Back in August, astronomers announced the discovery of what appears to be an Earth-like planet orbiting the Proxima Centauri – a red dwarf star in our closest neighbouring star system, Alpha Centauri. Named ‘Proxima b’, the planet is just 4.25 light-years away and there were early signs that it’s rocky just like Earth. It has the right distance from its star to sustain water in liquefied form. Now scientists have found evidence that it could in fact be ‘covered’ in oceans of liquid water. Just to put in perspective how amazing the discovery of Proxima b was, before the evidence of its Earth-like qualities was found, the closest known potentially habitable planet was Wolf 1061c – and it is 14 light-years away (126 trillion kilometres away from Earth). Proxima b has since shifted that goalpost to just 4.25 light-years away, which is still 40 trillion km – or 271,000 times the distance from Earth to the Sun – but there’s already a plan in place to get spacecraft there in 20 years. To put it another way, this thing is so close to us, we can actually see two stars in its star system – Alpha Centauri A and Alpha Centauri B – in the night sky. In fact, Alpha Centauri A is the fourth-brightest star seen from Earth. Now a team led by researchers at the Marseille Astrophysics Laboratory in France has strengthened the case of Proxima b’s habitability by calculating a number of size and surface properties in more detail than ever before. It’s estimated to orbit this star at a distance of 7.4 million km (4.6 million miles), which is a mere tenth of the distance that the closest planet to our Sun – Mercury – completes its rotations. Scientists have come around to the idea that tidally locked planets could potentially be habitable in recent years but it’s been suggested that Proxima b might still be too hot to sustain liquid water, Space.com’s Jesse Emspak explains. To investigate this, the French team created simulations of the planet’s composition based on its apparent size and estimated that the radius of the planet is between 0.94 and 1.4 times that of Earth. If we take that lowest limit, its radius would be roughly 5,990 kilometres, and the team’s simulations suggested that in this scenario, the planet would be very dense and contain a metallic core that makes up two-thirds of its total mass. Fortunately, there’s already a mission being bankrolled by Russian billionaire Yuri Milner – called Breakthrough Starshot – which hopes to laser-propel ‘nanocraft’ towards Proxima Centauri in the coming 20 years. NASA’s James Webb Space Telescope (JWST) – scheduled to launch in 2018 – could explain Proxima b’s atmosphere by merely sampling the star system’s light.