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Ground Temperatures. Updated on 2/23/2020.

15.1 Ground Temperature Problems.

      For most of the first year the MSL REMS Team reports did not include ground temperatures. Then they began to include them – right back to MSL Sol 10 at However when I tried to make some sense out of the relationship between air and ground temperatures, I found the caveat that,

“Ground temperature will be recorded with a thermopile on Boom 1 that views the Martian surface to the side of the rover through a filter with a passband of 8 to 14 microns. The requirement is to measure ground brightness temperature over the range from 150 to 300 K with a resolution of 2 K and an accuracy of 10 K.28  

       An accuracy of 10K is almost worthless when looking at so many temperatures hovering around 273K (0° C). In fact, looking at the data from MSL Sols 10 through 652, the REMS Team offered maximum and minimum ground temperature for 584 sols. Fully 413 of the highs (over 70%) were between 283K (10° C) and 263 K (-10° C). See Figure 65. In spring of MSL Year 3 a maximum ground temperature of +24° C was recorded on Sol 1428 at Ls 202.

       If there was an accuracy in the range 1 K or better we could probably deduce something intelligent about air density by looking at the rate of heat loss from the surface up to the boom, but with an accuracy of only 10K on the ground and 5 K in the air, it really isn’t worth the effort to do the math. The decision to go with such inaccurate sensors may be due to incompetence, or to design. All that can be said is that for $2.5 billion, we got inaccurate temperature sensors, nonfunctioning wind sensors, a relative humidity sensor that did not merit inclusion of its data on any daily weather reports, and, of course, the same pressure sensor as that on Phoenix that caused its designer so much distress. We also got data that was often suspiciously revised or deleted by JPL after I criticized it to JPL public relations man Guy Webster.  

       Because JPL often changed published data, all too often after I have published criticism of that data, I often captured what they are saying via print-screen images. This is necessary here too. The 10K accuracy above is captured on Figures 66 and 67. See Figures 68 & 69 for ranges of Martian monthly high and low temperatures.

Figure 65 above. If the accuracy of MSL ground temperatures is only 10K, this creates a huge problem when it comes to understanding heat loss and air density.

Figure 66 – REMS Team member Javier Gomez-Elvira summarizes REMS weather instrument abilities. The enlarged section is for temperature sensor range, accuracy and resolution.

       Note that Figure 67 comes with an excuse for the poor accuracy of the ground temperature sensor. It states, “A contact sensor as used on previous missions was not an option for MSL since it would have resulted in fewer operations when the rover performs driving Sols.” Which missions? The only missions on the ground for at least a Martian year were Viking 1 and Viking 2. They only measured air temperature at 1.5 meters above the ground.92

       Mars Pathfinder (MPF) had three temperature sensors. Their heights were at 0.25 meters, 0.5 meters and 1 meters.93 Figure 70 shows a plot of temperatures for MPF Sol 78, but again, none of these temperatures are ground temperatures although the lowest sensor was just 0.25 meters above the ground.

       It appears that the only lander to actually put a temperature probe into the Martian regolith was Phoenix, which landed in the Martian arctic at about 68° North. There a Thermal and Electrical Conductivity Probe (TECP) measured regolith temperatures from 253K (-20.15° C) down to 181K (-92.15° C) (A. P. Zent et al., 2009).94 Note that these temperatures are much warmer than the daytime temperatures of -100° C supposedly measured from a distance of 9,846 km by Mariner 4 in 1964.

Figure 67 – The MSL Ground Temperature Sensor manufactured by the Institute for Physical High Technology, Jena, Germany.


Figure 68 – Mars Science Laboratory high air and ground temperatures for 4 Martian years.

Figure 69 – Mars Science Laboratory low air and ground temperatures for 4 Martian years.


Figure 70 - Adapted from Unaveraged periodic temperature data from Mars Pathfinder. The data from all 3 sensors on Pathfinder’s 1 meter mast are shown.