The Mars Climate Orbiter crashed on the surface of Mars because

one program output thrust in termis of foot$-$pounds, and another program expected thrust to be expressed in terms of newtons.

the probe lost contact with the Jet Propulsion Laboratory when it entered the Martian atmosphere.

a bug in the computer program caused the vehicle to consume too much fuel on the way to Mars, leaving an inadequate supply for landing.

$$ the extreme cold of deep space caused the computer to crash.

before programmers went on strike at subcontractor Lockheed Martin, one of them sabotaged the flight control software.