Temperature and pressure at Gale, Suitable (for short periods) for liquid water? Options

[Blue Sky]

It is interesting that in the NASA presentation of the fan outflow pattern last week, there was no discussion of where all that water came from in the first place. Based on the location of Gale crater, it would seem to have been from the northern ocean that was assumed to exist in the Noachian age. A long time ago.

[abalone]

An interesting paper
http://online.liebertpub.com/doi/pdfplus/1...9/ast.2011.0660
Liquid water could be stable as little as 100-200m below the surface
and
"At temperatures below 0C, liquid water can exist as either
a thin film or a brine with a freezing point < 0C. Including
salts to estimate ‘‘average Mars salinity water’’ expands the
regions where liquid water can occur. Modeling by Mellon
and Phillips (2001) showed that a concentration of 15–40% of
salts (sulfates, chlorides, bromides, carbonates, and nitrates)
is sufficient to allow the melting of ground ice (or to maintain
liquid water) in the top few meters of soil."

[vikingmars]

As Vikingmars points out this occurred around LS 280 at the VK2 site. ( I think it was LS and not SOL, as you stated. Correct me if I'm wrong. The max pressure occurred around SOL277 at Vk1 and LS277 at VK2 )

...The max pressure occurred really on Sol 277.34 but the Ls is 279.93... You are right, not far from this value (see table herebelow as "pdf" file)
 VL2_Sol277.pdf ( 27.43K ) Number of downloads: 717

[mshell]

This is an update of my up-thread post here where I created phase diagrams for pure water and speculated (with input from Eyesonmars) on the maximum atmospheric pressures that we might see at Gale and on Mars as a whole. I spent a couple of blissful hours last night running down elevation figures, Viking Lander weather data, REMS data, and concepts such as “scale height”.

Here’s what I found …

1. Eyesonmars stated in his post here that the MSL site was “another 2km or so LOWER” than the Viking 2 landing site at Utopia Planitia. We can now update this based on the latest Mars Orbiter Laser Altimeter (MOLA) data. It was interesting to see that the original Viking elevation data was based on a different “reference ellipsoid” from what is now used for MOLA elevations. The MOLA elevations are based on a Mars geoid (an “areoid”) with a radius equal to the average equatorial radius of Mars and with a surface that has an equipotential gravitational field. This is just what we need to compare barometric pressures. It turns out that Curiosity’s MOLA elevation is virtually the SAME as the Viking 2 site:



The MOLA elevations are accurate to about +/- 1m. The references can be found on pp. 11-12, here.

I took the Curiosity elevations from the excellent profile map attached to this post by pgrindrod, which I am virtually positive are based on MOLA elevation data, since it seems to agree with other sources.

2. Since the elevations are virtually identical, it seems reasonable to expect that the barometric pressures at Gale will be similar to those at Viking 2. I found the weather data for Viking 2 here and the REMS weather data for MSL here for daily averages. You can press the “Data” button at the bottom of the weather display to access the (approximately) hourly data from Sols 9-12.

The Viking data was easy to cut and paste into a spreadsheet, but I had to type the REMS data in by hand. Does anyone know a place to get ALL of the REMS readings? Also, please contact me if you are interested in getting the weather data spreadsheet. The max average daily value for Viking 2 was indeed 8.20 mBar as Eyesonmars reported, and the single maximum pressure reading is indeed 10.72 mB as Vikingmars reported here.

I then plotted the average daily pressures from Viking against the Solar Longitude (a measure of the “season” on Mars) and overlaid Curiosity’s REMS average daily pressures:



The data are right on top of each other, which gives some credence to the concept that the atmospheric pressures at Gale through the summer are likely to be similar to what we have already seen with Viking 2 at Utopia Planitia. This leads me to estimate that we could very well see pressures above 10 mB at Gale.

3. With the updated elevations and using a “scale height” of 11.1 km (which varies a bit with temperature and is referenced here), we get a maximum pressure at the lowest point on Mars (an impact crater in Hellas Basin, see page 11 of this) of almost 15mB -- which is a bit more than the 14 mB that Eyesonmars had previously estimated. Although, given that Hellas is not in the “tropics” of Mars, the temperatures are likely to stay well below freezing year-round. Viking 2, for example, never got above -20 C.

Here is the updated phase diagram:



4. The most interesting thing that I found during my investigation was this press release from the principal investigator of the REMS instrument, who says that “in the daytime, we could see temperatures high enough for liquid water on a regular basis” (my emphasis).

Maybe, just maybe, djellison’s “tiny tiny wedge” at the bottom of the phase diagram is just big enough …

Mark

[Explorer1]

Very impressive work Mark!
So the pressure will tick up and up until the start of summer, but what happens then? Would a gas sample in SAM see any difference?

[mshell]

In a private message to me, Eyesonmars indicated that:

... southern summer daytime temperatures (are) about 30c warmer than the equivalent latitude in the northern hemisphere.

In my previous post, I had made the erroneous assumption that Mars would be symmetrical with regards to average temps at a given latitude. I knew that there is a big average elevation asymmetry between north and south, but I didn't know about the temperature difference. I have since learned that the difference is caused primarily by the high orbital eccentricity, whereby Mars is significantly closer to the sun during southern summer compared to northern summer.

With a little digging I found the TES (Thermal Emissions Spectrometer) data from the MGS (Mars Global Surveyor) mission. This graph shows clearly that the daily max temperatures are well above freezing in the Hellas Basin during many days in the local summer, just as Eyesonmars pointed out.

I apologize for the mistake -- I should have been more careful.

It seems clear to me that the pressure/temperature conditions are such that, at least in some places and at some times of the year (including Gale and Hellas), liquid water COULD exist during the day on the surface of Mars -- although, as has already been mentioned up-thread, the evaporation rate would likely be very high. And of course, this is only relevant IF there is any water left to be liquid.

Mark

[Explorer1]

There's also the fact that the Martian axis is more tilted than Earth's, at 25 degrees, so the seasons are more extreme than our own. But without a big moon to stabilize, it's obviously subject to change.

[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”.

[Eyesonmars]

Of course, I do have it backward. Atmospheric mass is maximized at larger obliquidity
Thank you for the correction
Here for example

But does it change the result ?
Any martian climate modelers out there ?

[Eyesonmars]

Although the albedo effect resulted in thick
perennial CO2 caps during some high obliquity periods, there were several times when the atmospheric
pressure reached 1000-1200 Pa followed by a rapid
drop to <100 Pa

This is a quote from the above paper ( thanks to mcaplinger)

also - from Fig. 8 it appears, at least from this model, that these brief periods of higher atmospheric density do not happen every 100,000 years but have occured several times in the last 1,000,000 years

[serpens]

I've never been able to get my mind around the very high obliquity effects. Wouldn't this result in an increased transfer of CO2 between poles on an annual basis. Large pressure swings between hemispheres but with limitations on the CO2 actually retained in the atmosphere in gaseous state?

[climber]

I watched the jump record of Baumgartner a few minutes ago! Pressure at 39 kms or so was 5mb...

[MichaelT]

Dear all,

I am trying to find out if it is possible to access the REMS data files somewhere. The data are displayed here and here and you can also view past data on the latter page. However, instead of copying all these values by hand, it would be great to be able to read the REMS data from the XML files directly and automatically to create a time series of e.g. the max and min temperatures.
I found that the current data are located in this XML file: http://cab.inta-csic.es/rems/rems_weather.xml

Does anybody know if it possible to access past data as well? I could not find any links on the respective websites.

Cheers,
Michael