[X] My Assistant

[Seryddwr]

Just a quick query from someone with no background in science. Obviously, MSL has AFAIK not returned evidence of recent (i.e. years/decades) liquid water in its vicinity; however, I was interested by the following graphs:

08.21.2012: First Pressure Readings on Mars

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=4501

08.21.2012: Taking Mars' Temperature

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=4502

The first indicates that the pressure between 15 Aug and 18 Aug never dropped below c. 690 millibars; the second shows that, for a period of a couple of hours on 16 Aug, the temperature rose above freezing. If water had been present on the surface, then, would it have been liquid during this brief period? The pressure and temperature seemed to satisfy the conditions for liquid water as I understand them (indeed, the pressure seems to be high enough (just) on a 24-hour basis to allow for the presence of liquid water). Thanks in advance for your opinions (corroborative or not!) on this.

[Eyesonmars]

Calculations suggest that the obliquity of Mars varies greatly with a period of about 100,000 years.
During minimum obliquity, with Mars standing more or less straight up on its axis, it has been shown that much if not all of the CO2 in the south polar cap returns to the atmosphere. Recently MRO discovered vastly more CO2 in the south polar cap than what was previously thought. You can read about it Here

While scientists were aware of seasonal CO2 ice layers atop the water ice this new discovery brings to light nearly 30 times more frozen CO2 than was previously believed to exist. In fact this particular deposit alone contains 80% the amount of CO2 currently present in the planet’s entire atmosphere.

This means, looking back at mshell's phase diagram, pressures as high as 27mb at Hellas and 18mb at Gale are then likely on this time scale. This puts the boiling point of water as high as 22c at Hellas - room temperature.

A less hostile environment for liquid H20 means less liquid water is initially required to form water related geologic features.

Delaying or slowing down the phase change from the liquid state will give any outflow more time to do its work

[Gsnorgathon]

... During minimum obliquity, with Mars standing more or less straight up on its axis, it has been shown that much if not all of the CO2 in the south polar cap returns to the atmosphere. ...

Do you have a link for that? My understanding is that minimum obliquity would result in minimum insolation at the poles, making them cold traps and thus reducing atmospheric pressure significantly.

[mcaplinger]

My understanding is that minimum obliquity would result in minimum insolation at the poles, making them cold traps and thus reducing atmospheric pressure significantly.

Yes. See, e.g., http://spacescience.arc.nasa.gov/mars-clim...d_SE_ExAbst.pdf

At low obliquity the polar regions of Mars receive less annual insolation and can reach a
point where the total CO2 sublimation at the pole becomes less than the total condensation – forming a
perennial CO2 ice polar cap. Below this critical obliquity the mass of the CO2 polar cap(s) increases at the
expense of the atmosphere, potentially leading to atmospheric “collapse”.