Episodic formation of cometary material in the outburst of a solar-like young star

TL;DR

This study shows that crystalline silicates in cometary material can form through thermal annealing caused by outburst heating in the inner disk of young stars, challenging previous shock heating theories.

Contribution

It demonstrates that outburst-induced thermal annealing can produce crystalline silicates, providing new insights into cometary material formation.

Findings

Crystalline forsterite was produced during the outburst.

Lack of cold crystals excludes shock heating at larger radii.

Thermal annealing occurs in the surface layer of the inner disk.

Abstract

Our Solar System originated in interstellar gas and dust; the latter is in the form of amorphous silicate particles and carbonaceous dust. The composition of cometary material shows that a significant fraction of the amorphous silicates was transformed into crystalline form during the early evolution of the protosolar nebula. How and when this transformation happened has been controversial, with the main options being heating by the young Sun or shock heating. Here we report mid-infrared features in the outburst spectrum of the young solar-like star EX Lupi that were not present in quiescence. We attribute them to crystalline forsterite; the crystals were produced via thermal annealing in the surface layer of the inner disk by heat from the outburst, a process that has hitherto not been considered. The observed lack of cold crystals excludes shock heating at larger radii.