On September 28th, 2015, in what could rightfully be considered one of the most significant announcements in the history of space exploration, planetary scientists studying Mars revealed a spectacular discovery – liquid water is, most likely, currently flowing on the surface of our solar system’s dry and rusty 4th planet. While astronomers and scientists widely suspected that liquid water had existed on the planet’s surface at some point in its 4 billion year history, as made evident by in-situ and in-orbit experiments and analysis carried out by a panoply of spacecraft, landers, and rovers, the present day status of that water was an uncertainty. Orbital and surface observations of Mars revealed a landscape rich in the types of surface topography and chemical composition that correspond to the presence of liquid water, but no water itself. Perhaps the last of Mars’ liquid surface water had sublimated into and out of the planet’s thin atmosphere; perhaps it was left trapped in the planet’s icy polar caps or in reservoirs underneath the planet’s surface. Mars may have once been a wet planet, but is it at all a wet planet any longer?
At last, this uncertainty was shattered with some confidence by a report analyzing photographs taken from the Mars Reconnaissance Orbiter, which has been studying the planet from orbit since 2006. These photographs were of peculiar Martian surface features called “recurring slope lineae,” dark streaks on the slopes of Martian hills which appear to ebb during Mars’ cooler seasons and flow during warm seasons. While these features would by appearance alone seem to hint at the presence of some flowing liquid darkening the Martian soil, the authors of this report went further with their investigation by exploring the “recurring slope lineae” using the Mars Reconnaissance Orbiter’s imaging spectrometer, an instrument that analyzes the chemical composition of the Martian surface. What they found in these downhill flows was a clue crucial in resolving their nature – the presence of hydrated salts.
The relationship between hydrated salts, liquid water, and seasonal downhill flows is a complex yet connected one. Hydrated salts lower the freezing point of Martian liquid water, similar to how salts on Earth cause ice and snow to melt more rapidly. The specific composition of the hydrated minerals found by the imaging spectrometer, known as perchlorates, have been shown to keep liquids from freezing even when conditions are as cold as negative 94 degrees Fahrenheit. During Mars’ warmer months, the freezing point would be low enough to allow shallow subsurface water to wick to the surface and darken and muddy the Martian soil as it is dragged downhill. Taken together, the dark streaking effect of the “recurring slope lineae” and the presence of hydrated salts around them is the most significant evidence yet of liquid water on the surface of today’s Mars.
Obviously, this announcement has left many in the space community excited, in particular the astrobiologists and scientists studying the possibility that Mars had, or has, life. As anyone who’s taken a high school biology course would know, water is a crucial ingredient in the conditions we understand to be conducive to the formation and sustenance of life. Indeed, life as we know it wouldn’t exist without the presence of water, and our search for extraterrestrial life is accordingly narrowed on the places where conditions are suitable for liquid water. Mars, with its wet past, is a prime candidate for potential life beyond the Earth – hence the unparalleled attention and effort given to exploring and studying the planet. The discovery of flowing liquid water on the planet’s surface thus offers a tantalizing opportunity to learn more about Mars’ wet past and present conditions, and perhaps even provides the chance of finding the signs and evidence of life. Even if the water producing the “recurring slope lineae” is inundated with salts, and thereby chemically unsuitable for life, studying it will offer clues about its as-of-yet unknown source. Figuring out where the water comes from, whether it be from ice melting underground, underground liquid reservoirs, or some other potential source, will be a key first step in determining the characteristics and composition of Mars’ present-day water and whether it may indeed be conducive for life.
To that end, the opportunities for future study seem limitless. NASA’s Curiosity Rover, currently operating on Mars and studying the planet for signs of habitability, is within driving distance of a mountain called Mount Sharp, which might contain these “recurring slope lineae.” The Mars 2020 Rover, scheduled to arrive at the planet early in the next decade, will be equipped with sensitive instruments that could analyze these spots with far greater detail than the orbiting satellites today, and indeed could even detect the bio-signatures of life past or present. Future human expeditions to the planet could conduct investigations on the water that would far exceed any robotic mission in scale and scope. With all this, it would seem there is great incentive to explore these peculiar Martian surface features and potentially answer one of humanity’s greatest and most lingering questions – can and does life exist elsewhere?
But, not so fast. While liquid water on the surface of Mars offers the opportunity for tremendous scientific and exploratory insights, it also poses an enormous problem which will need to be dealt with – that of contamination.
Life on Earth has proven itself to be extremely resilient and adaptable to even the harshest of conditions. Indeed, some “extremophiles” have shown themselves capable of surviving the deathly conditions of interplanetary space. Some organisms on Earth have demonstrated the ability to survive in conditions similar to those on Mars, and even in the exotic extremities of Jupiter’s icy moon Europa. As such, there is a sincere and credible fear among planetary scientists and mission planners, dating back to the beginning of the “Space Age,” that the exploration of these other worlds could lead to their contamination by organisms of an Earthly origin. While this may be a concern of marginal worth for “dead” worlds such as our Moon or Mercury and for extremely inhospitable planets such as Venus, it is of far more validity when it comes to a potentially habitable place such as Mars. Indeed, now that flowing liquid water has been found on Mars, water which very well may harbor or support life, these concerns are of an utmost importance. Should this water be contaminated through any in-situ study, its scientific worth toward discovering and analyzing extraterrestrial life would be tainted and therefore negligible.
