Near-Earth asteroids in main belt-crossing orbits

¹ Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP. Paseo del Bosque S/N (1900), La Plata, Argentina
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N (1900), La Plata, Argentina
³ Grupo de Ciencias Planetarias, Dpto. de Geofísica y Astronomía, FCEFyN, UNSJ - CONICET, Av. J. I. de la Roza 590 oeste, J5402DCS Rivadavia, San Juan, Argentina

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 September 2025
Accepted: 1 April 2026

Abstract

Aims. We study the dynamical and collisional evolution of Near-Earth asteroids (NEAs) in main belt-crossing orbits (NEACs).

Methods. We selected NEACs with H < 18 and integrated their orbits for 10⁷ 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.

Results. Median dynamical lifetimes decrease with increasing a : ∼1.3 × 10⁷ yr (G1), ∼2.1 × 10⁶ yr (G2), and ∼0.9 × 10⁶ 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 ∼0.55 for ∼10⁶ yr). DART-analog impacts occur on ∼10⁵ yr timescales for targets ≲300 m (rising to ∼10⁶ 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 ≈ 100 Pa for Bennu, young effective surface ages for Didymos, and short craterretention times of the order of 10⁴-10⁵ yr for craters with diameters < 100 m on Ryugu, consistent with rapid resurfacing.

Conclusions. 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.