Original Text of Paper Submitted by David A. Roffman to Embry-Riddle Aero. U. 11/9/2009

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EP 101 Technical Paper

Case For Higher Than Advertised Martian Atmospheric Pressure


David Alexander Roffman


      A dust devil is a whirlwind made visible by entrained dust and sand.  The upward, spiraling motion is caused by heating the near-surface by insolation.  They form in clear skies and, unlike tornadoes, have no link to thunderstorms.1 Experience with them on Earth (average atmospheric pressure of 1,013 mbar) suggests that higher pressures than reported on Mars (<10 mbar) would be required to generate them there too, yet they are common phenomena on the Red Planet. 

      There have been instrumentation failures before, and even programming errors due to unit conversions (Mars Climate Orbiter).  The possibility of an erroneously low set of pressure readings from Mars was at least indirectly checked with an attempt to duplicate Martian atmospheric, dust, and pressure conditions in a lab at the NASA Ames Research Center which simulated Martian dust devils at a pressure of 10 mbar.2 However, wind speeds required by the apparatus (70 meters per second) were 11+ times higher than typical recorded dust devil wind velocities seen (6 m/s) by landers (M.D. Ellehoj et al).3  This report uses available data points on dust devils in Utah4 and on Mars (including at altitudes above 16 km on Arsia Mons)5 to question anew whether NASA failed to draw the correct conclusions.  Data presented suggests that pressure there must be considerably higher than reported.  It will be shown that no pressure sensor ever landed on Mars that was designed to measure pressures above 25 mbar.

      Dust devils on Earth and Mars have great similarities or overlap with respect to geographic formation regions, seasonal occurrences, electrical properties, size, shape, diurnal formation rate, lifetime and frequency of occurrence, wind speed, core temperature excursions, and dust particle size.  The only significant differences lie in measured absolute and relative pressure excursions in the cores of Martian and terrestrial dust devils. 

      Differences between terrestrial and Martian dust devil pressure excursion measurements hinge on the accuracy of the 354-gram Tavis magnetic reluctance diaphragm used for the Vikings in 1976, and Pathfinder in 19966; and a 26-gram Vaisala7 Barocap ® sensor developed by the Finish Meteorological Institute (FMI) for the Phoenix in 2008.  A Vaisala representative informed me that the device used on Phoenix could only measure from 5 to 12 mbar.  As will be discussed further below, reports on test of the Tavis sensor pressure ranges for Viking show limits of transducers designed for 18 mbar8, or 25 mbar9, while the Tavis Pathfinder pressure sensor had a limit of about 12 mbar (see Figure 8).

      The limited pressure ranges chosen for sensors seem to trace back to the Mariners10 beginning with Mariner 4 in 1964.  It estimated surface pressure at 4.1 to 7.0 mbar, but never got closer than 6,118 miles to Mars, and it was very wrong about daytime surface temperatures which were estimated at -100oC11.  The Viking Orbiter Infrared Thermal Mapper showed the equator can be as warm as +27oC (81 F)12, though average daytime temperatures at the equator are about -5oC (20o F).13  Mariners 6 and 7 estimated pressure at 3.8 to 7.0 mbar,10 but got no closer than 3,430 km to Mars.  Mariner 9, in orbit about 1,500 km high, estimated pressure between 2.8 and 10.3 mbar10. These pressure readings were based on radio-occultation experiments; but like the temperature estimates, are not as accurate as in situ measurements.

      An effort was made at the Ames facility to simulate Martian dust devils at a pressure of 10 mbar.  The NASA articles2 states that, “The high-pressure air draws thin air through the tunnel like a vacuum cleaner sucks air. Scientists also compare this process to a person sucking water through a straw. The resulting simulated Mars wind moves at about 230 feet (70 meters) per second.”  Actual recorded Martian dust devil wind velocities seen by Pathfinder and Phoenix were about 6 meters per second on Mars.3 Seventy meters per second is 156.8 miles per hour, nearly the strength of a category 5 hurricane.  NASA was unable to replicate the dust devil with a fan spinning at the 10 mbar pressure level.  It certainly does not explain Martian dust devils operating at even lower speeds, or seen on Arsia Mons where pressure is 1 mbar.5

