Proxima Centauri is 4 light years away. Ambitious space mission Breakthrough Starshot is developing a way to push spacecraft there at a fifth of the speed of light

Sam Chivers

IF YOU left Earth now, travelling at the speed of light, you would get to the moon before reaching the end of this sentence. Getting to the sun itself would take 8 minutes at this speed. The furthest tendrils of human activity, Voyagers 1 and 2, which launched in 1977 and are only now reaching the outer edge of the solar system, would be overtaken by this time tomorrow. But getting to Proxima Centauri, our solar system’s nearest star, would take four years and three months.

And that is travelling at light speed, a velocity well beyond our reach. The quickest we could currently get to Proxima Centauri, using our fastest rockets, is 80,000 years. Small wonder interstellar travel hasn’t been much of a priority. But what if we could get to the Proxima system in 20 years?

At a highly publicised press conference in 2016, a team claimed to have assembled the scientific know-how to make a mission to Proxima Centauri not only possible, but doable within our lifetimes. Breakthrough Starshot, backed by a Silicon Valley billionaire and tapping into NASA expertise, provoked mostly cautious enthusiasm. Three years later, with a better sense of the challenges and published research to support the team’s optimism, the plans are gathering speed. If they succeed, we could be a decade or two away from embarking on the most ambitious mission of all time, and discovering the truth about a solar system different from our own. So what are the key challenges?

Getting to a distant solar system within a human lifetime means travelling fast. Very fast. And the pool …