The team operating NASA's Mars Exploration Rover Opportunity learned Thursday that the long-lived rover experienced a brief amnesia event related to its flash memory, the first since a reformatting of that nonvolatile type of memory a week earlier.

The amnesia event did not result in any loss of science data, and Opportunity subsequently continued its activities using tools on its robotic arm to examine a rock target called "Athens." The rover experienced dozens of similar amnesia events and more serious flash-related resets of the onboard computer prior to 2015, then operated without using flash memory until last week.

"We changed how the rover uses flash memory in an attempt to correct problems the rover had been experiencing," said John Callas, project manager for Opportunity at NASA's Jet Propulsion Laboratory, Pasadena, California.

"Although we are a little disappointed at the occurrence of an amnesia event only five days after reformatting, we are not surprised. There is still no clear understanding of what is causing the problems. Only time will tell if we have been successful in mitigating the most serious flash problems."

Use of flash memory enables the retention of stored data when power is turned off. Opportunity is powered down every night to conserve energy generated by its solar panels. The rover also has volatile memory, which can store data while powered. For three months until last week, the team operated the rover in a mode that avoided use of flash. Instead, the rover stored science data in volatile memory for downloading to Earth each day before shutting down for the night.

Opportunity has seven banks of flash memory. This month, the team revised the rover's onboard software to avoid use of Bank 7, where some of the earlier problems with flash memory had been traced.

After the March 20 reformatting, the rover resumed use of the other six banks. No root cause for the full combination of flash problems has been determined, since many of the past problems with flash could not be traced to a specific bank.

Before switching to the no-flash mode in December, Opportunity was experiencing multiple resets daily. The rover has experienced no resets so far in the first week after resuming the use of flash, so the remedy actions appear to have addressed the most serious flash problems, at least for now.

Earlier this week, Opportunity became the first vehicle ever to travel the distance of a marathon race on the surface of another world. The rover is examining outcrops on the western rim of Endeavour Crater, approaching "Marathon Valley," where clay minerals have been detected in observations by NASA's Mars Reconnaissance Orbiter.