This paper describes a novel activity to model the dynamics of a Jupiter-mass, trans-Neptunian
planet of a highly eccentric orbit. Despite a history rooted in modern astronomy, ‘Planet X’, a
hypothesised hidden planet lurking in our outer Solar System, has often been touted by conspiracy
theorists as the cause of past mass extinction events on Earth, as well as other modern-day doomsday
scenarios. Frequently dismissed as pseudoscience by astronomers, these stories continue to draw the
attention of the public by provoking mass media coverage. Targeted at junior undergraduate levels,
this activity allows students to debunk some of the myths surrounding Planet X by using simulation
software to demonstrate that such a large-mass planet with extreme eccentricity would be unable to
enter our Solar System unnoticed, let alone maintain a stable orbit.