Investigating the feasibility of an impact-induced Martian Dichotomy

Mars's Crustal and Volcanic Structure Explained by Southern Giant Impact and Resulting Mantle Depletion

“…Mantle convection sets the boundary condition for core dynamics, and is therefore very important for the dynamo activity. During a giant impact event, the majority of impact heat is deposited into the mantle (Ballantyne et al., 2023; Cheng et al., n.d.) and can shut down any core convection entirely, while any heat anomaly within the core should be homogenized quickly due to the core being liquid (Monteux et al., 2015). Thanks to various heat loss mechanisms in the mantle, including the enhanced heat loss through turbulent flow within the magma pond, core cooling takes place again within 10s Myr.…”

“…Our recent study (Ballantyne et al, 2023) investigated a similar problem concerning the Martian crustal dichotomy using a Smooth Particle Hydrodynamics (SPH) approach, where an impactor radius of 750 km and impact angle of 15°(from the normal) was favored. Given this near-vertical angle, the resultant thermal anomaly is sufficiently symmetric to be parameterized as a head-on impact, even though the size and amplitude of the anomaly (and hence the magma pond) estimated by the impact scaling law is much smaller when the same impactor radius and velocity are used (Figure S1 in Supporting Information S1).…”

“…Since we are mostly interested in studying the evolution and aftermath of a magma pond, instead of constraining the impact scenario, we simply use a larger impactor radius and velocity values to obtain a magma pond with a reasonable geometry. While it was suggested in Ballantyne et al (2023) that a very low basalt fraction of 0.1 is required for a satisfactory crustal thickness, the included crustal thickness calculation (thus basalt fraction estimation) was relatively simple and aimed to serve only as one of the many ways how crust thickness could be reduced. In fact, with a basalt fraction of 0.1, our model shows that the mantle would be completely depleted after hundreds of million years, which may not be realistic when considering the geologically recent Martian volcanism.…”

“…In this case, impact melt production is often a result of extreme pressure changes relevant to impact shock waves, leaving behind a thin layer of impact melt within the impact crater. On the other hand, hydrodynamical simulation methods show that giant impacts can warm up the planetary mantles on the impacted hemisphere by thousands of degrees (Ballantyne et al., 2023; Nakajima et al., 2021; Yuan et al, 2023; Zhu et al, 2019), creating magma oceans of various extents. In quest of the dichotomy formation mechanism, collision simulations demonstrate that a northern giant impact, within a range of impact angles and velocities, can strip the right amount of primordial crust necessary to form the thin lowland crust (Marinova et al., 2008; Nimmo et al., 2008).…”

A New Database of Giant Impacts over a Wide Range of Masses and with Material Strength: A First Analysis of Outcomes

“…The computer code used in this study is SPHLATCH (e.g., Reufer et al 2012;Asphaug & Reufer 2013 and includes additional updates and corrections presented in Ballantyne et al (2023). An earlier version of the same code was used to generate a previous collision database (Reufer 2011) on which the first machine-learning derived surrogate models were based (Cambioni et al 2019;Emsenhuber et al 2020), and an updated semiempirical scaling law was developed (Gabriel et al 2020).…”