We compare CLOUDY predictions for the equilibrium ionization in the in
terstellar cloud surrounding the solar system with pick-up ion data. T
he incident radiation held includes contributions from hot stars, the
emission from the conductive cloud boundary and the diffuse EUV backgr
ound. To within the observational uncertainties, CLOUDY predictions fo
r the ratios n(He degrees)/n(O degrees), n(N degrees)/n(O degrees), n(
Ne degrees)/n(O degrees), and n(He degrees)/n(Ne degrees) are consiste
nt with pick-up ion data, provided that O degrees and N degrees are fi
ltered by similar to 50% in the heliopause region and the outer helios
phere as predicted by others. Thus, the steady-state ionization model
and assumed radiation held appear approximately valid. However, the yo
uth and low intervening column density towards the Vela pulsar leave o
pen the possibility that the parent supernova explosion similar to 10,
500 years ago, and 200 pc distant, may also have affected LISM ionizat
ion, although the mechanism is uncertain. Support for this last possib
ility is provided by the apparent signature of the Vela explosion in t
he terrestrial geological record.