A small pile of pebbles is obstructing the operations of the Perseverance Mars rover.

The rover, which is collecting rock samples for its eventual return to land , began to have problems on December 29, after extracting a core from a rock that the mission team dubbed “Issole.” According to a NASA Blog , the problem occurred in the device that transfers the drill bit and the sample from the rover’s drill arm to a carousel inside the rover’s chassis for storage. During the transfer, sensors inside the rover registered a higher than normal amount of friction at an unexpected point in the process.