My first thought went to Bob Lazar and his claims of alien anti-gravity technology, including the then unknown “element-115”, that was used in these “spaceships”.
The same people who denied the existence of spaceships and element-115 also denied the existence of Area 51.
Since then, the US government admitted Area 51 exists and, in 2003, element-115 was synthesized by US and Russian scientists.
And its isotope with the longest half-life has a half-life less than 1 second.