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Potential Pressure on Mars, Methane, and Sky Color (Updated 9/6/2015)


        Read and Lewis (2004, pp. 269-270)79 note potential reserves of CO2-H2O clathrate in regolith that could raise surface pressure to 200 hPa (mbar) during periods of high-obliquity when, at some point in the future, Mars would have its axis inclined at a greater angle than it has today. If more clathrate is locked up under deeper polar deposits underground, pressure could go as high as 850 hPa (Jakosky et al., 1995).85 But if the soil became rich in water ice through precipitation and adsorption into the porous regolith, Read and Lewis state the value might be limited to 15-30 mbar.

      If the increase of density seen during aerobraking operations by MRO (30 to 350%) was correct, and could be applied to the Hellas Basin, then pressures there would reach 16.37 to 44 mbar. However, the 350% figure was only for operations over the Martian South Pole, and, as will be indicated below in conjunction with Figure 43, the true pressure at Hellas Basin might actually be higher than what is found at sea level on Earth.

12.1 Did NASA Ever Publically Back 20 Mbar on Mars?  In a work entitled SP-4212 On Mars: Exploration of the Red Planet 1958-1978 in Chapter 8, second paragraph (page 243)86 we read:

       Mariner 69's occultation experiment indicated that the atmospheric pressure at the surface of Mars ranged from 4 to 20 millibars, rather than 80 millibars as estimated earlier. This information had a definite impact on the aerodynamic shape of the Mars entry vehicle being designed, since weight and diameter would influence the craft’s braking ability. Langley engineers had determined that aerodynamic braking was the only practical method for slowing down a lander as large as Viking for a soft touchdown. The entry vehicle would have a diameter of 3.5 meters, an acceptable ballistic coefficient that would help ensure Viking's safe landing on Mars.

    It appears that by Mariner 69's, the article is referring to the Mariner 6 and 7 flyby spacecraft that had their closest approaches to Mars on July 31, 1969 and August 5, 1969.  But their NASA-advertised radio occultation pressures for Mars were only 3.8 to 7.0 mbar. The 20 mbar figure is almost 3 times higher. And what are we to make about the 80 mbar figure that is refuted with the 20 mbar estimate?  Mariner 4 had flown by Mars on July 14, 1965. Its estimate of pressure on Mars was pegged at 4.1 to 7 mbar on their website located at, though as mentioned earlier in Section 5, Kliore had it pegged at 4.5 to 9. 

       If NASA had the 20 mbar figure, and was publishing it too, the question must be asked, why in the world would it select pressure transducers for the Vikings that could only measure up to 18 mbar and why was a transducer that maxed out at 11.49 mbar chosen for MSL? Figure 40 shows there were pressure estimates of 20 mbar in 1965 (Evans), but after Mariner 6 and 7 the issue was supposed to be settled with a maximum pressure at 9 mbar (less than the 10.72 mbar measured by Viking 2). 

Figure 40 – History of Beliefs about Martian Atmospheric Pressure

12.2 Biology, Methane, and a Possible Hint of the Real Martian Air Pressure

          Given the discovery of methane plumes (identified back on Figure 25) that have a probable biological origin (Krasnopolsky87 et al., 2004) it was natural that MSL had instruments designed to detect methane. Of particular interest would be methane producing or consuming bacteria that might be attached to dust particles. Bloom of such organisms, with a means of encapsulating or producing methane (lighter than the ambient CO2) might explain the lifting process seen in dust storms and/or dust devils. When MSL landed there was brief, but temporarily unwarranted excitement when methane was detected by the Sample Analysis at Mars (SAM) shown in Figure 41A.

Where did initial the methane seen by SAM during its initial check out come from? SAM had miniature pumps (Wide Range Pumps - see Figure 41A). In a press conference (see , Mahaffy stated,

The really nice thing about these pumps is they exhaust naturally right at Mars pressure, 10 millibar, 7 millibar. Um, and it turns out there is a very slow leak, uh, into the Tunable Laser Spectrometer and so there was just a little bit of a residual atmosphere” (that is, from the Earth).

He went on to say,

“and so the tens of millibars that we had in there, I think we had 51 millibar and we had assumed that the pump would be fine evacuating that, we routinely evacuate Mars ambient out of the cell but it was just high enough the current sensor on the pump said, nah this is a little bit too high I‘m gonna turn myself off and it did but SAM continued merrily along its measuring path assuming that we had not turned off and so we measured that gas with both the mass spectrometer and the Tunable Laser Spectrometer. It really led to some excitement. The TLS (Tunable Laser Spectrometer) Team, Chris and Greg, their eyes were wide open. They saw all this methane, and it turns out it's terrestrial methane, but it was kind of a good test….

