NASA's Curiosity rover has a pet rock on Mars

Mars is probably a pretty lonely place.  The red planet is littered with rusty red rocks and, as far as we know, devoid of any kind of life. But even so, rovers still roam the surface of the world on humanity's behalf, making their solitary treks along previously unexplored paths.  And sometimes, they make friends.  SEE ALSO: NASA photo captures the loneliness of the Mars Curiosity rover NASA's Curiosity rover — which has been exploring the red planet's Gale Crater since 201