the mars climate orbiter was a space probe. it was launched by nasa on 11 december 1998 to study the martian climate and martian atmosphere. however, on 23 september 1999, communication with the spacecraft was lost, when the spacecraft was about to enter orbit. because the computer software was working with non-si units instead of the si units. the spacecraft entered mars on an orbit that brought it too close to the planet. however, what happened with the probe is still unknown, either it was destroyed in the atmosphere or entered in an orbit around the sun after leaving the martian atmosphere.