Accuracy of the Phoenix and Viking atmospheric pressure measurements: impact on detecting the climate change on Mars

Attempts have been made to detect secular changes in the Martian climate by comparing surface atmospheric pressure measurements separated by several decades [1][2]. Such multi-mission studies require information on the exact accuracies of the corresponding pressure measurements. In this presentation, we discuss results of our recently published study on the quality of the pressure data measured by the Mars Phoenix lander [3]. In addition, we evaluate the absolute accuracy of the Viking pressure data by using (less well known) sources in the literature [4][5].

Our results show that at the beginning of the Phoenix mission the offset of the pressure measurement was between -4.8 Pa and +0.1 Pa. The drift of the sensor during the mission was between -0.5 Pa and +3.4 Pa. Thus, the Phoenix pressure measurement was much more accurate than was reported immediately after the mission [6]. However, the systematic error of the Viking pressure data could be up to 8.8 Pa.

Haberle and Kahre (2010) found the Phoenix surface pressures to be ~10 Pa higher than the Viking surface pressures after correcting for elevation differences and dynamics [1]. Although our results show the Phoenix measurement to be more accurate than assumed by Haberle and Kahre (2010), the difference they found could still be explained by the uncertainty of the Viking pressure data. On the other hand, our results show that the Phoenix pressure data can be used as an accurate comparison point for future surface pressure measurements on Mars.

References:

[1] Haberle and Kahre, "Detecting secular climate change on Mars ", Mars, 5, 68–75, 2010.

[2] Batterson et al., "Secular Climate Change on Mars: An Update", AGU Fall Meeting, 2017.

[3] Kahanpää et al., "The quality of the Mars Phoenix pressure data", Planet. Space Sci., 181, 104814, 2020.

[4] Seiff, "The Viking atmosphere structure experiment - Techniques, instruments, and expected accuracies", Space Sci. Instrum., 2, 381–423, 1976.

[5] Mitchell, "Evaluation of Viking Lander barometric pressure sensor", NASA Technical Memorandum, NASA-TM-X-74020, 1977.

[6] Taylor et al., "On pressure measurement and seasonal pressure variations during the Phoenix mission", J. Geophys. Res., 115, E00E15, 2010.

Acknowledgments:

The contribution of H. Kahanpää in this study was supported by The Finnish Cultural Foundation [grant number 00170395]. The contribution of M. Daly was supported by the Canadian Space Agency. We wish to thank Germán Martínez (USRA/LPI) for providing a copy of reference article [4].