Evidence of Martian Life Found in a Holland and Barretts?

With my looming redundancy date and seemingly receiving even more rejections than jobs I’ve applied for it was refreshing to get some good news this morning. We’ve had another paper accepted on our work on why answering the question “Is there life on Mars?” is actually really difficult (with current techniques).

This one has the typically short and punchy title of:'Transformation of cyanobacterial biomolecules by iron oxides during flash pyrolysis: Implications for Mars life detection missions'. Sadly I couldn't get my preferred title (see above) passed my co-authors...

It'll probably be a few weeks until it's officially published online but there's an open access preprint here.

Around 4.5-4 billion years ago Mars was less of a Red Planet and much more like the early Earth. At this point in time Mars still had a CO₂ rich atmosphere, replenished by volcanoes and protected by an active magnetosphere. This provided both a greenhouse effects and increased surface pressure which meant liquid water was stable at the surface. Rivers flowed and filled asteroid impact craters to form crater lakes which may have provided an environment quite hospitable to life.

Early Mars was probably a much nicer place than it is today

For this project I needed a life form that represented the sort of organism that may have evolved and colonised these environments, the remains of which could be preserved in the sort of lake sediments that NASA’s Curiosity has been exploring at Gale Crater, Perseverance is exploring at Jezero Crater, and ESA’s Rosalind Franklin may find at Oxia Planum in 2022.

What I needed was a simple, single-celled, prokaryotic photosynthesiser, capable of adapting to extreme environments. I needed a cyanobacteria, one form of which is the blue-green algal ‘scum’ which can cause poisonous blooms in ponds, while another can be bought from your local health food shop as a supplement to put in nutritious smoothies…

That’s right, we’re using Spirulina as a stand in for alien life.

Tasty smoothie or alien life?

In our last paper we looked at how, when Mars rovers heat up sediment samples any fatty acids present, which could be evidence of biological processes, will react with iron oxides and be transformed into highly ambiguous aromatic organic molecules which won’t look much like evidence of life at all. There's loads of background detail about the search for life on Mars in that post and others (including here, here and here) so I'll keep this brief and won't repeat it all now (I'm quickly writing this while procrastinating rather than doing interview prep).

This time round we wanted to make the system a little more complex by using whole bacteria (the Spirulina) to see if the same thing happened with intact, pristine biological matter. Unsurprisingly we found out that, yes, on heating the organic molecules released from the bacterial cells will still react with the iron oxides, transform into more ambiguous phases, and make it very difficult to be 100 % sure whether we’ve found life or not! The detected organic products look pretty much identical to those which could just have been delivered to the surface of Mars by meteorite impacts.

We did find some hope in that haematite, which is a common iron oxide on Mars, is nowhere near as problematic as the other iron oxides we studied, and that some biomolecules (isoprenoid hydrocarbons) had better survivability than others, handily these are also the molecules most likely to survive over the billions of years since Mars  was widely habitable. We also established that suites of molecules, which would be pretty much useless on their own, could in combination be relatively strong evidence of life – and at least be a good sign we should take a second look at the sample using a wider variety of techniques.

Graph of detected products from the Spirulina pyrolysed on the various iron oxide minerals, quartz used as a less reactive comparison. The original biomolecules (the blue, purple, green) which would be solid evidence of life are lost and transformed into more ambiguous species represented by the yellow, red and black. AS can be seen survivability of 'useful' biomolecules is higher at lower Spirulina concentrations in the haematite than other iron oxides (quartz as expected only has minor adsorption effects)

As with the last paper, we came to the conclusion that despite the problems, we shouldn’t try to avoid iron oxides altogether (this would be pretty much impossible on Mars anyway, iron oxides being everywhere are the reason it’s red). This is because iron oxides are both good for long term preservation of organic matter (it sticks to iron which offers some protection, known as the ‘rusty sink’ effect) and may indicate habitability as they are often formed in the presence of water and could provide an energy source for specialist microorganisms.

Instead, we should look for areas where any of the more problematic iron-bearing species will have been transformed to more amenable haematite. These are areas with evidence of long-lived (or shorter but hotter) oxidising fluid flow in the subsurface. These areas, such as Vera Rubin Ridge at Gale Crater and the clay units at Oxia Planum, have the added bonus of potentially acted as a refugia for life as conditions at the martian surface became more inhospitable. Bacteria may have retreated to them and eeked out an existence in the subsurface, ‘feeding’ on energy produced in chemical reactions for millions/billions of years after the water on the surface dried out.

Vera Rubin Ridge, as viewed by Curiosity, may be a good place to search for evidence of ancient life (credit NASA)

The next step of this research, already submitted, is to look at how ancient organic matter preserved over millions of years (in the form of kerogen) reacts with these problematic iron oxides.  It could be expected that this would to be more resistant to transformation as it has already lost much of its reactant groups but, spoiler alert, it’s not. Hopefully more details on that soon!

I should add that the publication of this paper also involved one of the best experiences of peer-review that I have had. Both reviewers clearly knew the topics and methods involved well and provided highly insightful comments picking up on mistakes and pointing out gaps in the manuscript and encouraging me to make it into a better, more impactful piece of work. I wish more reviewers were like this!

Has NASA been covering up knowing about Life on Mars since the 70’s?

Apologies for the clickbait title but the short answer is no.

