Water flows on Mars. NASA announced the recently reached conclusion late in September, attracting considerable attention. But don’t break out your interplanetary kayaks just yet; NASA is actually describing something that looks more like a seep than a creek and only appears in the Martian summer.
As a student at the University of Arizona in 2010, Luhendra Ohja noticed the seasonal streaks on the steep slopes of craters, called Recurring Slope Lineae (RSLs). The thought that these might be related to water was not supported by any evidence until Ohja (now at Georgia Tech) looked at spectral signatures of areas around RSLs relayed back to Earth from the Mars Reconnaissance Orbiter. The spectral signatures were characteristic of hydrated salts and differed when the RSLs were wider and more prominent in the summer. The signatures were those of magnesium perchlorate, sodium perchlorate, and magnesium chlorate. Perchlorates, which are known to inhibit freezing of liquids at very low temperatures, are used in rocket fuel for this purpose. (They also make a great marker for a CAP source for recharge water, but that is another story.) So tying together hydrated salts, RSLs, and seasonal fluctuations, Ohja reasoned that liquid water could be the cause, potentially from melting ice just below the surface.
Of course, if there is liquid water, albeit briny, then there could be life on Mars. Indigenous life, that is — not the microbes that may have been carried to Mars by probes from Earth. The NASA rovers have been instrumental in revealing details of Martian geology and climatology. But sending a mission to look for life near the briny RSLs poses a huge risk of contamination from the robotic probe itself. It is very difficult to sufficiently sterilize a rover prior to interplanetary travel; those hardy little bacteria and viruses can survive truly harsh conditions. So the very act of investigating RSLs for Martian life may lead to its extinction by the introduction of Earth microbes that could out-compete the Martians. Like in H.G. Wells’ War of the Worlds, only we’re the invaders.
Mars isn’t quite as dead as we thought. And other frontiers await, like the moons of Saturn. Extra-terrestrial hydrology could give “ET” a whole new hydrological meaning. As long as we don’t violate the Prime Directive and destroy the life we are looking for, there should be a place for hydrologists in our outward trek across the Solar System.