Evidence against a Late Heavy Bombardment event on VestaOPEN ACCESS 

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J.A. Cartwright, K.V. Hodges, M.Wadhwa

Earth and Planetary Science Letters
Volume 590, 15 July 2022

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“Highlights

• Analysis of two howardite meteorites using targeted in-situ 40Ar/39Ar techniques.
• Aim to determine the impact history of Vesta, in the context of lunar data.
• Data show a broad age range of ca. 2.5 – 4.5 Ga, different from lunar samples.
• Research significantly expands dataset for Vesta-derived meteorites.
• Results highlight the advantages of microanalytical chronometry techniques.”

“Impact events on planetary surfaces can leave significant volumes of melt, archived in planetary regoliths, which provide important information regarding the timing and nature of these events. For example, an observed ca. 3.9-4.1 Ga age cluster within lunar samples has been interpreted as indicative of a significant Solar System-wide event: the so-called “Late Heavy Bombardment”. Here, we report data from a laser ablation microprobe 40Ar/39Ar study of clasts within two unpaired howardite meteorites (NWA 1929 and Dho 485) to explore the impact history of their asteroid parent body – (4)Vesta. Laser microprobe dates for the howardites varied broadly between 3.5 to 4.5 Ga (NWA 1929) and 2.5 to 4.5 Ga (Dho 485), but show no clear cluster in ages at ca. 3.9-4.1 Ga. Consistent with previously reported U-Pb dates for HED meteorites, our data suggest an extended impact bombardment period on (4)Vesta as compared to the distribution of 40Ar/39Ar impactite dates for available samples from the Apollo and Luna sample archives. The impact history of Vesta revealed here highlights that current models of the impact flux in the inner Solar System based on the Late Heavy Bombardment hypothesis require refinement.”

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