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.