February 22, 2021 at 6:00 am Planet Nine might be a mirage. What once looked like evidence for a massive planet hiding at the solar system’s edge may be an illusion, a new study suggests. “We can’t rule it out,” says Kevin Napier, a physicist at the University of Michigan in Ann Arbor. “But there’s not necessarily a reason to rule it in.” Previous work has suggested that a number of far-out objects in the solar system cluster in the sky as if they are being shepherded by an unseen giant planet, at least 10 times the mass of Earth. Astronomers dubbed the invisible world Planet Nine or Planet X.