We're getting close to the fifth anniversary of the landings of Spirit and Opportunity, but was we approach that milestone, we're passing another. I've been told that as of yesterday, Spirit and Opportunity have operated on Mars for a combined length of time that is longer than the combined number of sols that the twin Viking landers operated. Today is sol 1,774 for Spirit and 1,754 for Opportunity; that's a sum of 3,528 sols. Viking 1 operated on Mars for 2,245 sols and Viking 2 for 1,281, for a combined total of 3,526. Spirit or Opportunity will have to last nearly another 500 sols -- a goodly chunk of another Mars year -- for either rover to beat the age of Viking 1, but still, we now have more sols' worth of data from the Mars Exploration Rover mission than we do from the Viking landers. I'd say that's worth celebration!