This year, the US Congress has heard testimonies from "UFO witnesses", suggesting there is more evidence than ever of attempts by alien intelligence to make contact with Earth. But what have been the pivotal moments? When did scientists believe they had found undeniable proof that our little green friends truly exist? Here are five instances that seemed set to revolutionise our understanding of space , reports the Irish Star . The first notable moment belongs to the aptly named 'Wow!' signal.