In the hunt for life beyond Earth, we've been looking for planets and stars like our own. But that is flawed – and a new plan promises answers in our lifetimes

THE night sky is filled with stars you will never see with the naked eye. It’s not that they are too far away. In fact, they are some of our closest cosmic neighbours. Their lack of visibility is down to being cold and dim, at least as far as stars go. And yet they are anything but dull. Until recently, they held an astonishing secret.

In the quest to find life beyond our solar system, we have long sought the familiar: an Earth-like planet orbiting a sun-like star in the habitable zone or at just the right distance to have liquid water. Worlds around colder stars were not on the agenda. But then NASA’s Kepler space telescope spent the past decade snaring exoplanets. The haul revealed that most potentially habitable worlds, or at least the ones we are most likely to spot, exist in star systems quite unlike ours.

With Kepler due to run out of fuel at any moment, the next generation of exoplanet prospectors are shifting their focus to these worlds. Even as they do, however, planetary scientists are at odds over how habitable they are. One hallmark of colder stars is that their habitable zones are much closer in, which bestows some unfamiliar characteristics on the planets that reside there. Can life survive so close to a fiery ball of gas? And if so, what detectable signatures would it produce?

Video: The search for habitable exoplanets We are getting close to being able to see signs of life on different worlds, says exoplanet pioneer Didier Queloz

It has been more than two decades since we first …