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Martian Air Pressure, How much variance is there?
nprev
post Oct 1 2006, 04:46 PM
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Just thinking when looking at the Victoria pics...how much does the average air pressure increase with respect to the surrounding area at the bottom of the crater? Also, where is the lowest point on Mars (which also presumably has the highest air pressure)? I can't remember if it's in Hellas or Coprates Chasma.

Rationale here is that, given MRO's astonishing capabilities, these low areas should be given priority for long-term monitoring; if transient surface water exists anywhere, it's probably way down in a crater or a canyon.


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ngunn
post Oct 1 2006, 08:22 PM
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QUOTE (nprev @ Oct 1 2006, 05:46 PM) *
Just thinking when looking at the Victoria pics...how much does the average air pressure increase with respect to the surrounding area at the bottom of the crater? Also, where is the lowest point on Mars (which also presumably has the highest air pressure)? I can't remember if it's in Hellas or Coprates Chasma.

Rationale here is that, given MRO's astonishing capabilities, these low areas should be given priority for long-term monitoring; if transient surface water exists anywhere, it's probably way down in a crater or a canyon.


A very quick and simplistic response: Negligible difference over depth of Victoria. Globally? The atmospheric scale height is about 11km, of the same order as the height difference between Hellas and Olympus Mons, so a pressure and density ratio of about 2 or 3. I think that liquid water would be VERY transient, even in the most favoured spots.
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JRehling
post Oct 1 2006, 10:36 PM
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QUOTE (ngunn @ Oct 1 2006, 01:22 PM) *
A very quick and simplistic response: Negligible difference over depth of Victoria. Globally? The atmospheric scale height is about 11km, of the same order as the height difference between Hellas and Olympus Mons, so a pressure and density ratio of about 2 or 3. I think that liquid water would be VERY transient, even in the most favoured spots.


Olympus Mons is 25 km tall relative to the baseline, and Hellas is 7 km deep, so the range of 32 km is nearly triple the scale height, meaning a variation in pressure of about 3 factors of e = a factor of 18 (!) in pressure between the top of Olympus and the bottom of Hellas. Of course, there are also seasonal and diurnal pressure cycles, so the overall ratio of the maximum and minimum pressure on the surface of Mars is simply tremendous. But most of that is on the "low" side associated with the tall volcanoes.

To quote from
http://science.nasa.gov/headlines/y2000/ast29jun_1m.htm

"I used the model to look for regions that meet the minimum requirements for liquid water -- above the triple point and below the boiling point," explained Haberle. "According to the model, the highest surface pressure, 12.4 millibars, occurs at the bottom of the Hellas Basin (a low-lying area created by an ancient asteroid strike). The problem is that the boiling temperature there is only +10 C. It can't get very hot or the water will boil away."

It seems like a niche to look for would be places where the temperature never gets about 10C, but sometimes get above 0C. But if tempertures HAVE gotten above 10C over geological time, then subsurface ice stores may have been depleted relatively rapidly.

I'd say MRO should be surveying the heck out of Hellas. A small fraction of Mars's surface may turn out to be wildly more interesting than the other 99% of the planet if the water condition works out there.

---

A couple of less-authoritiative cites that sound not obviously wrong:

http://www.nfinity.com/~exile/marsweather.htm

"It may possibly be the last place where liquid water ever existed on the surface of Mars. In mid summer, it is one of the "garden spots" of the whole planet, with atmospheric pressure of over 10 millibars, more than twice what it is at the mean planetary horizon. Since the vapor pressure of water is lower than 10 millibars if the temperature is less than 60 deg. F (16 deg. C)(4), this may be one of the few places on the planet where any water on the surface will not immediately boil away."

And the Wikipedia article on Hellas states:

"The altitude difference between the rim and the bottom is 9 km (5.6 Miles). The depth of the crater (4 km (2.4 Miles) below the topographic datum, or "sea level" of Mars) explains the atmospheric pressure at the bottom: 840 Pa (8.4 mbar) (.25 InHG). This is 38% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar or .18 InHG). The pressure is high enough that water is speculated to be present in its liquid phase at temperatures slightly above 0 C (32 F)."
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nprev
post Oct 2 2006, 01:27 AM
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Wow...comprehensive & well-stated, J; thank you very much for the scholarly response! I completely agree that we have a high-priority target region for long-term monitoring by MRO based on your research!!! smile.gif

Now HERE'S a wild thought: What do you suppose the odds are that Mars has deep cave networks al a Carlsbad Caverns in the US? Such features might have been formed during volcanic events and/or any possible wet & warm epoch(s) a few billion years ago. This is way off the cuff, but what would the atmospheric pressure be in a cave that's maybe two miles below local ambient MSL ("S" in quotes)?

[EDIT] Yeah, I saw Robinson Crusoe On Mars many years ago (great flick, BTW)...still gotta wonder about the conditions inside deep Martian caves, if in fact there are any.


