Latest paper summary: Effect of Hydration State of Martian Perchlorate Salts on Their Decomposition Temperatures

Here’s an early Christmas present for everyone (so both of you who read this blog), our latest paper (my first out of this project) is now published online and completely open access for anyone to read.

Effect of Hydration States of Martian Perchlorate Salts on their Decomposition Temperatures

If you can’t be bothered to read it, here is a summary:

Since the Viking landers back in 1976, numerous missions have gone to Mars and attempted to find organic matter on the surface. However, to this date, none have succeeded in finding anything other than simple chlorinated hydrocarbons. We expect there to be a detectable amount of relatively complex organic molecules in the Martian near surface from meteoritic input (meteorites are full of organic matter), hydrothermal processes and maybe even left behind as evidence of extinct (or, unlikely but not impossible, extant) life. This lack of detectable organics was always a bit of a mystery…

Note: the presence of organic matter does not necessarily mean the existence of life, organic molecules are just those which have carbon and hydrogen and they can be formed by numerous non-biological processes – including in deep space.

However, since they were accidentally discovered by the Phoenix mission back in 2008 we’ve known that that there are these salts on Mars called perchlorates. These salts are very rare on Earth, only being known to exist in significant quantities in the Atacama Desert and the Antarctic Dry Valleys; two of the driest places on Earth.  As the name suggests perchlorates have 4 oxygens to each chlorine ion and so are very highly oxidising. While (relatively) stable on the Martian surface, as soon as these are heated within the sample analysis oven of a Martian lander or rover these literally explode, giving off loads of oxygen into the analytical system (which should be a vacuum). This means that any organic matter which may be in the Martian soil is combusted, reacting with the oxygen present and breaking down to carbon dioxide and carbon monoxide,  and the few surviving scraps are heavily broken up and react with the chlorine in the perchlorate, making small chlorinated hydrocarbons. Because of this destruction the molecules we are interested in cannot be detected – This is the perchlorate problem.

My attempt to summarise the Perchlorate Problem on the Sketch Your Science wall at AGU this year

My job as a postdoc researcher at Imperial College is to attempt to find a way around this ‘perchlorate problem’ by researching how these perchlorates (and other similar minerals) react with organic matter. The first step of this, however, is to try to understand a little more about the Martian perchlorates themselves. And this is what this recently published body of work was concerned with.

Since it landed on the Mars in 2012 the Curiosity Rover has drilled 15 holes into the Martian surface and analysed the drilled sample to see what it is made of. One of the techniques used is looking at the gases given off by the sample when it is heated. However, every time the Curiosity Rover has analysed one of these sample holes, the temperature that oxygen gas is released from the sample is very different (Sutter et al., 2016). Most of the oxygen given off is believed to have come from these perchlorates (based on other gases given off at the same time). It has been found by previous laboratory experiments that different types of perchlorate salts (magnesium perchlorate, iron perchlorate, calcium perchlorate, etc) break down and give off oxygen at different temperatures (Glavin et al., 2015), and also break down at different temperatures depending on whether other minerals which may act as catalysts are also present in the soil (Sutter et al., 2014). Therefore it has so far been concluded that different types of perchlorates and/or catalyst minerals have been present at each drill site.

Curiosity on Mars (credit: NASA)

The first 14 drill holes Curiosity drilled on Mars (credit: NASA)

This is a bit problematic. It is believed that most perchlorate forms in the Martian atmosphere and falls out onto the surface (as it does on Earth) and so there is no known mechanism for having different perchlorates in different places – they should all be pretty much the same across the Martian surface.

It is known that perchlorates are highly hydrophilic – they will suck up any water available (they are used as drying agents in industry) and can change their hydration state (how many molecules of water are bound to each molecule of perchlorate) really easily. The temperature and humidity of the Martian surface changes massively throughout the Martian day and year. Photographs taken on Mars by Phoenix show growing blobs on the lander struts which have been interpreted as perchlorate goos as they absorb water throughout the Martian day. So, my boss, Mark Sephton, had an idea that the hydration state of the perchlorates may actually have an important effect on their breakdown temperature and set me to investigate this.

