E.T.

This celestial electronic ballad that sees singing Perry singing about a lover from "a different dimension" was co-written and co-produced by Lukasz "Dr. Luke" Gottwald and Max Martin. The serial hitmakers were also behind Perry's breakthrough hit "I Kissed a Girl."

The song was originally intended for the rap group Three Six Mafia. Perry told MTV News: "I'll tell you, it's funny... this song, I remember writing with Max Martin and Dr. Luke, and there's this producer they wrote with, named Ammo as well, and they were just showing me different samples of songs or tracks or beats, and they accidentally pulled up this beat, and it was for Three 6 Mafia," she explained. "I heard it and I always knew I wanted to write this futuristic, alienistic song, and they pulled it up and I was like, 'Wait, I can wrap my head around this. I know this seems like a long shot, but I think I have the perfect material to put on top of this sound.' And I did, and it really worked out perfectly.

It's a whole different vibe for me. It's kind of a bit harder, it does have that urban feel underneath it. I think that's why Kanye added even another layer on top of it," the singer added. "And it has amazing sonics - I mean, there's so much to it, there's a lot in the song if you really put your headphones on and sink into the song."

Perry got her fans to help her in choosing the fourth single from Teenage Dream by means of Twitter. They selected this spacey dance tune and a new version was recorded with two additional verses by Kanye West about alien sex.