Science Background

Hence, after a series of robotic missions and given the fact that human explorers have a unique capability to do field research in a very effective way, the European, the United States’ and other Space Agencies have initiated programmes which will ultimately lead to a human mission to planet Mars. The key scientific issues include the characterization of the current and past climate and the question, if life ever arose on Mars. Both the US-led Vision for Space Exploration and the European Aurora programme envision a crewed expedition to the Red Planet within the next three decades.

One of the key challenges of such programmes is the control of potential contamination vectors to avoid an unwanted return of biological material back to Earth (“Backward-contamination”) or, more likely, an accidental insertion of a biological substrates into the Martian environment and as such contaminating the very samples which will be investigated for potential traces of (past) life (“Forward contamination”). For this purpose the International Council for Science’s Committee for Space Research (COSPAR), following guidelines et forth by the Unites Nations Outer Space Treaty proposed a detailed set of planetary protection recommendations which are generally observed by all entities launching interplanetary missions. These include the introduction of 5 classes of protection levels, whereas all levels relevant to a human Mars mission¹  will imply a set of stringent requirements for mission planners to adequately observe the issue of planetary protection.
“[…] the guideline to be used is that the probability that a planetary body will be contaminated during the period of exploration should be no more than 1x10^-3. The period of exploration can be assumed to be no less than 50 years after a Category III or IV mission arrives at its protected target. No specific format for probability of contamination calculations is specified.” [Cospar PP policy adopted 2004/Houston]

All past missions that have landed or crashed on Mars (even the rigorously heat-sterilized Viking missions) have virtually certainly delivered some viable microorganisms to the Martian surface. But even if these missions delivered microorganisms to the Martian surface, that does not imply, that these organisms have survived or even propagated. Laboratory experiments indicate that such a geographical expansion will be limited to the vicinity of the lander, rover or crash-site.

More specifically, COSPAR requires that “If the special region² is accessed […], either the entire landed system shall be sterilized to the Viking post-sterilization biological burden levels³ , OR the subsystems which directly contact the special region shall be sterilized to these levels […].” Such a required reduction of the bioburden is currently out of reach for human missions which would severely constrain crewed operations on the Red Planet, such as drilling operations in class IV regions. Hence, a substantial amount of research and development has to be done to ensure a (e.g. biologically) safe human exploration scenario in a mission which is beyond the complexity of the Apollo lunar missions.

Currently, various efforts are underway to prepare for a human expedition to Mars on a system level potentially leading to the creation of a nascent research field labelled as „exploration science“ which shall integrate results from engineering, space and life sciences into a holistic solar system exploration strategies and as such maximising science output, crew safety whilst minimizing costs and risks. In order to provide field test opportunities, terrestrial Mars analogues have been used for many expeditions.
The underlying assumption is, that terrestrial analogues are places on Earth that approximate the geological, environmental and putative biological conditions on Mars and other planetary bodies, either at the present-day or sometime in the past. Three key themes dominate terrestrial analogue activities: comparative planetary geology, including process studies and the characterization of analogue materials; astrobiology; and exploration science, which includes instrument testing and development, astronaut training, and exploration-related activities. Examples of such terrestrial analogues include the NASA Haughton impact crater site in the high Canadian arctic, the underwater laboratory NEEMO south of the Florida keys, the Mars Desert Research Station (MDRS), the AMASE expeditions to Svalboard and various others, some of them under construction. Although the focus of the experiments carried out under these research efforts is mainly human factors, engineering and geophysics, the issue of planetary protection in an integrated crewed expedition scenario are rare at best or solely rely on laboratory experiments. The proposed project shall therefore concentrate on the topic of studying planetary protection issues during a human expedition.

Laboratory experiments show evidence, that microorganisms may survive transits in interplanetary space (e.g. through catatrophic transport mechanisms such as asteroid impacts) and re-entry environments. Even on the exterior surfaces of spacecraft microorganisms are subjected to biocidal factors that immediately begin to reduce the viable biomass and species diversity of the launched bioload. The microbial bioloads on robotic spacecraft launched in the 1960's ranged between 1 x 10⁴ to 2 x 10⁸ microorganisms per space probe, although the amount of non-cultivable microorganisms is less understood⁴.

Laboratory experiments conducted by P. Ehrenfreud at Leiden University have shown that certain microbes may survive the harsh surface conditions of Mars under special circumstances. Above that, the contamination vectors during a crewed surface sojourn are even less known due to uncertainities in the exploration procedures, tools to be used and which areas are to be accessed by humans and/or robotic assistants. Environmental impacts may include issues such as direct shedding of humans during the surface expeditions (e.g. enteric bacteria, skin particles,..), mechanical disturbances of the local environment, airborne pollution (e.g. lander exhaust fumes), life support systems biota (e.g. leaking Extra-Vehicular-Activity (EVA-) suits), and in the opposite direction the issue of guaranteeing the biosafety of the crew and the Earths environment upon return. Probably the most challenging task in terms of planetary protection is a subsurface drilling, as –if there are traces of (extinct) life on the planet- they are commonly believed to reside in subsurface ecologies.

The challenge of studying these contamination vectors under terrestrial Mars analogue conditions is, that except for some exceptionally life-depleted areas such as the Atacama desert, most sites suited for integrated tests on system level, already show a significant “bioburden”. As a solution to that, microbiological proxy’s have been used. During PolAres, also the use of microbiological surrogates is envisioned to be implemented into the EVA-suit project as well as the Phileas-rover initiative.

¹ That is category III (no direct contact, such as spacecrafts in orbit around a potentially life bearing celestial object), IV (direct contact missions, such as landers) and V (Earth return missions, such as surface sample return projects…)
² Special Region is defined as a region within which terrestrial organisms are likely to propagate, OR a region which is interpreted to have a high potential for the existence of extant martian life forms.
³ That is “[…] treatment to a level of cleanliness of an assembled spacecraft […], resulting in a total of no more than 30 culturable microbial spores on the surface of the launched spacecraft.” (NRC 2006)
⁴ For example, Venkateswaran and coworkers [71,72] reported in two recent studies that several additional gram-negative bacterial species were identified through PCR amplification from witness plates deployed in a spacecraft assembly facility than were recovered though traditional culturing procedures alone. (Venkateswaran 2001)