The Population of Interstellar Objects Detectable with the LSST and Accessible for $\textit{In Situ}$ Rendezvous with Various Mission Designs

Abstract

The recently discovered population of interstellar objects presents us with the opportunity to characterize material from extrasolar planetary and stellar systems up close. The forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will provide an unprecedented increase in sensitivity to these objects compared to the capabilities of currently operational observational facilities. We generate a synthetic population of `Oumuamua-like objects drawn from their galactic kinematics, and identify the distribution of impact parameters, eccentricities, hyperbolic velocities and sky locations of objects detectable with the LSST, assuming no cometary activity. This population is characterized by a clustering of trajectories in the direction of the solar apex and anti-apex, centered at orbital inclinations of $\sim90^\circ$. We identify the ecliptic or solar apex as the optimal sky locations to search for future interstellar objects as a function of survey limiting magnitude. Moreover, we identify the trajectories of detectable objects that will be reachable for \textit{in-situ} rendezvous with a dedicated mission with the capabilities of the forthcoming \textit{Comet Interceptor} or proposed \textit{Bridge} concept. By scaling our fractional population statistics with the inferred spatial number density, we estimate that the LSST will detect of order $\sim 15$ interstellar objects over the course of its $\sim10$ year observational campaign. Furthermore, we find that there should be $\sim1-3$ and $\sim0.0007-0.001$ reachable targets for missions with propulsion capabilities comparable to \textit{Bridge} and \textit{Comet Interceptor}, respectively. These numbers are lower limits, and will be readily updateable when the number density and size frequency distribution of interstellar objects are better constrained.