1.   But this year, NASA lost contact with its Climate Orbiter probe as it maneuvered into Martian orbit.

2.   Four years ago, the Mars Observer went dead just three days before it was to enter Martian orbit.

3.   It is one of a bundle of instruments aboard the probe, which entered Martian orbit in September and is slowly lowering into a circular orbit around the planet.

4.   But for unexplained reasons, the vehicle stopped transmitting data three days before going into Martian orbit.