The Exchange of Mass and Angular Momentum in the Impact Event of Ice Giant Planets: Implications for the origin of Uranus. (arXiv:1811.05234v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kurosaki_K/0/1/0/all/0/1">Kenji Kurosaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Inutsuka_S/0/1/0/all/0/1">Shu-ichiro Inutsuka</a>
Uranus has a tilted rotation axis, which is supposed to be caused by a giant
impact. In general, an impact event also changes the internal compositional
distribution and drives mass ejection from the planet, which may provide the
origin of satellites. Previous studies of the impact simulation of Uranus
investigated the resultant angular momentum and the ejected mass distribution.
However, the effect of changing the initial condition of the thermal and
compositional structure is not studied. In this paper, we perform hydrodynamics
simulations for the impact events of Uranus-size ice giants composed of a water
core surrounded by a hydrogen envelope using two variant methods of the
smoothed particle hydrodynamics. We find that the higher entropy target loses
its envelope more efficiently than the low entropy target. However, the higher
entropy target gains more angular momentum than the lower entropy target since
the higher entropy target has more expanded envelope. We discuss the efficiency
of angular momentum transport and the amount of the ejected mass and find a
simple analytical model to roughly reproduce the outcomes of numerical
simulations. We suggest the range of possible initial conditions for the giant
impact on proto-Uranus that reproduces the present rotation tilt of Uranus and
sufficiently provides the total angular momentum of the satellite system that
can be created from the fragments from the giant impact.
Uranus has a tilted rotation axis, which is supposed to be caused by a giant
impact. In general, an impact event also changes the internal compositional
distribution and drives mass ejection from the planet, which may provide the
origin of satellites. Previous studies of the impact simulation of Uranus
investigated the resultant angular momentum and the ejected mass distribution.
However, the effect of changing the initial condition of the thermal and
compositional structure is not studied. In this paper, we perform hydrodynamics
simulations for the impact events of Uranus-size ice giants composed of a water
core surrounded by a hydrogen envelope using two variant methods of the
smoothed particle hydrodynamics. We find that the higher entropy target loses
its envelope more efficiently than the low entropy target. However, the higher
entropy target gains more angular momentum than the lower entropy target since
the higher entropy target has more expanded envelope. We discuss the efficiency
of angular momentum transport and the amount of the ejected mass and find a
simple analytical model to roughly reproduce the outcomes of numerical
simulations. We suggest the range of possible initial conditions for the giant
impact on proto-Uranus that reproduces the present rotation tilt of Uranus and
sufficiently provides the total angular momentum of the satellite system that
can be created from the fragments from the giant impact.
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