At the centre of the Solar System, the Sun – an almost-perfect sphere of hot plasma – provides the most important source of energy for life on Earth. It formed around 4.6 billion years ago from the gravitational collapse of matter in the universe within a region of large molecular clouds, which initiated the nuclear fusion we see today. Scientists have discovered this star – which fuses around 600 million tonnes of hydrogen into helium every second – is a ticking time bomb and will one day turn into a red giant, engulfing Mercury and Venus.