# Compositional evolution during rocky protoplanet accretion

**Authors:** Philip J. Carter, Zoë M. Leinhardt, Tim Elliott, Michael J. Walter, Sarah T. Stewart  
**arXiv:** [1509.07504](https://arxiv.org/abs/1509.07504)  
**Date:** 2015-09-24  
**Summary page:** https://www.summarizepaper.com/en/paper/1509.07504v1/

## Key points

- Study focuses on compositional evolution during rocky protoplanet accretion
- Earth's non-chondritic abundances of refractory lithophile elements challenge understanding of formation and evolution
- Hypothesis: Collisional erosion of differentiated planetesimals explains non-chondritic composition
- Researchers conducted N-body simulations to track growth of planetary embryos from planetesimals under Grand Tack model
- State-of-the-art collision model used in simulations to account for multiple outcomes like accretion, erosion, bouncing events
- Results show embryos exhibited range of core mass fractions with enough mantle stripping to match Earth's Fe/Mg ratio
- Diverse composition of remnant planetesimals observed, producing iron-rich and silicate-rich fragments through collisions
- Findings shed light on how collisional processes influence compositional evolution of terrestrial planets like Earth

## Summary

The study by Philip J. Carter, Zoë M. Leinhardt, Tim Elliott, Michael J. Walter, and Sarah T. Stewart delves into the compositional evolution during rocky protoplanet accretion, focusing on the Earth's non-chondritic abundances of refractory lithophile elements. This discrepancy challenges our understanding of the Earth's formation and evolution, leading to the hypothesis that collisional erosion of differentiated planetesimals could explain this non-chondritic composition. To investigate this further, the researchers conducted N-body simulations of terrestrial planet formation to track the growth of planetary embryos from planetesimals. These simulations followed the evolution through runaway and oligarchic growth phases under the Grand Tack model in the absence of giant planets. A state-of-the-art collision model was employed in these simulations to account for multiple collision outcomes such as accretion, erosion, and bouncing events. The results of the simulations revealed that during this intermediate stage of planet formation, embryos exhibited a range of core mass fractions. With significant dynamical excitation, enough mantle could be stripped from growing embryos to match the Earth's non-chondritic Fe/Mg ratio. Additionally, a diverse composition of remnant planetesimals was observed, with collisions producing both iron-rich and silicate-rich fragments. This comprehensive study sheds light on how collisional processes during rocky protoplanet accretion can influence the compositional evolution of terrestrial planets like Earth. The findings provide valuable insights into addressing the discrepancies in elemental abundances and offer a new perspective on understanding planetary formation and evolution processes in our solar system.