Chondrule Formation via Impact Jetting Triggered by Planetary Accretion

TL;DR

This paper explores how collisions during planetary formation can produce chondrules through impact jetting, supported by semi-analytical calculations based on N-body simulations, highlighting a plausible formation mechanism in the early Solar System.

Contribution

It demonstrates that planetesimal collisions during planetary accretion can efficiently produce chondrules via impact jetting, with a formulated abundance based on collision dynamics and protoplanet growth.

Findings

Impact velocities exceeding 2.5 km/s can melt ejected materials to form chondrules.

Chondrule abundance correlates with the fraction of ejected mass and protoplanet mass at isolation.

Impact jetting scenario is viable within certain parameter ranges during planetary formation.

Abstract

Chondrules are one of the most primitive elements that can serve as a fundamental clue as to the origin of our Solar system. We investigate a formation scenario of chondrules that involves planetesimal collisions and the resultant impact jetting. Planetesimal collisions are the main agent to regulate planetary accretion that corresponds to the formation of terrestrial planets and cores of gas giants. The key component of this scenario is that ejected materials can melt when the impact velocity between colliding planetesimals exceeds about 2.5 km s$^{-1}$. The previous simulations show that the process is efficient enough to reproduce the primordial abundance of chondrules. We examine this scenario carefully by performing semi-analytical calculations that are developed based on the results of direct $N$-body simulations. As found by the previous work, we confirm that planetesimal collisions that occur during planetary accretion can play an important role in forming chondrules. This arises because protoplanet-planetesimal collisions can achieve the impact velocity of about 2.5 km s$^{-1}$ or higher, as protoplanets approach the isolation mass ($M_{p,iso}$). Assuming that the ejected mass is a fraction ($F_{ch}$) of colliding planetesimals' mass, we show that the resultant abundance of chondrules is formulated well by $F_{ch}M_{p,iso}$, as long as the formation of protoplanets is completed within a given disk lifetime. We perform a parameter study and examine how the abundance of chondrules and their formation timing change. We find that the impact jetting scenario generally works reasonably well for a certain range of parameters, while more dedicated work would be needed to include other physical processes that are neglected in this work and to examine their effects on chondrule formation.