  Context: Co-orbital systems are bodies that share the same mean orbit. They
can be divided into different families according to the relative mass of the
co-orbital partners and the particularities of their movement. Janus and
Epimetheus are unique in that they are the only known co-orbital pair of
comparable masses and thus the only known system in mutual horseshoe orbit.
  Aims: We aim to establish whether the Janus-Epimetheus system might have
formed by disruption of an object in the current orbit of Epimetheus.
  Methods: We assumed that four large main fragments were formed and neglected
smaller fragments. We used numerical integration of the full N-body problem to
study the evolution of different fragment arrangements. Collisions were assumed
to result in perfectly inelastic merging of bodies. We statistically analysed
the outcome of these simulations to infer whether co-orbital systems might have
formed from the chosen initial conditions.
  Results: Depending on the range of initial conditions, up to 9% of the
simulations evolve into co-orbital systems. Initial velocities around the
escape velocity of Janus yield the highest formation probability. Analysis of
the evolution shows that all co-orbital systems are produced via secondary
collisions. The velocity of these collisions needs to be low enough that the
fragments can merge and not be destroyed. Generally, collisions are found to be
faster than an approximate cut-off velocity threshold. However, given a
sufficiently low initial velocity, up to 15% of collisions is expected to
result in merging. Hence, the results of this study show that the considered
formation scenario is viable.
