Cataclysm No More: New Views on the Timing and Delivery of Lunar Impactors

Zellner, N. E. B.

doi:10.1007/s11084-017-9536-3

Cited by 107 publications

(73 citation statements)

References 140 publications

(310 reference statements)

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“…Whether impact events during this basin-forming period largely occurred as a cataclysmic spike at ca. 3.9 Ga ago (e.g., Ryder 1990;Cohen et al 2000;Marchi et al 2012) or decayed monotonically after the end of planetary accretion from ∼4.3-4.2 Ga until ∼3.9-3.8 Ga ago (e.g., Hartmann 1970;Neukum et al 2001;Werner 2014;Morbidelli et al 2018), or even after (e.g., Fernandes et al 2013;Zellner 2017), remains highly debated. One of the explanations for the apparent concentration of chronometric dates at ca.…”

Section: Timing Of Lunar Bombardmentmentioning

confidence: 99%

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

et al. 2019

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The Moon is the only planetary body other than the Earth for which samples have been collected in situ by humans and robotic missions and returned to Earth. Scientific investigations of the first lunar samples returned by the Apollo 11 astronauts 50 years ago transformed the way we think most planetary bodies form and evolve. Identification of anorthositic clasts in Apollo 11 samples led to the formulation of the magma ocean concept, and by extension the idea that the Moon experienced large-scale melting and differentiation. This concept of magma oceans would soon be applied to other terrestrial planets and large asteroidal bodies. Dating of basaltic fragments returned from the Moon also showed that a relatively small planetary body could sustain volcanic activity for more than a billion years after its formation. Finally, studies of the lunar regolith showed that in addition to containing a treasure trove of the Moon's history, it also provided us with a rich archive of the past 4.5 billion years of evolution of the inner Solar System. Further investigations of samples returned from the Moon over the past five decades led to many additional discoveries, but also raised new and fundamental questions that are difficult to address with currently available samples, such as those related to the age of the Moon, duration of lunar volcanism, the

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Section: Timing Of Lunar Bombardmentmentioning

confidence: 99%

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

et al. 2019

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“…The possibility of explaining the heavy bombardment of the Moon dated at ~3.9 Gyr was one of the main arguments in support of the Nice model of the planetary system formation. However, it is necessary to mention here that the model, explaining the heavy bombardment of the Moon by asteroids, also faces criticism (Minton et al, 2015;Johnson et al, 2016); and, moreover, it has been questioned whether or not a sharp peak in the bombardment of the Moon around 3.9 Gyr is real (Zellner, 2017;Michael et al, 2018). Second, in the papers by Agnor and Lin (2012) and Kaib and Chambers (2016), it is pointed out that the present configuration of the inner planets could hardly survive the late dynamical instability of the giants.…”

Section: Introductionmentioning

confidence: 95%

Dynamics and Origin of Comets: New Problems Appeared after the Rosetta Space Mission

