Exploration of Spin-Orbit Dynamics in TNO Binary Borasisi-Pabu

Cold Classical Trans-Neptunian (TNO) Binaries have been assumed to have stable and slowly evolving orbits. We are exploring this hypothesis by investigating the effect of spin-orbit interactions, similar to the spin-induced orbital chaos inferred for TNO triple Lempo (Correia 2018; Ragozzine, et al., submitted). Previous work on spin-orbit dynamics in general has typically assumed that one component is spherical and/or massless and/or aligned with the orbit. Cold Classical TNO Binaries are usually similar in mass and have high eccentricities. Recent work has shown that they are often highly non-spherical and may be far from spin-orbit alignment (Proudfoot et al., accepted). Thus, the spin-orbit dynamics of TNO binaries may be in a new regime that is relatively unexplored. We are investigating the spin-orbit dynamics of the distribution of possible orbits for Cold Classical TNO Borasisi-Pabu based on non-Keplerian model fits to observed data. Preliminary results show possible chaotic behavior in the spins of the components, though orbital elements are periodic on short (hundred-year) timescales. Characterizing the spin-orbit dynamics of TNO binaries helps us understand them better, aiding in interpretation of past results (such as the orbital distribution of TNO Binaries) and potentially opening new paths for observational characterization (such as observing subtle spin period changes).