Numerical modeling of the ejecta distribution and formation of the Orientale basin on the Moon

Zhu, M. H.; Wünnemann, K.; Potter, Ross W. K.

doi:10.1002/2015je004827

Cited by 39 publications

(77 citation statements)

References 60 publications

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“…The hydrocode modeling results of Orientale basin ejecta thickness by Zhu et al . [] (using a power law exponent of −2.8) are, in general, in good agreement with the observations of Fassett et al . [] and, by extension, the parameters chosen here.…”

Section: Impact Modelingsupporting

confidence: 91%

Evaluating an impact origin for Mercury's high‐magnesium region

et al. 2017

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During its four years in orbit around Mercury, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft's X‐ray Spectrometer revealed a large geochemical terrane in the northern hemisphere that hosts the highest Mg/Si, S/Si, Ca/Si, and Fe/Si and lowest Al/Si ratios on the planet. Correlations with low topography, thin crust, and a sharp northern topographic boundary led to the proposal that this high‐Mg region is the remnant of an ancient, highly degraded impact basin. Here we use a numerical modeling approach to explore the feasibility of this hypothesis and evaluate the results against multiple mission‐wide data sets and resulting maps from MESSENGER. We find that an ~3000 km diameter impact basin easily exhumes Mg‐rich mantle material but that the amount of subsequent modification required to hide basin structure is incompatible with the strength of the geochemical anomaly, which is also present in maps of Gamma Ray and Neutron Spectrometer data. Consequently, the high‐Mg region is more likely to be the product of high‐temperature volcanism sourced from a chemically heterogeneous mantle than the remains of a large impact event.

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Section: Impact Modelingsupporting

confidence: 91%

Evaluating an impact origin for Mercury's high‐magnesium region

et al. 2017

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“…Also in large‐scale cratering processes, iSALE is capable of producing ejection data that agrees with observable constraints as shown for the Orientale basin on the Moon, where the simulated ejecta deposit (for different lunar thermal conditions) was compared with LOLA observations (Zhu et al. , ).…”

Section: Methodsmentioning

confidence: 65%

Effect of target properties and impact velocity on ejection dynamics and ejecta deposition

Luther

Zhu

Collins

et al. 2018

Meteorit & Planetary Scien

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Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s−1) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s−1. We compare the derived ejecta deposits with observations from natural craters and experiments.

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“…For example, the Imbrium basin, with the likely formation age ≃3.9 Ga, have been excavated by a D ∼ 130-km impactor (Miljković et al 2016) or by a D ∼ 250-km impactor (Schultz & Crawford 2016), with the later estimate giving larger size mainly because of the assumption of an oblique impact. The younger and smaller Orientale basin was probably made by a D ≃ 50-100 km impactor (Zhu et al 2015, Miljković et al 2016 with the lower values in this range probably being more reasonable.…”

Section: Discussionmentioning

confidence: 99%

Modeling the Historical Flux of Planetary Impactors

Nesvorný¹,

Roig²,

Bottke³

2017

117

221

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The impact cratering record of the Moon and the terrestrial planets provides important clues about the formation and evolution of the Solar System. Especially intriguing is the epoch ≃3.8-3.9 Gyr ago (Ga), known as the Late Heavy Bombardment (LHB), when the youngest lunar basins such as Imbrium and Orientale formed. The LHB was suggested to originate from a slowly declining impactor flux or from a late dynamical instability. Here we develop a model for the historical flux of large asteroid impacts and discuss how it depends on various parameters, including the time and nature of the planetary migration/instability. We find that the asteroid impact flux dropped by 1 to 2 orders of magnitude during the first 1 Gyr and remained relatively unchanged over the last 3 Gyr. The early impacts were produced by asteroids whose orbits became excited during the planetary migration/instability, and by those originating from the inner extension of the main belt (E-belt; semimajor axis 1.6 < a < 2.1 au). The inner main belt dominated the asteroid impact record after ∼3-4 Ga. The profiles obtained for the early and late versions of the planetary instability initially differ, but end up being similar after ∼3 Ga. Thus, the time of the instability can only be determined by considering the cratering and other constraints during the first ≃1.5 Gyr of the Solar System history. Our absolute calibration of the impact flux indicates that asteroids were probably not responsible for the LHB, independently of whether the instability happened early or late, because the calibrated flux is not large enough to explain Imbrium/Orientale and a significant share of large lunar craters. Comets and leftovers of the terrestrial planet formation provided additional, and probably dominant source of impacts during early epochs. The cometary impacts occur during a narrow interval after the instability and would not be recorded on surfaces if the planetary instability happened early.-2 -

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Numerical modeling of the ejecta distribution and formation of the Orientale basin on the Moon

Cited by 39 publications

References 60 publications

Evaluating an impact origin for Mercury's high‐magnesium region

Evaluating an impact origin for Mercury's high‐magnesium region

Effect of target properties and impact velocity on ejection dynamics and ejecta deposition

Modeling the Historical Flux of Planetary Impactors

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