Carbonate Origins

When robotic exploration of Mars began, many scientists expected to see large sedimentary deposits of carbonate on Mars. Evidence points to liquid water on the surface of ancient Mars, but questions remain as to how the planet was warm enough for this water to persist. It has been suggested that the planet’s carbon dioxide-rich atmosphere must have been thick enough at the time to create a global greenhouse. Climate models based on the idea of a thick CO 2 atmosphere have shown that if this scenario were true, weathering on Mars would have created large carbonate deposits on the surface over time. However, observations from numerous spacecraft have yet to identify deposits consistent with these predictions.

The largest carbonate deposit found thus far is in Nili Fossae, and this is one reason the site was selected for Mars 2020. Sampling efforts in the region could help solve the question of where the carbonates came from. Were they formed through serpentinization? Or are they left over from interactions between rocks and Mars’ atmosphere? A 2020 paper by Briony Horgan and colleagues even suggests that the carbonates could be the remains of stromatolites around the edge of the crater.

These are questions that the Perseverance rover will not directly answer when the rover touches down in Jezero crater, but the mission is the first step in further lines of study. Among its scientific objectives, Perseverance will use its drill to collect samples of Martian rock and soil in a process referred to as ‘sample caching.’ The idea is that the rover will store samples that could be returned to Earth at a later date by a Mars Sample Return mission. If the sample return effort is successful, scientists on Earth would then be able to study pristine pieces of the red planet with instruments and methods that are currently too large or complicated to be performed robotically on Mars.