Mars Pathfinder Pressure Findings
Pathfinder Data is Best Compared to Viking 1 Data (Updated 9/22/2014)
NOTE added on September 22, 2016: A major article comparing MPF and MSL temperatures is found at http://davidaroffman.com/photo5_13.html
Mars Pathfinder landing Data:
Landing Date: July 4, 1997. Date Operations Terminated: September 27, 1996
Martian Month: 5 (summer) Martian Month terminated:7 (fall)
Ls at landing: 142.7 Ls at termination: 188.4
Martian Sol at landing: 304. Martian Sol at termination: 387
Altitude of MPF: -3.682 km.
Comparative altitudes of other landers with MET capability:
Viking 1: -3.627 km (most similar to Pathfinder). Based on scale height calculations, at a time when pressure at areoid is 6.1 mbar, pressure at Viking 1 would be expected to be about 8.5345 mbar and at Pathfinder it would be about 8.5781 mbar.
Viking 2: -4.505 km
Phoenix: -4.126 km
This page addresses Pathfinder pressure data published at:
The Mars Pathfinder Atmospheric Structure Investigation/Meteorology (ASI/MET) Experiment
Vol. 278 no. 5344 pp. 1752-1758
The relevent pressure text and figures from the above article are include below. This author's comments are added in red.
Pressure data. During sols 1 through 30 (Roffman note: Martian sols 304 to 333; Ls 142.7 to 158) surface pressure at the landing site underwent substantial daily variations of 0.2 to 0.3 mbar, which were associated primarily with the large thermal tides in the thin martian atmosphere (11) (Fig.3A). Daily pressure cycles were characterized by a strong semidiurnal oscillation, with two minima and two maxima per sol, together with diurnal and higher-order components, although there was considerable day-to-day variability (Fig. 3B). The presence of a large semidiurnal tidal oscillation is indicative of atmospheric dustiness over broad regions of Mars and over an altitude range of at least 10 to 20 km (19).
UPDATE OF 11/19/2014: Schofield et al. (1997)1 indicate that while Pathfinder was operational from July 4 to September 27, 1997, it had no pressure data for the most crucial sol – its first operational day on Mars. The reason given by the above reference is there were “various spacecraft software reset and downlink problems.” If the problems only occurred after the first day; and if the first day’s pressure data was consistent with the Vikings, then Pathfinder’s data could be used to refute the claims made herein. However, that is not the case. We are still dealing with a Tavis transducer with no way to keep the dust out of its pressure tube on or in the seconds before landing, and no way to change a clogged dust filter. The critical time is in the final landing process. So when the spacecraft has to reset the software and correct downlink problems then, the issue of exactly what is entailed in these corrections becomes one of extreme importance.
A long-term trend in daily mean pressure was also seen. A third-order polynomial fit to the data shows that mean pressure fell slowly at the beginning of the period and rose at the end, with a minimum just under 6.7 mbar near sol 20 (L s ∼ 153°) (Fig. 3A). This time corresponds to the annual deep minimum in the seasonal pressure cycle associated with CO2 condensation and sublimation in the polar regions of Mars and was seen previously by the Viking landers (11).
The ASI/MET pressure sensor detected a variety of pressure variations on relatively short time scales. These ranged from seconds to hours and had magnitudes of 1 to 50 μbar. The shorter time-scale variations (<10 to 15 min) appear to be correlated with wind and temperature fluctuations and tend to be largest during late morning and early afternoon, when the boundary layer is most turbulent. The most dramatic pressure features were minima of 10 to 50 μbar, usually less than a minute in duration, associated with vortices (dust devils) passing over the lander. A particularly good example was seen during the continuous sampling of sol 25.