Metal-silicate mixing upon Giant Impacts into magma oceans

• DOI: 10.5194/epsc2024-1126
• Publication Date: 2024-07-03T12:38:20Z
• Authors: Laetitia Allibert; Maylis Landeau; Randolph Röhlen; Augustin Maller; Miki Nakajima; Kai Wünnemann

Introduction: Planetary formation models suggest that Earth experienced multiple high-energy impacts. They can produce substantial melt in the proto-Earth’s silicate mantle, possibly forming a global magma ocean. Mixing of impactor’s metallic core into molten Earth's mantle controls chemical equilibration between metal and silicates, which defines respective compositions mantle. Previous studies explore mixing upon large impacts either with numerical modelling or analog laboratory experiments. Numerical simulations are efficient reproducing shock physics hypervelocity However, their spatial resolution is limited does not allow for turbulent features responsible metal-silicate On other hand, liquid impact experiments do small-scale turbulence subsonic: they neglect compressibility effects.  Here, we investigate degree by coupling various results from fluid [1] extending crater depth to supersonic conditions [2].Methods: The used extend regimes consist volume impacting tank water. denser impactor dyed, enabling optical estimate evolving sinking plume right after impact. gives, once corrected material, an analogue entrained silicates given collision. We have extended on growth subsonic using grid-based Eulerian code iSALE [3,4,5,6] simulate scaling-law produced [2] supersonic, conditions, here be further applied mixing. density ρi lighter target ρt  involves two main stages: opening at early times fall central jet had been formed collapse crater. That latter event release material target. At later times, buoyancy forces become important, thermal descending competition total momentum collapsing dynamics [1], hence surrounding silicates. It has showed height scales as maximum  and [7]. use these scalings, coupled those regarding extension accounting both effects Froude number (measure importance kinetic energy its gravitational impact) Mach (impact velocity sound speed ratio).Results: Figure 1 shows mass prior descent magma. provides direct measure so-called during find decreases estimates derived extent effect however depends parameters such size. larger compared size, number. For M>3, underestimated more than factor 3 if shock.Figure 1. Mass mixed stage, magma, Δ, function radius, R/Rt , varying number, M, cases: a) escape velocity, U = Ue b) twice 2 Ue. Circle: 100 km radius onto Earth-sized Diamond: canonical Moon-forming scenario Mars-sized [8]. Square: 20 smaller fast-spinningEarth [9].Discussion: studied statistics how often typical classical scenarios accretion collisions would occur analogs through history. collision files N-body Grand Tack [10] that, depending impacted 24% 74% amount endured may M>3. If considering only giant impacts, when most significant, this drops 4% 28%. mixing, extreme, need accounted following reequilibration entire stage planetary formation.  Acknowledgments: gratefully acknowledge developers iSALE-2D, including Gareth Collins, Kai Wünnemann, Dirk Elbeshausen, Tom Davison, Boris Ivanov Jay Melosh. This work was funded Deutsche Forschungsgemeinschaft (SFB-TRR170, subproject C2 C4).References: Landeau M. et al. (2021) Plan. Sci. Lett. 564, 116888. Allibert L. (2023) JGR: Planets 128 (8), e2023JE007823. [3] Collins. G. S. (2004) Meteoritics & Science 39:217-231. [4] Wünnemann K. (2006) Icarus 180:514-527. [5] D. (2009). Icarus, 204(2), 716-731. [6] Elbeshausen (2011). Proceedings 11th Hypervelocity Impact Symposium (HVIS), Fraunhofer Verlag. [7] Ghabache É. (2014) . Fluid Mech. 761, 206–219. [8] Canup R. 168 (2), 433–456. [9] Ćuk, Stewart (2012) 338 (6110), 1047–1052. Jacobson A. Morbidelli Phil. Trans. Roy. Soc. A 372, 20130174.