       The easiest match between Martian and terrestrial dust devils is due to the fact that all of Mars is dry, and the fact that dust devils most often form on Earth in arid areas like the southwestern U.S. and Middle East.  But they can also form in the Canadian sub-Arctic.  On Earth they are most active on hot, flat areas.  Balme and Greeley state that the most active latitudes on Mars appear to be at 30o and 65o North and South.1 At 30o North latitude on Earth we find northern Mexico including the Sonoran desert; the Sahara Desert, the Sinai Desert, the Negev Desert, and, the Arabian desert in Saudi Arabia.  The Great Victorian Desert in Australia is at 30o South. The 65o North latitude for Mars matches  the Canadian sub-Arctic. 

     Thousands of dust devils per week occur in the Peruvian Andes near the Subancaya volcano (Metzger, 2001).14 They form in areas where there are 3-meter boulders that are aerodynamically rough. It is 5,900 meters high there.  Air pressure at that altitude would be about 478 mbar.15   Dust devils are also seen in abundance on the Martian volcano, Arsia Mons.  But the base altitude of some storms there has been about 17,000 meters.  On Earth there are no mountains or dust devils this high, but such an altitude would result in pressure of about 79.6 mbar here.  The Instuitut fur Planetalogie5 in Munster, Germany states that 28 active dust devils were reported in their study region for Arsia Mons on Mars, with 11 of them at altitudes higher than 16 km, and most inside the caldera (see Figure 1).  They indicate that they don't fully understand how particles that are a few microns in size can be lifted there, and state that 1 mbar, "requires wind speeds 2-3 times higher than at the Mars mean elevation for particle entanglement." Perhaps they don’t understand how these particles can be lifted because they are drawing their conclusions based on faulty pressure readings that are in fact, far too low.  As for  passage of air around boulders that are aerodynamically rough, this is reminiscent of how snow devils form on Earth.16 When wind flows past an obstacle, the air can develop a short vertical eddy that spins off downwind. The larger the obstacle and stronger the wind speed, the greater the chance a large snow devil will form on Earth.  This might explain what we see inside the Arsia Mons caldera, but again, the model from Earth requires a lot more than 1 mbar.

      Dust devils usually occur in the regional summer on Earth.  On Mars their tracks are most often spotted during regional spring and summer (Balme et al, 2003).17 But tracks are not always the best way to spot Martian dust devils as many active dust devils have been seen in Amazonis on Mars with few tracks, while many tracks were seen in Casius on Mars without any accompanying active dust devils seen (Fisher et al, 2005).18

       There are indications that there may be high voltage electric fields associated with Martian dust devils. If so, this would also mirror terrestrial dust devils, where estimates are as large as 0.8 MV for one such event [Farrell, W.M., et al, 2004].19 

      About 8% of terrestrial dust devils exceed 300 feet in height.  F. Bell (1967)20 reports dust devils seen from the air that are 1,000 to 2,500 m high.  Mars orbiters have shown dust devils there to often be a few kilometers high and hundreds of meters in diameter, matching or outdoing the larger terrestrial events in height.  Martian dust devils can be up to 50 times as wide and 10 times as high as terrestrial dust devils (Smith, Peter, et al 2001).21 But there are many smaller Martian dust devils, and the NASA Spirit press release of 19 August 2005 stated that, “Martian and terrestrial dust devils are similar in morphology and can be extremely common.”  

      Time lapse pictures from the Spirit Rover22 closely match six of them chased and run into on the beach by this writer on a windy afternoon in Daytona Beach on October 16, 2009.  Sand from them stung my face.  Martian dust devils also lift and quickly move around the surface material there, but we are asked to believe they operate in a near vacuum. The statement by NASA Ames that, “The simulated (10 mbar) Martian atmosphere in the wind tunnel is so tenuous that a fan would have to spin at too high a speed to blow thin wind through the test section” simply does not make sense in light of the remarkably similar characteristics of these systems.  

