Staying faithful to Earth

The history of Western astronomy is a history of the displacement of Earth as special. From Copernicus through Bruno to Galileo and beyond, each insight nudged us further away from being at the centre of the universe. No, the sun does not revolve around us – we are just one of several worlds that orbit it, and those other stars out there, those faraway ones, are actually other suns and have worlds around them, too. The perspective-­altering consequences of what it means to live in a galaxy where planets are more plentiful than stars are still percolating through to us; there are so many exoplanets that a leading astrophysicist calls them ‘commonplace’, nothing but ‘specks of dirt that collect around stars, like lint in a navel’.
Of course, the burning question that follows is: are any of those planets like Earth?
You may think that ‘Earth-sized’ or ‘Earth-­like’ exoplanets – as often heralded in the media – are common, and habitable by humans if we could just figure out how to travel that far. They are not.