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

[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]

I searched the web and couldn't find a phase diagram for water that showed the “area of interest” in much more detail than the one that Udo posted up-thread, so I created my own using Excel and the equations found here:

http://www.iapws.org/relguide/MeltSub2011.pdf (Eqns 1 and 6)

and here:

http://www.iapws.org/relguide/IF97-Rev.pdf (Eqns 29b and 30)

I have attached a couple of phase diagrams for water over the different ranges of temperatures and pressures that have been discussed.





I used the “max pressures” as estimated by Eyesonmars for Hellas and Gale at summer solstice. As djellison said, we are indeed “dancing around a tiny tiny wedge.” I have also attached the values in tabular format:



As Udo noted, if the pressure is below the triple-point of water (6.11657 mBar = 6.11657 hPa = 611.657 Pa), then it doesn't matter the temperature, there can be NO pure liquid water on the surface.

Of course, this all is based on pure water. Impurities (e.g., salts) change both the boiling point (usually elevated) and freezing point (usually depressed) at a given pressure. I couldn't find any easily accessible (and understandable to me) information on how the phase diagram changes with molality, particularly at these low pressures. Maybe someone else can find some Mars-specific info. At Earth pressures, very salty water (think Dead Sea) doesn't freeze until -20 C or lower (from the CRC Handbook of Chemistry and Physics for a 4.6 M solution of NaCl). The boiling point is less affected -- it elevates about +2 C for a 4 M solution.

So, as others have said, liquid water on Mars today seems POSSIBLE, but probably short-lived, if it exists at all.

I’m not going to worry too much more about the fate of glasses of pure water on Mars -- I’m going to put on my brand new, VERY cool, red-cyan clip-on, flip-up glasses and go see if I can talk anyone else in the family into imagining what the waterfalls and rushing waters of Gale Crater could have been like a couple of billion years ago.

Mark

[vikingmars]

I used the “max pressures” as estimated by Eyesonmars for Hellas and Gale at summer solstice. As djellison said, we are indeed “dancing around a tiny tiny wedge.” I have also attached the values in tabular format:

GREAT post Mshell !
For your info, the max pressure measured by VL2 for its entire mission was 10.72 mb on Sol 277...
=> Could you, please, adjust your last (and nice) table ?
==> Besides, what would be the max pressure at Hellas at Winter solstice ?
(I guess your 14 mb figure is valid for the lowest part of Hellas at -8530m altitude)
Warm welcome and thanks again !

[serpens]

GREAT post Mshell !
For your info, the max pressure measured by VL2 for its entire mission was 10.72 mb on Sol 277...

Weren't these readings attributed to the diurnal heating and consequential expansion of gas in the Tavis pressure transducers used for the Vikings (and Pathfinder I think), which were assessed as jammed with dust during the landing process? Wasn't this why the Phoenix pressure sensors were not activated until the landing dust had settled?

[vikingmars]

"...which were assessed as jammed with dust during the landing process?

Well... I was not aware of those being "jammed" nor people doing both experiments for VLs and MPF.

The problem of dust pollution was well foreseen by scientists when designing their instruments before their integration within the landers.
The VL pressure sensors could not be "jammed" by dust, because they were protected from engine exhauts during the landing inside an housing located 1 meter above ground. they were released 5 mn after landing at the end of the meteo boom. And the 1st imaging sequence show that the dust took less than a minute to settle down.
The MPF pressure sensors (derived from the VLs) were protected from dust because they were packed inside the folded petals of the lander, itself protected inside the airbags during its landing on Mars...
So I think that both measurements are perfectly valid, like most scientists involved in both missions. Please, see link :
http://www-k12.atmos.washington.edu/k12/re...e_overview.html
This is why I think that this "10.72 mb" value is real.
Enjoy !

[Tom Dahl]

The VL pressure sensors could not be "jammed" by dust, because they were protected from engine exhauts during the landing inside an housing located 1 meter above ground. they were released 5 mn after landing at the end of the meteo boom. And the 1st imaging sequence show that the dust took less than a minute to settle down.

Please forgive me, but I don't think the Viking lander pressure sensor was part of the Meteorology Sensor Assembly on the met boom. The MSA had detectors for temperature, wind speed, and wind direction only.

The lander pressure sensor was located inside the lander body mounted to an interior bracket near leg 2. That Tavis sensor was fed via a tube passing through the lander body to a Kiel Probe located a bit below the lower edge of the body sidebeam. The general arrangement of the sensor and probe are indicated in the following diagram at center-right:

Here is a photo of the Kiel Probe on the Proof Test Capsule in the Smithsonian NASM. (A few other photos of the probe can be seen via the next and prev PicasaWeb image widgets.) The Flight Capsule 3 (backup) body in the Seattle Museum of Flight has the tube but not the Kiel Probe itself.

The location of the Keil Probe opening below the lander (and the angle of the probe's cylindrical shroud) was deliberately chosen to enable measurement during the rocket-borne final phase of descent (after aeroshell jettison), as well as while on the surface. Whether the probe opening was susceptible to dust during touchdown may be debatable but it does seem like a possibility. Edited to add: nevertheless, I have no reason to doubt the results obtained.
-- Tom