Formation of super-Mercuries via giant impacts
arxiv(2024)
摘要
During the final stage of planetary formation, different formation pathways
of planetary embryos could significantly influence the observed variations in
planetary densities. Of the approximately 5,000 exoplanets identified to date,
a notable subset exhibit core fractions reminiscent of Mercury, potentially a
consequence of high-velocity giant impacts. In order to better understand the
influence of such collisions on planetary formation and compositional
evolution, we conducted an extensive set of smoothed particle hydrodynamics
giant impact simulations between two-layered rocky bodies. These simulations
spanned a broad range of impact velocities from one to eleven times the mutual
escape velocity. We derived novel scaling laws that estimate the mass and core
mass fraction of the largest post-collision remnants. Our findings indicate
that the extent of core vaporization markedly influences mantle stripping
efficiency at low impact angles. We delineate the distinct roles played by two
mechanisms – kinetic momentum transfer and vaporization-induced ejection – in
mantle stripping. Our research suggests that collisional outcomes for
multi-layered planets are more complex than those for undifferentiated
planetesimal impacts. Thus, a single universal law may not encompass all
collision processes. We found a significant decrease in the mantle stripping
efficiency as the impact angle increases. To form a 5 M_⊕
super-Mercury at 45^∘, an impact velocity over 200 km s^-1 is
required. This poses a challenge to the formation of super-Mercuries through a
single giant impact, implying that their formation would either favor
relatively low-angle single impacts or multiple
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