      About 80 convective vortices were recorded by Pathfinder.  Most occurred between 1200 and 1300 local time (Murphy, J., and S. Nellis, 2002).23 This matches what is seen on Earth where noon is about the peak time. While dust devils may deposit the bulk of the dust responsible for the color of the Martian sky, it is also alleged that they might cause up to two thirds of all windblown dust for particles under 25 microns in the U.S., and in the U.S. southwest could be a major cause of poor air quality (Gillette, D.A., and P.C. Sinclair, 1990). 24

       The six dust devils that I ran into on the beach lasted 10 to 20 seconds.  Phoenix found that on Mars they take about 20 seconds to pass,3 but to know how long they continue beyond the camera range, tracking equipment is needed.  For larger terrestrial dust devils there seems to be a relation of 1 hour for every 300 meters of height (Ives, R.L., 1947).25  Ives reports a large migratory one in Utah that lasted over7 hours and traveled about 60km.

      Balme and Greeley1 state, “Positive temperature excursions in vortices measured by Viking and MPF landers had maximum values of 5-6 K. These values are similar to terrestrial measurements.”  But they note low sampling rates on Mars, and state that here, “Temperature excursions <10oC are found consistently, but measurements with an order of magnitude higher sampling rate show temperature excursions as great as 20oC.”  Indeed, Ellehoj et al. (2009)  indicate that core excursions for Martian dust devils can, in fact, be up to 10 K (oC).3

     Balme and Greeley1 also state, “The Martian atmosphere is thinner than Earth’s… so much higher wind speeds are required to pick up sand or dust on Mars.  Wind tunnel studies have shown that, like Earth, particles with diameter 80-100 μm (fine sand) are the easiest to move, having the lowest static threshold friction velocity, and that larger and smaller particles require stronger winds to entrain them into the flow.  However, much of Mars’ atmospheric dust load is very small, and the boundary layer wind speeds required to entrain such fine material are in excess of those measured at the surface (Magalhaes et al., 1999).26  Nevertheless, fine dust is somehow being injected into the atmosphere to support the observed haze and to supply local… and global… dust storms." 

      Roy E. Wyatt of the Weather Bureau Regional Office in Salt Lake City, Utah reported that a small, approximately 50 foot high, 50 to 60 foot wide dust devil had its center pass within 8 to 10 feet of a microbarograph on August 12, 1953 in St. George, Utah (see  Figure 2) at an altitude of 2,951 feet above sea level.4 A decrease from 26.98 inches of mercury down to 26.94 inches of mercury was recorded (Figures 3 and 4).  It equals a pressure drop of 1.48%.  Balme and Greeley1 report that Mars Pathfinder, “identified 79 possible convective vortices from pressure data, and recorded pressure drops from ~0.075% to ~0.75%.   The Utah event (Figures 2-4) showed a relative pressure drop between 1.973 (1.48/.75) to 19.73 (1.48/.075) times greater than seen by Mars Pathfinder.  So we are asked to believe that incredibly small absolute and percent pressure drops on Mars are producing almost the exact same storms (often bigger storms) than we see on Earth. 

      Were there again errors on the units?  Mars Climate Orbiter was intended to enter Martian orbit at an altitude of 140.5–150 km. But Lockheed Martin used imperial units (pounds-seconds) instead of the metric system.27  This caused that spacecraft to dip to 57 km. It was destroyed by atmospheric stresses and friction at this low altitude.   Perhaps somebody failed to double check the units again on the 4 landers that took pressure readings. In fact, many countries use a comma where Americans use a decimal point.  This includes Finland, which developed the 26-gram Vaisala pressure sensor for the Phoenix lander.28 With international staffs and instrumentation vendors, commas rather than decimal points provide more opportunity for critical errors. Errors in reporting may also be due to problems associated with lander equipment design (as with uncoordinated movement of heat sources near the Vaisala Barocap® and Thernocap® sensors on Phoenix) 29 or to choice of sensors with inappropriate pressure range sensitivity. 

