The recently published paper Should we invest in Martian brine research to reduce Mars exploration costs? (Astrobiology, available online), authored by Professor Javier Martín-Torres and Professor María Paz Zorzano, focuses on one transcendent problem posed by the discovery of the formation of transient liquid brines on the surface of Mars: the presence of liquid water will mark the most interesting points to be explored by the coming missions, which are at the same time the points where an extreme caution must be observed in order to avoid an eventual and catastrophic contamination of the Martian environment with terrestrial organisms. The likely rise in the costs of those missions as a consequence of the more astringent requirements imposed by the planetary protection policies, could be reduced by developing previous and dedicated studies to the Martian brines, as proposed by the authors.
The discovery of perchlorate liquid brines was reported for the first time on the paper Transient liquid water and water activity at Gale crater on Mars (Nature Geoscience vol.8, pp.357–361 (2015), doi:10.1038/ngeo2412), published on April 2015. Since then, the phenomenon has been confirmed by spectral observations, and it is thought to be common all over the Martian surface, according to the distribution of detected perchlorates, the localization of subsurface water reservoirs, and the registered values of environmental parameters. These findings have opened several and transcendent research lines which will strongly determine the course of the future exploration of the planet. Apart from the investigation of the phenomenon itself and its implications in the characterization of the Martian environment, there are a number of derived but not less important matters to enquire into, such as the explanation of the until now mysterious formation of the surface features known as Recurrent Scope Lineaes (RLS’s), the possibilities to use the Martian water as an in situ resource by future manned missions to the planet, or the interaction of the corrosive brines with the present and future surface probes. Remarkably, the presence of liquid water is closely linked to the assessment of the habitability potential of the environment and to the search of traces of life on Mars, two main referential questions in the upcoming exploration missions to the planet. Therefore, the zones in which the presence of liquid water is more likely are the most suitable to send the scheduled missions, namely, ESA’s ExoMars 2020 mission and NASA’s 2020 rover, intended to go into depth on the Martian habitability and Martian life (past or present) conundrums.
On the other hand, and taking into account that liquid water is an essential requirement for known life, its detection on Mars’ surface has triggered the concern about the possible contamination of the landing sites with terrestrial organisms brought on board the spacecrafts, since precisely the places in which it is available are the most favourable for them to thrive. This circumstance has enhanced the interest of the space agencies in delimiting by common agreement the so called “Special Regions”, which are those whose exploration entails a higher risk of contamination. Presumably, the sterilization procedures and other kind of cautions to be applied to the spacecrafts reaching these regions will increase significantly the costs of the correspondent missions.
In its paper, Martín-Torres and Zorzano put forward a series of studies to be carried out in advance in order, among other things, to get a deeper comprehension of the behaviour of the brines with relation to their geographical location, which would refine the capability to assess the risks of contamination when choosing a given landing site, so that the costs in planetary protection could be adjusted in each case with relation to the particular scientific goals.