On the Solar EUV Deposition in the Inner Comae of Comets with Large Gas Production Rates

In this letter we have made a comparative study of degradation of solar EUV radiation and EUV‐generated photoelectrons in the inner comae of comets having different gas production rates, Q, with values 1 × 10 28 , 7 × 10 29 , 1 × 10 31 , and 1 × 10 32 s −1 . We found that in higher‐Q comets the radial profile of H 2 O + photo‐production rate depicts a double‐peak structure and that the differences in sunward and anti‐sunward photoionization rates are pronounced. We show that photoelectron impact ionization is an order of magnitude larger than photoionization rate near the lower photoionization peak in comets with Q > ∼1 × 10 31 s −1 . The present study reveals the importance of photoelectrons relative to solar EUV as the ionization source in the inner coma of high‐Q comets.