Magnetic fields are fundamental in governing how planetary atmospheres circulate and escape into space, but directly measuring these fields on planets orbiting very close to their host stars has proven to be a persistent challenge. For an ultra-hot Jupiter like KELT-9 b, theoretical models suggest that an atmospheric dynamo—a process where conductive fluids generate magnetic fields—could create substantial magnetic fields ranging between 400 and 4000 Gauss. To investigate this, measuremen...