Top 5 cosmic threats to life on Earth

时间:2019-02-27 01:08:01166网络整理admin

By Kate Ravilious Compared with being scorched on Mercury, suffocated on Venus or frozen on Pluto, our ride on planet Earth seems like a fairly safe option. But life here has been fraught with danger in the past. Close shaves with extraterrestrial hazards could explain some of the biggest catastrophes the Earth has seen, from the largest mass extinctions to the most widespread ice ages. Astronomers differ on what poses the greatest threat – whether it’s giant clouds of choking dust or magnetic neutron stars – but many agree that the alarming roller-coaster ride is far from over. Fasten your seat belts and take a deep breath as New Scientist reveals the five greatest astronomical threats to life on Earth. Kate Ravilious is our guide Most serious cosmic hazards for life on Earth are a result of the sun’s regular passage through the Milky Way’s spiral arms. Our solar system completes an orbit of the galaxy every 250 million years. The spiral arms rotate too, but at a slower pace, because the clustering of stars in the arms tends to slow them down. “The spiral arms move slower than the stars and this creates a stellar traffic jam,” says Nir Shaviv of the Hebrew University of Jerusalem, who studies galactic hazards. About once every 150 million years, the sun catches up with a spiral arm and passes into it. For the few million years the solar system takes to traverse the arm, it’s at high risk from the first three dangers: The Milky Way contains a hundred billion stars,