According to Bob Lazar, who allegedly once worked in the enigmatic Area 51 military base, Element 115 is a transuranic element with an atomic number of 115, which supposedly is the catalyst for the gravitic propulsion of the UFO's and powers many other alien artifacts used by the extraterrestrials.
Dr. Robert Sarabacher, a prominent US government scientist, had been quoted as confirming that many of the assertions in popular UFO mythology were "essentially true", and that UFO's were classified by the US government two points higher than the hydrogen bomb. Before his death in 1986 he was interviewed by noted UFO researcher Stanton Friedman and he had a very interesting bit to say (SF = Stanton Friedman, RS = Robert Sarabacher):
SF: Were you guys talking about nuclear powered flight at that time?
RS: Oh, we were possibly, yes, but I held, had certain ideas see, one of the problems today, we really don't know what gravity is. We don't know and I had an idea, I'm willing to work on it in one of my theses but then my professor didn't believe me, but I had determined that bismuth did not obey the laws of gravity.
So I thought that, "Gee, there's a leak". I might be able to get nature to tell me something.
RS: But they wouldn't let me, they didn't believe me. Well, they believed me but he said "Hell, that's a second order effect".
RS: Which is implying it was in the, in the area of, of the accuracy of the instrument.
RS: Well it was, it was and it was clearly, God somebody's going to do something about it one day,....
Well, a quick look at the periodic table shows that right under bismuth is, guess what, Element 115! Well, given the way the periodic table works, elements in the same column of the table tend to have similar properties. If bismuth has very subtle anomalous properties, then probably element 115 has them too, to a much greater degree.
Source: The Bob Lazar corner, at http://www.serve.com/mahood/lazar/lazarmn.htm