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ngunn
post Oct 2 2006, 08:41 AM
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QUOTE (JRehling @ Oct 1 2006, 11:36 PM) *
Olympus Mons is 25 km tall relative to the baseline, and Hellas is 7 km deep, so the range of 32 km is nearly triple the scale height, meaning a variation in pressure of about 3 factors of e = a factor of 18 (!) in pressure between the top of Olympus and the bottom of Hellas. Of course, there are also seasonal and diurnal pressure cycles, so the overall ratio of the maximum and minimum pressure on the surface of Mars is simply tremendous. ---


Thanks for correcting my minor innacuracy(!) Do we have any good temperature measurements for the bottom of the Hellas basin in summer? If I haven't got this completely wrong too the Sun's elevation at noon should be about 80 degrees. I still think liquid water is unlikely, though, unless there is a process that releases it rather quickly, because warmish air near the Martian tropics would have very low relative humidity. If there were any active water-producing process in Hellas today I think we would have observed it in the form of anomalous cloud formations. Even so I agree it would be an exceptionally interesting place to visit as it must have had a unique watery history.
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serpens
post Nov 30 2016, 10:36 PM
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The hydrological history of Hellas was the subject of a well reasoned paper at the 2014 LSPC. I have linked the abstract.

http://www.hou.usra.edu/meetings/lpsc2014/pdf/1511.pdf

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HSchirmer
post Dec 1 2016, 04:35 PM
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QUOTE (serpens @ Nov 30 2016, 11:36 PM) *
The hydrological history of Hellas was the subject of a well reasoned paper at the 2014 LSPC. I have linked the abstract.

http://www.hou.usra.edu/meetings/lpsc2014/pdf/1511.pdf



Curious about the initial question, highest air pressure on mars,
it seems it might also need to time the obsevations based on daily air tides
so that you observe at highest pressure during the day.


"from the Mars Climate Sounder, we have observed Mars' semidiurnal tide. These waves can cause large variations in atmospheric density in regions where engineers would typically rely on atmospheric braking to slow down vehicles. "
http://www.planetary.org/blogs/guest-blogs...-awareness.html

I haven't found what exactly is a "large variation".
Curious if anybody has found numbers?
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Floyd
post Dec 1 2016, 05:29 PM
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If the topic drifts from liquid water to slowing down spacecraft, then we are not interested in pressure but rather density. Density is proportional to pressure and inversely to temperature. So land at deep cold spots.


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serpens
post Dec 2 2016, 09:39 PM
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QUOTE (HSchirmer @ Dec 1 2016, 05:35 PM) *
Curious about the initial question, highest air pressure on mars,
it seems it might also need to time the obsevations based on daily air tides
so that you observe at highest pressure during the day.

I haven't found what exactly is a "large variation".
Curious if anybody has found numbers?

Well the largest variation is seasonal with the transfer of CO2 between poles that varies pressures up to 30%. Over the course of a sol the variation at Gale has been measured as up to some 100Pa peaking around sunrise. The pressure increases at night and reduces during the day.
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scalbers
post Dec 3 2016, 06:22 PM
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In figure 2 we see in these summary statistics that Viking was around a few percent: http://journals.ametsoc.org/doi/pdf/10.1175/JAS3718.1. I would suppose this ratio could be larger at high altitudes where aerobraking is being considered.

On Mars the semidiurnal tide is generally stronger than the diurnal tide, kind of like ocean tides on Earth. I recall this being discussed by Conway Leovy during my internship on the mission. Here is an example for Viking & Pathfinder over a few sols: https://mars.jpl.nasa.gov/MPF/ops/ss007.jpg

Further discussion of the semidiurnal tide is in this TPS blog: http://www.planetary.org/blogs/guest-blogs...atmosphere.html


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HSchirmer
post May 18 2017, 10:15 PM
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Would "UP" balloons work on Mars?
Eh, guess this is as good a place as any to ask....

Let's suppose a future mars rover uses bounce airbags for landing.
Could those airbags be re-purposed to hoist a balloon drone(s)?

Back of the envelope scribbles suggest that thin air on Mars precludes propeller drones, and disfavors winged drones.

So, what about an "UP" mission?
A balloon hoisted-but-tethered eye in the sky hoisted over the rover by multiple balloons?
Or a "dandilion" probe, each balloon that survives gets re-inflated with a small science payload, and goes its own way.
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djellison
post May 18 2017, 10:35 PM
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So - propeller based drones can work on Mars ( and one is proposed to accompany the 2020 rover ) . https://mars.nasa.gov/news/helicopter-could...for-mars-rovers

Winged drones have been proposed ( see the ARES scout proposal ) https://en.wikipedia.org/wiki/Aerial_Region...onmental_Survey

The balloons of the kind used for EDL are far far too heavy to be used for lift. Even bespoke balloons are pretty marginal on performance, but they are possible. http://www.gaerospace.com/wp-content/uploa...ars-Aerobot.pdf
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