Should We Invest in Martian Brine Research to Reduce Mars Exploration Costs?

S ince publication of the first evidence of liquid water on present-day Mars (Martı́n-Torres et al., 2015) according to Curiosity data, scientists have wondered how best to further investigate the presence of brines. Initial evidence was acquired at Gale Crater, near the equator of the planet, a location where this presence of liquid water was highly unexpected. This evidence was later corroborated by the detection of spectral evidence for hydrated salts in martian recurring slope lineae by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on board the Mars Reconnaissance Orbiter (Ohja et al., 2015). Such findings have opened a new frontier of exciting scientific challenges. The spatial and temporal distribution of transient liquid water on Mars has wide implications for our understanding of the availability and history of water on Mars, the plausible preservation of organics, the corrosive interaction of these brines with spacecraft materials, and other geological water-related and climate processes on present-day Mars. Most importantly, however, the presence of liquid water on Mars has enormous implications for planetary protection and planetary protection policies. The mission of NASA’s Office of Planetary Protection is to protect the study of Solar System bodies—including planets, moons, comets, and asteroids—from contamination by Earth life and to protect Earth from possible life-forms that may be returned from other Solar System bodies (NASA, 2016a). Since April 2015, the direction of the strategy of NASA’s Mars exploration has changed. In particular, on June 24, nearly 4 years after the landing of the rover Curiosity on Mars, NASA published its intention to use the rover to image potential Mars water sites (NASA, 2016b) to detect brine signatures at Gale Crater. Though for many this might have been a prime goal from the beginning of the Mars Science Laboratory mission, NASA’s decision to change strategy now renews hope of finding liquid water at the martian surface. However, plans for such a search elicit a call for extreme caution. Ironically, the presence of water is a complication for the operation of any surface spacecraft as well as for the search for life. The reason for this is that regions where water is available are potentially more favorable for Earth life to survive, and we do not want to contaminate Mars with Earth life-forms that are brought within the spacecraft. We do not want to discover life on Mars and later realize that this life is a contamination from Earth, which would indicate a ‘‘false positive’’. If there are brines on the surface or near the subsurface of Mars, how can we search for evidence of life without contaminating these sites with microorganisms from Earth? The presence of brines on Mars raises a new question: How close could a robotic spacecraft, such as Curiosity, safely investigate a region with brines? The scientific value of such an investigation aside, the detection of liquid water in the form of brines would have impacts from operational, economical, and political points of view in the Mars Exploration Program. From an operational point of view, interaction between the operation team of a robotic spacecraft and planetary protection offices of various space agencies would be more important than ever, and discussions would need to take place as soon as the scientific community acquired any plausible evidence of frost, ice, seasonal or diurnal morphological changes, flowlike structures, biomarker detections (e.g., methane), salt deposits detectable by visual inspection of images, and of course any liquid water–related observation.