Artist’s illustration of Planet Nine, a world about ten times more massive than Earth that may lie undiscovered in the far outer Solar System
A stronomers searching for our Solar System’s elusive Planet Nine, a theoretical world that may lurk deep in a cloud of icy rocks far beyond the orbit of Neptune, have come up short once again. In a recent study, researchers pored over six years of telescope data in an attempt to identify potential signs of Planet Nine in the southern sky. Captured with the Atacama Cosmology Telescope (ACT) in Chile between 2013 and 2019, the observations covered about 87 per cent of the sky visible from the Southern Hemisphere.