    Until Phoenix landed in 2008, the only landers carrying dedicated meteorology instruments were Vikings 1, 2 and Pathfinder. There was little wind speed data for Mars due to calibration problems with the wind sensor for Pathfinder (Schofield, J.T. et al, 1997). 30 But if basic assumptions about air pressure on Mars were wrong, they might have caused the wind sensor calibration problem.  This is because the formula for Wind speed u is related to pressure through Equation 1 from a NASA article about the Mars Pathfinder Windsock Experiment:


u = sqrt{[2 R(1) M g tan(theta)]/[R(2) A(d) rho]}


Above, R(1) = distance between pivot and center of mass, M =  non-counter-balanced mass, g = acceleration of gravity, R(2) =  distance between pivot and center of aerodynamic pressure, A(d) =  effective aerodynamic cross-section, and rho = atmospheric  density (a function of pressure, temperature, and molecular weight.31

      For Pathfinder, pressure was measured by a Tavis transducer similar to those used on Viking.  Thus, if the Vikings were flawed by the wrong pressure range selected, the error could be repeated on Pathfinder.  Successive mission failures due to the same parts are rare, but do happen as with re-entries in 2007 and 2008 of Soyuz TMA-10 and 11 (due to failure of 8 X 55 explosive bolts, thus initiating the ballistic return for their three person crews).32

      For Phoenix the pressure observations were performed by the new FMI instruments, Barocap capacitive pressure sensor heads manufactured by Vaisala Inc.  An error for the transducers could be due to design or previous pressure assumptions, or the fact that Finland uses a comma rather than a dot to mark the decimal radix point.  True, a comma problem would likely lead to an error of 3 orders of magnitude, but it's also true that dust devils are common on Arsia Mons where pressure is supposed to be about 1 mbar at best.

     The range of sensitivity and accuracy of the Vaisala Barocap® and Tavis sensors are crucial. With Mars Phoenix, three Barocaps sensors [LL(B1), and RSP1 (B2, B3)] were used.  Again, they could only detect up to 12 mbar, and there were problems associated with a nearby heat source.  Problems were particularly noted when temperatures rose above 0o C.  Calibration coefficients were also withheld from the Finish Meteorological Institute (FMI) due to International Traffic in Arms Regulations (ITAR). 29  Obviously, the limited range of Vaisala sensors was due to the data from the Tavis sensors before.  But what range of sensitivity did Tavis employ? The Tavis transducers were too limited due to findings by the Mariners.  Remember, Mariner 4 daytime temperatures were estimated at -100 degrees Celsius, when in fact they can get as high as +27o Celsius.12 Gas pressure varies with absolute temperature.

     The Alvin Seiff Papers9 indicate that the Viking 1 was restricted to only 25 mbar capacity, and CAD drawings of the Viking parts provided by Tavis backed the 25 mbar range for Viking (see Figure 7); but the report by Michael Mitchell8 in 1977 put it at18 mbar (see Figure 6).   Pathfinder, the Tavis spokesman thought, used Part 10484 (Tavis Dash No. 2) which a CAD drawing listed as having a 0.174 psia limit (12 mbar, the same exact limit was later imposed by Vaisala on Phoenix). Apparently NASA also ordered the 110 to 150 gram Tavis transducer (Part 10484, Tavis Dash No. 1 – see Figure 8) that supposedly remained on Earth (probably for a calibration check).  This second sensor could measure from 0 to 15 psia.   The Tavis transducers sent to Mars were apparently designed based on data obtained in the Mariner probes that never got closer than 1,500 km from Mars.  Those estimates, from 2.8 mbar to 10.3 mbar (Mariner 9), became enshrined as fact, and were built into every probe that ever landed on Mars.  The issue of pressure sensors is clouded by restrictions on information related to ITAR (International Traffic in Arms Regulations) that handicapped the Finish Meteorological Institute (and Vaisala) with respect to the calibration coefficients needed for analysis of raw pressure data on Phoenix (Peter A. Taylor, et. al, 2009).29 Apparently missile reentry issues and related security clearances interfere with data analysis.  This was hinted at in a second reference to ITAR by Taylor et al. that indicates a number of problems associated with pressure analysis for Phoenix. Barocap® pressure sensors used on Phoenix depend on Vaisala Thermocap® temperature sensors.  But, “After Phoenix landed it appeared that the actual thermal environment was worse than the expected worse case. The temperature was not only changing rapidly, but there were also fast changes in the temperature gradient due to a nearby heat source.  Information on a re-location of the heat source had not been provided initially due to ITAR restrictions.” The Mitchell report8 on Tavis Viking sensors show that they were designed for a temperature range of -28.89o C to +71.11o C.  But it gets down to -100o C at night, and never above +27 C during the day. 

