The Mars Climate Orbiter spacecraft, a joint effort between Lockheed Martin and NASA’s Jet Propulsion Laboratory (JPL), was supposed to go into orbit around the red planet on September 23, 1999. Instead, the Martian craft lost all contact with Earth. After much deliberation, a review panel for the incident came to a disconcerting conclusion: A thruster error developed when project teams used different measuring systems for the navigation commands—NASA used metric units; Lockheed Martin used English standard units, and no one caught the discrepancy (for more about metric and standard units, see “Mathematics throughout History”).

To this day, scientists can only speculate as to what happened to the orbiter, a craft sent to study the climate and weather patterns of the Martian atmosphere. Some say that because the orbiter dropped down to within 36 miles (60 kilometers) of the planet—about 62 miles (100 kilometers) closer than planned—atmospheric friction probably overheated the propulsion system and tore the vehicle apart. Others believe the craft was propelled through the atmosphere (or bounced off) and out into space again and is now perhaps circling the Sun like an artificial asteroid or comet.