4. They Never Reached The Moon
The main mission of the Apollo 13 was clearly defined. The astronauts were supposed to perform an inspection, conduct a survey and also bring back some sample materials from a region of the Fra Mauro Formation, just north of the crater Fra Mauro. They were also supposed to activate an Apollo Lunar Surface Experiments Package, to help scientists study the surface better.
Ironically, the fated mission was supposed to be the third moon- landing for NASA, but the Apollo 13 never made it to the lunar surface of the moon at all.