Understanding the geology of Mars in the hunt for life

On 18 February 2021, in the midst of COVID restrictions and lockdowns, the NASA Perseverance rover touched down on Mars.

Landing in a region known as Jezero crater, it has a number of key goals including figuring out if Mars ever hosted environments suitable for life, if life existed and was preserved in these places, testing oxygen production for potential future crewed missions and collecting samples of rock and dust for detailed analysis on Earth.

The rover has so far spent over 12 months trundling over the surface, snapping pictures, firing x-rays and lasers at rocks, and storing samples in special tubes. It will not be until the next decade that these samples will be brought back to Earth to laboratories around the world, but the data being collected from the surface of Mars are already providing a glut of information about Jezero crater, from its geological history to whether or not organic materials are present.

Dr Keyron Hickman-Lewis and Dr Joby Razzell Hollis, are two research fellow at the Museum who have been working with NASA on the Perseverance rover.

Keyron has documented a number of the samples collected, and is a co-author on four recent papers published that have been looking into the geology and geochemistry of Mars. Joby has been planning surface operations and analysing data for one of Perseverance's scientific instruments, called SHERLOC, and is a leading author of one of those papers.

'At the moment we are collecting a range of samples which help us to pose numerous questions about the geological history of Mars,' explains Keyron. 'While we are exploring Mars, we acquire large amounts of data at each locality visited, and these data tell us much about the environment and the chemistry of the rocks.'

'Through this, we are building the context for the samples collected, and we can begin to ask ourselves questions about the geological processes that formed them.'

Some of these questions have been answered in the flurry of recent papers published in Science and Science Advances.

Where to look for Martian life

Jezero crater is located on the western edge of a flat plain called Isidis Planitia, just north of the Martian equator. Out of many possible landing sites, this location was chosen specifically for the potential that it once supported life in the ancient past.

Satellites orbiting Mars have been able to plot the timeline of the crater. Around 3.5 billion years ago, a river of water spilled over the rim of the crater, forging a river delta that spread outward into a lake. During this process, sedimentary minerals were transported down into the lake and created conditions that, were they found on Earth, would almost certainly be teeming with microbial life.

But other forces have also been in play in the crater. Two of the recent studies have looked in detail at the rocks that form the crater floor, identifying two distinct formations of igneous rock, or those that often have a magmatic origin.

The team were able to determine that these rocks, rich in minerals known as olivine and pyroxene, formed due to the cooling of a magma, meaning that at some point in Mars' history Jezero crater was filled with magma as a result of either volcanic activity or some sort of impact. 

The study that Joby and his co-authors published in Science has shown that these olivine grains were later altered by episodes of aqueous activity and deposition of chlorides, sulfates, and perchlorate salts as briny water evaporated. The final paper, published in Science Advances, has used X-rays to confirm the chemical diversity of these rocks, demonstrating that the olivines have been altered and replaced by a host of minerals, including amorphous silicates.

Taken together, these studies support the idea that billions of years ago this region hosted an environment that was dynamically changed by flowing water, and is rich in minerals that could have preserved organic materials from that time. The sample cores that Perseverance is collecting in Jezero Crater will give scientists on Earth the chance to analyse these rocks in more detail and determine whether any of the organic material present in these rocks could have been produced by living organisms.

What would life look like?

One of the most intriguing findings so far is that of organic molecules in the igneous and altered rocks of the Jezero crater floor. While this might initially suggest that the mission has been successful and alien life detected, Keyron and Joby are keen to point out that this is not the case. More tests will need to be done to formally address this possibility.

'All life on Earth is based on organic material, but not all organic material arises from life,' explains Keyron. 'And so without identifying specific molecules or organic signatures that are of unambiguously biological origin, we cannot say that we have found life.' 

'We may have found evidence of organic molecules trapped in the rocks of Jezero Crater,' says Joby. 'These kinds of molecules include some of the constituent molecules used by life on Earth, but they are also formed by non-biological processes. So at the moment we can say that we have some particularly interesting samples, but we have not discovered unambiguous evidence of life.'

The unambiguous detection of life – if it ever existed on Mars – will require that these samples are brought from Mars to be studied in more detail by specialized laboratories on Earth.

But even if these tests eventually reveal that the molecules are indeed of non-biological origins, that is still a fascinating outcome. It opens a whole raft of questions as to why Mars, despite having a similar origin and climatic conditions to Earth billions of years ago, failed to develop life of its own while on Earth it flourished.  

'This would be an interesting comparison to what we see here on Earth,' says Keyron. 'It could mean that some crucial processes toward life happened here on Earth which may never have happened on Mars.'

'I think understanding that possibility would be tremendously interesting and would tell us a great deal about the distribution of life in the universe, if indeed it occurs elsewhere.'

That is part of the reasoning behind the sample return mission. So far, the rover has used 14 out of 38 sample tubes that will be sealed up and left on the surface of the red planet. These samples will then be picked up by a second mission called Mars Sample Return, which will hopefully touch down on Earth by the mid-2030s.

In the meantime, Joby, Keyron, and their colleagues will continue to pore over the wealth of data being beamed back from our enigmatic neighbour.