Viking 1, Viking 2, and MSL High and Low Pressures Reported Normalized to Areoid

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Politics cast dust on the results. Updated 7/30/2018.

This article will look at highest and lowest Martian air pressures reported for Viking 1, Viking 2 and Mars Science Laboratory (MSL) landers and how they compare when normalized to Mars areoid (the equivalent of Martian sea level). All of these landers touched down well below areoid. For Viking 1 the landing altitude was 4,495 meters below areoid. Viking 2 was only 3,637 meters below areoid, while MSL was 4,400 meters below areoid. Vikings 1 and 2 were stationary, but MSL is a rover (Curiosity) which does change altitude, however such changes are not part of the calculation (yet, at least). Table 1 shows the average pressures anticipated at landing altitudes as well as the highest and lowest pressures reported from these sites. The Viking Computer Facility Viking 1 and Viking 2 data source offered something akin to hourly pressues rather than average daily pressures provided by the MSL Rover Environmental Monitoring Station, so average pressures for sols with Viking mission high or low pressures are calculated on Table 2 with results posted also posted in the J column for Table 1.

Table 1 above: Average pressure calculations for Viking 1, Viking 2 and MSL based on 6.1 mbar at areoid and a scale height of 10.8. Table 1 shows actual highest and lowest pressures published, as well as what are the averages for essentially hourly pressures for Vikings 1 and 2 for sols with maximum and minimum pressure. Table 2 below shows the pressures for 25 time bins for Viking sols when maximum or minimum pressures were posted by the Viking Computer Facilty. Average pressure for the same Viking sols are also shown.

       As of the date of this article we only have sol-averaged pressures for MSL, and a good bit of evidence that shows this data was revised or altered for reasons that are very questionable. But for Vikings 1 and 2 we have pressures that were reported for 25 time bins (about 59 minutes long) for the sols concerned. While we thus have 25 pressures per Viking sol, we wanted to compare "apples with apples" rather than "apples with oranges. To do this we looked at the sols with highest and lowest pressures reported and then calculated what the average pressure was for each of these sols of concern. As mentioned earlier, this is shown on Table 2 above.  While this procedure did not necessarily identify the highest or lowest sol-averaged pressure for these landers, the assumption was that it would be close. For Vikings 1 and 2 the highest pressures ever reported were 9.57 (Sol 318.38) and 10.72 mbar/hPa (Sol 277.34) respectively. The sol-averaged pressures for these sols were 8.9292 and 10.1728 respectively. For Vikings 1 and 2 the lowest pressures ever reported were 6.51 (Sol 110.66 and 110.70) and 7.29 mbar/hPa (Sol 56.74) respectively. The sol-averaged pressures for these sols were 6.8096 and 7.392 mbar/hPa respectively, however these figures were clouded by issues of digitization discussed in section 2.6.1 of our Basic Report. Viking surface pressure measurement and resolution were limited by digitization to 0.088 mbar (0.088 mbar = 1 DN (A-D Converter, 8 bits).  An audit showed 0.09 mbar was the most common change for VL-2 on its sols 1 to 199. That's fairly obvious on Figure 2 for VL-2 Sol where most pressures are 7.29, 7.38 or 7.47 mbar and only two readings appear to be interpolations (7.32 and 7.44 mbar), but not so obvious for the other three sols shown on Figure 2. 

Table 3: Pressure calculations for Mars aeroid based on pressures seen at the VL-1, VL-2 and MSL landers which were all below areoid.


       Average pressure at Mars areoid is generally given as 6.1 mbar, however Smith and Zuber (see claim that “Seasonal variations in atmospheric pressure associated with the exchange of CO2 between the atmosphere and polar caps are expected to produce vertical variations in the height of the 6.1 mbar surface of 1.5 to 2.5 km over the course of the Martian year.”

