Ultra-dense materials with a density of >10 28 cm −3 can probably only be formed by hydrogen atoms. Ultra-dense deuterium D(−1) is the first ultra-dense material discovered. The second ultra-dense material, ultra-dense protium p(−1) is now studied. This material is observed on a vertical laser target surface, creeping over the surface after being formed in a source of the same type as used for the production of D(−1). Time-of-flight (TOF) spectra and time-of-flight mass-spectra (TOF-MS) from laser-induced Coulomb explosions in p(−1) clusters on the surface are studied, with variation of the accelerating voltage between +500V and −300V. Simultaneous spectra observed at two different flight lengths differing by a factor of 11 show that the spectra are due to massive particles. p(−1) is not identical to D(−1) but has a more complex form, giving a p–p 2 distance of 3.7pm in p 3 groups with in p(−1) clusters. Two theoretically supported p–p distances are observed at 2.3pm, as for D(−1), and 5.0pm.