This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.

David Minton (Arizona State)

Abstract

We use published models for the formation of the $\sim1 \times 10$ km Borealis Basin on Mars from a ~2000 km impactor to investigate the fate of ejected debris. We use an n-body integrator to show that debris from this event could have been an important contributor to the cratering history of the Earth, Moon, and Mars well aOer the basin formed. We investigate whether this event could have been responsible for the Late Heavy Bombardment (LHB) on these planets. We show that the giant impact debris model has a number of features that are more favorable for explaining the LHB compared with giant planet instability models, such as the Nice model.

Notes

• Craters
  • fossil record of small bodies
  • previously thought:
    • Strom et al. 2005: Heavily cratered terrains of Moon, Mars, Mercurywere dominated byMBAs ejected in a size-dependent way.
      • resonant sweeping of asteroid belt
    • Gomes et al. 2005: classic Nice model
    • Kring & Cohen 2002: impactors had asteroidal geochemistry
  • But…
    • Nice model only works if Jupiter jumps
      • Only ~1-5 percent of simulations produce required jump.
  • Cratered terrain evolution model
    • Input impactor size & velocity distributions.
    • Constraints:
      • must reach observed crater density in Lunar highlands
      • cannot make more Lunar basins than seen
  • Results:
    • MBA is not a good model for the Lunar highlands
  • So, what was the highlands impactorSFD?
    • Size distribution primordial “bump” around ~100 km is missing in the model
    • SPH codes: not very good at these scales
    • N-body sims:
      • Mars sucks as a scatterer.
      • Collisional evolution then produces the bump.
      • Gets about the right number of basins on Moon and Mars.
      • Bodies collect in theHungarias, kind of no matter what.
        • Thus, we can’t use Hungarias as a constraint.