Near-Earth asteroids in main belt-crossing orbits

We study the dynamical and collisional evolution of Near-Earth asteroids (NEAs) in main belt–crossing orbits (NEACs). We selected NEACs with H<18 and integrated their orbits for 10^7 yr with N-body simulations. Objects were grouped based on their initial semi-major axis (G1: a<2.06 au; G2: 2.06<a<2.5 au; G3: a>2.5 au). We computed the fraction of each orbit spent within the main belt (MB), dynamical occupancy maps in the $(a,e)$ plane, and median lifetimes. Using collisional evolution, we obtained size-dependent timescales and the change in the NEA size-frequency distribution (SFD) over 1 Myr, along with the impactor and crater SFDs on 150 m to 1 km targets, representative of NEAs visited by space missions. Median dynamical lifetimes decrease with increasing a: sim1.3 yr (G1), sim2.1 yr (G2), and sim0.9 yr (G3). NEACs in G2–G3 maintain nearly constant MB residence fractions, with short intervals of full containment, while G1 exhibits stronger 0–0.8 oscillations (median sim0.55 for sim10^6 yr). DART-analog impacts occur on sim10^5 yr timescales for targets łesssim300 m (rising to sim10^6 yr for larger bodies), whereas catastrophic collisions are negligible within NEAC lifetimes. Over a timescale of 1 Myr, collisional erosion reduces the metre-sized NEA population by only 0.1–1.4%, depending on Q_D^*. Comparisons with the observed crater SFDs on Bennu, Didymos, and Ryugu indicate target strengths of Y Pa for Bennu, young effective surface ages for Didymos, and short crater-retention times of the order of 10^4--10^5 yr for craters with diameters $<100$ m on Ryugu, consistent with rapid resurfacing. NEACs spend a substantial fraction of their lifetimes inside the MB and undergo frequent small-scale impacts; however, collisions weakly modify the global NEA SFD on Myr timescales. Our combined dynamical-collisional framework constrains NEAC lifetimes, orbital pathways, collisional timescales, and surface processing.