'Blobs' of perchlorate 'goo' moving across the struts of the Phoenix lander (Renno et al., 2009)

I did this by taking a single one of the perchlorate salts (magnesium perchlorate) and drying it out in the glassware drying oven to drive off water in an attempt to reduce its hydration state. After three weeks I removed some sample, flash heated it and analysed the gases given off using pyrolysis-GCMS at 100 °C temperature steps from 200-1000 °C to create oxygen (and other lesser gases) release-temperature profiles. A sample of the perchlorate was also left out on the lab bench to rehydrate and analysed in the same way after 24, 48 and 72 hours of exposure and rehydration. This whole experiment was repeated after another week and then after a fortnight so oxygen release profiles were created for 3, 4 and 5 week drying times and corresponding 24, 48 and 72 hour re-exposure samples.

It was confirmed that these drying and re-exposure experiments were definitely changing the hydration states of the perchlorates by testing them (by X-ray diffraction) next door in the Natural History Museum. This involved transporting them through crowds of tourists under an inert atmosphere (in a sealed lunchbox filled with nitrogen gas) to prevent further hydration state change.

What we found was that different hydration states did indeed affect the temperature of decomposition so that the oxygen release profiles were as different for different hydration states of this one kind of perchlorate as the previous studies had found for all the different kinds they tested. This, therefore, gave a much simpler answer to this puzzle: Curiosity has been analysing different samples with different hydration states of perchlorate in them. This makes sense as the different samples drilled have been analysed at different times of the Martian day and year and samples spend varying amounts of time stashed inside the temperature-controlled innards of the rover before they get round to being analysed – which could allow further changes in their hydration state. Our data show that is it possible for numerous hydration states of perchlorate to exist within a sample and this leads to multiple peaks in the oxygen release profile, some of the Martian samples have multiple peaks in their oxygen release profile and so we suggest that this is due to unstable mixtures of perchlorate hydration states being present on the Martian surface.

This figure from the paper shows how the data from this study (A) compares to select samples analysed on Mars by Curiosity (B) and various types of perchlorate from a study by Glavin et al. (2015) (C). It can clearly be seen that the variation in the samples of magnesium perchlorate that were dried out for various numbers of weeks and analysed in this study is almost as great as the variation in different perchlorates from the Glavin et al. study. So, different hydration states may offer a simpler explanation for the variation seen in the Martian samples. 

We tried to see if the oxygen release profile of the Martian samples (and therefore, based on our findings, the perchlorate hydration state) corresponded to the climate conditions at the time they were sampled at but did not find any relationship. There did seem, however, to be a vague suggestion in the data that they were related to the time of the year that they were sampled at, although more data would be needed to be sure about this.

All in all, we conclude that the hydration state of perchlorate salts is yet another thing to make making sense of Martian data yet more complicated.

Science, Sazerac and Steamers: AGU 17, New Orleans

After a heavy night with a few of the ex-UEA mountaineering club members visiting us in The London it was an unpleasant early morning trudge to the tube station nursing a hangover. With perfect timing it just so happened that I was flying out on the one day that Hell (sorry, London, nope, right the first time) froze over. Heavy snow meant minor panic, as all public transport was buggered and it started to look as though a tube might not turn up at all. Thankfully it did and it turned out that there was no worry of missing my flight as it ended up delayed for 3 hours. There was only one de-icing truck available and it was snowing so heavily that once they’d defrosted one side of the plane the previous side had re-frozen up and needed doing again….This, of course, meant I missed my connecting flight which took off 5 minutes before I landed in Atlanta. Luckily, avoiding a repeat of last time this happened to me, they managed to get me the last seat on the last plane to New Orleans that evening. Although, from the sound of things, plenty were not so lucky, airports around the west coast of the US must have been full of stressed out scientists snuggling up to their poster tubes that night.

AGU was intense, having been to EGU (the European version in Vienna) during my PhD and thinking that was pretty big, I was expecting something of a similar scale. I was wrong, it was unfathomably massive. There were over 25,000 geoscientists in attendance and over 20,000 talks and posters to see….that is a fuck ton of exciting new scientific research being shared. The conference centre was over a kilometre long, it took over 20 minutes to get from one end to the other with all the crowds; thankfully all the Planetary Science talks were clustered together so I didn’t have to run about much – although still managed to average about 15,000 steps a day just getting about!

Due to the sheer number of coevally running sessions it was not possible to see everything I had an interest in (if you’ve read this blog before you may have noticed I get involved in an eclectic mix of sciences) so I stuck with the Planetary Science sessions as that’s what I work with at the moment. Running between talks on Martian surface processes and outer solar system geochemistry – my main 2 things at the moment. There was some exciting results being presented from all the current missions that are on the go at the minute – especially from Mars Curiosity and the recently deceased Cassini probe, so lots of cool space pictures.

