Opportunity found tiny spherules that look like blueberries when images of them are processed in false color, a technique that enables scientists to better discern the geological elements in the primarily monotone rusty red-orange landscapes present day Martian landscapes. Since they were found to be the source of the hematite signal orbital instruments had picked up and since hematite generally forms in water, the MER scientists hypothesized they are evidence of water on this site billions of years ago. Spirit found evidence in a rock called Humphrey (right). By grinding into its surface, she found a bright material filling internal cracks. Such material may have crystallized from water trickling through the volcanic rock, the MER scientists theorized.
There were a couple of frightening problems early on. As Opportunity landed, Spirit had just gotten back to work after the team’s software engineers pulled the rover out of a confounding reboot loop by fixing a software ‘bug.’ And, perfect as her landing was, Opportunity had and electric heater at the shoulder joint of her robotic arm that was stuck in the ‘on’ position and draining her power. The team would soon resolve that problem by commanding the rover to shut down each night, the time when the heater was usually running. They called it DeepSleep and it’s a power-saving strategy Opportunity uses to this day.

With those issues resolved, Spirit and Opportunity began their adventures. Both rovers found evidence of past water and each met the mission objectives during their primary 90-day missions. In early March 2004, Opportunity still inside Eagle Crater, found evidence of past liquid water, in sulfates and minerals, including a rare mineral known as jarosite that forms in the presence of water, and other geologic structures that form by way of aqueous action. It was evidence, the MER science team hypothesized, that indicated an ancient salty sea was once present there, once that could have been a habitat suitable for the emergence of life.

“That was pretty big news for us if you think back to 14 years ago,” said Golombek. “People were still arguing about whether there was water on Mars and we had the first evidence from a rover on the surface, evidence that was pretty much indisputable.”