Since the halcyon days of Apollo, NASA’s science budget has always been stretched to the limits. The approximate $1.5 billion that is denoted for planetary science must cover all the missions exploring the planets of our solar system, as well as the development of new technologies for future missions. There is always a line-up of new projects clamoring for funding along with the ongoing projects and the competition is Olympic. Consider that MRO, Curiosity (Mars Science Laboratory), Mars Odyssey, Maven, and MER are just the Mars missions seeking an extension.

Being a robot, Opportunity is oblivious, of course, and the MER ops team doesn’t have time to stop and wait. From the moments Opportunity and her twin Spirit landed, the MER teams members have viewed every day of this first overland expedition of Mars as a gift. That has never changed. They’ve got ops everyday and the rover has places to go, new Martian mysteries to uncover, and more records to set.

The MER mission’s prime directive is to “Follow the Water” by searching for geological signs of it and that’s exactly what the mission has been doing. The twin robot field geologists each returned scientific evidence for past water: Opportunity returned evidence for an ancient salty sea during her primary mission and Spirit found solid evidence for past underground water at Home Plate.

But when Opportunity pulled up to the rim of the Noachian Period Endeavour Crater in August 2011, a floodgate of sorts opened. The rover began a journey farther back in Martian time, uncovering geological history that no other surface mission ever had, and the mission began anew.

With Opportunity’s ground-truthing of clay minerals and the team’s discovery of the most ancient Martian terrain on Matijevic Hill in 2012–2013, this rover has sent home some of the most compelling evidence ever acquired on the surface of Mars that long ago there were water-rich environments on the planet where life could have emerged. The research the rover sent home from Marathon Valley in May is giving the scientists fertile ‘grounds’ that may well help them enhance the latest chapter in the story of water at Meridiani Planum, a story they have been writing for the last twelve and a half years.

And yet, there is so much more to uncover at Endeavour. More ancient Martian history is beckoning from just down the crater road a bit, and the MER team is anxious to get Opportunity time trekking back to the past.

“We presented a really exciting story of the extended mission to the Senior Review Board as to what we're going to do when we leave Marathon Valley and we're all just itching to get on with it,” Squyres said. “But we have just come across some of the most surprising chemistry we've found here and as eager as we are to get going, we have to wrap this up properly before we move on.”

So Opportunity continued her study of the colorful bounty in the trough and ended her 13th merry month of May focusing on a yellow pebble (as it appeared the Pancam false color images) that the team named after Private Joseph Field, who like his brother, Reubin, was considered to be among the best shots and hunters accompanying Lewis & Clark in the Corps of Discovery.

Once Field is in the can, the science team will decide what Opportunity will do next. Wherever she is commanded to go, Opportunity is ready to roll. “I sound like a broken record, but the rover is doing absolutely fantastic,” said Bill Nelson, chief of MER engineering at JPL. “We have great energy, the temperatures are pretty much in the sweet spot, neither too warm or too cold, we have experienced no additional anomalies, and everything is going just beautifully right now.”

“Twelve and a half years after landing,” summed up Callas, “we still have a great rover and a great mission.”