Professional Pilot, March 2016

Is there substantial liquid water on Mars now One of the biggest announcements of 2015 concerning Mars came from orbital studies In the Mars community there is a bit of a joke that every year or so there is an announcement of finding water on Mars for the first time or at least that is how it comes out in the press Most of these findings are related to water ice which we know exists in Martian polar caps and in the tundra like subsurface that surrounds the Martian polar regions But several weeks ago it was finally announced that there is liquid water on Mars Lets discuss the evidence first and then the implications Dark features called recurring slope lineae RSLs appear on some steep Martian slopes including on those of impact craters and canyons Many have been observed to form over yearly timescales Observations over the last few years by the Mars Reconnaissance Orbiter have shown they form during warmer seasons warmer being a relative term on cold Mars on Sun facing slopes In September 2015 it was announced that spectral observations found deposits of hydrated salts at some of these features likely a salty residue from 18 PROFESSIONAL PILOT March 2016 a salt rich water flow Salt lowers the melting temperature of water so it could allow for these small flows to exist even under current Mars conditions The combination of the salty residues seen where recent RSLs have formed on what would be warmer slopes though still cold led to the conclusion that liquid water was involved On the one hand this is a big deal because we did not think wed find liquid water on Mars And on the other hand it is unclear that this has big implications either for astrobiology or large scale geology because the liquid water we have observed likely only exists in that form briefly and in small quantities and is probably very salty All of this adds up to not being significant for biology Also we still dont know the exact mechanism behind RSL formation One possibility is that its coming from the subsurface which would be intriguing if it implied subsurface liquid water reservoirs But the currently more favored hypothesis is that the observed water is coming from the small amount in the atmosphere condensing or adsorbing sticking onto the surface onto the dust and sand particles which is interesting but doesnt have implications for liquid hanging out in the near subsurface which is what makes a cozy home for microorganisms Bottom line If the evidence holds up then this discovery of liquid water on Mars is very interesting but likely doesnt have significant biological implications Where did the Martian atmosphere go There may be a tiny bit of transient liquid water on Mars now but as mentioned there was plenty of water on Mars in the distant past The most likely way for that to have occurred is having a much thicker atmosphere that would have made liquid water stable at the surface So where did the atmosphere go Answering that question is the main goal of the Mars Atmosphere and Volatile Evolution MAVEN mission and they announced results a few months ago Ill give you some background The current Mars atmosphere is mostly carbon dioxide and its surface pressure is less than 1 the surface pressure on Earth The atmosphere is really thin with the pressure at the surface about the same as the pressure 100000 ft up on Earth But all the evidence of liquid water in the past particularly standing water for any period implies that Mars was warmer and wetter in the past because of a thicker atmosphere So where did the atmosphere and all the carbon dioxide go Carbon dioxide can be tied up in rocks Thats where most of the carbon dioxide that was in the Earths atmosphere has gone helped out by ample liquid water and even by life For example sea shells eventually form carbonate rocks on Earth However orbiters and landers have found very little carbonate rock on Mars after extensive studies looking for it Another way to lose carbon dioxide as well as other atmospheric constituents is to lose them to space Charged particles mostly protons flow from the Sun at extremely high speeds of up to 15 million kilometers per hour which is known as solar wind When solar winds slam into the atmosphere of a planet their particles and their associated magnetic fields can knock individual atmospheric atoms hard enough that they have sufficient speed to completely escape the planets gravity Earth is protect As of November 2015 Curiosity had drilled and sampled at 9 locations on Mars Drilling into the rock exposes the unaltered unweathered rock critical to learning about the its origin which in many cases also helps tell the story of liquid water on Mars in the past That material is then sampled by Curiositys instruments to help piece together the history of that region of Mars As can be seen just from color variations a variety of rocks have been sampled during the mission Image courtesy NASA JPL MSSS Emily Lakdawalla Curiositys Drill Sites John Klein sol 182 Confidence Hills sol 759 Buckskin sol 1060 Cumberland sol 279 imaged sol 283 Mojave sol 882 Big Sky sol 1119 Windjana sol 621 imaged sol 627 Telegraph Peak sol 908 Greenhorn sol 1137