Three centuries have passed since the polymath Sir Christopher Wren predicted that ‘a time will come when men will stretch out their eyes-they should see planets like our Earth. By most astronomers’ accounts, that time is just about nigh. Indeed, detecting big planets orbiting other stars is no longer tricky-nearly 450 such exoplanets have been catalogued. Smaller, rocky planets orbiting at a comfortable distance from their stars-as the Earth does-remain more elusive. Most exoplanets have been discovered by inferring their presence from the rhythmic wobble their gravity imparts on their home star-like a waltz between two dancers of markedly different weights. The problem is that this method favours the discovery of large planets close to their stars. As a result, the catalogue of planets is filled with ‘hot Jupiters, huge bodies baking brightly in the light of their sun. To find places that might support life it is necessary to look for planets a little farther away from their stars, but not so far away that they are frozen lumps of ice and rock, like the dwarf planet Pluto. But it isn’t easy. Spotting the light from a tiny planet across astronomical distances is akin to discerning a […]