Bourbon Street in the French Quarter

I was there to present a poster on our latest paper on the effects of hydration state on Martian perchlorate salts, about which a summary blog post will be coming soon once the open access version of the article is out (you can read the pre-proofed version of the article here, although it is temporarily pay walled). Unfortunately, despite good intentions of being well rested and fresh for the 8am session, the night before got pretty heavy. It is apparently impossible to have a quiet drink in New Orleans and we ended up in a bar with a pretty cool band drinking Sazeracs (the local speciality cocktail, laced with absinthe) with random other scientists until the early hours. This was partly because my mate fancied the band’s singer (oh, shit, I was supposed to never mention that again) but also because this is what happened EVERY SINGLE NIGHT.

Bourbon Street at night, watching people 'get got'

As it turns out, an AGU poster session is not the place to be with an absinthe-derived hangover, they are intense AF. What was cool was that everyone was super positive about the results and I now have a few things to try in the lab for future work that have come out of the chats we had. The argument I was sort of expecting with the research group whose work our work is directly contradicting never came, which I guess is good as it would probably have ended with me spewing up on a senior NASA scientists shoes… I did have a minor fan-girly moment when one of the old professors who’s big on the Curiosity Rover team came up to collect a copy of our paper though.

New Orleans is a great locality for a conference, as somebody who hates being in cities, this is definitely one of the best I’ve been to. Every evening was spent exploring the French Quarter or the Riverside area, hanging out in ridiculously cool bars listening to spectacular live music – lots of Jazz – and drinking great local craft ales and Sazerac. The food was also amazing, blackened fish, shrimp, deep fried catfish and crawdads, so good, although I didn’t get round to trying any ‘gator.

Apparently everything that lives in the river/gulf can and will be deep fried

 While really cool, the area does have quite the seedy side and there were plenty of con-artists out trying to swindle tourists – they must have seen the conference attendees from a mile off, us scientists are not known for our street-smarts. The popular scam is offering a shoe shine then betting the tourist they can tell them exactly where, on what street in which city they got their shoes. The scam answer being ‘On the bottom of yo’ feet, in this street’ and then getting all up in their face and calling over their mates if they don’t hand over the ‘Ten for the shine, and ten for the line’. Must’ve made a killing this week based on the number of guys getting got we spotted while sat up on a balcony overlooking Bourbon Street. Also, someone had altered a pedestrian roadworks diversion to funnel you into a grotty looking strip club, we noticed we were being herded just in time to avoid this one, sneaky bastards.

 On Wednesday afternoon we skipped out the conference to do some touristy stuff. The choice was an airboat swamp tour or a paddle steamer jazz cruise. Sadly at this time of year the alligators would’ve all been hibernating at the bottom of the swamp, so we opted for the steamer. Best. Idea. Ever. Cruising down the Mighty Mississippi, seeing the sights, learning a bit of history from the captain (who had the Louisiana accent ever), listening to jazz and chilling with a few beers was clearly the highlight of the week.

Steaming down the Mississippi

All in, it was an amazing week; exciting science and great times, I wonder if Washington will be able to compare next year? Somehow I doubt it…

Adventures in Peer Review or There and Back and Again and Again and Again

So my latest paper (and my first on Martian geochemistry rather than corals) is now online at JGR: Planets in its pre-proof form. I’ll be posting an easy to understand summary of the science once the finalised article is up in all of its open access glory but for now, so not to anger our publisher overlords with potential copyright violations, here is the saga of this paper’s epic journey through the peer-review process. I'm posting this story as it feels very disparaging getting your submissions that you've worked hard on knocked back, and I think it's good to know that behind many successful publications there is a back story of rejection and so a light at the end of the tunnel.

The work for this paper was one of the first projects I carried out here at Imperial; investigating the relationship between the hydration state of perchlorate salts and the temperature they decompose at. This is an important issue as it is believed that the thermal decomposition of these salts when heated during analysis of Martian soil may be confounding our attempts to detect organic matter on Mars – but more on that next time.

