Dynamical Origin of (469219) Kamo`oalewa of Tianwen-2 Mission from the Main-Belt: $ν_6$ Secular Resonance, Flora Family or 3:1 Resonance with Jupiter

TL;DR

This study tests whether Earth co-orbital Kamo'oalewa could originate from main-belt reservoirs rather than lunar ejecta. It conducts 100 Myr forward integrations with the MERCURY6 Hybrid integrator, including gravitational perturbations from all planets and a fixed Yarkovsky force, for 42,825 particles drawn from $ν_6$, the Flora family, and the 3:1J MMR. The results yield transfer efficiencies of about $3.31\%$ for $ν_6$, $2.54\%$ for the Flora family, and $0.39\%$ for the 3:1J MMR, showing that main-belt pathways can dynamically reach Kamo'oalewa-like orbits. The work also identifies representative dynamical channels and notes that Tianwen-2 observations will test these origins by constraining composition and physical properties, potentially distinguishing main-belt delivery from lunar ejecta scenarios.

Abstract

China's Tianwen-2 mission, launched on 29 May 2025, targets the near-Earth object (469219) Kamo`oalewa, an Earth quasi-satellite trapped in a 1:1 mean-motion resonance with our planet. Determining the origin of Kamo`oalewa is central to understanding the formation pathways and dynamical evolution of Earth's quasi-satellite population. Here we show a strong possibility of main-belt origin for Kamo`oalewa using long-term dynamical simulations. We examine three candidate source regions: the $ν_6$ secular resonance ($ν_6$), the 3:1 mean-motion resonance with Jupiter (3:1J MMR), and the Flora family. A total of 42,825 test particles were integrated over 100 Myr. We find that asteroids from all three regions can be transported onto Kamo`oalewa-like orbits, albeit with markedly different efficiencies. Particles originating near the $ν_6$ show the highest transfer probability (3.31%), followed by the Flora family (2.54%) and the 3:1J MMR (0.39%). We further identify representative dynamical pathways linking these source regions to Earth quasi-satellite orbits. The Tianwen-2 spacecraft is expected to rendezvous with Kamo`oalewa in 2026, performing close-proximity operations and returning samples. The mission will provide decisive observational constraints on the asteroid's composition and physical properties, offering a critical test of its proposed origin.

Figures (3)

• Figure 1: Initial distribution of simulated particles in the $a$--$i$ plane. Blue circles, cyan squares, and green plus symbols denote particles initially located near the $\nu_6$, the Flora family, and the 3:1J MMR, respectively. Red open symbols indicate particles from the candidate sources that eventually evolve onto Kamo'oalewa-like orbits during the integrations. For particles initially associated with the 3:1J MMR, red open plus and cross symbols represent those evolving onto Kamo'oalewa-like orbits via the $\nu_6$ and 3:1J MMR, respectively, while red star symbols denote particles that first cross the 3:1J MMR and subsequently evolve via the $\nu_6$.
• Figure 2: From top to bottom, the A, B and C panels show the representative orbital evolutions of simulated particles from the $\nu_6$, the Flora family, and the 3:1J MMR, respectively, from the main-belt (time $T=0$) to Kamo'oalewa-like orbits in the $a$--$e$ (left) and $a$--$i$ (right) planes. Colors indicate time progression from purple (early stages) to red (approaching Kamo'oalewa-like orbits). Black squares mark initial particle positions, and the black stars denote the current position of Kamo'oalewa. Gray dashed lines indicate representative mean-motion resonances, with unlabeled ones corresponding to closely spaced resonances. Green and blue dashed lines show the approximate location of the $\nu_6$ and the loci where the perihelion distance equals that of the Earth or Venus, respectively. For clarity, the scattered points are shown after down-sampling.
• Figure 3: Statistical distribution of the time required for simulated particles originating from the three candidate source regions to evolve from their initial locations into Kamo'oalewa-like orbits.