Planet Formation Group
Astrophysics Department, School of Physics, University of Bristol

Planet Formation Group: Mia Mace

The current most widely-accepted scenario for Moon formation is a large impact between the proto-Earth and another smaller planet. This impact theory must be able to explain any compositional differences/similarities between the Earth and Moon; there are various flavours of the impact theory that attempt to do this (canonical, fast-spinning Earth, two sub-Earths), each of which tells a different story about the chemical composition/state of the disk. After the impact a debris disk comprised of material thrown out from both objects forms around the Earth.

Forming Moonlets

There is disagreement in the field about the physical state of this disk - is it mostly solid/liquid material or mostly gas? We run N-body simulations of a circumterrestrial disk comprised of solid particles as a starting point to investigate energy considerations of the disk. Self-heating by mutual collisions is negligible, most of the kinetic energy is deposited in the inner edge of the Roche limit. Reduction in potential energy of the Earth-disk system by accretion onto the Earth is converted mainly into heating the inner disk (i.e. within the Roche limit), whereas the outer disk is not heated sufficiently to vapourise condensates.

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