This work was completed, written up and initially submitted to a well-known geophysical research journal back in October last year (2016). Unfortunately despite our research group having published similar themes in their before it was rejected by the editor for being ‘too specialist’. Not to be beaten, the manuscript was quickly reworked to another geochemical journal’s format and resubmitted. However, they thought it was ‘better for consideration for another journal’. It seemed salts on Mars weren’t in vogue at the moment – all the cool geo-astro-bio-chemists-or-whatver-the-hell-I-am-now are researching Enceladus now…

After another round of reformatting (thank fuck for Mendeley and its instantaneous citation-style-reformatting) and re-registering into another publisher’s online submission machine we submitted to a more specialist (think space-chemistry not bondage) journal in November (2016). Thankfully, this time there was no instantaneous letter of rejection from the editor as the manuscript was sent out for peer review.

To those who don't know, all legitimate scientific work has to be checked over by other experts in the field before it can be released into the wider scientific community. This is the peer-review process and it keeps the amount of bad science out there down to a minimum - or at least it did until you could say whatever you wanted on the internet and people would lap it up and tinfoil hat wearing nutters started having their own journal and conferences.

We received two reviews of the paper at the beginning of February 2017, both reviewers reasonably wanted proof that the perchlorates I was experimenting on were indeed changing their crystal structure when dehydrated, as I hypothesised, rather than just losing superficial water. They requested, therefore, that we carried out additional tests on the samples to prove this – by X-Ray Diffraction (XRD). This was fair enough, it would make our argument much stronger.

Unfortunately we do not have our own XRD machine in the lab, they’re pretty big, specialist expensive pieces of kit. Also, all of the samples that I had used had spent much longer either in the drying oven or exposed to the laboratory atmosphere than they had when I analysed them, this meant the whole month-and-a-half drying and subsequent re-exposure experiments had to be repeated on fresh perchlorate. So, I booked time on the XRD machine next door at the Natural History Museum and put the samples in the oven for 6 weeks at about gas mark 0.25. The flip side to this was that I got to go behind-the-scenes at the Natural History Museum which is always cool – getting a security pass, jumping the queues (it was half term) and getting let through the mysterious door hidden behind the giant sloth skeleton, going from the mad noisy crowds to the peace and quiet of the underground laboratories. However, repeatedly running from our lab, through the crowds of tourists on Exhibition Road carrying a lunchbox filled with nitrogen gas to preserve my sample was interesting to say the least.

The guardian of the secret science caves (Image credit)

While the truth was somewhat more complicated than we had expected, the XRD data did indeed prove that the conditions we were subjecting the samples to was enough to change their hydration state. Bolstering our conclusions that it was changes in hydration state that were affecting the breakdown temperature. The manuscript was updated to include these findings (along with making many more minor changes suggested by the reviewers) and sent back to review at the end of March.

Just over a month later the second round of reviews came back, this time they didn’t agree. 

Reviewer One’s was basically,

‘Ah, I see you did as I asked and it proved your point, nice work, this should be published 😊’

Reviewer Two on the other hand,

‘Ah, I see you did as I asked, I still don’t believe it, I think my idea is the best, REJECTION 

😞’

Unfortunately for us, although probably good for scientific integrity, the Editor has to go with the harshest review and the paper was rejected by the journal. I thought in this case, however, that this was unfair, after the amount of work I’d put in to, fulfill everything this reviewer had asked for. As there was such disparity between the two reviews, it felt like they had an axe to grind, maybe they were one of the many that this work was disagreeing with and didn't like that. Unfortunately, from talking to people, this seems to happen a lot during the peer-review process, which isn’t cool, if the work is solid, but doesn't agree with your ideas, then it’s up to you to prove its wrong with your own research later, not block it from coming out, that’s how science progresses.

So I sent a whiny letter to the editor, telling on Reviewer Two for being mean. Surprisingly this worked and the editor promised to send the paper out to new reviewers IF we made a few concessions and elaborated on why we didn’t think the alternative hypothesis Reviewer Two washing pushing was correct.

After some improvements we re-re-submitted at the end of June, a tense few months followed as we waited to hear what the new reviewers thought of our work – would they be kind? Thankfully both reviews we received at the beginning of November were very positive and it only took a few days to put right the points they made – which were mostly just things needing re-wording to make more sense/be less ambiguous, or typos that had somehow made it this far unspotted.

Finally on the 16 November 2017, almost exactly a year after the first submission, the paper was accepted. The battle was over, we had won, now to wait and see what the wider community thinks…

Why Cassini had to Die

This morning, the 15^th September, after 20 years in space, Cassini ended her mission exploring the Jovian and Saturnian systems, intentionally vapourising itself by crashing into the atmosphere of Saturn. Due to the huge distance they had to be relayed, signals of the data collected right up until the moment of destruction took several hours to reach Earth.

