# A Radiative Heating Model for Chondrule and Chondrite Formation

## TL;DR

This paper presents a new radiative heating model for chondrule and chondrite formation involving close encounters between primitive and differentiated planetesimals, explaining their simultaneous formation and specific compositional features.

## Contribution

It introduces a novel scenario where chondrules and chondrites form together during a brief radiative heating event caused by planetesimal flybys, supported by thermal models and laboratory experiments.

## Key findings

- Chondrules can be formed by gradual heating during planetesimal flybys.
- The model explains the compositional features of chondrules and chondrites.
- Rare impact events can account for the abundance of chondrules in meteorites.

## Abstract

We propose that chondrules and chondrites formed together during a brief radiative heating event caused by the close encounter of a small (m to km-scale), primitive planetesimal (SPP) with incandescent lava on the surface of a large (100 km-scale) differentiated planetesimal (LDP). In our scenario, chondrite lithification occurs by hot isostatic pressing (HIP) simultaneously with chondrule formation, in accordance with the constraints of complementarity and cluster chondrites. Thermal models of LDPs formed near t=0 predict that there will be a very narrow window of time, coincident with the chondrule formation epoch, during which crusts are thin enough to frequently rupture by impact, volcanism and/or crustal foundering, releasing hot magma to their surfaces. The heating curves we calculate are more gradual and symmetric than the "flash heating" characteristic of nebular models, but in agreement with the constraints of experimental petrology. The SPP itself is a plausible source of the excess O, Na and Si vapor pressure (compared to a solar nebula environment) that is required by chondrule observations. Laboratory experiments demonstrate that FeO-poor porphyritic olivine chondrules, the most voluminous type of chondrule, can be made using heating and cooling curves predicted by the "flyby" model. If chondrules are a by-product of chondrite lithification, then their high volume abundance within well-lithified chondritic material is not evidence that they were once widespread within the Solar System. Relatively rare events, such as the flybys modeled here, could account for their abundance in the meteorite record.