Tunguska, Siberia is an obscure region known to the outside world for only one thing. In 1908 an asteroid is believed to have crashed there, flattened 2,000 sq km with 1,000 times the energy of the Hiroshima atomic bomb. On Monday, a space rock of about the same size as Tunguska soared past the earth, unsettlingly close. Named 2008 DD45 by astronomers, the asteroid was only twice the distance from our planet as our outermost commercial satellites. Impact in a populated region would have been cataclysmic. Had it hit the earth it seems it would have come down near Tahiti.