Far from just a noble goal held by scientists, the effort to prevent the contamination of other worlds, known as planetary protection, is explicitly enumerated in decades-old policy and practice. The primary piece of international law dealing with conduct and activity in outer space, known as the Outer Space Treaty, contains a section specifically dealing with planetary protection. The United States, as a signatory to the Outer Space Treaty, is therefore bound to an adherence of its provisions. Article IX of the treaty states that “Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose.” As is the case with most of the language in the Outer Space Treaty, which was written with a degree of ambiguity so as to not unduly constrain state activity in outer space during the active era of the “Space Race,” there exists a legal uncertainty over what “harmful contamination” entails. For NASA, this language has been interpreted as entailing the protection of scientific investigation; indeed, NASA policy explicity states that “the conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized.” One can easily see how the study of flowing liquid water on present day Mars may jeopardize that aim.
To put these policy provisions into practice, NASA follows a set of planetary protection guidelines issued by an interdisciplinary, international committee known as the Committee on Space Research (COSPAR). The COSPAR guidelines establish a set of categories, dependent on the characteristics of the world being visited and the nature of the exploration mission, which delineate what steps and practices must be taken to ensure that contamination from Earth-origin organisms does not occur. In the case of Mars exploration, which falls under Category IV of the COSPAR guidelines, contamination controls included requirements to reduce biological contamination of the spacecraft, constraints on spacecraft operating procedures, the taking of inventories of organic constituents of the spacecraft and organic samples, as well as the documentation of spacecraft operations, impact potential, and the location of landing or impact points on the planetary surface. Often, a rigorous sterilization process within a biologically-contained “clean room” is a major step in ensuring that biological contaminants are accounted for and dealt with.
Yet, even then, the current processes for dealing with biological contaminants are inadequate for the scope of a mission hoping to directly investigate Mars’ “recurring slope lineae.” The most advanced of NASA’s Mars rovers, the Curiosity Rover, which itself is on a mission to determine the habitability of the planet and whether life exists or existed there, fell under Category IV-B of the COSPAR guidelines; the category above it, Category IV-C, which entails even more stringent measures for preventing biological contamination, would be the baseline for any mission coming into direct contact with Martian surface water. As such, even the Curiosity Rover, if it were to find liquid water flows on or around Mount Sharp, would be prohibited from the direct study and analysis of them. To date, no spacecraft or interplanetary mission has been designed and sterilized per the COSPAR Category IV-C guidelines.
Herein lies the matter of why water on Mars poses problems for NASA’s future missions of scientific investigation. Any spacecraft sent to the “recurring slope lineae” would need to be sterilized entirely per COSPAR Category IV-C guidelines, yet the sterilization process established by this category may be prohibitive. As mentioned by UNSW astrobiologist Malcolm Walter, the intense heat and ultraviolet radiation used to kill biological contaminants residing on space-bound rovers and landers would, if used to meet Category IV-C requirements, also destroy or severely cripple these spacecrafts’ sensitive electronics and instruments. Any human missions to Mars, aside from still being decades away, would undoubtedly carry far more contaminants and entail more significant possibilities for contamination than a robotic mission; aligning a human mission with the COSPAR guidelines has yet to be seriously attempted.
As such, while there is tantalizing evidence of liquid water currently flowing on Mars and while the insights to be gained from the direct study of this water are clearly recognizable and scientifically desirable, actually conducting such an investigation is currently prohibited – and may be for the considerable future. NASA will need to develop strategies, technologies, and procedures, or revisit and revise existing ones, which will allow spacecraft designers and mission planners to bring their hardware in line with the COSPAR Category IV-C sterilization requirements. Fortunately, significant thought and effort has been made and is being made toward that end. In 2006, the National Academy of Sciences released a comprehensive report which analyzed the potential contamination of Mars and issued recommendations to NASA which could resolve the current issues surrounding Category IV-C and future Mars exploration missions, particularly those interacting with areas on Mars where life may be present. In short, the report found that many of the existing policies and practices for preventing the contamination of Mars are outdated in light of new scientific evidence about Mars and current research on the ability of microorganisms to survive in severe conditions on Earth. It concluded that a host of research and development efforts are needed to update planetary protection requirements so as to reduce the uncertainties in preventing the contamination of Mars.
However, the report noted that updating planetary protection practices, so as to enable a robotic or human exploration mission to areas such as Mars’ “recurring slope lineae,” will require additional budgetary, management, and infrastructure support and will require a roadmap, including a transition plan with interim requirements, as well as a schedule. This could pose a significant challenge for the United States’ cash-strapped space agency, which may not have the money or resources to undertake such an effort. Yet, until it does, or until another approach toward resolving the issue of possibly contaminating Mars’ flowing liquid water is found, NASA will, for better or worse, need to stay away from directly interacting with this tremendous discovery.
Of course, even despite these challenges, NASA still has it within its present-day capabilities to investigate these fascinating features in further depth. Orbital observations of the “recurring slope lineae” could shed further insight on the patterns and characteristics of their flow, which would allow for a more accurate modeling of the surface water and its possible subsurface sources. If the Curiosity Rover, or any other Mars rover, found “recurring slope lineae” within its line of sight, it could take photographs and make direct observations from a distance. Up-close surface observations of these water flows would be of far more scientific value than those currently taken by spacecraft miles up in orbit. Alternatively, in a more unconventional approach, NASA could deploy hardware upon the Martian surface which would self-produce 3D-printed sterile robots that would then be sent to directly study the water. NASA is already working on such technology.
The recent announcement of liquid water found flowing on today’s Mars is of tremendous significance, and raises a number of major questions. Could this water harbor life? What does it say about the present or past state of Mars’ habitability? Perhaps most importantly, how will NASA develop the capabilities to actually investigate this discovery directly? The water is there; now its on NASA along with the scientific and technological community to develop strategies for “tasting” it. Water on Mars may pose problems for NASA today, but it need not in the future.