  We present a detailed dynamical analysis of the orbital stability of the BD
+20 2457 system, which features planets or brown dwarfs moving on relatively
eccentric orbits. We find that the system exhibits strong dynamical instability
on astronomically short timescales across a wide range of plausible orbital
eccentricities, semi-major axes, and inclinations. If the system truly hosts
massive planets or brown dwarfs, our results suggest that they must move on
orbits significantly different to those proposed in the discovery work. If that
is indeed the case, then it is likely that the best-fit orbital solutions for
the proposed companions will change markedly as future observations are made.
Such observations may result in the solution shifting to a more
dynamically-stable regime, potentially one where stability is ensured by
mutually resonant motion.
