Shuhan Zheng, University of Toronto; M. Reza Emami, University of Toronto
https://doi.org/10.64861/BSEI1269
Keywords: Temporarily Bound Objects, Temporarily Captured Orbiters, Temporarily Captured Flybys, Near-Earth Objects, Cislunar Space Domain Awareness
Abstract:
Temporarily Bound Objects (TBOs) are a class of naturally occurring Near-Earth Objects (NEOs) that experience negative Keplerian energy, for a rather short period of time, within 3 Earth Hill (EH) radii from the Earth-Moon System (EMS), and have approached Earth to a distance as close as 1 EH. Depending on whether or not a TBO completes one closed orbit around Earth in the synodic frame, it can be further classified as either a Temporarily Captured Orbiter (TCO) or Temporarily Captured Flyby (TCF). With longer resident time than their counterparts, TCOs present significant potential for telescope observations, as well as exploration or resource exploitation missions. The physical and kinematic characteristics of TBOs make their discovery and tracking especially difficult. There have been four TBOs discovered to date, namely, 2006 RH120, 2020 CD3, 2022 NX1, and 2024 PT5. Among these objects, 2006 RH120 and 2020 CD3 meet the conditions of TCOs, while 2022 NX1 and 2024 PT5 are characterized as TCFs. The most recent TBO, 2024 PT5, was estimated to have a radius of about 10 m, and it was only detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey on August 7th, 2024, about a day before it reached its perigee at 1.475 Lunar Distances (LD). The small sizes, high speeds, and long distances from an Earth-based observer, present a fundamental conundrum, making TBOs detectable with sufficient confidence only by a few highly sensitive telescopes. These telescopes are typically limited in their ability to cover a large enough area of the sky, not to mention their busy schedule for other tasks. While there exist several investigations about origins, size-frequency distributions, and capture dynamics of TBOs, this work expands the limited body of knowledge on the distinction between the TCOs and TCFs. A set of statistical guidelines are presented to quickly identify likely TCOs, using only their osculating geocentric Keplerian state vector at the point of capture, thereby reducing the number of subjects for follow-up observations and further numerical trajectory propagations. A database of over 20,000 TBOs is used in this study. The database was initially created from a steady-state analysis of the NEO population, and was later expanded and revised through refining the definition of “full orbit.” The relevant literature on TBOs generally accepts the revised synthetic population as representative. The population distribution is first randomly sampled, before propagated with an n-body propagator that accounts for gravities of all major bodies and the Moon. The resulting database consists of the portion of the propagated trajectories that have been captured by the EMS, i.e., having epochs where geocentric eccentricity e < 1. The results are further truncated to focus analysis on the dominant statistical structure. The Keplerian orbital elements for TCOs and TCFs are compared by fitting parametric Probability Density Functions (PDFs) onto each element, then measuring the difference in the distributions through a distance metric. The preliminary results show that the TCO and TCF populations differ the most in their orbit eccentricity (e), inclination (i), and true anomaly (θ) elements, with some minor discriminants potentially extractable from the other elements. The population densities of TCOs and TBOs in (e, i) and (e, θ ) spaces also show distinct statistical structures, hinting the existence of a higher-dimensional statistical structure in the Keplerian state space for TCO/TCF dichotomy. This work will constrain and quantify these statistical structures to produce a framework for early priority assessment of newly discovered TBOs, which informs tasking of follow-up sensors and reduces unnecessary high-fidelity propagation.
Date of Conference: September 15-18, 2026
Track: Cislunar SDA