Aliens exist — they just haven’t visited Earth, a NASA veteran has claimed. Dr. Gentry Lee has worked at the US space agency since 1968, when he first got involved with the Viking mission to Mars. He has since spent more than half a century designing probes to land on distant planets — but argues Earth has not yet been visited by otherworldly beings. “There exists nothing today that says any alien or any alien machine has ever landed on the planet Earth,” he told the American Association for the Advancement of Science (AAAS) conference in Phoenix. “If you believe...