Emmy-nominated television composer Mark Snow, best known for creating the instantly recognizable theme to the science-fiction series “The X-Files,” died at 3:30 a.m. on Friday at his home in Connecticut, his representative confirmed. He was 78. No cause of death was disclosed. Born Martin Fulterman in Brooklyn on Aug. 26, 1946, Snow studied at the Juilliard School and began composing for television in the late 1970s. Over a five-decade career he received 15 Emmy nominations and became one of the medium’s most prolific scorers. Snow wrote the music for more than 200 episodes and two feature films of “The X-Files”; the theme was released as a single in 1996 and charted internationally. His other credits include the long-running police drama “Blue Bloods,” the superhero series “Smallville,” “Hart to Hart,” and “Ghost Whisperer,” among dozens of television movies and specials. Snow is survived by his wife, Glynnis, and their three daughters. Plans for memorial services have not been announced.