Astrobiological Aspects of Mars and Human Presence: Pros and Cons

Abstract

After the realization of the International Space Station, human exploratory missions to Moon or Mars, i.e. beyond low Earth orbit, are widely considered as the next logical step of peaceful cooperation in space on a global scale. Besides the human desire to extend the window of habitability, human exploratory missions are driven by several aspects of science, technology, culture and economy. Mars is currently considered as a major target in the search for life beyond the Earth. Understanding the history of water on Mars appears to be one of the clues to the puzzle on the probability of life on Mars. On Earth microorganisms have flourished for more than 3.5 Ga and have developed strategies to cope with so-called extreme conditions (e.g., hot vents, permafrost, subsurface regions, rocks or salt crystals). Therefore, in search for life on Mars, microorganisms are the most likely candidates for a putative biota on Mars and the search for morphological or chemical signatures of life or its relics is one of the primary and most exciting goals of Mars exploration. The presence of humans on the surface of Mars will substantially increase this research potential, e.g., by supporting deep subsurface drilling and by allowing intellectual collection and sophisticated in situ analysis of samples of astrobiological interest. On the other hand, such long-duration missions beyond LEO will add a new dimension to human space flight, concerning the distance of travel, the radiation environment, the gravity levels, the duration of the mission, and the level of confinement and isolation the crew will be exposed to. This will raise the significance of several health issues, above all radiation protection, gravity related effects as well as psychological issues. Furthermore, the import of internal and external microorganisms inevitably accompanying any human mission to Mars, or brought purposely to Mars as part of a bioregenerative life support system needs careful consideration with regard to planetary protection issues. Therefore, before planning any human exploratory mission, the critical issues concerning human health and wellbeing as well as protection of Mars in its pristine condition need to be investigated.

1. Astrobiology, a New Approach to Tackle Earliest Questions of Mankind

The emerging science of astrobiology is a multidisciplinary approach to study the origin, evolution, distribution, and future of life on Earth and in the universe¹. Its central focus is directed towards questions that have intrigued humans for a long time: Where do we come from? What is life? Are we alone in the Universe? These questions are jointly tackled by scientists converging from widely different fields, reaching from astrophysics to molecular biology and from planetology to ecology, among others. This spilling beyond the boundaries of classical sciences opens completely new opportunities for research, a state described by some contemporaries as the "Astrobiology Revolution of the Sciences".

Mars is considered as key target for the search of life beyond the Earth. The quest for life on Mars has received increased attention within the current space exploration programs of ESA² and NASA³. As well as carbon based chemistry and an adequate energy source, water in liquid phase has been considered a prerequisite for habitability. By analogy with terrestrial extremophilic microbial communities, e.g., those thriving in arid, cold, salty environments and/or those exposed to intense UV radiation, potential oases on Mars are suggested. They are connected with areas where liquid water still exists under the current conditions, but also sulfur rich sub-surface areas for chemoautotrophic communities, rocks for endolithic communities, permafrost regions, hydrothermal vents, soil or evaporite crusts are of interest. Currently, several missions to Mars are envisaged, including the ESA Exo- Mars mission⁴ to learn more about the habitability of our neighbour planet Mars.

2. Rationale for Human Missions to Mars

Several aspects in science, technology, culture, and economy have inspired humankind to explore the neighbourhood of the Earth, above all the Moon and the terrestrial planet Mars⁵.

2.1. Science Aspects of Human Exploration of Mars

Mars is a major target in the search for life also since it is the only planet – except the Earth – located within the habitable zone of our solar system⁶. Dry river beds indicate that huge amounts of water and a denser atmosphere were present there about 3.5 billion years ago. During this warmer and wetter period, life may have originated on Mars and may even subsist today in special "oases" or "ecological refuges" (e.g., geological formations below the surface with favorable conditions for life). The published, but controversial, discoveries of possible fossil life forms in Martian meteorites may warrant optimism. Therefore, the search for morphological or chemical signatures of life or its relics is one of the primary and most exciting goals of Mars exploration^7–9. In addition to astrobiology, disciplines like geology, mineralogy, and atmospheric research play a central role in the scientific exploration of Mars. The general goal is to understand planetary formation and evolution processes including, if possible, the evolution of life itself. Mars is the planet most similar to Earth, and the question of climatic changes, especially the loss of water and atmospheric gases, is fascinating. There is good reason to think that the study of the evolution of the Martian climate will also contribute to the understanding of the history and future of the terrestrial climate. And furthermore, the study of the evolution of Mars may even contribute to the understanding of the evolution of the whole solar system. Human spaceflight may be important in this research context, since a number of items have been identified where the action of astronauts in situ could be beneficial to reaching the scientific goals: site identification by local analysis, sample acquisition at these sites, sampling and – if a laboratory is available on Mars – supervision of sample analysis, etc. (see part 3).