    Further complicating the situation is an article by Smith and Zuber in the Smithsonian/NASA Astrophysics Data System that states that, “The MOLA topography of Mars is based on a new mean radius of the planet and new equipotential surface for the areoid. The mean atmospheric pressure surface of 6.1 mbars that has been used in the past as a reference level for topography does not apply to the zero level of MOLA elevations. The MOLA mean radius of the planet is 3,389,508 meters and the mean equatorial radius is 3,396,000 meters (Zuber incorrectly gives it as 339,600 meters). The areoid of the zero level of the MOLA altimetry is defined to be the potential surface with the same potential as the mean equatorial radius. The MOLA topography differs from the USGS digital elevation data by approximately 1.6 km, with MOLA higher. The average pressure on the MOLA reference surface for Ls =0 is approximately 5.1 mbars and has been derived from occultation data obtained from the tracking of Viking, Mariner, and MGS spacecraft and interpolated with the aid of the Ames Mars GCM. The new topography and the new occultation data are providing a more reliable relationship between elevation and surface pressure.”

     Having stated the above caveats, we use the mean atmospheric pressure surface of 6.1 mbars as a starting point. Using s scale height of 10.8, we move up from the landing latitudes with the high and low pressures reported to areoid to see how the pressures projected there stack up, As is indicated on Table 2, with respect to high pressures reported (and in the case of MSL Sol 370, altered after we pointed out that an 11.49 mbar (1149 Pa – see Figure 1) first reported as an average daily pressure implies that the Vaisala pressure sensor on MSL must have pegged out at its maximum capacity. Their fudged new report is prima fascie evidence for why we think their published data is not trustworthy.

       So what were the high pressure normalization results? The VL-2 maximum pressure and official maximum pressure ever measured by a lander (10.72 mbar) was seen at Ls 270.930 (early winter at VL-2, but early summer at the Martian South Pole. The VL-1 maximum pressure was seen at Ls 277.724. The same seasons apply. For MSL, which sits slightly south of the Martian equator, there are now two Martian years of what looks to be maximum pressure at 9.25 mbar (925 Pa). These pressures were advertised for Ls 252 to 253 in MSL Year 1 and again at 9.25 mbar at Ls 257 in MSL Year 2. This is late fall in the northern hemisphere, but late spring in the southern hemisphere. The initial advertised maximum pressure for its sol 370 of 11.49 mbar was at Ls 9 = early spring in the northern hemisphere, but early fall in MSL’s southern hemisphere. This pressure was obviously enormously out of place in terms of seasons because “the party line” was that the CO2 ice at the Martian South Pole had to return to a gaseous state to drive up pressures worldwide on Mars. Note how much variation was seen in the above figures, but also note that in the end JPL ensured (at least to this point) that the maximum pressure given, (likely allowed) was exactly the same on both Martian years, 925 Pa (9.25 mbar). It is this lack of variation that first attracted our attention (and suspicion) when examining pressures given for much of the Martian year for the Vikings (especially for Viking 1 - see Figure 2 below).

       Without considering the controversial Sol 370 pressure at areoid are calculated as:


      (1) 7.07 mbar for Viking 2 Year 2.


      (2) 6.83 mbar for Viking 1.


      (3) 6.15 for both MSL years. 


       With inclusion of the controversial Sol 370 pressure of 11.49 mbar, then at areoid pressures are calculated as:


     (1) 7.64 mbar for MSL Year 1 (but the pressure would have been higher because the 11.49 figure represents a maxed out pressure sensor that was only rated at 11.5 mbar (these ratings tend to be approximate).


     (2) 7.07 mbar for Viking 2 Year 2.


     (3) 6.83 mbar for Viking 1.


     (4) 6.15 for both MSL Year 2


       The above figures overlook the issue of single daily average pressures given for MSL vs. maximum pressures given for the Vikings. If we use the averages generated on Table 2, then the ranks would be:


(1) 7.64 mbar for MSL Year (same caveat as above)


(2) 6.709 mbar for Viking 2 Year 2.


(3) 6.376 mbar for Viking 1.


(4) 6.15 for MSL Year 2. 


           A caveat for understanding the differences in high pressure seen as that Vikings 1 and 2 were experiencing global dust storms when they measured maximum pressures. However, based on how pressure increased at Luke Air Force Base by 6.6 mbar (see Sections 8 and 9 of our Basic Report and in particular Figure 35), we think that even with gravity that is only 38% of Earth's, a similar storm on Mars should drive up pressures by at least 2.5 mbar, and that big an increase is not shown on Figure 2. Frankly, having seen how many times JPL's REMS Team revised its data, especially after we challenged it, we would recommend placing no confidence in REMS generated pressures.