       We considered that the 51 mbar mentioned by Dr. Mahaffy might be the first real clue about how high Martian pressure really is. On Earth that pressure would equate to an altitude of about 63,057 feet or 19,220 meters. But based on Figure 43 we think the pressure is higher, closer to 511 at areoid.

       On December 16, 2014 JPL announced that it had found methane spikes of 5.5, 7, 7 and 9 ppbv (parts per billion volume), about 10 times higher than the background methane measured earlier (0.7 +/- 0.2 ppbv (see Figure 41B). Other organic chemicals found in the Cumberland sample at Gale Crater included chloromethane, dichloromethane, trichloromethane, dichloroethane, 1,2 – dichlorpropane, 1,2 – dichlorobutane and chlorobenzene. This is quite a change from NASA’s Viking stance of no organic chemistry on detected on Mars. Thus there appears to be ample reason to revisit NASA’s dismissal of positive results about detection of life by the Labeled Release (LR) life detection experiment on both Vikings (Levin, 1997).88 The new finding reinforces the position of Dr. Christopher McKay of NASA Ames on January 4, 201189 when he found that NASA’s 30-year rejection of organic chemicals was wrong.

       Previously, the 1997 Levin paper mentions what looked like lichens seen on Mars (at least until a technician under the order of NASA administrator Dr. James Fletcher went through the JPL control room and manually turned the color knobs on the monitors to make everything look red (see Figures 42A and 42B). If Levin were right about lichens living on Mars now, could we extrapolate an air pressure based on maximum altitude where lichens are found on Earth? While one article described lichens (Cordyceps sinensis) living at Dolpa in the Himalayan mountains of Nepal at 5,177 m (16,984 feet) where pressure would be about 527 mbar, Sancho et al. (2007)90 described an ESA astrobiology experiment on the Foton-M2 mission aboard a Soyuz rocket launched on May 31, 2005. They state that,

 “It returned to Earth after 16 days in space. Most lichenized fungal and algal cells survived in space after full exposure to massive UV and cosmic radiation, conditions proven to be lethal to bacteria and other microorganisms… Moreover, after extreme dehydration induced by high vacuum, the lichens proved to be able to recover, in full, their metabolic activity within 24 hours.”

Figure 41A below – Sample Analysis at Mars (SAM)

Figure 41B below - Methane spikes seen by MSL at Gale Crater, Mars.

Thus it must be determined at what altitude (and minimum pressure) the lichens would go into a protective mode. Aware of all this controversy the MSL SAM had, as one of its purposes, an assignment to revisit the question of organic chemistry on Mars. Mahaffy stated at the August 27, 2012 press conference that,

The SAM is a key tool in Curiosity’s search for signs of life, past or present, and is more sensitive and sophisticated than the sensors on the Viking lander which came up negative for organics. The system is designed, for example, to examine a wider range of organic compounds and can therefore check a recent hypothesis that perchlorate - a reactive chemical discovered by the Phoenix Mars Mission – may have masked organics in soil samples taken by Viking."

Figures 42-A to 42-I plus Plates 5 and 6 ( illustrate the controversy over Martian sky color ever since Viking 1 touched down. 42A shows what NASA released in 1976 after Dr. James Fletcher ordered manual adjustments on monitors that destroyed blue sky color and hid green on rocks. 42B shows true sky color in accordance with colors of the U.S. flag. 42C shows that for Earth once pressures drop to 11.3 mbar the sky is a dark blue, not bright as seen in day time photos from Mars. 42D shows the Martian sky near sunset. 42E shows sky as seen from MSL with a dust cap over the camera lens. 42F shows what has often been portrayed as the Martian sky color as seen from MER Opportunity. Figure 42G shows the same area as 42F, but with “false color applied.” 42-H and 42-I show what MSL sees without a cover over its camera lens. Variations on sky color may be due to amount of dust in the air, which varies seasonally. Blue appears to be the correct color when dust loads are low.

12.3 The High End of Pressure Estimates for Mars. There were five pressures published by the Remote Environmental Monitoring Station Team with Earth-like pressures of 742 to 747 hPa (mbar) for September 1 to 5, 2012 (Ls 164.1° to 166.3° - shown on Figure 17A).

       While the 51 mbar estimate based on the SAM is almost an order of magnitude greater than accepted pressures, it equates to an altitude of 63,057 feet (19,220 meters) above Earth. Walking around at such a low pressure would still require a pressure suit. But there is evidence that suggests pressure far higher than this. While there are caveats, pressures this high make Martian weather far easier to understand. The evidence begins with photos and wording found on a JPL web site.

       With regard to the Earth-like high pressure reports from the REMS Team, most of them are shown on Figure 17A. The red and green comments are our comments. Could these pressures be real? Such pressures would explain the weather plainly seen much better than pressures under 10 mbar, but one particular photo of Martian Weather with JPL commentary may have given us a glance at proof that the five really high pressures were actually accurate.

