  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.