       We believe that JPL/REMS Team figures are generated based on political considerations. As an example, from the August, 2012 landing of the Mars Science Laboratory until May, 2013, JPL via the REMS Team and Ashima Research published false information showing an absolutely constant wind of 2 m/s (7.2 km/hr) from the East. They knew they had a problem early on. In fact, Curiosity Deputy Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California stated early on that "One possibility is that pebbles lofted during the landing hit the delicate circuit boards on one of the two REMS booms." He also said," We will have to be more clever about using the remaining wind sensor to get wind speed and direction." But they were neither clever enough to get the winds right at Gale Crater, nor honest enough to pull the erroneous daily reports until after we gave Guy Webster, their P.R. man, holy hell about it. During an argumentative phone call with Webster we reminded him that he was responsible because he was the man in charge of what got released to the public, and because he knew that what he was publishing under his name was wrong. He couldn't defend his position, and so, shortly after, as we demanded, he ensured that all wind reports for MSL were changed to Not Available. Ashima Research then did the same. See Figure 44 in our Basic Report.

Figure 1 - After we called JPL and pointed out several problems with their Sol 370 pressure (highest ever claimed, proof that the sensor had pegged out, larger daily pressure change than ever seen before, and the spike was in the wrong season) they altered the pressure to 865 Pa (8.65 mbar) which was the same pressure that they published for sols 369 and 371.

Figure 2 - Annual pressure variations reported for Viking 1, Viking 2, and MSL (a small data return by Phoenix is also noted).

Ls of Minimum Pressure.

In conducting the research for this report, and most especially in seeing how our questioning of pressures reported by JPL seemed to cause JPL to alter those pressures (see Table 5 below) to match the Viking pressure curves shown on Figure 21, it became apparent that to question the Viking pressure curves was tantamount to heresy in JPL eyes and other eyes. These curves were primarily due to the efforts of Professor James Tillman at the University of Washington’s Viking Computer Facility. In explaining the pressure curves Tillman wrote: 

 "The first minimum of pressure, about sol 100 (aerocentric longitude (Ls) 145) corresponds to the maximum amount of carbon dioxide sublimation in the south polar region, while the second, about sol 434 (Ls 346), corresponds to northern winter. Because of the elipticity of the Martian orbit, the difference in the semiannual heating and cooling produces this semiannual difference in the amount of carbon dioxide in the polar regions.”41

 With regard to the absolute minimum pressure seen by landers on Mars, we now have 4 Martian years of data for the time around Ls 145 – one for Viking 1, two for Viking 2, and one for MSL. The data is summed up on Table 4. If we assume that the data was accurate, the average Ls was actually 149.8.

When low pressures seen by VL-1, VL-2 and MSL are normalized to areoid, they rank as follows (from lowest to highest pressure): 

      (1) 4.6487 mbar for Viking 1 that indicated 6.51 mbar


      (2) 4.777 mbar for MSL original pressure of 7.18 mbar.


      (3) 4.8572 mbar for MSL revised to 7.3 mbar (this seems to have changed again to 7.32 mbar).     


      (4) 4.8080 mbar for Viking 2 Year 2 that indicated 7.29 mbar.


       The above figures overlook the issue of single daily average pressures given for MSL vs. maximum pressures given for the Vikings. If we use the averages generated on Table 2, then the ranks would be:


      (1) 4.777 mbar for MSL original pressure of 7.18 mbar.


      (2) 4.8572 mbar for MSL revised to 7.3 mbar (this seems to have changed again to 7.32 mbar).     


           (3) 4.8626 mbar for Viking 1 that indicated 6.51 mbar.


           (4) 4.8735 mbar for Viking 2 Year 2 that indicated 7.29 mbar.


