Main-sequence progenitor configurations of the NN Ser candidate circumbinary planetary system are dynamically unstable

Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exo-planets. Under the assumption that these planets are real and survived from the binary's main-sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions about binary evolution, we find that survival of the planets through the entire main-sequence lifetime is very unlikely. Hence, we conclude that the planets are not survivors from before the common envelope phase, implying that either they formed recently out of material ejected from the primary or that the observed signals are of non-planetary origin.