Emel’yanenko

2018

Sol Syst Res

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The data obtained in the recent Rosetta space mission to comet 67P/Churyumov-Gerasimenko have had a profound impact on the understanding of the nature of comets. In addition to revising the notions on the physical properties and structure of comets, this addresses dynamical aspects of the formation of the observed cometary populations (short-and long-period comets, Centaurs, trans-Neptunian objects, and Oort-cloud objects). In the review, we discuss new problems that have appeared in the theory of dynamical evolution and origin of comets due to the Rosetta mission. POPULATIONS OF COMETS IN THE SOLAR SYSTEMAlong with visible features, especially the presence of a coma in the objects of the inner Solar system, there are two characteristic features in comets that set them apart from the other Solar system bodies. First, comets move along high-eccentricity orbits; and, second, there are often substantial nongravitational effects in their motion. In the mid last century, attempts to explain these features resulted in two remarkable achievements in understanding the nature of comets. It was found that comets with near-parabolic orbits exhibit a concentration of values w = 1/a (where a is the semimajor axis of an orbit) in a range of w<10 -4 au -1 . This led J.H. Oort to a concept of a cometary cloud on the periphery of the Solar system (Oort, 1950); this cloud now bears his name. The nongravitational effects were explained by the model, supposing the presence of a solid rotating nucleus composed of frozen volatile compounds, mainly water with admixed dust (Whipple, 1950). In our days, the Oort cloud model and the cometary nucleus model have been substantially modified and improved; however, in general, these achievements provided a basis for the approaches currently developed in the studies of cometary dynamics and physics.While Oort (1950) had only 14 sufficiently exact orbits with w<10 -4 au -1 at his disposal, now the number of such orbits has increased substantially. For near-parabolic comets with a perihelion distance q <5 au, typical changes in the value of w due to the planetary perturbations for one passage through the planetary region considerably exceed 10 -4 au -1 (Fernandez,1981; Emel'yanenko, 1992). Consequently, there is no doubt that the majority of observed comets with the Oort-cloud values of w are "new": they enter near-Earth space for the first time after long being in orbits with large perihelion distances. As shown in papers by Duncan et al. (1987), Dones et al. (2004), andEmel'yanenko et al. (2007), the Oort cloud is a natural result of a long dynamical evolution of objects ejected from the planetary region. The main features in the orbit distribution of the Oort cloud weakly depend on dynamical characteristics specific to the bodies at the first stages of the Solar system formation and are mainly determined by the long-term influence of planetary, stellar, and galactic perturbations. Due to the effects of stellar and galactic perturbations, the orbits of most objects are currently far from the pl...

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“…Mercer et al (2015) and Crow et al (2017) interpreted strong signals in Ar-Ar of Apollo 17 impact melt breccias at 3.81-3.83 Ga and in U-Pb ages of lunar zircons at 3.9-4.1 Ga as signatures of Imbrium, once again providing ages in the range of interest, but not settling the question of whether Imbrium was the only contributor to the apparent ages in that range. Zellner (2017), too, has suggested the duration of lunar bombardment extends from 3.5 to 4.2 Ga, based on a collation of sample and remote sensing data with dynamic models of impactor fluences.…”

Section: Introductionmentioning

confidence: 99%

Evidence for multiple 4.0–3.7 Ga impact events within the Apollo 16 collection

Niihara

Beard

Swindle

et al. 2019

Meteorit & Planetary Scien

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In a histogram of lunar impact ages from the Apollo 16 site, there is a spike circa 3.9 Ga that has been interpreted to represent either a large number of nearly synchronous events or an abundance of samples that were affected slightly differently by the event that produced the Imbrium basin. To further scrutinize those age relationships, we extracted six centimeter‐sized clasts of impact melt from ancient regolith breccia 60016 and performed petrological and geochronological (40Ar‐39Ar) analyses. Three clasts have similar poikilitic textures, while others have porphyritic, aphanitic, or intergranular textures. Compositions and abundances of relict minerals are different in all six clasts and variously imply Mg‐suite and ferroan anorthosite target sequences. Estimated bulk compositions of four clasts are similar to previously defined group 1 Apollo 16 impact melt rocks, while the other two have higher Al2O3 and lower FeO+MgO compositions. All six clasts have similar K2O and P2O5 concentrations, which could have been derived from a KREEP‐bearing component among target sequences. Eighteen 40Ar/39Ar analyses of the six clasts produced an age range from 3823 ± 75 to 4000 ± 23 Ma, consistent with estimates for the proposed late heavy bombardment. Four clasts have multiple temperature steps that define plateau ages. These ages are distinct, so they cannot be explained by a single impact event, such as the one that produced the Imbrium impact basin. The conclusion that these represent distinct ages remains after considering the possibility of artifacts in defining plateaus.

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Cataclysm No More: New Views on the Timing and Delivery of Lunar Impactors

Cited by 107 publications

References 140 publications

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

Dynamics and Origin of Comets: New Problems Appeared after the Rosetta Space Mission

Evidence for multiple 4.0–3.7 Ga impact events within the Apollo 16 collection

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