Artistic visualisation of Cassini starting her final plunge towards Saturn (Credit: NASA)

The death of Cassini was of utmost importance for the Planetary Protection of the outer solar system (see PPOSS.org). The more Cassini’s observations have taught us about the icy moons of Saturn and Jupiter, the more we have realised just how complex, interesting and important these extraterrestrial worlds are.

Enceladus, Europa and Ganymede are all now known to contain vast internal water oceans under a protective icy shell, Titan has a complex atmosphere full of organic molecules and lakes of hydrocarbons on its surface. There is a chance that these environments may harbour life or at least have complex systems of pre-biotic chemistry. In this respect Cassini created more questions than it answered, creating massive interest in further exploration of these bodies, with specific life detection missions.

Cassini discovered Enceladus has a subsurface ocean and water vapour plumes which contain organic matter and evidence of water-rock interactions - the building blocks and  a potential energy source for life (Credit: NASA)

Cassini saw through Titan's thick hazy atmosphere to discover  a hugely complex world with hydrocarbon lakes, methane rain and active geology (Credit: NASA)

In order for future missions to study these questions, we must not contaminate these bodies with terrestrial microbes or organic contaminants which may accidentally be detected and mistaken for indigenous alien life. This is where planetary protection comes in. Cassini was dirty, not having undergone strict contamination control cleaning procedures and so will have been carrying an unfortunate payload of microbes and organic molecules. If Cassini had been allowed to continue its orbit around Saturn unchecked, its orbit could have decayed over time leading to a crash landing on one of the moons which may have led to uncontainable and irreversible contamination.

Cassini’s fiery death therefore saves the pristine conditions on these fascinating moons for future generations of scientists to explore. 

Goodbye Cassini and thankyou

Artistic visualisation of the Cassini's final moments burning up in Saturn's atmosphere (Credit: NASA)

3 Days, 3 Rock Types and 100 Million Years: Climbing in Devon

This (extended) weekend just gone, Dan, one of our regular ex-Norwich climbing partners, took us on a climbing tour of his home crags in Devon. This was an excuse for me to look at some nice rocks and we managed to get on three different rock types, covering over 100 million years of the geological history of the UK, over the three days.

Simplified geological map of Devon showing the three locations (adapted from Kirkwood et al., 2016)

Day 1: Baggy Point - Sandstone

Saturday, starting off at Baggy Point near Croyde. The climbing here is on the 360-370 million year old, Upper Devonian Baggy Sandstone Formation. They overlie the Upcott Slates and are themselves overlain by the Pilton Mudstones, all together a making up a 450m thick succession of interbedded sands, silts, muds and thin limestones charting a changing river delta succession which at first built outwards as sea level fell and then retreated inland as sea level rose again.

Due to their age and the pressures and temperatures they have been subjected to these sandstones are slightly metamorphosed and so are much harder than more recent sandstone deposits (such as those known to climbers as the Southern Sandstones around Kent) and so are a lot more solid to climb on. Routes (such as the classics Lost Horizon and Shangri-Lai) follow angular fractured cracks up otherwise sheer faces while harder routes tackle the blank slabs themselves, relying on delicate footwork and careful movement with little means of protection.

Rob leading Lost Horizon following a steep crack system

The sheer faces plunging steeply into the sea that characterise the climbing here were originally horizontal as the sedimentary sequence was deposited on the sea bed. However, during the Late Devonian and Carboniferous Periods these rocks felt the distal effects of the mountain building event known as the Variscan Orogeny. The continents of Gondwana and Laurussia collided to form the supercontinent Pangea highly folding and faulting the rocks as they were compressed together. At Baggy Point this tilted the sequence very steeply to bring the ancient sea bed to a near vertical orientation and creating the sheer, almost featureless, delicate slabs which are a feature of the climbing here.

Dan leading while I belay on the second pitch of a route up one of the steeply dipping slabs at Baggy Point (credit: C. Wade)

Unfortunately due to the interbedded weaker muds and the highly erosive sea cliff environment a lot of the rock here is quite fragile and we pulled a few dangerous chunks off into the sea as we climbed.

