Travis Yeager (LLNL): "The MEGASIM: The Multitudinous Earth Greek (not Trojan) Asteroid Simulation: A Study of Orbital Stability and Detectability of Earth Trojan Asteroids"

We present an analysis of lifetimes and resonances of Earth Trojan Asteroids (ETAs) in the MEGASIM data set along with spatial distributions of Earth Trojan Asteroids and assess the detectability of the population in current and next-generation ground-based astronomical surveys. Trojan asteroids co-orbit the Sun with a planet but remain bound to the Lagrange points, L4 (60 deg leading the planet) or L5 (60 deg trailing). In the circular three-body approximation, the stability of a Trojan asteroid depends on the ratio of the host planet mass and the central mass. For the inner planets, the range of stability becomes increasingly small, so perturbations from the planets have made primordial Trojans rare. To date there have been just two ETAs (2010 TK7 and 2020 XL5), several Mars Trojans, and a Venus Trojan discovered. The estimated lifetimes of the known inner system Trojans are less than a million years, suggesting they are interlopers rather than members of a stable and long-lasting population. With the largest ETA N-body simulation to date, we are able to track their survival across a wide initialized parameter space. We find the remaining fraction of ETAs over time is well fit with a stretched exponential function that when extrapolated beyond our simulation run time predicts zero ETAs by 2.33 Gyr. We also show correlations between ETA ejections and the periods of the Milankovitch cycles. Though Earth's orbital dynamics dominate the instabilities of ETAs, we provide evidence that ETA ejections are linked to resonances found in the variation of the orbital elements of many, if not all the planets. Our high-fidelity Earth Trojan Asteroid (ETA) distribution maps show never-before-seen high-resolution spatial features that evolve over timescales up to 1 Gyr. The simulation was synchronized to start times and timelines of two observational astronomy surveys, 1) the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) and 2) the Zwicky Transient Facility (ZTF). We calculate upper limits for the number of ETAs potentially observable with both the ZTF and LSST surveys. Due to the Yarkovsky Effect, we find no stable ETAs on billion year timescales likely to be detected by any ETA survey, as no C-type or S-type ETAs (with H < 22 and H < 24, respectively) are likely to be stable on billion year timescales, and ETAs large enough to remain stable on billion year timescales are very rare relative to the rest of the ETA population. We find that a twilight ETA survey will not drastically increase the likelihood of individual ETA detection but would provide orders of magnitude more observations of select ETA populations. The null detection to date from ZTF restricts the potential ETA population to hundreds of objects larger than 100 meters (at H ≈ 22, Lifset et al. 2021), while a null detection by LSST will further restrict the ETA population to tens of objects larger than 100 meters.