The far reaches of the outer solar system may be home to an icy giant â€” a hypothetical planet scientists have dubbed â€œPlanet Nine.â€
Meanwhile, archives back on Earth are home to dozens of medieval records documenting the passage of comets through the heavens. Now, two researchers from Queenâ€™s University Belfast in Northern Ireland are hoping to use these old scrolls and tapestries to solve the modern astronomical mystery of Planet Nine.
â€œWe have a wealth of historical records of comets in Old English, Old Irish, Latin and Russian which have been overlooked for a long time,â€ said university medievalist Marilina Cesario, one of the leaders of the project. â€œEarly medieval people were fascinated by the heavens, as much as we are today.â€
The records include dates and times, Cesario said, which makes them useful to modern-day astronomers.
Planet Nine, if it exists, would have about 10 times the mass of Earth and orbit 20 times farther from the sun than Neptune does. (Planet Nine is not Pluto, which was once considered the ninth planet but was demoted to mere â€œdwarf planetâ€ in 2006. Nor is it Nibiru, the completely fictional â€œrogue planetâ€ that conspiracy theorists sometimes claim is about to destroy the Earth.)
Scientists suspect the existence of Planet Nine because it would explain some of the gravitational forces at play in the Kuiper Belt, a stretch of icy bodies beyond Neptune. But no one has been able to detect the planet yet, though astronomers are scanning the skies for it with tools such as the Subaru Telescope on Hawaiiâ€™s Mauna Kea volcano.
Medieval records could provide another tool, said Pedro Lacerda, a Queenâ€™s University astronomer and the other leader of the project.
â€œWe can take the orbits of comets currently known and use a computer to calculate the times when those comets would be visible in the skies during the Middle Ages,â€ Lacerda told Live Science. â€œThe precise times depend on whether our computer simulations include Planet Nine. So, in simple terms, we can use the medieval comet sightings to check which computer simulations work best: the ones that include Planet Nine or the ones that do not.â€