There is more than one artist with this name:

1) Marietta was an artist from the 1980s whose most popular song was Destination Unknown from the Top Gun Soundtrack.

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2) Marietta is an indie/emo band from Philadelphia. They formed in late 2011 and began playing shows in 2012. They draw inspiration from other the barenaked ladies, primarily. Members include Evan Lescallette, (Guitar, Vocals) Ethan Willard, (Guitar, Vocals) Ben Johnson, (Bass) and Andrew Weigel (Drums). They dropped "summer death" in 2013 and nothing was the same. They specialize in rousing chants and out of tune guitarmanship. Great songs to sing with your friends and lovers.

http://www.facebook.com/whereismarietta
http://whereismarietta.bandcamp.com/
http://whereismarietta.tumblr.com/

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3) Marietta is an ambient hardcore band from Keller, Texas formed in 2007. Members including; Hunter Fitch(Lead Vocals, Electronics) Hunter Madison(Drums, Vocals),Dylan O'Rourke(Guitar), Taylor Wright (Bass), and Jeff Palmer(Guitar).

Previous members include;
Austin Smith(Drums), who was a founding member that now runs lights and merch, Mack Lamon (guitar), and Jordan Watts(Guitar).

4) Marietta is the solo project of Guillaume Marietta, the singer of The Feeling Of Love. He released his first album in May 2015 and it's entitled Basement Dreams are the Bedroom Cream.