However, this is something that came up a few times during our live Reddit Q & A session yesterday in the run up to Perseverance’s landing. I only had time to go into it briefly then so I thought I’d expand here for anyone who is interested in the details.

The real interesting question is: ‘Do some NASA scientists believe they found evidence of life on Mars in the 70’s and still think they’re being undeservedly ignored/silenced by the rest of the scientific community?’ Because the answer to that is a surprising yes.

Planning for the first landed missions to Mars started almost 70 years ago in the 1950’s. Back then it was thought that the surface of Mars was a much more benign environment than we know it to be today. Early observations of the planet seemed to suggest that there was seasonal vegetative cover and serious scientists (including Carl Sagan) postulated the idea of large martian animals roaming a landscape similar to Earth's in serious journals. It wasn’t until the Mariner Mars orbiter missions in the mid-late ‘60s that we got clear images back of the martian surface. While these showed it to be a more hostile, empty desert environment with no signs of animal or plant life, nor liquid water at the surface, the low resolution meant it did not preclude the existence of even macrofauna. Because of this, it was a real worry that microorganisms hitching a ride on Mars landers could invade the surface, outcompeting and leading to the extinction of any putative microscopic Martians, and wiping out our ability to ever know that life had ever existed on another planet.

This led to the Viking mission having the most intense planetary protection effort and the production of the cleanest, most sterile spacecraft, Viking 1 & 2, that have ever been launched. The expectation that we would find habitable surface conditions and martian microbes also led to one of the most interesting experiments ever carried out on another planet.

Viking lander, Carl Sagan for scale (credit: NASA)

The Labelled Release Experiments carried by both Viking landers were devised by Gilbert Leven and Patricia Straat. These experiments involved scooping up a sample of martian surface soil, ‘feeding’ it a nutrient broth labelled with radioactive isotopes and providing a little heat and water, then measuring any radioactive gas produced as the broth was ‘eaten’ by respiring martian microbes. On Mars, these experiments ‘worked perfectly’. When ‘fed’ the soil produced the radioactive gas exactly as would be expected if martian microbes were present. If the soil was first heat sterilised to kill any microbes present then less gas was produced as would be expected. The designers of the experiment and many others saw this as a huge success and clear evidence of life on Mars and published papers to that effect.

The first evidence that not all was as it seemed came quickly. The Viking landers were also equipped with instruments to analyse the martian soil to look for organic matter – which would be direct evidence of either the microbes themselves or their normal food source. Despite multiple attempts, no organic molecules were detected other than simple chlorinated molecules accompanied by large releases of carbon monoxide and carbon dioxide. This was problematic, a lack of organic matter in the soil meant no food for martian microbes to live on (when they weren’t being fed by us). This meant that very soon, most scientists preferred the hypothesis that the results of the Labelled Release Experiment could be caused by some strongly oxidising mineral, present in the martian soil, acting like a bleach to break down the nutrient broth, instead of the presence of martian microbes. At best the results were ambiguous. Levin and Straat disagreed, and have continued publishing support for their ‘life detection’ up to the present (Patricia Straat died in October 2020).

The mystery of the strong oxidant persisted for 40 years until the Phoenix lander detected perchlorate in the martian soil. Perchlorates and other oxychlorines have since been detected all over Mars by subsequent missions. Perchlorates are strongly oxidising chlorine containing salts. It is their presence that is believed to have caused the gas release measured in the Labelled Release Experiment as they oxidised the organic carbon ‘food’ in the nutrient broth on heating, mimicking biological activity. The presence of perchlorates also explains the lack of detection of organic matter by Viking’s thermal decomposition GCMS experiments. On heating in the sample oven, the perchlorates break down, releasing large amounts of oxygen and chlorine. This reacts with any organic matter present, causing it to combust and essentially burn away. This neatly explains the carbon dioxide and carbon monoxide, and the simple chlorinated molecules which were detected by Viking 1 & 2 and, more recently (since 2012), the Curiosity Rover.

Phoenix (credit: NASA)

So no, we haven’t yet detected evidence of life on Mars, the results of the Labelled Release Experiment can be more simply explained abiotically.

With everything we now know about the hostility of the martian surface we really don’t expect to find anything living there. The deep subsurface, sheltered from the harsh effects of UV radiation, solar and galactic rays, oxidising chemicals, extreme temperature fluctuations and aridity, is another matter entirely though. I would be very surprised if we never find evidence of at least extinct life on Mars, and am hopeful we will one day find weird microbes living deep beneath its surface.

Being the first step of eventual Mars Sample Return, planned for completion sometime in the 2030’s, the successful landing of NASA’s Perseverance rover yesterday will hopefully bring us one step closer to finally answering the question of whether there was ever life on Mars.

The first image sent back by Perseverance last night, minutes after landing (credit: NASA)

One final point for anyone who is not convinced about the lack of some great NASA conspiracy covering up life on Mars, and which also covers things like aliens visiting us, Oumuamua being an alien spaceship and flat Earth battshittery: If you saw the live coverage of the landing last night, or follow the Twitter accounts of the hundreds of NASA employees and thousands of scientists actively involved in these missions, you’ll see just how excited everyone gets and just how much they want to share EVERYTHING with the whole world. You really think these people could keep come massive discovery like that quiet? That’s just stupid...