     If we saw minimum Martian pressure at night (when part of the atmosphere sublimated out) and maximum pressure at noon, that might make sense.  We might speculate that everything that froze out the night before went back into the air during the day.  But the maximum pressures were at midnight and 1000. for Viking and Pathfinder.  The minimums were at 0400 and 1800 p.m. (Balme and Greeley, 2006).1 Perhaps these times correlate with operating times of other equipment on board, or they may represent sensor problems; because on Phoenix maximum pressures were at 0830 and 1530 local Mars time (Taylor, Peter et. al 2009).29

      Traditional wisdom is that we could not have had so many successes on Mars if we did not understand the pressure there.  Perhaps, but there have been many failures, some unexplained, and only four landers that actually measured in situ pressure. None of them had the ability to measure more than 25 mbar. Phoenix used a Vaisala device that had calibration problems due to ITAR. Our successes may have been despite of our misunderstanding of pressure there, and not because of our accurate data about it.  In fact, the first successful landers (the two Vikings) were designed to land with no prior in situ pressure data.  Martian dust devils almost perfectly match those seen on Earth in every respect except with respect absolute and relative pressure changes.  It seems highly unlikely that there could be so much similarity if the Martian atmosphere was as tenuous as asserted by NASA.  At the very least, the evidence strongly suggests that NASA Ames should revisit its own failure to replicate Martian dust devils at 10 mbar without fudging the results and jacking up wind speeds to from 13 to 156 miles per hour.   It is unwise to ignore weather systems that should not occur in a near vacuum.  Consideration should also be given for a future mission to include a barometer than can measure pressures up to levels close to those seen on Earth. 


1. Balme, M., and R. Greeley (2006), Dust devils on Earth and Mars, Rev. Geophys., 44, RG3003, doi:10.1029/2005RG000188. 


2.  http://www.nasa.gov/centers/ames/research/exploringtheuniverse/vaccumchamber_prt.htm

3.  Ellehoj, M.D., H.P. Gunnlaugsson, P.A.Taylor, B.T.Gheynani, J. Whiteway, M.T. Lemmon, K.M. Bean, L.K. Tamppari, L. Drube1, C. Von Holstein-Rathlou, M.B. Madsen, D . Fisher and P. Smith (2009), Dust Devils and Vortices at the Phoenix Landing Site on Mars.  40th Planetary and Lunar Conference (2009) 1558.Pdf.


4. Wyatt, Roy E. (1954), Pressure Drop on a Dust Devil, Monthly Weather Review, Jan. 1954, pp. 7-8


5. Reis, D., D. Lüsebrink, H. Hiesinger, T. Kel-ling, G. Wurm, and J. Teiser, (2009) High altitude dust devils on Arsia Mons, Mars: Testing the greenhouse and thermophoresis hypothesis of dust lifting, Lunar Planet. Sci. [CD-ROM], XXXII, Abstract 2157, Lunar Planet. Sci., 1961pdf


6.  http://mars.jpl.nasa.gov/MPF/mpf/sci_desc.html

7.  http://www.vaisala.com/weather/products/barometers.html and


8. Mitchell, Michael, Evaluation of Viking Lander Pressure Barometric Sensor, NASA Langley Research Center, Hampton, Va., March 1977.  NASA TM X-74020.

9.  Guide to the Alvin Seiff Papers


10.  http://nssdc.gsfc.nasa.gov/planetary/mars/mariner.html

11.  http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1964-077A

12. http://www-k12.atmos.washington.edu/k12/resources/mars_data-information/temperature_overview.html

13. http://www.planetary.org/explore/topics/our_solar_system/mars/facts.html

14. Metzger, S. (2001), Recent advances in understanding dust devil processes and sediment flux on Earth and Mars, Lunar Planet. Sci. [CD-ROM], XXXII, Abstract 2157


 15. http://www.csgnetwork.com/pressurealtcalc.html

16.  http://www.weathernotebook.org/transcripts/2004/03/24.php

 17. Balme, M.R., P.L. Wheeley, and R. Greeley (2003b), Mars: Dust devil track survey in Argyre Panitia and Hellas Basin, J. Geophys. Res, 108(E8) , 5086, doi:10.1029/2003JE002096.

