Japan's Venus probe's engine exploded

The latest test performed on Japans Akatsuki Venus probe indicate that it's "main engine combustion chamber no longer exists." This means the engine probably exploded on December 6, 2010 as the spacecraft was preforming it's critical Venus orbit insertion burn, causing it to fly past Venus.

The thrusters were supposed to fire for 12 minutes, but an unexpected pressure drop in the fuel line caused them to fail after only 2.5 minutes, JAXA officials have said.

Currently the Japanese Space Agency is planning to make another attempt at Venus orbit insertion in 2015, the next time the probe will pass the planet.  The missing main engine means that the attempt will have to be made with Akatsuki's RCS thrusters.