A sawtooth-like timeline for the first billion years of lunar bombardment

By A. Morbidelli, Simone Marchi, William Bottke, D. Kring. 2012

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Abstract We revisit the early evolution of the Moon's bombardment. Our work combines modeling (based on plausible projectile sources and their dynamical decay rates) with constraints from the lunar crater record, radiometric ages of the youngest lunar basins, and the abundance of highly siderophile elements in the lunar crust and mantle. We deduce that the evolution of the impact flux did not decline exponentially over the first billion years of lunar history, but also there was no prominent and narrow impact spike ∼ 3.9 Gy ago, unlike that typically envisioned in the lunar cataclysm scenario. Instead, we show the timeline of the lunar bombardment has a sawtooth-like profile, with an uptick in the impact flux near ∼ 4.1 Gy ago. The impact flux at the beginning of this weaker cataclysm was 5–10 times higher than the immediately preceding period. The Nectaris basin should have been one of the first basins formed at the sawtooth. We predict the bombardment rate since ∼ 4.1 Gy ago declined slowly and adhered relatively close to classic crater chronology models ( Neukum and Ivanov, 1994 ). Overall we expect that the sawtooth event accounted for about one-fourth of the total bombardment suffered by the Moon since its formation. Consequently, considering that ∼ 12 – 14 basins formed during the sawtooth event, we expect that the net number of basins formed on the Moon was ∼ 45 – 50 . From our expected bombardment timeline, we derived a new and improved lunar chronology suitable for use on pre-Nectarian surface units. According to this chronology, a significant portion of the oldest lunar cratered terrains has an age of 4.38–4.42 Gyr. Moreover, the largest lunar basin, South Pole Aitken, is older than 4.3 Gy, and therefore was not produced during the lunar cataclysm.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/b158d9dc4d1bb0a8a54d4332e557e72990aa52a0

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Citations in the corpus

The Compositional Structure of the Asteroid Belt (2015, background): “Apart from the Os and Ru evidence, and model support that the LHB and the late veneer material were volatile-poor, there is evidence for oceans 4.4-4.3 Byr ago (Cavosie et al., 2005; Mojzsis et al., 2001; Wilde et al., 2001), i.e., 300-400 Myr before the LHB.”
Mercury’s Weather-Beaten Surface: Understanding Mercury in the Context of Lunar and Asteroidal Space Weathering Studies (2014, methodology): “…on the basis of Apollo 16 Descartes terrain samples that the age of the Nectaris impact is 3.9 Ga, in which case the same crater counting statistics would indicate a much steeper de- cline in the impact flux between 3.9 and 3.5 Ga (Ryder 1990, 2002; Stöffler and Ryder 2001; Morbidelli et al. 2012).”
The primordial nucleus of comet 67P/Churyumov-Gerasimenko (2015, background): “This dramatic event is most probably the explanation for the late heavy bombardment (LHB; Gomes et al. 2005) and occurred ∼400 Myr after the primordial disk formed (Morbidelli et al. 2012; Marchi et al. 2013).”
Large impact crater histories of Mars: The effect of different model crater age techniques (2013, methodology): “In Section 4, we assign absolute ages to these craters and basins based on both the Neukum et al. (2001) and Hartmann (2005) isochron systems using the Ivanov (2001) impact flux; we also discuss some of the inconsistenc ies between these methods and our preferred age method based on these”
Origin and Evolution of Short-period Comets (2017, background): “…studies, because of concerns with the delay of planetary instability, which was thought to be needed to explain the Late Heavy Bombardment (LHB) of the Moon and terrestrial planets (e.g., Gomes et al. 2005, Levison et al. 2011, Bottke et al. 2012, Marchi et al. 2012, Morbidelli et al. 2012).”
Origins of volatile elements (H, C, N, noble gases) on Earth and Mars in light of recent results from the ROSETTA cometary mission (2016, unknown): “Estimates of the mass contribution to Earth during the TLHB, based on the Lunar cratering record, range from 2.2 × 1023 g (Hartmann et al., 2002) down to 4 × 1022 g (assuming that the TLHB started at the time of formation of Nectaris basin; Morbidelli et al., 2012).”
The timeline of the lunar bombardment: Revisited (2018, methodology): “Like Ryder (2002) and Morbidelli et al. (2012) we consider that n important constraint is provided by the abundance of HSEs in he lunar (and martian) mantle(s).”