SIR – Scientists were so busy monitoring asteroid 2012 DA14 they were unaware that a ten-tonne meteor had entered the Earth’s atmosphere at a hypersonic speed of at least 33,000mph.

Had it not exploded over Russia’s Ural Mountains, it would have devastated about 750 square miles of planet Earth.

How come astronomers tracked an asteroid knowing full well it would harmlessly pass us by, yet were oblivious of a fast-approaching meteor that could have wiped out millions?

D Rhodes, Croscombe Walk, Bradford