Document text
Since You Asked: 5 billion more years before sun engulfs earth Saturday Feb 17, 2018 at 6:29 PM Feb 17, 2018 at 6:29 PM Everybody knows it'll happen way past anyone's lifetimes, but just how much time's left until the sun expands past our planet? — Troy H., via email As you might've guessed, there's no sense building a bunker because this is a problem millions of generations in the future — especially considering that the previous generation didn't have iPhones. The sun is presently expanding at a gradual rate because the star is midway through its "main sequence," according to a Cornell University blog post, Phys.org and a BBC news story with more terrifying natural ways for the world to end than we wanted to consider. The sun's main sequence, converting hydrogen in its core to helium, typically lasts more than 8 billion years, and our sun's just past its halfway point, about 4½ billion years. As the BBC article was from 2015, you may want to add a few years to the sun's age — but if you can't tell, why should we? In another 3½ or 4 billion years, a star will start cooling from white-hot to red-hot, while changes in gravity cause a star to expand outward, according to the Cornell post. Stars in this phase of their life are typically called "red giants." A few billion years into that "red giant" stage, the sun will expand past earth's present orbit, or 7 billion years give or take a few hundred million. The sun's gravitational pull may change our fair planet's orbit, but a 2008 Royal Astronomical Society study predicts it might not be enough to save itself on its own. Other scientists predict that the sun goes from life's friend to foe in about one billion years from now, according to Space.com, because progress during that growing sequence will cause oceans to boil until earth turns into a global desert. Either fiery outcome puts taxes in perspective. — Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to [email protected]. We’re sorry, but the volume of questions received prevents us from answering all of them.