetic power source such as mechanical stirring from mantle precession the extended history of the lunar dynamo appears to demand long lived power sources such as mantle precession and core crystallization outlook measurements of the intensity of the ancient lunar dynamo have shown that it was surprisingly intense and long lived the next phase of lunar magnetic exploration will be to obtain more accurate measurements of field paleointensities and to determine when the dynamo initiated and finally disappeared this will be coupled with the continued development of magnetohydrodynamic models for characterizing mechanical and other unusual dynamo mechanisms and further investigations into the thermal structural and geodynamical history of the lunar core and mantle the eventual availability of absolutely oriented samples and in situ spacecraft measurements of bedrock should enable the first measurements of the paleo orientation of lunar magnetic fields such directional data could determine the lunar field s geometry and reversal frequency as well as constrain ancient local and global scale tectonic events

magnetic fidelity of lunar samples and implications for an ancient core dynamo abstract some lunar rocks have stable magnetizations that provide compelling evidence for an ancient lunar core dynamo however a longstanding problem has been interpreting the unstable alternating field af demagnetization behavior observed in the remaining majority of the apollo lunar sample suite similar unstable behavior has also been observed for many meteorites it is unclear whether the behavior of these samples indicates that they formed in the absence of an ancient magnetizing field or whether they simply have poor magnetic recording properties it is necessary to distinguish between these two possibilities in order to determine whether paleomagnetic fields were present on a sample s parent body to address this issue we analyzed five samples whose rock magnetic properties span the full suite of observed demagnetization behaviors mare basalts 15556 15016 12017 10020 and troctolite 76535 we demonstrate that the effects of spurious anhysteretic remanent magnetization arm during af demagnetization in combination with multidomain magnetic carriers and magnetic remanence anisotropy are likely responsible for the apparently poor magnetic behavior of many lunar samples therefore the unstable af demagnetization behavior observed for many lunar samples is not alone sufficient for ruling out the presence of an ancient lunar core dynamo nevertheless spurious arm may explain the observation of surprisingly high 1 t apollo era paleointensity measurements for samples thought to have formed after the cessation of a lunar core dynamo

early lunar magnetism it is uncertain whether the moon ever formed a metallic core or generated a core dynamo the lunar crust and returned samples are magnetized but the source of this magnetization could be meteoroid impacts rather than a dynamo here we report magnetic measurements and 40ar 39ar thermochronological calculations for the oldest known unshocked lunar rock troctolite 76535 these data imply that there was a long lived field on the moon of at least 1 microtesla approximately 4 2 billion years ago the early age substantial intensity and long lifetime of this field support the hypothesis of an ancient lunar core dynamo

an impact driven dynamo for the early moon recent palaeomagnetic and seismological studies have strengthened the suggestion that the moon once possessed a core dynamo despite its importance as a constraint on lunar evolution there is currently no consensus on how such a dynamo was driven two groups working independently have arrived at the idea that the lunar dynamo was powered by mechanical stirring of the liquid core dwyer et al investigate the mechanism of a dynamo driven by continuous mechanical stirring arising from the differential motion between the solid silicate mantle and the liquid core beneath they show that the fluid motions and the power required to drive a dynamo operating continuously for more than 1 billion years are readily obtained by such mechanical stirring le bars et al propose a model whereby the dynamo action comes from impact induced changes in the moon s rotation rate they show that basin forming impact events are energetic enough to have unlocked the moon from synchronous rotation and that the subsequent large scale fluid flows in the core excited by the tidal distortion of the core mantle boundary could have powered a lunar dynamo the origin of lunar magnetic anomalies1 2 3 4 5 remains unresolved after their discovery more than four decades ago a commonly invoked hypothesis is that the moon might once have possessed a thermally driven core dynamo3 but this theory is problematical given the small size of the core and the required surface magnetic field strengths6 an alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins7 but many magnetic anomalies exist that are not associated with basin antipodes here we propose a new model for magnetic field generation in which dynamo action comes from impact induced changes in the moon s rotation rate basin forming impact events are energetic enough to have unlocked the moon from synchronous rotation8 and we demonstrate that the subsequent large scale fluid flows in the core excited by the tidal distortion of the core mantle boundary9 could have powered a lunar dynamo predicted surface magnetic field strengths are on the order of several microteslas consistent with palaeomagnetic measurements5 and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins

coupled thermal orbital evolution of the early moon abstract coupled thermal orbital histories of early lunar evolution are considered in a simple model we consider a plagioclase lid overlying a magma ocean overlying a solid mantle tidal dissipation occurs in the plagioclase lid and heat transport is by conduction and melt migration we find that large orbital eccentricities can be obtained in this model we discuss possible consequences of this phase of large eccentricities for the shape of the moon and geochronology of lunar samples we find that the orbit can pass through the shape solution of garrick bethell et al garrick bethell i wisdom j zuber m 2006 science 313 652 but we argue that the shape cannot be maintained against elastic deformation as the orbit continues to evolve

