“There was something about seeing that number with the 4 and all those zeros and realizing, 'Okay, we are today planning Sol 4000.' You kind of go, 'Really? Wow! We just cracked 4,000. I don't know what else to say other than it’s astonishing and gratifying at the same time.”
Steve Squyres, astronomy professor and principal investigator on the Mars Exploration Rover project, commenting on the 4000th sol or Martian day of surface operations.











