A Delta 2 rocket's second stage arrives at Cape Canaveral launch pad, similar to the one suspected of falling in South Africa after surviving reentry. The bottom view shows the internal tank that landed. Photo: NASA/KSC and Case Rijsdijk/South African Astronomical Observatory

The sound of thunder filled the air over Worcester in South Africa's Western Cape province on April 27.

A ball of white-hot metal weighing 60lbs, moving at twice the speed of sound, hurtled its way across the sky and finally collided with the dry desert floor before burying itself under a foot of topsoil.

According to Nick Johnson, a chief scientist with NASA's orbital debris programme, the object is most probably part of a Delta rocket launched in March 1996. Curiously, just the following day, the same region was visited by another rectangular piece of space junk weighing in at 110lbs.

This kind of scene, though rarely witnessed, is becoming more common. "On average one object a day falls back to earth. This sort of thing has been going on for four decades now and nobody has been hit so far," says Johnson.