‘Walden’ Review: My Sister! My Twin! My Astronaut!

Despite its name and original mission, Second Stage Theater, founded in 1979, has in recent years expanded its reach to include many new works by early-career playwrights.

The latest beneficiary of that expansion is Amy Berryman, who makes her professional New York debut with “Walden,” the promising but unconvincing story of twin astronaut sisters on opposite sides of a philosophical divide in a devastating climate dystopia. It opened Thursday at Second Stage’s Off Broadway space, the Tony Kiser Theater in Midtown Manhattan.

The promising part of the play is the new angle it offers on an old sci-fi setup. In Berryman’s vision of the near future, Earth has reached what the sisters call P.O.N.R., for “point of no return.” NASA, having (like Second Stage) expanded its original mission, decides to accelerate plans to build habitations on Mars. But unlike movies with a similar premise, the prime movers here are women.

That makes for fresh takes on the usual questions of home and hearth and the fate of humanity. It’s nice to see that, at least at first, Cassie (Zoë Winters) is a gung-ho adventurer. Having just returned from a year on the moon, where she became the first person to “grow something from nothing” on its inhospitable surface, she has now been asked to lead an epochal mission to Mars.

Not that Earth’s surface is much more hospitable, with violent weather and rising tides killing millions and causing wars. In response, Cassie’s skittish sister, Stella, has retreated to the American interior to nest in a corrugated but strangely chic wilderness cabin. Stella (Emmy Rossum) is also an astronaut — or was. Though she left NASA under mysterious circumstances, her design for a new habitation called Walden will be the one used on Mars. Cassie will likely live there for the rest of her life.

On the weekend before she begins training for that future, Cassie visits Stella after a long estrangement. Inevitably, a debate breaks out between them about whether to prioritize saving the planet (as Stella favors) or preparing an escape route (as Cassie does). Encouraging Stella’s view is her boyfriend, Bryan (Motell Foster), a so-called Earth Advocate for whom expanding the reach of human depravity to virgin new worlds is a poor excuse for not cleaning up the old one.