       The all-important page is at The photo can be found at The quote of interest for the photo is as follows:

“This is the first color image ever taken from the surface of Mars of an overcast sky. Featured are pink stratus clouds coming from the northeast at about 15 miles per hour (6.7 meters/second) at an approximate height of ten miles (16 kilometers) above the surface… The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken about an hour and forty minutes before sunrise by the Imager for Mars Pathfinder (IMP) on Sol 16 at about ten degrees up from the eastern Martian horizon.”

The color photo mentioned above is shown on Figure 43. The evidence is based on stratus clouds seen 16 km above Mars Pathfinder.

           Pathfinder landed at 3.682 km below areoid, so 16 km above that would be an altitude of 12.318 km above areoid. Pathfinder is unlikely to have changed its own altitude very much over 16 sols.

       We first focus on what minimum pressure is required for stratus clouds to form in Earth’s atmosphere. The highest stratus clouds are cirrostratus. They occur at altitudes up to 13,000 meters.91 As is shown on Figure 43, at 13,000 meters the expected pressure on Earth is 163.33 mbar. With this pressure in mind we can make an estimate of pressure on Mars, but first we state the caveats. The pressures calculated do not factor in higher than terrestrial dust loads in the Martian atmosphere. Nor do they consider the gas composition of the Martian atmosphere (95% CO2 vs. about 0.04% on Earth). So at best we are shooting here for a ball park estimate.

       As is also shown on Figure 43, if we assume that (cirro) stratus clouds on Mars cannot form at a lower pressure than similar clouds on Earth, then using a scale height of 10.8 our spreadsheet indicates pressures of around 511 mbar at areoid, and pressures as high as 1,054 mbar at the bottom of the Hellas Basin. Using this same logic the indicated pressure for the MSL, 4.4 km below areoid, is about 767 mbar (767 hPa). While most of the data put out by the MSL Remote Environmental Monitoring Station (REMS) Team is only about 1% of this, for five days   - September 1 to September 5, 2012, they published pressures that were 97% in agreement with this calculation. The essential issue thus comes down to whether REMS published results that confused 747 hecto Pascals with 747 Pascals (7.47 hPa or 7.47 mbar). Or, did someone in the REMS Team rebel against expected results and in fact give us the truth until silenced? One REMS Team member was Henrik Kahanpää, the designer of the Vaisala pressure sensors used for both Phoenix and MSL. He was discussed earlier in Section 2.4. Again, he wrote, "We should find out how the pressure tube is mounted in the spacecraft and if there are additional filters etc." We challenged the above statement on November 14, 2009. Kahanpää’s partial response to my assertion that "something stinks" about his request for information on additional filters was:

       “Your nose smelled also a real issue. The fact that we at FMI did not know how our sensor was mounted in the spacecraft and how many filters there were shows that the exchange of information between NASA and the foreign subcontractors did not work optimally in this mission!” (Kahanpää, personal communication on 12/15/2009).

       And so when this particular man allows reports to be issued for five days that back our projected pressures; issues of personnel, agendas, and possible disinformation should not be overlooked. The REMS reports in question were shown earlier on Figure 17A.

       While Kahanpää was clear about his dissatisfaction with NASA is his discussion about how his sensor was employed with Phoenix, I have not seen him write anything about the massive confusion that occurred again with his sensor on MSL. I can only state that the Phoenix and MSL sensors were essentially the same (as was shown back on Figure 11A) and both delivered to NASA in 2008.35 However, with Kahanpää as the man on the REMS Team directly responsible for pressure reports from MSL (at least until possible censorship), we see that all four incidents of highest pressures reported have been eliminated – the first five days in September 2012 (cut a hundred-fold), the 1149 Pa pressure for Sol 370 (reduced to 865 Pa), the 940 Pa pressure (changed to N/A for Sol 192 on February 19, 2013) and 937 Pa for Sol 200 (February 27, 2013) also changed to N/A.

Figure 43- Stratus clouds on Earth are found up to altitudes of 13,000 meters, where pressures are about 163.33 mbar. They are not found over Earth at pressures below this level. The same kind of clouds is found on Mars. If the same minimum pressure is required on Mars, where these clouds were seen 16 km above Mars Pathfinder which was 3.682 km below areoid, it means that the stratus clouds were about 12.318 km above areoid. Based on an accepted scale height of 10.8, this implies a pressure at areoid of about 511 mbar, at Pathfinder of about 718 mbar, with 768 mbar at MSL, 835 mbar at Valles Marineris, and 1,054 mbar in Hellas Basin. The 768 mbar figure for MSL should be compared to REMS Team results for September 1 to 5, 2012 shown earlier on Figure 17.