Accretion of Ornamental Equatorial Ridges on Pan, Atlas and Daphnis. (arXiv:2007.13227v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Quillen_A/0/1/0/all/0/1">Alice C. Quillen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zaidouni_F/0/1/0/all/0/1">Fatima Zaidouni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nakajima_M/0/1/0/all/0/1">Miki Nakajima</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wright_E/0/1/0/all/0/1">Esteban Wright</a>
We explore scenarios for the accretion of ornamental ridges on Saturn’s moons
Pan, Atlas, and Daphnis from material in Saturn’s rings. Accretion of complex
shaped ridges from ring material should be possible when the torque from
accreted material does not exceed the tidal torque from Saturn that ordinarily
maintains tidal lock. This gives a limit on the maximum accretion rate and the
minimum duration for equatorial ridge growth. We explore the longitude
distribution of ridges accreted from ring material, initially in circular
orbits, onto a moon that is on a circular, inclined or eccentric orbit. Sloped
and lobed ridges can be accreted if the moon tidally realigns during accretion
due to its change in shape or because the disk edge surface density profile
allows ring material originating at different initial semi-major axes to impact
the moon at different locations on its equatorial ridge. We find that accretion
from an asymmetric gap might account for a depression on Atlas’s equatorial
ridge. Accretion from an asymmetric gap at orbital eccentricity similar to the
Hill eccentricity, might allow accretion of multiple lobes, as seen on Pan. Two
possibly connected scenarios are promising for growth of ornamental equatorial
ridges. The moon migrates through the ring, narrowing its gap and facilitating
accretion. The moon’s orbital eccentricity could increase due to orbital
resonance with another moon, pushing it into its gap edges and facilitating
accretion.
We explore scenarios for the accretion of ornamental ridges on Saturn’s moons
Pan, Atlas, and Daphnis from material in Saturn’s rings. Accretion of complex
shaped ridges from ring material should be possible when the torque from
accreted material does not exceed the tidal torque from Saturn that ordinarily
maintains tidal lock. This gives a limit on the maximum accretion rate and the
minimum duration for equatorial ridge growth. We explore the longitude
distribution of ridges accreted from ring material, initially in circular
orbits, onto a moon that is on a circular, inclined or eccentric orbit. Sloped
and lobed ridges can be accreted if the moon tidally realigns during accretion
due to its change in shape or because the disk edge surface density profile
allows ring material originating at different initial semi-major axes to impact
the moon at different locations on its equatorial ridge. We find that accretion
from an asymmetric gap might account for a depression on Atlas’s equatorial
ridge. Accretion from an asymmetric gap at orbital eccentricity similar to the
Hill eccentricity, might allow accretion of multiple lobes, as seen on Pan. Two
possibly connected scenarios are promising for growth of ornamental equatorial
ridges. The moon migrates through the ring, narrowing its gap and facilitating
accretion. The moon’s orbital eccentricity could increase due to orbital
resonance with another moon, pushing it into its gap edges and facilitating
accretion.
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