After 200,000 years or so of human existence, climate change threatens to make swathes of our planet unlivable by the end of the century. If we do manage to adapt, on a long enough timeline the Earth will become uninhabitable for other reasons: chance events like a comet strike or supervolcano eruption, or ultimately — if we make it that long — the expansion of the sun into a red giant in around five billion years, engulfing the planet completely or at a minimum scorching away all forms of life. Planning for potential escape routes from Earth is, if not exactly pressing, then at least a necessary response to a plausible threat.

The most obvious destination is our neighbor Mars. We’ve already sent multiple probes there, and NASA is planning another moon landing in 2024 with the eventual plan of using it as a waypoint on a mission to Mars. Elon Musk’s Space X claims to be aiming for a crewed trip to Mars in the same year. But Mars is a desert planet, cold and barren, with no atmosphere save for a thin blanket of CO2. Sure, we could survive there, in protective suits and hermetically sealed structures, but it’s not a great place to truly live.

Some scientists have another favorite relocation candidate: Proxima b, a planet that orbits a star called Proxima Centauri, some 4.24 light years distant from our sun. Located in the triple-star Alpha Centauri solar system, Proxima b has a mass 1.3 times that of Earth and a temperature range that allows for liquid water on the surface, raising the possibility that it could support life.

The biggest challenge is getting there. Proxima b is almost unimaginably far away. There is a program underway, Breakthrough Starshot, to send a probe to Alpha Centauri with a journey time of just 20 years, but the entire craft will weigh only a few grams, being propelled by a 100-billion-watt laser fired at it from Earth rather than carrying any of its own fuel or, for that matter, human passengers. Even by generous estimates, traveling one light year in a vessel large enough to transport humans will take centuries; reaching a planet in the range of Proxima b would take a thousand years or more.

This means that no one cohort of crew members would be able to survive the journey from start to finish, so those on the craft for the launch would have to pass on the torch to the next generation, and the next, and the next, and the next.

While it might sound like science fiction, a small network of researchers is tackling the problem of multi-generation space travel in a serious way. “There’s no principal obstacle from a physics perspective,” Andreas Hein, executive director of the nonprofit Initiative for Interstellar Studies — an education and research institute focused on expediting travel to other stars — tells me in a call from Paris. “We know that people can live in isolated areas, like islands, for hundreds or thousands of years; we know that in principle people can live in an artificial ecosystem like Biosphere2. It’s a question of scaling things up. There are a lot of challenges, but no fundamental principle of physics is violated.”

As one might expect from such an undertaking, the difficulties are many and broad, spanning not just physics but biology, sociology, engineering, and more. They include conundrums like artificial gravity, hibernation, life support systems, propulsion, navigation, and many problems that are nowhere near to being solved. But even if we never make it to Proxima b, in the process of exploring the question of how to escape Earth, some of the scientists involved in the work may stumble upon solutions for surviving on our planet, as resources like energy and water become increasingly scarce.