"Star Trek" debuts in movie theaters on Thursday backed by huge hype, but whether the film based on a 43-year-old franchise can win young fans and big box office returns has industry watchers scratching their heads. Paramount Pictures, the movie studio wing of media giant Viacom Inc., has walked a fine line between adding new actors and stories to appeal to teenage boys and maintaining the old characters favored by "Trekkies" who adore the space saga that began with the 1966 TV show of the same name. As a result, box-office estimates are all over the map, much as the Starship Enterprise zooms all around the universe ferrying Captain James T. Kirk and his crewmates Spock, Scotty and Dr. "Bones" McCoy on far-flung adventures. "It`s clearly going to be a really popular movie, it`s just tough to peg exactly how popular," said Brandon Gray, president of tracking firm Box Office Mojo. Paul Dergarabedian of Hollywood.com Box Office said "Star Trek" has crossover appeal to wider audiences and could make between $80 million and $100 million on its opening weekend. "It`s poised for a really strong opening," he said. But sources at the studio behind the $130 million film have sought to downplay expectations, describing "Star Trek" as a reboot of an aging franchise that sets the stage for future, more successful installments. There have been 10 previous "Star Trek" movies. One source at Paramount said advance audience research indicated the opening weekend would be slightly above $50 million, a figure the studio would welcome as a success. To appeal to young audiences, Paramount says it spent $30 million on special effects alone. YOUNG CAST, GOOD REVIEWS It brought on as director J.J. Abrams, who made explosive, effects-filled "Mission: Impossible III" and hit TV shows "Lost" and "Fringe." The plot revolves around the characters as young men and women before the period in which the television show took place. Abrams hired mostly young actors in lead roles, including Chris Pine as Kirk, Zachary Quinto as Spock and Zoe Saldana as Nyota Uhura. "Star Trek" has received strong reviews, scoring a 93 percent approval rate at aggregator Web site Rottentomatoes. Claudia Puig of USA Today wrote that Trekkies could find plenty to pick apart, but wider audiences were "likely to be transported by this latest voyage on the mothership of sci-fi sagas." The movie will play in 3,800 theaters, including 138 widescreen IMAX venues, where higher ticket prices could boost overall box-office results, Paramount said.