Recently, the mission team behind NASA’s Perseverance Mars rover announced the detection of an exciting rock formation it had come across. Nicknamed Cheyava Falls, the arrowhead-shaped rock is the most promising find in the search for ancient life on Mars yet. There are structures visible in the rock that are consistent with being modified by microorganisms – it doesn’t mean that this is a discovery of life, but there is plenty to be excited about.

Before we get into the intriguing details of the discovery, it is important to consider two things. First is NASA’s Confidence of Life Detection (CoLD) scale, which has seven steps. The first one is detecting a possible signal, followed by ruling out contamination, making sure that the biology is possible, and ruling out a non-biological explanation. The final three are the discovery of an additional independent signal, ruling out other hypotheses, and finally an independent confirmation. Cheyava Falls is a detection of a possible signal, so step 1 – but a good step 1.

There are chemical changes happening making the minerals go from red to white, this often happens due to microbial activity. Often, not always!

Professor Sanjeev Gupta

Analysis from Perseverance immediately showed there was something to be excited about, and that the weird structures in the rocks were going to raise eyebrows the moment they were made available to the general public. The rock sample was collected on July 21, and the press release was shared on July 25. It was important to immediately contextualize what was visible in these images but also provide plenty of reasons to be excited about them.

“We looked at this rock, pinkish in color, which had lots of veins running through it and we saw these little spots. The spots are white with a black rim. We call them leopard spots because they look like the spots on a leopard,” Professor Sanjeev Gupta, part of the Perseverance team from Imperial College London, told IFLScience.

The main color of the rock is due to hematite, a common iron mineral. The leopard spots are also made up of iron minerals, but minerals that have undergone chemical reactions. This was the first intriguing find followed by more contextual evidence for a possible biosignature.

“Basically there are chemical changes happening making the minerals go from red to white, this often happens due to microbial activity. Often, not always,” Professor Gupta continued. “Then we saw the black halos containing iron and phosphate, which are important minerals and elements for life. Also, the SHERLOC instrument detected organics in these rocks.”

This is why this rock is so exciting, and got on the first step of the CoLD scale. While there is no guarantee that what was seen was created by living organisms, the rock is potentially the most important rock investigated by Perseverance yet.

“The fact that we had two things, we had organics present and these spots which on Earth are related to chemical changes in the rock, led us to suggest that this was what we call a potential biosignature,” Professor Gupta told IFLScience.

We could find compelling evidence for biological processes, that's possible. It's also possible that even after we bring the rocks back, we still have questions. 

Professor David Flannery

The question now is can we move this detection higher on the CoLD scale? The answer we are getting is a solid maybe. Based on the rover's capabilities and mission plan, what has been observed and is being analyzed won’t dramatically change the announced findings. However, the sample has been collected and placed in a canister for future analysis.

Everything going well, that analysis won’t be performed on Mars, but rather on Earth. The samples will be collected by the troubled Mars Sample Return mission (troubled because it has experienced severe delays and spiraling costs). The project to collect the samples taken or dropped by Perseverance is certainly ambitious.

The discovery of this rock certainly shows the importance of a sample return mission. To find out more about this sample, we need Earth’s laboratories. That doesn’t mean we would know if life was at work here, or if there is (or was) life on Mars.

“There are no guarantees and there are many possibilities. One thing I think we can be certain about is that we need to get these rocks back to study in our laboratories on Earth before we can start to answer some of these questions,” Professor David Flannery, also a member of the Perseverance team from the Queensland University of Technology, told IFLScience. 

“We could find compelling evidence for biological processes, that's possible. It's also possible that even after we bring the rocks back, we still have questions. And one of the reasons that's a significant possibility, I think, is that we don't have much experience with this particular type of biosignature on Earth.”

On Earth, the focus has been on seeing structures that ancient microbes formed on the surface, such as stromatolites. There have been plenty of controversies when it comes to evidence of life in ancient rock samples. A single rock sample from Mars might not suddenly show beyond any doubt that life existed there, but this is sample 23 out of 43 canisters. Together, they can paint a picture of what ancient Mars was like and if life above or below the surface existed. 

Perseverance will continue to study the edge of Jezero Crater, and is going to approach rocks that settled there more than 3.5 billion years ago. There are only a handful of regions older than that on Earth, so the industrious rover is not only on a quest to understand the possibilities of life beyond Earth but also to understand what rocky planets were like in infancy. These questions have implications for how our world and the creatures that live in it came to be.