For those of us who still can’t forget the first time they saw Sigourney Weaver wandering around a spaceship in her panties in “Alien,” James Cameron (who directed her in the sequel, “Aliens”) has some terrific news. As Variety reports today, the still-gorgeous Weaver — Hollywood first bona fide female action hero — will play a “veteran interplanetary explorer” in Cameron’s new 3-D film, “Avatar,” which is due out on 2009.