2.2. Technology Aspects of Human Exploratory Missions

It has frequently been observed that new and demanding situations require new technologies and thereby cause a push in technology development. Moving humans away from their home planet and establishing a new habitable environment on the Moon or on Mars may be such a new and demanding situation.

Meeting the scientific objectives of a Mars mission will require autonomous and smart tools, such as intelligent sample selection and collection systems on a very high level of automation and robotics. As soon as human travelers are involved, the need for integrated advanced sensing systems will become obvious, such as for biodiagnostics, medical treatment, and environmental monitoring and control. Furthermore, the development and test of technologies for in-situ resource utilization (for producing propellant from atmospheric CO₂ or from water ice, but also for life support purposes) may turn out to be a powerful technology stimulus.

2.3. Cultural Aspects of Human Exploratory Missions

Of the terrestrial planets, Mars is by far the most attractive and fascinating one. When the first telescopes were directed towards Mars, channels and shaded areas were interpreted as huge agricultural plantations or lichens covering the surface. This latter conception was not ruled out until the two Viking spacecrafts landed on Mars in 1976 and encountered a hostile and chemically highly reactive surface. But Viking and the follow-on missions also told us that the early Mars had probably experienced a climate similar to that of the early Earth, when life started here. Hence, Mars has even been considered as a suitable and attractive target for terraforming, e.g., by using modern techniques of planetary and genetic engineering¹⁰.

After the realization of the International Space Station (ISS), human exploratory missions to the Moon or Mars, i.e. beyond the Earth orbit, may be the next step in the human desire to conquer the outer limits of habitability. Does human spaceflight have the potential of promoting peaceful cooperation on a global scale? The ISS is the first example of an international cooperative venture for the joint development, operation, and utilization of a permanent space habitat in low Earth orbit (LEO), involving nearly all space-faring nations. Hence, with the ISS, a new era of peaceful international cooperation in space has started. Major potential partners are the USA, Russia, Japan, Europe and Canada, with the USA taking the leading role. China has just recently joined the nations involved in human spaceflight. Lessons learned from this experience gained with ISS may help all nations to be engaged in future large international space projects, creating harmony through common scientific endeavour.

2.4. Economic Aspects of Human Exploratory Missions

Human exploratory missions targeting Mars are very expensive. For an exploratory Mars programme, comprising three human missions over 20 years, a budget of several several tens of billion Euros has been estimated. On the other hand, a comparable annual budget is presently spent by the USA and partners for the operation of the ISS only. Hence, a Mars programme might become financially affordable, if it is carried out following the construction and operation phase of the ISS, especially if it is done through an international costs- and tasks- sharing scheme. Synergies with terrestrial applications are expected in various fields, such as nanotechnology, autonomous health control systems and/or telemedicine systems, to mention just the biomedical aspects. However, even considering the possibility of in-situ resource exploitation and the faint prospects of a future bloom in space tourism, it will require a major investment which probably can only be provided by joint international enterprises.

3. Benefits to Astrobiology from Human presence on Mars: the Pros

In the endeavour to search for signatures of life on Mars, it is expected that several robotic missions will and have to precede any human landing on Mars. Finally human and robotic missions should be complementary and then astrobiology can immensely benefit from human presence on Mars. Activities that can exclusively performed by humans, include (i) critical in-situ inspection and decisions, (ii) analysis of samples directly on Mars, (iii) remote control of on site activities, (iv) support of deep drilling activities which might be required if liquid water and with that a habitable zone resides kilometers below the Martian surface, and (v) in situ repair of explorative and analytical facilities and instruments, as has been successfully demonstrated by the repeated repair of the Hubble Space Telescope by the astronauts during extravehicular activity in space.