Day 2: Daddyhole - Limestone

Sunday, now we’re climbing a little further back in time to the mid-Devonian at the cliffs of Daddyhole in Torquay. This is very close to the Devonian type section at Torbay (which I have written about before as part of the UEA Slapton fieldtrip). The plan was to climb on the lower part of the sequence at Daddyhole Main Cliff, however, due to the long commiting nature of the routes down there and the incoming rain we were forced to visit the uppermost part of the sequence instead at Daddyhole Upper.

The mid-Devonian Limestones here were deposited around 400 million years ago when the UK was located within the tropics and Devon was beneath a warm, shallow, tropical sea. The limestones here represent a sequence from a thriving offshore reef system, well away from any polluting terrestrial input, with corals, sponges, shellfish and other organisms being highly abundant in the fossil record. Overtime (up the sequence/cliff face) the limestone becomes ‘dirtier’ as more sand and mud reaches the area from the nearby landmass and the reef life is gradually choked out, a process helped by nearby volcanoes occasionally burying the reef in ash deposits.

Spot the Dan, he's pretty much at the boundary between the cleaner massively bedded limestones and the siltier, finer bedded sequence above

The impurity of the limestone and interbedded siltier layers mean that the climbing at Daddyhole Upper is somewhat ‘esoteric’ with plenty of loose, crumbly rock and so it is not the most popular venue. This does however mean it has not taken on the smooth mirror-polished quality of more popular limestone crags (such as much of the climbing in Portland or Cheddar) and the combination of weathered out juggy limestone cracks and grippy rock is a rare delight (as long as you don’t think about how sketchy all the gear placements are. Unfortunately rain quickly stopped play here and we only got a single route in before retreating for a seaside Devonshire cream tea.

Charlotte's favourite type of climbing

Day 3: Dartmoor - Granite

Monday and its back to the future on the granite of Dartmoor. This is part of the massive Cornubian Batholith (batholith = large body of magma) that welled up underneath the southwest of England around 300-275 million years ago, during the Late Carboniferous-Early Permian. This outcrops at various localities all the way from the Isles of Scilly to Dartmoor, but is known (from a low density gravity anomaly) to extend more than 100 km further southwest under the sea.

The formation of this huge body of molten rock is related to the same mountain building event as the folding of the Devonian sediments (that we climbed on the previous two days) it intruded into. Partial melting of the lower crust occurred at a late stage during the mountain building process (after the majority of the folding had already occurred) and extension of the crust allowed the batholith to rise irregularly as ‘blobs’ to higher levels.

Over time, the softer sedimentary rocks that were intruded into have preferentially eroded away, leaving behind these granite ‘blobs’ exposed as Tors on areas such as Dartmoor. As the overlying rocks were removed the granite was unloaded and expanded, fracturing both horizontally and vertically and peeling itself apart. This produced the horizontal breaks, vertical cracks and juggy flake systems that characterise climbing on the Tors of Dartmoor.

Dan wedging himself in a nice big crack, note the horizontal joints too (credit C. Wade)

Large, sharp phenocrysts (big crystals) of plagioclase stand out proud from the otherwise surprisingly smooth and slippery blank sections of granite face. These tell the geologist that the granite cooled in stages, the big crystals grew slowly at depth before the magma rose upwards to shallower, cooler levels and finished solidifying quicker so the rest of the crystals (the groundmass) are much smaller. For the climber, delicate, precise footwork or desperate crimping and hauling with the fingertips on these small protrusions is often the only way to make progress on the harder routes. The sharpness of these crystals tears into the skin restricting the number of attempts you can have at a hard move before bloody fingers stop play, but gives excellent friction allowing your climbing shoes to stick to the smallest nubbin.

Me climbing Vandal & Ann, run out and sketched out trying to figure out the best way of using a series of crappy little crystals to get to the safety of the next big break (credit C. Wade)

Clearly in three days it is only possible to scratch the surface of the number of different rock types and climbing venues available in the southwest and we will return soon to sample more of their esoteric delights. Although it’s back onto my favourite Peak Grit for the upcoming bank holiday weekend.

Mars Sample Return

This week I’ve been at a NASA and National Science Academies hosted planetary protection workshop in Washington DC, representing the European Science Foundation and the Planetary Protection of the Outer Solar system  (PPOSS) team (everyone important was busy/on holiday). The workshop was focused on planetary protection for the Mars 2020 mission which has an extra element of complication as it is a sample return mission – well, the 2020 mission is actually a sample caching mission, they haven’t quite figured out when and how the collected samples will be returned by a future mission….

