ESA’s Milky Way-mapper Gaia has completed the sky-scanning phase of its mission, racking up more than three trillion observations of about two billion stars and other objects over the last decade to revolutionise our view of our home galaxy and cosmic neighbourhood.Launched on 19 December 2013, Gaia’s fuel tank is now approaching empty – it uses about a dozen grams of cold gas per day to keep it spinning with pinpoint precision: this amounts to 55 kg of cold gas for 15 300 spacecraft ‘pirouettes...