$125 million robotic spacecraft, the first ever dispatched especially to investigate weather on another world, was missing on Thursday and presumed destroyed just as it was supposed to go into an orbit around Mars. As the slenderest hopes of re-establishing radio contact diminished with each passing hour, project officials announced that the spacecraft, the Mars Climate Orbiter, was "believed to be lost due to a suspected navigation error." It probably flew too close to the planet, within 37 miles of the surface, disintegrating or burning up in the atmosphere or, possibly but less likely, crashing into the surface.