No one doubts that asteroids have hit Earth in the past, with nasty consequences, but because the chances of any such event happening in a given year are so low, most people have been content to ignore the risk.

Yesterday, however, a meteorite was seen streaking through the sky above Yekaterinberg in Russia. It hit the ground (possibly landing in a lake) near another city, Chelyablinsk. It is thought to be the biggest meteor to hit Earth in more than a century. The shock wave it caused as it passed overhead blew out windows and injured hundreds of people. Also today, a 50 metre-wide asteroid called 2012 DA14 is zipping past Earth inside the orbit of some man-made satellites, marking the closest shave on record for an asteroid of that size.