The EUV emission from sun-grazing comets

TL;DR

This paper reports on observations of two sun-grazing comets by SDO/AIA, showing that their interaction with the solar atmosphere causes enhanced EUV emission due to sublimation, dissociation, and ionization of cometary molecules.

Contribution

It provides the first detailed explanation of EUV emission from sun-grazing comets based on their atmospheric interaction with the Sun.

Findings

EUV radiance increases during comet passages.

Cometary molecules sublimated and dissociated, producing ions.

Ionization leads to observable EUV emission in AIA bands.

Abstract

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) has observed two sun-grazing comets as they passed through the solar atmosphere. Both passages resulted in a measurable enhancement of Extreme Ultraviolet (EUV) radiance in several of the AIA bandpasses. We explain this EUV emission by considering the evolution of the cometary atmosphere as it interacts with the ambient solar atmosphere. Molecules in the comet rapidly sublimate as it approaches the Sun. They are then photodissociated by the solar radiation field to create atomic species. Subsequent ionization of these atoms produces a higher abundance of ions than normally present in the corona and results in EUV emission in the wavelength ranges of the AIA telescope passbands.