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Origin of TNO and Centaur Ring Systems from Surface Regolith

Presentation #110.02 in the session Many Planets, More Rings Posters (Poster + Lightning Talk)

Published onOct 23, 2023
Origin of TNO and Centaur Ring Systems from Surface Regolith

Among the population of Outer Solar System Bodies (OSBs), ring systems have been found around two Trans-Neptunian Objects (Haumea and Quaoar) and the Centaur Chariklo. These are the only ring systems in our Solar System that are not found around the outer planets. Since these rings were discovered by stellar occultation surveys that require highly favorable observing conditions, we expect more of such ring systems to exist. However, the origin and stability of these rings is unknown.

We hypothesize that surface regolith shed from the surface may be a source of material for these ring systems. A surface mass spill event ejects surface regolith, and the fast rotation combined with the highly non-spherical shape of the OSB may trap some of the regolith into orbit (Laipert & Minton, 2014). Imaging missions show that surface regolith grains vary in size from 10-4 to 1 m (Mottola, et al. 2015; Gundlach & Blum, 2013) and imply that OSBs are composed of regolith held together by surface cohesive forces. Thus, these small regolith grains can be easily ejected by a surface mass spill.

We present preliminary results on orbit trapping with constraints for the initial velocity of the surface regolith as it leaves a Chariklo-like OSB. This helps constrain the surface dynamics needed for regolith to form a ring system. The spilled regolith is modelled with an avalanche-like motion where it is ejected from the equatorial zone of the body. The contribution to the velocity from the OSBs rotation in this zone. By mapping the OSB as a triaxial ellipsoid, we can model higher order gravitational acceleration terms with the help of spherical harmonics (SHTOOLS, Wieczorek, et al, 2019). This accurately quantifies the effect of the highly oblique shape of the OSBs. The next steps are to find constraints across the parameter space of OSB rotation rate and shape.

The modelling for the spilled surface regolith is done using the N-body integrator Swiftest (Wishard et al, in review). Swiftest is a newer version of Swifter (Duncan, Levinson, & Lee, 1998) that incorporates General Relativity and Fraggle (a collisional fragmentation algorithm based on Leinhardt & Stewart, 2012), along with modern programming techniques and performance improvements. Fraggle can also show us if collisions serve as an important part of stabilizing the ring.

Future work will incorporate spherical harmonics for shape models and RINGMOONS (Hesselbrock & Minton, 2017, 2019) to model the long-term behaviour of the rings in a hybrid manner, include shepherding effects from moons, and surface relief grids.

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