Nasa's InSight lander on Mars is no longer drilling into the surface of the planet as intended amid fears that rocks or gravel are blocking its instruments, the American space agency has said.
The lander, which arrived on Mars last November, started hammering into the soil on February 28 to measure the planet's internal temperature.
Scientists had hoped there would be a limited number of rocks below ground to impede the Heat and Physical Properties Package operation, as there are few rocks on the surface near the lander.
Nasa said the Heat and Physical Properties Package – or HP3 – had got about three-quarters of the way out of its housing structure before stopping, and had made no progress after a second attempt to dig on March 2.
The device is designed to be able to push any small rocks obstructing its path or find a way around them, so for now the team have decided to pause attempts at digging to analyse the situation.
"The mole is healthy and performed a round of hammering on the weekend," said Tilman Spohn, instrument lead from the German Aerospace Centre (DLR) which provided the instrument.
"It has, thus far, continued to work against some resistance without clear evidence for progress.
"The team has therefore decided to pause the hammering for about two weeks to allow the situation to be analysed more closely and jointly come up with strategies for overcoming the obstacle.
"In the meantime, we are planning on carrying out thermal conductivity measurements for the first time on Mars and start to conduct observations of the shadow of Phobos, which will be travelling through the radiometer's field of view on 5, 6 and 8 March 2019.
"A lot to do and still a lot of excellent science to be expected from HP3 and from InSight! Planetary exploration is not as easy as pie!"
The team is aiming to go up to 16ft (5m) beneath the surface, which would set an otherworldly record.