The cross-disciplinary project, which avails of the help of Dr Pedro Lacerda (School of Maths and Physics), is the first study that aims to investigate and compare records of comets in medieval chronicles from Ireland, Britain and continental Europe, from the 9th to the 12th centuries, to state of- the-art computer simulation of comet dynamics. By combining the skills of a medievalist and an astronomer it proposes to use the timing of comet sightings recorded in medieval European chronicles to test the Planet Nine theory. It will take the current orbits of Halley-type comets and propagate them back to the period from the 9th to the 12th century to determine when they were likely to be visible in the night sky.  Calculations will be then performed with and without Planet Nine, which produce different patterns of comet apparitions. From a humanities point of view, it investigates the evolution of ideas about nature and the cosmos, to produce a lexicon of astronomical vocabulary in the early Middle Ages, and to challenge the idea that these were dark times for scientific enquiry and study of nature. From a scientific point of view, it aims to test a state-of-the-art theory of the architecture of our solar system using thousand year old texts.