Mars 2020 Rover (nature.com)

Sample return is a double problem for planetary protection as we have to worry about both forward and backward contamination. Forward contamination is an issue for all life detection missions, this is when the spacecraft is contaminated by hitchhiking microorganisms and organic molecules which could confound the results of the scientific experiments. This may lead us to believe we’ve found life on Mars (or wherever we’re visiting) in what is known as a false positive, or, signals from contaminants could swamp the instruments so that we miss small crucial signals of extraterrestrial life, or prebiotic organic molecules (the building blocks of life) – a false negative. Backward contamination is the worry that a sample return mission may bring back dangerous microorganisms or other infective agents such as viruses or prions (what is a prion?). This is only a concern for sample return missions that bring back material from localities which are potentially habitable, including certain areas of Mars which may have just enough water to host microbial life under the surface where it would be protected from the deadly radiation on the surface (which is why both Mars 2020 and ExoMars will have drills for subsurface sampling).

The likelihood of a sample return mission bringing back something dangerous is incredibly low, we currently have no evidence of life on Mars (whatever the conspiracy nutjobs claim). It is unlikely that Martian life would be compatible with, and therefore able to infect pathogenically, Earth life as it would have either evolved completely independently or had billions of years since a last common ancestor. However, despite the low chances, NASA (amongst others) is still taking this risk very seriously as the consequences of a Martian pathogen could be catastrophic (think Andromeda Strain) as no life on Earth would have antibiotic resistance to it.

Because of this, a large proportion of this meeting was given over to US governmental policy makers to discuss how the spread of invasive species are stopped, how disease outbreaks are dealt with and current biosafety and biosecurity policies and procedures. The overall take home message from this is that even though there is a lack of data and low chance of anything dangerous happening, the public will be very concerned about back contamination and it is public opinion which will force policy change rather than the science. Because of this we need to get the public interested and on side, through risk communication and societal participation – such as citizen science type projects (as SETI have done in their search for extraterrestrial signals) – to combat scaremongering groups early on (there is already a committee against Mars Sample Return although they appear to be currently inactive). It was also made clear that we need an international input as consequences, however unlikely, would be global.

Lessons for preventing backward contamination from Mars Sample Return can be taken from looking back at how it was dealt with for Apollo 11, the first mission to bring lunar samples back. As we knew so little about the moon at that point the astronauts were immediately quarantined on return and the samples were tested for infectious or toxic agents by exposing a wide variety of plants and animals to them before they could be released to labs around the world and the astronauts could be let out (obviously there was nothing living in the samples as we now know that the moon is a very inhospitable place).

Crew of Apollo 11 in quarantine (NASA)

Other than this it was interesting to hear a recurring point, by the presenting scientists, on the Podium principle which was just how much evidence you need to have gathered to be able to stand up and say ‘Yes, we’ve found life’. The answer, it seems, is a lot, much more than anyone has found so far. This principle has not always been followed quite extensively enough. In the ‘70s, proof for life on Mars was claimed (and still is to this day by the lead author) after life detection experiments carried out by the Viking lander seemed to show an active metabolism in the Martian soil with nutrients being consumed and carbon dioxide given off when warmth, water and food were provided. However, the results of this experiment can be explained more simply by the presence of reactive oxidising minerals in the soil (such as the perchlorates I work on) which we know are definitely there from other analyses carried out. In the ‘90s structures in the Alan Hills meteorite were claimed to be fossilised Martian bacteria, although these were later shown to be abiotic (non-life) mineral structures the study of this meteorite really kicked off the field of astrobiology as interest in finding alien life was dragged into mainstream science.

Structures in the Allan Hills meteorite suggested to be fossil bacteria (NASA)

Outside of the meeting I had to go visit the Smithsonian Air and Space Museum to go and look at relics of the Apollo space missions which collected all of the lunar samples that I have been working on. Putting the work I do into context with the amount of effort that went into getting these samples was quite humbling although it was odd to see people queuing up to touch a tiny polished piece of moon rock when I’ve destroyed a fair amount of this priceless material. And of course I couldn’t miss a chance to get a selfie with a life size model of Curiosity!

Unfortunately the trip hasn’t gone completely smoothly as I’m writing this whilst stuck in Detroit airport where I spent last night sleeping (well attempting to) under a bench after I missed my connecting flight home to London thanks to storms delaying my flight leaving DC. So I’ll be spending 17 hours in Detroit airport before flying over to Boston to connect to Heathrow and getting home a day later than planned – fun times.