Sci-Fi’s "Stargate SG-1," which began its eighth season last week, has been using ancient alien portals to send American military teams through wormholes onto distant worlds — but always returning to a base on Earth.

"Stargate Atlantis" — a new spin-off — begins on Earth then goes far, far away.

In the opening episode, "SG-1" regulars Gen. Jack O’Neill (Richard Dean Anderson) and archaeologist Daniel Jackson (Michael Shanks) head down to Antarctica to help diplomat Dr. Elizabeth Weir (Torri Higginson, replacing Jessica Steen, who played Dr. Weir last season on "SG-1") explore a newly discovered portal and some superpowerful alien hardware.

Before long, Weir and astrophysicist Dr. Rodney McKay (David Hewlett, reprising his "SG-1" role) discover that the portal leads to the fabled lost city of Atlantis, which, as it turns out, is in the Pegasus Galaxy (in the "Stargate" universe, most myths have alien origins).

Reckoning they have enough power for a one-way trip, Weir assembles a team of military personnel and scientists to explore the city. The military contingent includes two pilots, Maj. John Sheppard (Joe Flanigan), who has a genetic ability to interface with the alien technology (and a problem with authority), and the eager Lt. Aiden Ford (Rainbow Sun Francks). Their commander is Col. Marshall Sumner (guest star Robert Patrick), who isn’t nuts about answering to the civilian Weir — who has bigger problems than Sumner’s ego.

"Right now," Higginson says, "Weir is so excited and overwhelmed at this opportunity. Eight months ago, she didn’t know Stargates existed, so this is brand new to her. She learns that aliens exist, and now she’s having a conversation with them.

Once arriving at Atlantis — a sleek set that combines Frank Lloyd Wright elements into a sort of "Alien Deco" — Weir and her team learn that Atlantis, which has been slumbering for eons, is not quite equipped to handle the visitors. So, exploration begins immediately for fresh sources of power.

"We made up our own Atlantean mythology," said executive producer and writer Brad Wright, who also works on "SG-1."

"If it’s based on anything, it’s based on the mythology we created in the ’Stargate’ universe, of the Ancients," said Wright. "So Atlantis was a city of the Ancients. When we find it, it’s pristine and untouched."

The team’s first mission brings it into conflict with the pasty, insatiable Wraiths. These galactic baddies with serious dental issues hear about Earth and immediately start thinking of it as an all-you-can-eat buffet.

But Earth likely can rest easy for a little while, because, for practical and story reasons, Wright intends to keep the "Atlantis" crew off in the Pegasus Galaxy for at least the show’s first season, during which "SG-1" will play out its eighth and supposedly final season.

Along with the mythology, "Atlantis" keeps the storytelling style of "SG-1," which includes saving the galaxy one wisecrack at a time. It’s a tradition that began in the original "StarGate" movie in 1994, with Kurt Russell as a cranky O’Neill, and continued with Anderson’s droll, nonplussed O’Neill in the TV version.