Nasa's Mars rover Spirit is "healthy" again for the first time since it stopped working properly 10 days ago.
The US space agency said its engineers had carried out recovery work on the robot's troubled flash memory system.
Spirit, which landed on Mars on 4 January, will now complete its study of the Red Planet's soil and rocks.
With the twin rover Opportunity also on the planet, Nasa said it was the first time in history that two mobile robots were exploring Mars at the same time.
"We have confirmed that Spirit is booting up normally. Tomorrow we'll be doing some preventative maintenance," said Dr Mark Adler of Nasa.
The agency said its engineers were able to repair Spirit by deleting thousands of files - many left over from its seven-month flight to Mars - from its flash memory.
Clean software
Onboard software had problems managing the flash memory, which retains information even when the power is off.
This triggered Spirit's computer to reset itself about once an hour, the agency added.
Engineers managed to put Spirit into an operations mode that avoided use of flash memory and this enabled the computer to stabilise.
"To be safe, we want to reformat the flash and start again with a clean slate," Dr Adler said.
The reformatting is planned for Monday and will delete everything in the flash file system and install a clean version of the flight software.
Spirit is being told to transmit priority data remaining in the flash memory. The information includes data from atmospheric observations made on 16 January in coordination with downward-looking observations by the European Space Agency's Mars Express orbiter.
Grey haematite
On Saturday, the Mars rover Opportunity rolled off its lander on to the surface of the Red Planet, a week after arrival.
Opportunity landed on Meridiani Planum, a region containing exposed deposits of the mineral haematite, which usually forms under watery conditions.
The presence of haematite has been confirmed, said Phil Christensen, lead scientist for both rovers' miniature thermal emission spectrometers (MiniTes), which are infrared-sensing instruments used for identifying rock types from a distance.
The concentration of haematite appears strongest in a layer of dark material above a light-covered outcrop in the wall of the crater where Opportunity sits, Dr Christensen said.
"As we get out of the bowl we're in, I think we'll get on to a surface that is rich in haematite," he added.
Opportunity is on the opposite side of Mars to Spirit, which is sitting in Gusev Crater which may once have held a lake.
The mission of both rovers is to explore the rocks and soil of their landing sites for evidence of past wet environments.
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