4. Risks to Astrobiology from Human Presence on Mars: the Cons

The risks of contamination involved in the presence of humans on Mars are threefold: (i) the risks to the crew from Martian microbes (if any exist), (ii) the risk to life on Earth via returned Martian samples (accidentally or deliberately brought back to Earth), and (iii) the risk to Mars from imported terrestrial microorganisms. For the latter case, the planetary protection concept as accepted by the Committee on Space Research (COSPAR) ¹¹ requires a contamination control to be elaborated specifically for each space-mission/target-planet combinations, such as orbiters, landers, or sample return missions^11,12. In view of the current and planned landing activities on Mars, with robotic and finally human visits, the planetary protection guidelines are currently under review within ESA and NASA. Special attention has to be given to the so-called "special regions" which are currently 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^13,14. These requirements reflect the need to prevent contamination of the Martian surface with terrestrial microorganisms – which would jeopardize the chance to detect life forms indigenous to Mars – and thereby preserving the integrity of the "search for signatures of life experiments" as part of the scientific payload.

Strict requirements to keep Mars clean can only be met with robotic missions to Mars. The scenario changes when humans are involved in the mission. Since humans carry vast amounts of microbes required to sustain important body functions, Mars will become inevitably contaminated with terrestrial microorganisms as soon as humans arrive on its surface. Although the surface of Mars seems to be very hostile to microbial life, it cannot be excluded that some terrestrial microorganisms accidentally imported may find protective ecological niches where they could survive or even metabolize, grow, and eventually propagate. This concern emphasizes the vital importance of a substantial series of robotic missions to precede a human mission to Mars in order to carry out the essential exploratory search for life by in situ measurements at selected sites. There is a need for implementing appropriate planetary protection guidelines for human missions to Mars, especially for missions with long stay times on the Martian surface.

5. Human health issues of Mars exploration

In addition to planetary protection considerations, several human health issues need further consideration before sending humans to Mars. These are as follows: (i) radiation risks, especially from solar particle events, (ii) very long 0-gravity levels during interplanetary transfers, followed by very high gravity levels at Mars arrival (up to 6 g during aerocapture and landing) with severe consequences on the human body, (iii) almost no mission abort nor fast return capability, (iv) psychological issues which pertain crew size, composition and corresponding education¹⁵. Substantial research and development activities are required in order to provide the basic information for appropriate integrated risk management, including efficient countermeasures and tailored advanced life support systems, as outlined in a roadmap for future European activities in life sciences in preparation of human exploratory missions (Figure 1), recommended in the HUMEX study of ESA⁵.

Figure 1.

6. Recommendations for Future Sustainable Exploration of Mars

Prior to "search for extant life" experiments on Mars, more data are required on the geology, climate and radiation environment of Mars, present state and past evolution as well as organic molecules in sediments. Such data will facilitate the search for possible biological oases where liquid water, probably subsurface, still exists under the current conditions. The presence of humans on the surface of Mars will substantially increase this research potential, if sufficient precautions have been met to control the import of internal and external microorganisms inevitably accompanying any human mission to Mars.

Activities associated with human missions to Mars will interact with the environment in three ways:

1. the mission needs to be protected from the elements of interplanetary space and Mars that can be harmful to human health, to the equipment and/or to the operations;

2. the specific natural environment of Mars must be protected so that it retains its value for scientific and other purposes, and the requirements for planetary protection as adopted by COSPAR need to be extended for human presence on Mars;

3. the Earth and its biosphere need to be protected from potentially harmful agents brought back on return of the explorers to the Earth. These issues need to be solved before humans enter the surface of Mars.

Finally the question arises, whether the increasing robotic exploration of Mars and the eventual human exploration and settlement of that planet is likely to cause an environmental impact to scientifically important sites, regions of natural beauty and historically important regions, in the form of contamination with spacecraft parts and microbiota^16,17. Sustainable exploration of Mars requires establishing regulations to preserve the planetary environment. The concept of natural parks and wilderness regions used on Earth might be the right concept for establishing natural reserves or planetary parks on Mars¹⁷. Already the presence of crashed robots on Mars begs important questions on the type of wilderness ethic one may apply to Mars and how this ethic is embodied within practical environmental policy. It is assumed that under the auspices of COSPAR – in addition to the current planetary protection policy which is merely based on the scientific interpretation of the Outer Space Treaty¹⁸ – recommendations should be elaborated how to deal with these ethical issues.