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

transitions in the wintertime near surface temperature inversion at dome c antarctica in this work we study the dynamics of the surface based temperature inversion over the antarctic plateau during the polar winter using 6 years of observations from the french italian antarctic station concordia at dome c we investigate sudden regime transitions in the strength of the near surface temperature inversion here we define near surface as being within the domain of the 45 m measuring tower in particular we consider the strongly nonlinear relation between the 10 m inversion strength t 10m t s and the 10 m wind speed to this end all individual events for which the 10 m inversion strength increases or decreases continuously by more than 15 k in time are considered composite time series and vertical profiles of wind and temperature reveal specific characteristics of the transition from weak to very strong inversions and vice versa in contrast to midlatitudes the largest variations in temperature are not found at the surface but at a height of 10 m a similar analysis was performed on results from an atmospheric single column model scm overall the scm results reproduce the observed characteristics of the transitions in the near surface inversion remarkably well using model output the underlying mechanisms of the regime transitions are identified the nonlinear relation between inversion strength and wind speed at a given level is explained by variations in the geostrophic wind speed changes in the depth of the turbulent layer and the vertical divergence of turbulent fluxes moreover the transitions between different boundary layer regimes cannot be explained without considering the contribution of subsidence heating

a long lived lunar dynamo powered by core crystallization the moon does not possess an internally generated magnetic field at the present day but extensive evidence shows that such a field existed between at least 4 2 and 3 56 ga ago the existence of a metallic lunar core is now firmly established and we investigate the influence of inner core growth on generating a lunar core dynamo we couple the results of a 3 d spherical thermochemical convection model of the lunar mantle to a 1 d thermodynamic model of its core the energy and entropy budget of the core are computed to determine the inner core growth rate and its efficiency to power a dynamo sulfur is considered to be the main alloying element and we investigate how different sulfur abundances and initial core temperatures affect the model outcomes for reasonable initial conditions a solid inner core between 100 and 200 km is always produced during its growth a surface magnetic field of about 0 3 t is generated and is predicted to last several billion years though most simulations predict the existence of a core dynamo at the present day one way to stop magnetic field generation when the inner core is growing is by a transition between a bottom up and top down core crystallization scheme when the sulfur content becomes high enough in the outer core according to this hypothesis a model with about 6 to 8 wt sulfur in the core would produce a 120 160 km inner core and explain the timing of the lunar dynamo as constrained by paleomagnetic data

decline of the lunar core dynamo abstract recent analyses of apollo samples have demonstrated that a core dynamo existed on the moon between at least 4 25 and 3 56 billion years ago ga with surface field intensities reaching 70 t however it is unknown when the moon s magnetic field declined determining the temporal evolution of the dynamo is important because it constrains secular changes in power at the lunar core mantle boundary and by implication the moon s thermal and orbital evolution and the field generation mechanism here we present paleomagnetic data from several younger mare basalts which demonstrate that the surface magnetic field had declined precipitously to 4 t by 3 19 ga it is currently unclear whether such a rapid decrease in field strength reflects either the cessation of the dynamo during this period or its persistence beyond 3 19 ga in a drastically weakened state

global mapping of lunar crustal magnetic fields by lunar prospector abstract the lunar prospector electron reflectometer has obtained the first global map of lunar crustal magnetic fields revealing that the effects of basin forming impacts dominate the large scale distribution of remanent magnetic fields on the moon the weakest surface magnetic fields 40 nt are diametrically opposite to these same basins this pattern is present though less pronounced for several other post nectarian impact basins larger than 500 km in diameter the reduced strength and clarity of the pattern for older basins may be attributed to 1 demagnetization from many smaller impacts which erases antipodal magnetic signatures over time 2 superposition effects from other large impacts and 3 variation in the strength of the ambient magnetizing field the absence of fringing fields stronger than 1 nt around the perimeter of the imbrium basin or associated with craters within the basin implies that any uniform magnetization of the impact melt must be weaker than 10 6 g cm3 g 1 this limits the strength of any steady ambient magnetic field to no more than 0 1 oe at the lunar surface while the basin cooled for tens of millions of years following the imbrium impact 3 8 billion years ago

ocean worlds in the outer solar system many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells this article first reviews how such oceans are detected we then discuss how they are maintained when they formed and what the oceans likely characteristics are we focus in particular on europa ganymede callisto titan and enceladus bodies for which there is direct evidence of subsurface oceans we also consider candidate ocean worlds such as pluto and triton

