Numerical Simulations of Tidal Deformation and Resulting Light Curves of Small Bodies: Material Constraints of 99942 Apophis and 1I/`Oumuamua

In this paper, we present an open source software ($\texttt{SAMUS}$) which simulates constant-density, constant-viscosity liquid bodies subject to tidal forces for a range of assumed viscosites and sizes. This software solves the Navier-Stokes equations on a finite-element mesh, incorporating the centrifugal, Coriolis, self-gravitational, and tidal forces. The primary functionality is to simulate the deformation of minor bodies under the influence of tidal forces. It may therefore be used to constrain the composition and physical structure of bodies experiencing significant tidal forces, such as 99942 Apophis and 1I/`Oumuamua. We demonstrate that $\texttt{SAMUS}$ will be useful to constrain the material properties of Apophis during its near-Earth flyby in 2029. Depending on the material properties, Apophis may experience an area change of up to 0.5\%, with similar effects on the photometric brightness. We also apply $\texttt{SAMUS}$ to constrain the material dynamic viscosity of 1I/`Oumuamua, the first interstellar object discovered traversing the inner Solar System. `Oumuamua experienced a close approach to the Sun at perihelion ($q\simeq 0.25$ au) during which there were significant tidal forces that may have caused deformation of the body. This deformation could have lead to observable changes in the photometric light curve based on the material properties. The application of $\texttt{SAMUS}$ to produce synthetic observations which incorporate tidal deformation effects demonstrate that no deformation -- an infinite dynamic viscosity -- best reproduces the photometric data. While these results indicate that `Oumuamua did not experience significant tidal deformation, a sophisticated model incorporating non-principal axis rotation is necessary to conclusively analyze both `Oumuamua and Apophis.

Comment: 26 pages, 15 figures, 5 tables. Accepted by AAS Planetary Science Journal. Split into two papers based on reviewer and editor suggestions. Comments welcome. Publicly available software at https://github.com/astertaylor/Oumuamua