  The occurrence of a bubble, due to an inversion of s$_{1/2}$ state with the
state usually located above, is investigated. Proton bubbles in neutron-rich
Argon isotopes are optimal candidates. Pairing effects which can play against
the bubble formation are evaluated. They cannot prevent bubble formation in
very neutron-rich argon isotopes such as $^{68}$Ar. This pleads for a
measurement of the charge density of neutron-rich argon isotopes in the
forthcoming years, with the advent of electron scattering experiments in next
generation exotic beam facilities such as FAIR or RIBF.
