Was the Tunguska explosion of 1908 caused by a comet hitting Earth? That's the claim of a new study based on the behaviour of water vapour from the space shuttle's exhaust. But other scientists dispute the claim, and say the evidence still points to a stony meteoroid as the culprit. En español:
www.elpais.com/articulo/sociedad/cometa/Tunguska/vez/probable/elpepuso 
