ESA Planetary Protection: Preventing Microbes Hitchhiking to Space

Bioburden assay on the back cover flight model of the ExoMars 2016 Schiaparelli lander module at EADS Airbus Space and Defence's facility in Toulouse, France. 

Assays are performed as part of the Agency's efforts to prevent microbial lifeforms hitching a ride on missions to other planets and moons in our Solar System. 

Teams regularly scour cleanrooms and launch facilities, on the hunt for any microbial inhabitants. 

Image: EADS Airbus Space and Defence

While astronauts might dream of discovering unknown life one day in their future career, Gerhard Kminek ESA's Planetary Protection Officer oversees activities that achieve it on a regular basis.

Gerhard Kminek

As part of the Agency's efforts to prevent microbial lifeforms hitching a ride on missions to other planets and moons in our Solar System, teams regularly scour cleanrooms and launch facilities, on the hunt for any microbial inhabitants.

The sites used to prepare certain types of space hardware are among the cleanest places on Earth, cleaner than a standard hospital operating theatre thanks to filtered air, application of rigorous cleanliness procedures and workers who - as they enter through air-showers into the bioburden-controlled cleanrooms = remain fully shrouded within "bunny suits".

"We have a long-term programme at ESA - and also NASA - to regularly monitor and evaluate biological contamination in cleanrooms and on certain type of spacecraft," explains Gerhard Kminek, ESA's Planetary Protection Officer (PPO).

"That includes launch facilities at Kourou in French Guiana and Baikonur in Kazakhstan, and cleanrooms at ESA's ESTEC technical centre in the Netherlands and of our industrial partners.

"The work is done under ESA contract by the Astrobiology Research Group of the DLR German Aerospace Center, with participation from the Institute for Microbiology (IMHR) at the University of Regensburg, and the German Collection of Microorganisms and Cell Cultures (DSMZ).

"The aim is to quantify the amount of biological contamination, to determine its diversity - finding out what is there using gene sequence analysis, and to provide long-term cold storage of selected samples."

Samples are acquired in various ways: air samplers collect a certain amount of air on a filter, while wipes dampened with ultra-pure water are run across space hardware or cleanroom surfaces.

Swabs are used to sample smaller items such as payloads or electronics.

To quantify the biological contamination, the samples are then filtered onto culture plates and incubated for between seven hours and three days depending on the specific method used, to see how much turns up.

Statistical analysis is used to assess the overall cleanroom or flight hardware "bioburden', and check whether it falls within the required standard or if further measures are needed to reduce it.

Any lifeform hardy enough to endure the hostile, largely nutrient-free cleanroom environment is potentially interesting to science in its own right, so further investigation is actively encouraged.

"We end up with hundreds of 'isolates' but we simply cannot scientifically investigate them to a comprehensive enough level," adds Kminek.

"So we do the critical ones and leave the rest to the scientific community. We have a website and every scientist who is interested can look at it and order some of these isolates to investigate them in more detail."

New Bacterial Contaminant Found
Last November this effort made the headlines after a paper was published in the International Journal of Systematic and Evolutionary Microbiology.

It concerned a new type of bacteria first found in NASA's Kennedy Space Center Payload Hazardous Servicing Facility as the Mars Phoenix Lander was prepared for launch in 2007 and later at the Kourou Space Centre Final Assembly Building during the Herschel and Planck observatories launch campaign in 2009.

Tersicoccus phoenicis

Dubbed Tersicoccus phoenicis, the bacterium turned out to be very different from existing species, not just a new species but actually a new genus - the next taxonomic category up - and so far isolated solely in cleanrooms.

On the Agency side, the main operational interest is knowing how much bioburden there is, rather than identifying its component microbes.

"But every couple of years or at critical events we need to check whether our bioburden reduction and control procedures are still good enough," Kminek explains.

"If, for instance, we turned up a certain biological contamination that is very resistant to heat, we might end up reviewing our cleanroom control procedures or the heat sterilisation process, potentially increasing the time and temperatures of application."

Despite all the precautions taken, some microbes will always make it in, along with human beings, the air and the hardware itself transitioning in from the outside environment representing the main "contamination vectors".

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Red dwarf stars could strip away planetary protection

An artist's impression of how Mars lost most of its atmosphere after the loss of its magnetic field. 

Planets around red dwarfs may suffer a similar fate. Credit: NASA

Red dwarf stars are the commonest type of stars, making up about 75% of the stars in our Galaxy.

They are much smaller and much less massive than our Sun and for that reason a lot dimmer.

If planets are found around these stars, then given the number of red dwarfs, life could then be commonplace.

But a group of scientists led by Dr Aline Vidotto of the University of St Andrews has cast doubt on this idea.

Their work suggests that the magnetic fields of red dwarfs could squash down those found around planets like the Earth, leaving any life vulnerable to radiation from space.

Dr Vidotto will present her work on Tuesday 2 July at the National Astronomy Meeting in St Andrews, Scotland.

Because of their faintness, even small planets in orbit around red dwarf stars block out a significant amount of light if they pass between the star and the Earth.

The low masses of these stars also mean that the gravitational pull of an Earth-sized planet is enough to make its star wobble as the planet moves around it.

This motion leads to a back and forth shift in lines in the spectrum of the star that can be detected with telescopes on Earth.

Red dwarf stars are cooler than the Sun, so the so-called habitable or 'Goldilocks' zone where life could develop is much closer in than in our own Solar System.

Planets in the Goldilocks zone are at just the right temperature for liquid water to be found on their surfaces.

All this makes red dwarfs prime targets in the search for Earth-like planets elsewhere in the Galaxy. But there are other important factors that make planets good places to live such as a reasonably thick atmosphere.

Over billions of years, the impact of charged particles from space can erode a planetary atmosphere.

Planets that have relatively strong magnetic fields (like the Earth) deflect these particles, at least within the surrounding region known as the magnetosphere, adding in a layer of protection for their atmospheres and making them more suitable for the creation and development of life.

A large proportion of the particles hitting a planet originate from the 'stellar wind' flowing off its host star.

The pressure of these particles pushes against the magnetosphere of a planet, so whenever the stellar wind is strong, it compresses this magnetic shield. In the case of the Earth, the magnetosphere normally extends out to about 70000 km.

Especially when they are relatively young, red dwarf stars have powerful magnetic fields of their own, with about a dozen of these being seen directly in recent years.

These may have a very different effect on orbiting planets. Aline and her team have found that the extreme pressure from these fields may be strong enough to compress planetary magnetospheres enough that their atmospheres are stripped away completely over time, effectively rendering these worlds uninhabitable.

The new work shows that if the Earth was in orbit at the inner edge of the Goldilocks zone of a young red dwarf star, equivalent to the way it orbits the Sun, its magnetosphere would extend no more than 35000 km and could even be crushed into the surface of the planet.

To be benign environments for the development of life, Earth-like planets around red dwarfs will need very strong magnetic fields or be significantly further away from their stars, in which case they might be too cold for liquid water.

As stars age, their magnetic fields weaken, offering some respite for any planets in orbit around red dwarfs.

The pace at which this happens will be a critical factor in how well the planetary atmospheres survive, but one way of refining the search for these objects will be to measure the speed of rotation of their stars, which also declines with age.

"Our work suggests that red dwarf stars with rotation periods larger than about one to a few months will have magnetic fields that won't significantly squash the magnetosphere of an Earth-analogue planet orbiting inside the habitable zone of its host star", says Aline.

"Astronomers will have to take this on board in their search for life elsewhere – the conditions for habitability are turning out to be a lot more complex than we thought."