[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.

[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