Natasha Henstridge is a believer. ''I'm so far out there I think there are aliens,'' the 20-year-old Canadian says, widening her oxidized-copper eyes. And why not? It's about as likely as getting plucked from catalog pages to star opposite Ben Kingsley and Forest Whitaker as a sex-driven abomination. In this summer's frightfest Species, Henstridge plays Sil, a government science experiment gone awry the world's first human enhanced with extraterrestrial genes who escapes to find a mate so she can be fruitful and multiply. ''I know I'm going to be judged,'' she says. ''Being a model-turned-actress, I've got two strikes against me. But I've come to realize I'm only human.'' Actually, she'll be just that in her next role: In the thriller Adrenaline, due out next year, Henstridge plays a cop who gets to chase a cannibalistic serial killer in the year 2008. Though she couldn't land a choice role as a park ranger who guides Christian Slater through the desert in John Woo's Broken Arrow, though the Kelsey Grammer comedy Down Periscope eluded her, it's not Henstridge's career that keeps the skydiving, scuba-diving, motorcycle-riding ingenue up nights in her Manhattan bedroom. ''We're such a small entity of life in this massive universe,'' she offers. ''Do you ever sit in bed and think: What's beyond space more space? What's beyond that?'' Try Hollywood.