arXiv subjects

P. S. Zain

Publications and source records attributed to P. S. Zain.

3 recordsLinked to original sources

arXiv2026

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 select NEACs with H < 18 and integrate their orbits for 1e7 yr with N-body simulations. Objects are grouped by initial semi-major axis (G1: a < 2.06 au; G2: 2.06 < a < 2.5 au; G3: a > 2.5 au). We compute 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 obtain size-dependent timescales, the change in the NEA size-frequency distribution (SFD) over 1 Myr, and 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: ~1.3e7 yr (G1), ~2.1e6 yr (G2), and ~0.9e6 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 ~1e6 yr). DART-analog impacts occur on ~1e5 yr timescales for targets smaller than about 300 m (rising to ~1e6 yr for larger bodies), whereas catastrophic collisions are negligible within NEAC lifetimes. Over 1 Myr, collisional erosion reduces the meter-size NEA population by only 0.1-1.4% depending on Q_D*. Comparison with the observed crater SFDs on Bennu, Didymos, and Ryugu indicates target strengths of Y ~ 100 Pa for Bennu, young effective surface ages for Didymos, and short crater-retention times of order 1e4-1e5 yr for craters with diameters smaller than 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, yet 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.

astro-ph.EP↗

arXiv2025

Collisional study of Hilda and quasi-Hilda asteroids

The Hilda asteroids are located in the outer main belt in a stable 3:2 mean-motion resonance with Jupiter, while the quasi-Hildas (qH) have similar orbits but are not directly under the effect of the MMR. Moreover, cometary activity has been detected in qH. In this study, we investigate the collisional evolution of Hilda asteroids and apply it to study the cratering on asteroid 334 Chicago, as well as to determine whether impacts between Hildas and qH can serve as a viable mechanism for inducing cometary activity. We simulated the collisional evolution of Hilda asteroids over a period of 4 Gyr. We considered three initial size-frequency distributions (SFD) and two scaling laws for the collisional outcomes and performed a large set of simulations for each scenario which we used to construct median SFDs of the Hilda population. We also derived impactor SFD on asteroid 334 Chicago and used it to calculate the crater SFD on 334 Chicago. Additionally, we evaluated the subcatastrophic impact timescale between Hilda and qH objects. The observed SFD of Hilda asteroids larger than 3 km is best matched by scenarios assuming that such SFD is mostly primordial, implying minimal collisional activity over time. For smaller sizes, although unconstrained, the SFD steepens significantly due to the catastrophic fragmentation of a small number of multikilometer-sized bodies. We determined that the largest impactor on 334 Chicago measures a few kilometers in size, resulting in a maximum crater size of approximately 30 km. Furthermore, the slope of the crater SFD mirrors that of the initial SFD for subkilometric bodies. While impact events between Hildas and qH can induce observable activity and although stochastic in nature, the timescale of such events exceeds the dynamical lifetime of qH, making them an unlikely primary mechanism for inducing observable activity.

astro-ph.EP↗

arXiv2020

New multi-part collisional model of the main belt: The contribution to near-Earth asteroids

Aims. We developed a six-part collisional evolution model of the main asteroid belt (MB) and used it to study the contribution of the different regions of the MB to the near-earth asteroids (NEAs). Methods. We built a statistical code called ACDC that simulates the collisional evolution of the MB split into six regions (namely Inner, Middle, Pristine, Outer, Cybele and High-Inclination belts) according to the positions of the major resonances present there ($ν_{6}$, 3:1J, 5:2J, 7:3J and 2:1J). We consider the Yarkovsky effect and the mentioned resonances as the main mechanism that removes asteroids from the different regions of the MB and delivers them to the NEA region. We calculated the evolution of the NEAs coming from the different source regions by considering the bodies delivered by the resonances and mean dynamical timescales in the NEA population. Results. Our model is in agreement with the major observational constraints associated with the MB, such as the size distributions of the different regions of the MB and the number of large asteroid families. It is also able to reproduce the observed NEAs with H < 16 and agrees with recent estimations for H < 20, but deviates for smaller sizes. We find that most sources make a significant contribution to the NEAs; however the Inner and Middle belts stand out as the most important source of NEAs followed by the Outer belt. The contributions of the Pristine and Cybele regions are minor. The High-Inclination belt is the source of only a fraction of the actual observed NEAs with high inclination, as there are dynamical processes in that region that enable asteroids to increase and decrease their inclinations.

astro-ph.EP↗