A new study hasrevealed that during the period in which the red planet's distinctivevalleys supposedly formed, the Martian atmosphere may have alreadybeen too depleted to maintain the free-running water that it isbelieved to have carved out the geological features.
The Martian atmosphereis predominantly made up of carbon dioxide (CO2). It isbelieved that during the period of valley formation, a much greateramount of the gas was present in Mars' atmosphere, creating a denseshield that protected the Red Planet against the inhospitable spaceenvironment, and preventing water from instantly evaporating.
The new researchfocused on the largest deposit of carbonate (carbon which had beendrawn from the Martian atmosphere and locked into the ground)discovered on the Martian surface, Nili Fossae, bringing togetherdata from numerous missions surveying the Red Planet.
The results of thestudy cast doubt on the prevailing model of the Martian atmosphere atthe time of valley creation – "The biggest carbonate deposit onMars has at most, twice as much carbon in it as the current Marsatmosphere," states Bethany Ehlmann of the California Instituteof Technology and NASA Jet Propulsion Laboratory, Pasadena. "Evenif you combined all known carbon reservoirs together, it is stillnowhere near enough to sequester the thick atmosphere that has beenproposed for the time when there were rivers flowing on the Martiansurface."
Prior to the arrival ofprobes such as NASA's Mars Reconnaissance Orbiter, scientistsbelieved that many large deposits of carbonate such as that at NiliFossae would be present on the Martian surface, accounting for theCO2 that had previously, as part of the Red Planet's atmosphere,allowed liquid water to exist.
But according to thestudy, there would have to be at least 35 carbonate deposits the sizeof Nili Fossae close to the Martian surface to support the theory.The researchers state that such an abundance of carbonate is unlikelyto exist, as Nili Fossae is roughly the size of the state of Arizona,and that similar deposits would almost certainly have been detectedby satellite-based spectrometers.
But if Mars could notmaintain free running water in the creation period, just how were thevalleys cut into the Martian landscape?
"Maybe theatmosphere wasn't so thick by the time of valley network formation,instead of a Mars that was wet and warm, maybe it was cold and wetwith an atmosphere that had already thinned" explainsChristopher Edwards of the US Geological Survey in Flagstaff,Arizona. "How warm would it need to have been for the valleysto form? Not very. In most locations, you could have had snow and iceinstead of rain. You just have to nudge above the freezing point toget water to thaw and flow occasionally, and that doesn't requirevery much atmosphere."
The researchers pointout that it is possible that the atmosphere on Mars may have beendense enough to maintain liquid water at the time of valleyformation, and that the carbonate deposits simply aren't telling thewhole story. Another theory is that following the period of valleyformation, the carbon in the atmosphere was subsequently siphoned offinto space from the top of the atmosphere rather than locked into theplanet's surface via chemical reaction from the bottom.
This would leave notrace for instruments to find, and would create a workable model forthe Martian atmosphere for the period. It is possible that a relativenewcomer to the Red Planet, NASA's MAVEN orbiter, may shed light onthe conundrum as it observes the upper layers of Mars' atmosphere.
Source: NASA