further evidence for early lunar magnetism from troctolite 76535 the earliest history of the lunar dynamo is largely unknown and has important implications for the thermal state of the moon and the physics of dynamo generation the lunar sample with the oldest known paleomagnetic record is the 4 25 billion year old ga troctolite 76535 previous studies of unoriented subsamples of 76535 found evidence for a dynamo field with a paleointensity of several tens of microteslas however the lack of mutual subsample orientation prevented a demonstration that the magnetization was unidirectional a key property of thermoremanent magnetization here we report further alternating field demagnetization on three mutually oriented subsamples of 76535 as well as new pressure remanent magnetization experiments to help rule out shock magnetization we also describe new 40ar 39ar thermochronometry and cosmogenic neon measurements that better constrain the rock s thermal history although the rock is unbrecciated unshocked and slowly cooled its demagnetization behavior is not ideal due to spurious remanence acquisition despite this limitation all three subsamples record a high coercivity magnetization oriented in nearly the same direction implying that they were magnetized by a unidirectional field on the moon we find no evidence for shock remanence and our thermochronometry calculations show no significant reheating events since 4249 12 million years ago ma we infer a field paleointensity of approximately 20 40 t supporting the previous conclusion that a lunar dynamo existed at 4 25 ga the timing of this field supports an early dynamo powered by thermal or thermochemical core convection and or a mechanical dynamo but marginally excludes a dynamo delayed by thermal blanketing from radiogenic element rich magma ocean cumulates

a long lived lunar core dynamo paleomagnetic measurements indicate that a core dynamo probably existed on the moon 4 2 billion years ago however the subsequent history of the lunar core dynamo is unknown here we report paleomagnetic petrologic and 40ar 39ar thermochronometry measurements on the 3 7 billion year old mare basalt sample 10020 this sample contains a high coercivity magnetization acquired in a stable field of at least 12 microteslas these data extend the known lifetime of the lunar dynamo by 500 million years such a long lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior the inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory

tides and the evolution of the earth moon system summary a model of the tides in a hemispherical ocean is used to investigate the effect of changes in the earth s rotation rate on the power dissipated by the ocean tides the results obtained are then used in an idealized astronomical model to investigate how they affect the history of the earth moon system using the tidal model it is found that at rotation rates higher than that of the present earth the power dissipated by the semi diurnal tides in the ocean drops off rapidly as a result of the increased tidal frequency thus if the earth s rotation rate is doubled from its present value then the rate of energy dissipation in the ocean is reduced to approximately one third of its present value and the tidal torque is reduced by a factor of about 6 the present value for secular acceleration of the moon calculated from the results of the tidal model is 30 5 arcsec century 2 using this value in the astronomical model which has the moon and sun in circular orbits above the equator and assuming that the tidal torque is independent of the tidal frequency the gerstenkorn event is predicted to have occurred 1 3 109 yr ago when the astronomical model is run with a torque determined at all times from the tidal model the reduction in the energy dissipated early in the history of the system leads to a gerstenkorn date of 5 3 109 yr ago however dissipation within the solid earth is found to be important early in the history of the system and when this effect is included it gives a date for the gerstenkorn event of 3 9 109 yr ago

persistence and origin of the lunar core dynamo the lifetime of the ancient lunar core dynamo has implications for its power source and the mechanism of field generation here we report analyses of two 3 56 gy old mare basalts demonstrating that they were magnetized in a stable and surprisingly intense dynamo magnetic field of at least 13 t these data extend the known lifetime of the lunar dynamo by 160 my and indicate that the field was likely continuously active until well after the final large basin forming impact this likely excludes impact driven changes in rotation rate as the source of the dynamo at this time in lunar history rather our results require a persistent power source like precession of the lunar mantle or a compositional convection dynamo

tidal evolution of the moon from a high obliquity high angular momentum earth in the giant impact hypothesis for lunar origin the moon accreted from an equatorial circum terrestrial disk however the current lunar orbital inclination of five degrees requires a subsequent dynamical process that is still unclear in addition the giant impact theory has been challenged by the moon s unexpectedly earth like isotopic composition here we show that tidal dissipation due to lunar obliquity was an important effect during the moon s tidal evolution and the lunar inclination in the past must have been very large defying theoretical explanations we present a tidal evolution model starting with the moon in an equatorial orbit around an initially fast spinning high obliquity earth which is a probable outcome of giant impacts using numerical modelling we show that the solar perturbations on the moon s orbit naturally induce a large lunar inclination and remove angular momentum from the earth moon system our tidal evolution model supports recent high angular momentum giant impact scenarios to explain the moon s isotopic composition and provides a new pathway to reach earth s climatically favourable low obliquity