MARK GARLICK/SCIENCE PHOTO LIBRARY
IT ALL seemed so simple when we knew the date of Earth’s demise. In 5 billion years from now, so the story went, the solar system will have dramatically transformed. Instead of being the benign presence we are used to, the sun will have ballooned into a giant, hundreds of times bigger than it is today. In the process, it will wipe out the rocky, inner planets, including our own.
Or will it? We have recently caught sight of the dying stages of other stars for the first time. And, miraculously, some planets seem to be able to survive these apocalyptic periods. Such observations are challenging the story of how Earth will die and giving us hope that it might somehow outlast the sun. Even if it doesn’t, all is not lost. The research is also giving us clues to where humanity could best take refuge.
How will the sun die?
The sun is powered by nuclear fusion, in which hydrogen atoms are melded together into helium, releasing vast amounts of energy in the process. But our star’s fate is sealed by one fact: it has a finite supply of hydrogen. As this begins to run out – in about another 5 billion years – the sun’s internal structure will change and it will expand to around 200 times its present size. It will transform from the yellow dwarf it is today into a red giant. After a further billion years or so, and another round of shrinking and ballooning, it will then die and shrink back down into a stellar corpse called a white dwarf.
As it grows to become a…