Skywatchers in Australia were startled Monday night to see a slow-moving, comet-like object appear in the night sky, and then flare as if something had blown up. A mystery for days, it has finally been identified as the explosion of an old booster rocket. Read more about it here.

It's a problem well-known to those who monitor orbiting space craft and space junk. As old booster rockets deteriorate in space, leftover fuel and oxidizer - normally kept separate until the rocket is fired - break through seals, and combine explosively. The blasts shatter the rockets and scatter hundreds of new pieces of space debris.

International protocols have been issued to minimize such events. Mission designers are supposed to reserve enough fuel to send obsolete spacecraft to burn up in the atmosphere before such accidents can occur, or park them in harmless, out-of-the-way orbits where they won't cause problems for active spacecraft. But older rockets and defunct objects launched before these protocols took effect - and new ones that get out of control or break down prematurely - can still cause problems like this one over Australia.

But old junkers and accidents are one thing. Deliberately turning one piece of space junk into thousands - deliberately - is quite another.

It was only last month that the Chinese tested a satellite-killing missile on one of their obsolete weather satellites. In addition to proving they could knock out satellites (presumably an enemy's spy satellites), they also scattered more than 700 new pieces of space junk big enough to track (and likely thousands of smaller, but still hazardous ones), infuriating the space-faring community. All those shards have now become potential hazards to every nation's spacecraft, both manned and unmanned.