An asteroid half a mile long will fly past the earth tomorrow morning, missing us by an astronomical hair's breadth of half a million kilometres or so.

The asteroid, dubbed 2004 XP14, had been flagged as a potentially hazardous object when it was discovered in 2004. Australian astronomers have been tracking its approach to make sure the calculations showing it would miss us were correct. Their work shows that the object will zip past Earth at 05:25 tomorrow morning, barely further away than the moon.

In astronomical terms, this is a very near miss. If an asteroid of this size were to hit the planet's surface, it would do a substantial amount of damage. On land, it would create a crater between 10-15 km across, and if it hit the sea, it would create a big set of waves.

One of the astronomers, Gordon Garradd, told ABC news: "Six hundred metres diameter would do a lot of damage if it did hit, we're talking a crater many kilometres across. If it's in the ocean you're going to get one huge tsunami."

The asteroid was discovered by NASA's Lincoln Near Earth Asteroid Research (Linear) project, which was set up to spot exactly this kind of object. Initially, scientists were worried XP-14 might collide with Earth later this century, but say now that its path is not a threat to Earth, after all. ®

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