NASA bit off more than it could chew when it sent the Perseverance rover to Mars to collect samples.

The US$2.4 billion mission landed the rover in Jezero Crater, the site of an ancient lake. It's the ideal spot to search for the fossils of Martian microbes that may have existed when the planet was lush with lakes and rivers.

Perseverance's main mission is to collect samples of the rock and sediment along the lake bed and the crater rim, in hopes of finding a sign that life once thrived on the red planet. The rover has done a fine job – so far it's secured 24 samples – but NASA no longer knows how it's going to bring them to Earth for analysis.

NASA's original design for the retrieval mission, called Mars Sample Return, has fallen apart. The agency is asking companies to step in and propose better ideas.