Charge Transfer Data Needs for Cometary X‐ray Emission Modeling Available to Purchase

The emission of x‐rays has been observed from nearly twenty comets and evidence exists that it is the result of radiative decays from highly‐excited, highly‐charged solar wind ions following charge exchange with neutral species, mostly water, in the cometary atmosphere. We review the progress to date in constructing models of the x‐ray emission. However, the construction of accurate models is impeded by the near lack of reliable state‐selective charge exchange cross section data for the relevant neutral species (H₂O, CO, CO₂, etc.). The progress, and difficulties, of theoretical studies for the relevant collision processes is discussed with a particular focus on the breakdown of approximations made in the emission models.