Higher than Advertised Martian Air Pressure: Part 9
By David A. Roffman and Barry S. Roffman (updated 4/29/2013).
12.3 The High End of Pressure Estimates for Mars.
“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.”
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 its own changed altitude significantly 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 (http://voices.yahoo.com/how-clouds-predict-weather-2147190.html). As is shown on Figure 38, 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 shown on Figure 38, 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, the REMS Team published figures 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 from the FMI to my assertion that "something stinks" about his request for information on additional filters was a follows:
“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, December 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 17 (repeated below for the sake of convenience).
Figure 17 repeated for the sake of convenience.
The enigma of dust devils on a planet with extremely low air pressure first led to this investigation into whether or not the public was being given correct data about Mars. In the course of this study it was found that Martian dust devils matched terrestrial dust devils in every respect except absolute and relative pressure excursions.
Traditional wisdom is that we could not have had so many successes on Mars if we did not understand the pressure there. But there were many failures, some unexplained, and only five landers that attempted to measure in situ pressure, all with questionable dust filter capabilities and other design problems. Problems for the traditional view include the facts that
- Pressures at Viking 1 and 2 during Year 1, varied closely with Gay-Lussac/ Amonton’s Law-based predictions for a gas trapped in a closed container. This may imply that the Tavis transducers employed measured the pressure of air caught behind dust clots. They did not measure pressure outside the lander.
- Highly consistent pressure increases in the mornings at 0730, afternoon at 1630 and nights at 2330 Local True Solar Time at Vikings 1 and 2 suggest that the pressure sensors were reacting to the RTG heaters or scheduled internal events that generated heat rather than ambient pressures. A similar pattern was seen for limited MSL data released.
- Accuracy of the Viking pressure readings was questionable where pressure changes asserted were under .08 mbar because surface pressure measurements were limited by digitization to ≈ 0.088 mbar. Data was especially suspicious where pressures remained stuck for days even though huge hourly temperature changes were being recorded (see Annex C).
- In Annex E, a check of the percent differences were between measured and predicted pressures provided for each time-bin (25 per Martian day/sol between Viking 1 sols 200 and 350) showed that the percent differences for the period of greatest interest (time-bins 0.3 and 0.34) was only 2.67%.
- Annex F demonstrates that there was great repeatability in the times each Martian day for when the percent difference between measured and predicted pressures was under 2%. The data indicates that when heaters were expected to come on, pressure predictions based on Gay-Lussac/Amonton’s Law for a gas being heated in a confined space (behind the dust clots) were quite accurate. But when the heaters were likely to be off, the accuracy of Gay-Lussac/Amonton’s Law prediction fell. How much it fell was likely related to how effective insulation was on the Vikings.
- Mariner 4, 6, and 7 only provided occultation points for six places on Mars. NASA History Office document SP-4212 On Mars: Exploration of the Red Planet 1958-1978 (chapter 8, page 243) reported occultation pressures for Mariner 6 and 7 (Mariner 69's) at the surface of Mars that ranged from 4 to 20 millibars, and it implied 80 millibars for the Mariner 4 estimate.
- No lander ever included instruments that could measure pressures over 18 mbar, two of the four landers could not measure over 12 mbar, and MSL was limited to only 11.5 mbar).
- There were several Tavis sensors with widely different pressure sensitivity ranges. Similar looking and sized Tavis transducers could measure up to 0.1 psia (6.9 mbar), 0.174 psia limit (12 mbar), 0.2 psia (13.79 mbar), 0.26 psia (17.9 mbar), 0.36 psia (24.82 mbar), or 15 psia (1,034 mbar). Given their outward similarity and the enigma of Martian weather, the possible installation of the wrong Tavis sensor cannot be overlooked. For detailed information about Tavis transducers and their performance tests, see Annex G.
- An example of simple mistakes made by Mars “experts” can be seen by examining pressures reported by the REMS Team for MSL. See Figure 17. In fact, for at least the first eight months after MSL landed, there have been many obvious errors in daily reports issued by the REMS Team and the associated Ashima Research Company. These mistakes by the REMS Team include what appears to be confusion between hPa and Pa pressure units, the wrong Martian month (often reported as 3 when 6 was correct), and constant wind at 2 m/s from the east when in fact, with a broken meteorological boom, there was no accurate wind information available, and failure to include relative humidity. With Ashima Research there were daily reports that sunrise was at 6 AM and sunset was at 5 PM local Martian time, from Ls 160.4 until at least Ls 294 on April 3, 2013 (except for Oct. 2, 2012). The constant 13 hours of night and 11 hours of daylight, whether in late winter or early spring is wrong. It shows that experts are capable of huge mistakes.
- Due to ITAR, the Finnish Meteorological Institute (FMI, which designed the pressure sensor used on Phoenix and MSL) did not have access to critical information required to both construct the sensor and interpret its results. This caused calibration problems.
- The tiny Vaisala dust filter on Phoenix did not perform in a manner that FMI could understand. The REMS reports provide reason to believe that this remains true for MSL. We are documenting all the REMS and Ashima Research daily weather report problems on our web site at http://davidaroffman.com/rich_text.html.
- Diurnal pressure fluctuation maximum and minimum pressure times seen by Tavis pressure transducers on Vikings and Pathfinder did not match times for these events recorded by the Vaisala (FMI) transducer on Phoenix or MSL, however to this point the REMS Team has only released hourly pressures for Sols 9.5 to 13, and hourly temperatures for Sol 10 to 11.5.
