Formation of Lunar Basins from Impacts of Leftover Planetesimals by David Nesvorny et al. on Monday 21 November
The Moon holds important clues to the early evolution of the Solar System.
Some 50 impact basins (crater diameter D>300 km) have been recognized on the
lunar surface, implying that the early impact flux was much higher than it is
now. The basin-forming impactors were suspected to be asteroids released from
an inner extension of the main belt (1.8-2.0 au). Here we show that most
impactors were instead rocky planetesimals left behind at 0.5-1.5 au after the
terrestrial planet accretion. The number of basins expected from impacts of
leftover planetesimals largely exceeds the number of known lunar basins,
suggesting that the first 200 Myr of impacts is not recorded on the lunar
surface. The Imbrium basin formation (age 3.92 Gyr; impactor diameter d~100 km)
occurs with a 15-35% probability in our model. Imbrium must have formed
unusually late to have only two smaller basins (Orientale and Schrodinger)
forming afterwards. The model predicts 20 d>10-km impacts on the Earth 2.5-3.5
Gyr ago (Ga), which is comparable to the number of known spherule beds in the
late Archean.
arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.10478v1