TABLE 4 – Pressures at Ls 90 and minimum pressures seen by VL-1,  VL-2 and MSL



Mbar pressure at Ls 90

Mbar Minimum






Year 1


(7.51 at Ls 97)




Year 1

N/A (7.72 at Ls 118)




Year 2

N/A (8.06 at Ls 100)


148.48 and 



Year 1

(June 13, 2014)


*7.30 on Sol 1 changed to N/A. Then 7.32 on Sol 664

150 changed to N/A. Then Ls 147.


Year 2 (May 7 to 9, 2016)


7.32 on Sols 1334, 1335 and 1336.

Ls 148 to 149


Year 3 (March 25, 2018)


7.15 on Sol 2002


Average Ls of minimum


Table 4: *Originally JPL published a pressure of 7.05 mbar for Sol 1 at Ls 150, and 7.18 mbar for Sol 9 at Ls 155, however they later changed these pressures to N/A. VL- 1 and VL-2 data from



TABLE 5 – Pressures revised by JPL/REMS after we highlighted them or published them in earlier version of our Report




Initial Pressure Reported

Pressure for the previous sol

Final Pressure Reported after JPL Revisions

Aug 25, 2012



785 Pa


719 Pa– then changed to N/A

Aug 27, 2012



790 Pa


741 Pa

Sept 1 to Sept

5, 2012



 742 to 747 hPa

74200 to 74700 (Pa)

743 Pa

745, 743, 745, 747 and 747 Pa

Sep 12, 2012 (This date later changed to 9/11/2012)



799 Pa

749 Pa

750 Pa

Sep 16, 2012

(date later altered)



804 Pa

750 Pa

753 Pa - then changed to 751 Pa 


Oct 3, 2012

Series alteration starts here and goes to 10/12/2012



779 Pa

770 Pa

769 – Pa. Note the steady progression without reversals that were seen between 10/3/2012 and 10/12/2012 in initial results. This series looks very fudged.

Oct 4, 2012



779 Pa


769 Pa

Oct 5, 2012



781 Pa


771 Pa

Oct 6, 2012



785 Pa


772 Pa

Oct 7, 2012



779 Pa


772 Pa

Oct 8, 2012



782 Pa


774 Pa

Oct 9, 2012



786 Pa


775 Pa

Oct 10, 2012



785 Pa


776 Pa

Oct 11, 2012



785 Pa


777 Pa

Oct 12, 2012



781 Pa


778 Pa

Nov 11, 2012



815.53 Pa

822.43 Pa

822 Pa

Dec 8, 2012



865.4 Pa

867.5 Pa


Feb 19, 2013



940 Pa – a high until now. Pressures had been declining since a high of 925 Pa in late January 2013.



Feb 22, 2013



886 Pa – quite a large drop

Last 2 reports were 940 Pa on Feb 19 and 921

Pa on Feb 18, 2012


Feb 27, 2013



937 Pa

917 Pa


May 2, 2013



900 Pa

868.05 Pa


Aug 21, 2013



1,149 Pa

865 Pa

865 Pa

Aug 27, 2014



754 Pa

771 Pa

771 Pa

Oct 11, 2014



823 Pa

838 Pa

838 Pa

April 16, 2015



823 Pa

N/A  - next sol 848 Pa


Nov 10, 2015



1177 Pa

898 Pa

899 Pa

Nov 12, 2015



1200 Pa

899 Pa (revised)

898 Pa

April 2, 2016



945 Pa

753 Pa

752 Pa

April 3, 2016



1154 Pa

753 Pa (2 sols earlier, 751 Pa on Sol 1302

752 Pa

Oct 17, 2016



921 Pa

906 Pa

910 Pa

Oct 23, 2016



897 Pa

909 Pa

907 Pa

Oct 27, 2016



928 Pa

903 Pa

907 Pa

Jan 10, 2017



860 Pa

868  Pa

871 Pa

Feb 10, 2017



815 Pa

850 Pa

846 Pa

Aug 13, 2017



1294 Pa

879 Pa

883 Pa

Mar 24, 2018






Mar 25, 2018




913 revised to 716 715

Table 5 shows some (not all) of how JPL/REMS altered off the curve data for August and September 2012 and August 2013 and on through at least April 4, 2018, after we either brought the deviations up to JPL Public Relations Director Guy Webster, or published on our and websites.