18.  Fisher, J. A., M. I. Richardson, C. E. Newman, M. A. Szwarst, C. Graf, S. Basu, S. P. Ewald, A. D. Toigo, and R. J. Wilson (2005), A survey of Martian dust devil activity using Mars Global Surveyor Mars Global Orbiter Camera images, J. Geophys. Res, 110 ,E03004, doi:10.1029/2003JE002165

19. Farrell, W. M et al 2004 Electric and magnetic signatures of dust devils from the 200-2001 MATADOR desert tests, J Geophs. Res., 109, E03004, doi: 10.1029/2003JE002088

20.  Bell, F. (1967), Dust devils and aviation, report, Meteorol. Note 27, Aust. Bur. of Meteorology, Melbourne, Victoria.

21. Smith, Peter, Renno Nilton (6 June 2001). Studying Earth Dust Devils for Possible Mars Mission, UniSci News


23. Murphy, J. and S Nellis, (2002), Mars Pathfinder connective vortices: Frequency of occurrences, Geophy. Res. Lett., 29(23, 2001, doi: 10.1029/2002GL015214

24. Gillette, D.A., and P.C. Sinclair (1990), Estimation of suspension of alkaline material by dust devils in the United States, Atmos. Environ. Part A, (245), 1135-1142

25. Ives, R.L. (1947), Behavior of dust devils, Bull. Am. Meteorol. Soc, 28, 168-174

26. Magalhaes, J.A., J.T. Schofield, and A. Seiff (1999), Results of the Mars Pathfinder atmospheric structure investigation, J. Physics. Res., 104, 8943-8955

27.  http://marsprogram.jpl.nasa.gov/msp98/news/mco990930.html

28.  http://www.turkupetcentre.net/analysis/doc/decimal_separator.html

29. Peter A. Taylor, Wensong Weng, Henrik Kahanpää, Ayodeji Akingunola, Clive Cook, Mike Daly, Cameron Dickinson, Ari-Matti Harri, Darren Hill, Victoria Hipkin, Jouni Polkko and Jim Whiteway, 2009, On Pressure Measurement and Seasonal Pressure Variations at the Phoenix landing site, Subm to J.Geophys. Res. (Planets).


30. Schofield, J.T. et al, (1997) The Mars Pathfinder atmospheric structure investigation meteorology (ASI/MET experiment, Science, 278, 1752-1758

31. http://starbrite.jpl.nasa.gov/pds/viewInstrumentProfile.jsp?INSTRUMENT_ID=WINDSOCK&INSTRUMENT_HOST_ID=MPFL

32. http://www.nasaspaceflight.com/2009/04/soyuz-investigation-findings-backed-by-nominal-soyuz-tma-13-return/





     Special thanks to my father, Barry S. Roffman, for suggesting that I research the relationship between Martian air pressure and dust devils on Mars. 

     Further thanks are due to Professor Jason Aufdenberg, Assistant Professor of Physics at Embry-Riddle Aeronautical University in Daytona Beach, Florida for giving me reference (1), the article by Balme, M., and R. Greeley (2006), Dust devils on Earth and Mars, Rev. Geophy.  That article provided enough common points for terrestrial and Martian dust devils.  It encouraged me to pursue my research in this area despite the pressure of set beliefs in the scientific community about Martian atmospheric pressure based on NASA analyses of previous missions to Mars.

     Finally, special thanks are appropriate to April Gage, Archivist, NASA Ames History Office, MS 207-1, Moffett Field, CA 94035.  She provided me with abundant guidance and the March, 1977 report by Michael Mitchell about Tavis sensors.  Thanks are also due to the Tavis and Vaisala companies for technical data and diagrams related to their sensors, and (by Vaisala) for forwarding a draft copy of the report by Peter A. Taylor et al. (2009) entitled On Pressure Measurement and Seasonal Pressure Variations at the Phoenix landing site.  That report has recently been submitted to J.Geophys. Res. (Planets).