sentences:  For each Earth–Mars cycler that is not a multiple of 7 synodic periods, an outbound cycler intersects Mars on the way out from Earth while an inbound cycler intersects Mars on the way in to Earth.The only difference in these trajectories is the date in the synodic period in which the vehicle is launched from Earth.Earth–Mars cyclers with a multiple of 7 synodic periods return to Earth at nearly the same point in its orbit and may encounter Earth and/or Mars multiple times during each cycle.