The depot will serve as a reserve cache to be brought back to Earth in the event Perseverance is unable to complete the next stage of its mission.

Photos downlinked from the robot on Monday showed the last of the 10 titanium cylinders intended for the depot, lying in the dust between the vehicle's wheels.

This is a structure created from the silt and sand dumped by a river as it slows on entry into a wider body of water.

Perseverance has drilled a mix of volcanic and sedimentary rocks that should tell the story of the crater and the lake it once held.

But Nasa can't risk the scenario where the rover breaks down with all the rocks stuck inside it.

Perseverance is going to investigate what appears to be evidence of flood activity, judging from the large size of some of the boulders scattered across the top of the delta.