Most people will think of a dry arid landscape when they think of Mars. When seen from orbit, dry river channels and lake-beds can be seen along with mineral deposits thought to be the created in the presence of liquid water. A team of researches now suggest that liquid carbon dioxide could also explain the features seen. On Earth, a process known as carbon sequestration liquefies CO2 which is buried underground. There are a number of mechanisms that could explain the liquid CO2 underground the researchers suggest.
Mars is often referred to as the ‘red planet’ due to its visual appearance. It’s the fourth planet from the Sun and has been a real focus for exploration and research for decades. The red colour is caused by iron oxide (rust) on its surface which can often be lifted up into the atmosphere by the Martian winds giving stunning pink skies. It’s just over half the size of the Earth, has a thin atmosphere mostly made of carbon dioxide and a surface composed of deserts and volcanoes like Olympus Mons. One of the key focusses of the exploration on Mars has been to establish whether the conditions are suitable for life, have been suitable in the past or whether liquid water exists on the surface.
The presence of dry riverbeds and lake beds points to a surface that had liquid flowing long ago. Quite what that liquid is has been the cause for debate. Observations of minerals from orbit and from more direct analysis on the surface, suggest that the liquid was just water. However a team of researchers have published a paper in Nature Geoscience that suggests otherwise. They explain that water is only one of two possible liquids that could have existed on ancient Mars. The other is liquid carbon dioxide or CO2. Given the atmospheric conditions it may have been more likely and easier for CO2 in the atmosphere to condense into a liquid than for surface ice to melt into water.
It has been the general consensus that the minerals point to liquid water. The paper suggests that processes like carbon sequestration, liquid CO2 buried underground can alter the composition of minerals even faster than water can. Lead author Michael Hecht, research scientist at MIT’s Haystack Observatory said “Understanding how sufficient liquid water was able to flow on early Mars to explain the morphology and mineralogy we see today is probably the greatest unsettled question of Mars science. There is likely no one right answer, and we are merely suggesting another possible piece of the puzzle.”
The paper explores our current understanding of the Martian atmosphere and combine it with the carbon sequestration research to conclude that the processes do support the evidence and mineralogy seen on Mars. They note however that this proposal does not suggest all Martian surface liquid was CO2 but rather there could have been a combination of the two.
They explain that liquid CO2 on the surface of Mars could exist as a stable surface liquid, as melted CO2 under CO2 ice or in subsurface reservoirs. Which actually took place would have dependent entirely on the distribution of CO2 at the time and the surface conditions too. The paper acknowledges that further testing is required under more realistic Martian conditions to test whether the same processes still occur.