NASA's Mars rover Curiosity has halted its trek up a mountain filled with potentially habitable niches for life while engineers troubleshoot a problem with one of its key instruments.
Curiosity landed on Mars four years ago to determine if the planet most like earth in the solar system ever had the ingredients for life.
To answer the question, Curiosity has been drilling into rocks and chemically analysing the samples.
NASA's Jet Propulsion Laboratory project scientist Ashwin Vasavada said its work had been suspended due to a suspected problem with the instrument's motor.
The problem first appeared about a week ago and project engineers thought they had resolved it, but the problems cropped back up, Vasavada said at a conference in San Francisco.
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The problem comes as scientists are beginning to gather a glimpse of the history of Mars replete with life-friendly, water-rich environments and intriguing chemistry, including the first detection of the element boron.
Scientists believe boron may have led to the formation of the sugar ribose and ribonucleic acid, or RNA, which is present in all living cells on earth.
The concentrations of boron are increasing as Curiosity ascends Mount Sharp, a 5km mound of sediment rising from the floor of Gale Crater, where the rover made a daring sky crane-landing in August 2012.
Scientists have learned that the crater was filled with water several times in its history.
Curiosity is currently in an area known as the Murray Formation, located about 200 metres above where the rover landed.
The span represents tens of millions to hundreds of millions of years of geologic time, said California Institute of Technology geologist John Grotzinger.
"It turns out that this Murray Formation is really sort of a bonanza of all the things we intended to study when we picked the landing site," Grotzinger said.
