7 research outputs found
A hit-and-run Giant Impact scenario
The formation of the Moon from the debris of a slow and grazing giant impact
of a Mars-sized impactor on the proto-Earth (Cameron & Ward 1976, Canup &
Asphaug 2001) is widely accepted today. We present an alternative scenario with
a hit-and-run collision (Asphaug 2010) with a fractionally increased impact
velocity and a steeper impact angle.Comment: 11 pages, 2 figures, in press in ICARUS note
On the origin and composition of Theia: Constraints from new models of the Giant Impact
Knowing the isotopic composition of Theia, the proto-planet which collided
with the Earth in the Giant Impact that formed the Moon, could provide
interesting insights on the state of homogenization of the inner solar system
at the late stages of terrestrial planet formation. We use the known isotopic
and modeled chemical compositions of the bulk silicate mantles of Earth and
Moon and combine them with different Giant Impact models, to calculate the
possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in
each model. We compare these ranges to the isotopic composition of carbonaceous
chondrites, Mars, and other solar system materials. In the absence of
post-impact isotopic re-equilibration, the recently proposed high angular
momentum models of the Giant Impact ("impact-fission", Cuk & Stewart, 2012; and
"merger", Canup, 2012) allow - by a narrow margin - for a Theia similar to
CI-chondrites, and Mars. The "hit-and-run" model (Reufer et al., 2012) allows
for a Theia similar to enstatite-chondrites and other Earth-like materials. If
the Earth and Moon inherited their different mantle FeO contents from the bulk
mantles of the proto-Earth and Theia, the high angular momentum models cannot
explain the observed difference. However, both the hit-and-run as well as the
classical or "canonical" Giant Impact model naturally explain this difference
as the consequence of a simple mixture of two mantles with different FeO.
Therefore, the simplest way to reconcile the isotopic similarity, and FeO
dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic
composition and a higher (~20%) mantle FeO content.Comment: 53 Pages, 10 Figures, 1 Table, 3 Supplementary Table
Morphology and orientational behavior of silica-coated spindle-type hematite particles in a magnetic field probed by small-angle x-ray scattering
Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a coreâshell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles
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Gravity-dominated Collisions: A Model for the Largest Remnant Masses with Treatment for âHit and Runâ and Density Stratification
We develop empirical relationships for the accretion and erosion of colliding gravity-dominated bodies of various compositions under conditions expected in late-stage solar system formation. These are fast, easily coded relationships based on a large database of smoothed particle hydrodynamics (SPH) simulations of collisions between bodies of different compositions, including those that are water rich. The accuracy of these relations is also comparable to the deviations of results between different SPH codes and initial thermal/rotational conditions. We illustrate the paucity of disruptive collisions between major bodies, as compared to collisions between less massive planetesimals in late-stage planet formation, and thus focus on more probable, low-velocity collisions, though our relations remain relevant to disruptive collisions as well. We also pay particular attention to the transition zone between merging collisions and those where the impactor does not merge with the target, but continues downrange, a âhit-and-runâ collision. We find that hit-and-run collisions likely occur more often in density-stratified bodies and across a wider range of impact angles than suggested by the most commonly used analytic approximation. We also identify a possible transitional zone in gravity-dominated collisions where larger bodies may undergo more disruptive collisions when the impact velocity exceeds the sound speed, though understanding this transition warrants further study. Our results are contrary to the commonly assumed invariance of total mass (scale), density structure, and material composition on the largest remnants of giant impacts. We provide an algorithm for adopting our model into N-body planet formation simulations, so that the mass of growing planets and debris can be tracked