In the metal pantheon, lyrical subjects go in and out of style almost as fluidly as fashion and whether a song should have breakdowns or not. It seems almost a guarantee that every few years the entire scene will shift to a new fixation. Just a few years ago, everyone was screaming about their feelings and how much they hated their ex-girlfriend for breaking up with them. Now? To quote Giorgio A. Tsoukalos, I'm not saying it's aliens, but... it's aliens.

That's right. The allure of the extraterrestrial has lately overtaken the world of metal, especially extreme metal and the popular "djent" form. Of course, there were earlier examples, including Megadeth's classic "Hangar 18," but the fixation really took hold around 2008 with the release of the Faceless' Planetary Duality.

Ever since, aliens are the thing. How has that turned out? Well, it's a hell of a lot better than the misogyny that pervaded metal in the mid-'00s and it's actually produced some awesome tracks like these.

5. Emmure, "Area 64-66" While the alien trend has really predominated in more progressive forms of metal, Emmure takes the theme and applies it to a background of pure brutal deathcore, featuring a bouncy drum beat and a breakdown featuring the band's signature guitar squeals and scratches.

An especially notable aspect of the song though is that front man and primary lyricist Frankie Palmeri claims that the song is based on a true experience he had, in which he saw an extraterrestrial being standing outside of his window. Go figure.

4. Devin Townsend, "Ziltoidia Attaxx!!!" Beating the trend slightly, Devin Townsend released his alien concept album Ziltoid the Omniscient in 2007. Though initially intended to be a pastiche of Townsend's various styles and a form of self-parody, the humorous look at an alien named Ziltoid who comes to Earth in search of a great cup of coffee won the hearts of fans by a) having really fucking awesome music; and b) being hilarious and charming.

Townsend has been teasing a sequel for a few years now, but as yet there are no concrete signs of progress. Nevertheless, Ziltoid remains a fan favorite among Townsend's legion of skullet-wearing devotees.

3. Between the Buried and Me, "Obfuscation" Between the Buried and Me has always danced around paranormal concepts in their music, and on 2009's The Great Misdirect, they went all in on the aliens. For this "single" (it's nine minutes long, so I don't think they were expecting radio play) the band shot a full-length video featuring clowns, magicians, UFOs, and aliens, all in the heart of Marfa, Texas.

Musically, it's an epic composition ranging between prog metal styles and jazzier instrumentals that goes on an extensive journey through its nine minute running time, culminating in a guitar solo that would impress legends like Marty Friedman in its flurry of shred.

2. The Faceless, "Planetary Duality" The song that basically started the trend. The Faceless weren't pioneering musically at the time, though their sound certainly had a huge effect on their descendants. Where Planetary Duality is a solid album, it really stands out in its lyricism. For the duration of the record, the Faceless weave a melodramatic story of an alien invasion, culminating in this title track.

Every band that has come after them which deals in alien themes seems to crib that idea of an extraterrestrial soap opera playing out over a technical death metal and progressive metal background. Arguably, however, none have managed to pull it off in quite such an exciting way as the Faceless.

1. The Contortionist, "Flourish" In 2010, the Contortionist released their long-awaited debut to much critical acclaim. Exoplanet is a progressive, technical death metal album heavily influenced by some of the great bands that preceded them like Cynic.

In "Flourish," my pick for the best song off the album, they combine brutal, crushing death metal breakdowns with spacey, progressive singing vocals and exploratory instrumental interludes. It's a contrast that only works because of the virtuosity employed by the band's extremely skilled musicians.