A NASA probe launched in January 1999 to search for evidence of water or ice beneath the surface of the planet Mars. The probe was lost in December 1999 when it was scheduled to land close to the planet's south pole. The spacecraft's disappearance was blamed on a faulty sensor that switched off the spacecraft's landing rockets too soon, causing it to crash. It was NASA's second consecutive Mars mission to fail in just over two months, following the disappearance of the Mars Climate Orbiter in September.