Have you heard the story of the twin sisters who explored the surface of Mars? They were NASA's twin rovers, Spirit and Opportunity (or Oppy for short).

The two sisters traveled to Mars in 2003 and explored the vast planet. Although Oppy's mission was only meant to last 90 days, she explored for over 15 years overcoming obstacles with creative solutions. When Oppy's right front wheel got repeatedly stuck in the sand, she drove backwards The sisters showed the world just how much two small rovers can do right up until the end of their missions.