- The $37,000,000 meteorological package used on Phoenix did not include an anemometer to accurately measure wind speed – this after it was known that Pathfinder could not measure wind speed due to calibration problems. A misunderstanding of pressure conditions might have contributed to the calibration failure. See Annex H.
- Dust storms on the surface caused dynamic pressures at 121 km to increase by a factor of 5.6. This has not been correlated with pressure increases at the surface, but when opacity values increase to levels high enough to block 99% of light, pressures are likely to increase dramatically.
- Mars Global Surveyor and Mars Reconnaissance Orbiter both encountered unexpectedly highly deceleration during aerobraking operations at Mars.
- The Vikings found no organic chemistry, but since then, methane has been found to be emitted from 3 sites on Mars. Results of the Labeled Release life detection experiment on both Vikings backed the detection of microorganisms (Levin, 1997). If correct, these results may point to higher than assumed pressures, and the failure of Viking pressure instruments to correctly record pressure due to clogged dust filters.
- Prior to MSL which used rockets for a controlled entry, the previous 4 successful landers all were downrange by 13.4 to 27 km, but 3 landers were lost since 1999. All could have landed short. NASA has requested help with its modeling of the Martian atmosphere. This paper is in part our response to that request.
- During MPF pre-launch calibration of its Tavis transducer, both the flight and pressure sensor was inadvertently exposed to temperatures 30 K below their design limits See Annex H.
- NASA Ames could not replicate dust devils without jacking up winds to 11+ times greater than speeds associated with Martian dust devils.
- New HiRISE findings about bedfroms, and in particular, photos of MER Spirit tracks being filled in by sand demonstrate that air must be denser than assumed. Wind tunnel tests by NASA show that 80 mph (35.76 m/s) are required to move sand at 6 mbar. No such wind velocity was reported in the 8,331 wind measurements that were reported upon in this report.
- Stratus clouds at altitudes up to 16 km above Mars Pathfinder (that is, clouds at 12.318 km above aeroid) suggest pressures at areoid of around 511 mbar, and at the Hellas Basin above average pressures on Earth.
- REMS Team reports published between September 1 and September 5 showed pressures between 742 and 747 mbar. These pressures closely match our prediction of 767 mbar at MSL based on the height of stratus clouds above Pathfinder.
Successful landings may have been despite NASA’s misunderstanding of pressure there, not because of accurate data about it. In fact, the first successful landers (the two Vikings) were designed to land with no prior in situ pressure data. No probe from another nation ever landed successfully on Mars after the Viking pressure information was published and accepted by the scientific community. Acceptance of low pressure values may actually have caused some of the crashes to follow Vikings. It is unwise to ignore weather systems that should not occur in a near vacuum.
An independent review of the pressure-related data from Mars should be conducted. The original Viking, Pathfinder, Phoenix and MSL pressure transducers should be retested for the effects of dust and cold temperatures that are more consistent with assumed values on Mars. As ITAR restricts sharing of sensitive technology with foreign contractors, contracts with these restrictions should only be awarded to U.S. firms. Future missions should include barometers that can measure pressures up to 1,100 mbar.
Thanks are due to Professor James E. Tillman for making much of the Viking data available to the public. He answered some of our questions; but left the most important outstanding one unanswered. Exactly how is the rate of heat flow from radioisotope thermoelectric generators to internal components regulated? Was it a specific external or internal temperature or a timer that was set to shift as sunrise occurred later in the Martian calendar?
Further thanks are due to Embry-Riddle Aeronautical University’s Professor Associate Dean, Michael Hickey, Professor Olivero, Physical Science Department Head, Assistant Professor Jason Aufdenberg, and Associate Professor Yongho Lee.
Thanks are due to Henrik Kahanpää for his insight into ITAR, and to Dr. Prasun Desai at NASA. Both men answered many questions in depth.
Special thanks are appropriate to April Gage, Archivist, NASA Ames History Office and to the Tavis and Vaisala companies for technical data, diagrams and reports related to their sensors.
LINKS TO ANNEXES OF THIS REPORT:
Abstract of the Audit of the Viking Project Pressure Data and ANNEX A to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Viking 1 Morning Pressure and Temperature Changes. Posted March 7, 2012.
ANNEX B to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Viking 2 Morning Pressure and Temperature Changes, Posted March 7, 2012.
ANNEX C to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Viking 2 Stuck Pressure Gauge. Posted March 7, 2012.
ANNEX D to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Percent Differences between Measured Pressures on Viking 1 and Gay-Lussac/ Amonton’s Law-Based Predictions. Posted March 7, 2012.
ANNEX E TO HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Measured vs. Predicted Pressure Percent Differences for Viking-1 Time-bins 0.3 and 0.34. Posted March 7, 2012.
ANNEX F to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Percent Difference Flow Chart for Viking-1 Sols 1 to 113, and 134 to 350. Posted March 7, 2012.
ANNEX G to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Tavis Transducer Specifications and Test Results, Posted March 7, 2012.
ANNEX H to HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE. Calibration Efforts for the Mars Pathfinder Tavis Pressure Transducer and IMP Windsock Experiment. Posted March 7, 2012.
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