NASA's exploration robots have rumbled around Mars, swooped around Saturn, and flown well beyond the planets(opens in a new tab), into interstellar space.

But the space agency's engineers often direct their machines to peer back at the vivid blue dot in the distance.

"During almost every mission we turn around and take a picture back home," NASA's former chief historian, Bill Barry, told Mashable. "There seems to be an irresistible tendency to look back at home."