Episodic planetesimal disruptions triggered by dissipation of gas disk

TL;DR

The study demonstrates that gas-disk dissipation can drive episodic catastrophic planetesimal disruptions via sweeping secular resonances of Jupiter and Saturn, coupled with Jovian mean-motion resonances, producing a collision-rich phase in the inner Solar System. It employs high-resolution N-body simulations with a dissipating gas disk to reveal three collision episodes and a transition to embryo-driven dynamics after gas dispersal. The results connect meteoritic records of early high-velocity collisions, such as CB chondrites, to dynamical excitation in a gas-rich protoplanetary disk without requiring giant-planet migration, while also implying continued, embryo-driven disruption later. This mechanism may be common in protoplanetary disks during nebula dissipation and has implications for early planet formation and the delivery or disruption of core- and mantle-rich material to forming planets.

Abstract

Catastrophic disruptions of planetesimals occur in high-velocity collisions. Radioisotope dating of planetesimal disruption events recorded in meteorites confirms frequent catastrophic collisions in the first $\sim$10 Myr of the Solar System, reflecting a violent environment of the time. However, the nebula gas can damp the eccentricity of planetesimals and suppress the frequency of planetesimal collisions. Strong dynamical mechanisms that excited the protoplanetary disk are required. Here we show that the sweeping secular resonances of Jupiter and Saturn induced by the nebular gas dissipation, together with the mean motion resonances of Jupiter, can trigger a large number of catastrophic collisions, which occur episodically when the secular resonances are at $\sim$2-3 au and continue thereafter. After the gas dissipation completes, catastrophic collisions decrease in frequency, with scattering by planetary embryos becoming the major driving force of the collisions. Our results suggest that the violent environment excited by secular and mean motion resonances can be ubiquitous in protoplanetary disks during nebula dissipation.

Figures (9)

• Figure 1: Temporal evolution of impact velocity and the surface density of the gas disk. Three simulations with gas dissipation timescale ($\tau$) of 1 Myr (a), 2 Myr (b), and 3 Myr (c) are shown. Each dot is one collision event, with colors representing the ratio of impact velocity to the mutual escape velocity of impactors ($v/v_{\rm esc}$). The solid curves show the gas surface density at 1 au. The solid and open triangles on the $x$-axes represent 1.2$\tau$ and 2.4$\tau$, which are the beginning of episodic (Episode I) and continuous (Episode II) high-velocity collisions, respectively.
• Figure 2: Semi-major axes of projectiles in catastrophic collisions. The $x$-axis is the ratio of time to gas dissipation timescale ($t/\tau$). The results of the simulation with $\tau=1$ Myr are shown. The sweeping secular resonances ($\nu_5$ and $\nu_6$, nominal locations shown in solid and dashed red curves) and four Jovian MMRs (dashed black lines) are plotted. (a) Instantaneous semi-major axes of projectiles in catastrophic collisions at the time of collision. The catastrophic collisions are divided into Episode I ($t\leq2.4\tau$), Episode II ($2.4\tau<t\leq5.5\tau$), and Episode III ($t>5.5\tau$). (b) Evolution of semi-major axes of projectiles in Episode I collisions. The four groups of catastrophic collisions that occur episodically are color-coded based on the collision times, corresponding to the spikes of impact velocity in Fig. \ref{['figure1']}. The curves show the evolution of semi-major axes, ending by dots indicating the collisions.
• Figure 3: Orbital evolution of planetesimals in Episode I. Shown are the results of a simulation with $\tau=1$ Myr, including semi-major axis ($a$), eccentricity ($e$), and the difference in longitudes of periapsis between a planetesimal and Jupiter ($\varpi-\varpi_5$). The solid and dashed red lines show the locations of $\nu_5$ and $\nu_6$. The black lines are Jovian MMRs. (a) A snapshot of semi-major axis and eccentricity evolution of planetesimals at 1.5 Myr (Supplementary Video \ref{['v2']}). Each dot represents a planetesimal. The projectiles in Episode I catastrophic collisions are color-coded as in Fig. \ref{['figure2']}b. Other planetesimals are gray. (b) Orbital evolution of a projectile of catastrophic collision. The projectile gains $\sim$$0.6$ eccentricity at 5:2 MMR of Jupiter and collides with a planetesimal at 1.52 Myr. (c) Evolution of the critical angle of secular resonance $\nu_5$ for the projectile.
• Figure 4: Comparison between the radioisotope ages of collision events and the simulated frequency of catastrophic collisions. (a) Radioisotope ages of collision events. The ages of CB chondrules and metal grains dated using different isotope systems Bollard2015Wolfer2023Pravdivtseva2017Yamashita2010 and the disruption times of three iron meteorite parent bodies Hunt2022 are shown. (b-d) Temporal evolution of collision frequency. Three simulations using different gas dissipation timescales ($\tau$) are shown. Every 0.1 Myr, the frequencies of catastrophic collisions, super-catastrophic collisions, and super-catastrophic collisions with impact velocity $>$13 km s$^{-1}$ that potentially cause vaporization of planetesimal cores are shown relative to the total number of catastrophic collisions. The kernel density estimates of all collisions (black curves) are plotted with a different scale.
• Figure 5: Locations of catastrophic collisions. The $x$-axis is the ratio of time to gas dissipation timescale ($t/\tau$). The results of high-resolution simulation with $\tau=1$ Myr are shown. The sweeping secular resonances ($\nu_5$ and $\nu_6$, solid and dashed red curves) and four Jovian MMRs (dashed black lines) are plotted.