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, and the case of $^{46}$Ar is analyzed. Several experimental data favor the bubble hypothesis, such as the B(E2) value of the first 2$^+$ state, the energy level of the first 3$^-$ state as well as the ground state properties of $^{47}$K. Pairing effects which can play against the bubble formation are evaluated. They cannot prevent bubble formation in more neutron-rich argon isotopes such as $^{68}$Ar. This pleads for a measurement of the charge density of $^{46}$Ar in the forthcoming years, with the advent of electron scattering experiments in next generation exotic beam facilities such as FAIR or RIBF.