Comments on 'A high resolution Mars surface gravity grid' (Gorski et al., 2018, Planetary and Space Science 160, 84-106)

摘要

Gorski et al. (2018, Planetary and Space Science 160, 84106, https://doi.org/10.1016/j.pss.2018.03.015) developed a high-resolution surface gravity grid for Mars. They presented a comparison with the Mars Gravity Model 2011 (MGM2011) by Hirt et al. (2012, Planetary and Space Science 67, 147154. https://doi.org/10.1016/j.pss.2012.02.006), which is based on similar input data, but a different computational methodology. These two models do not agree very well in their higher-frequency constituents, that is, the parts related to topography-induced gravity. In the spatial domain, the gravity accelerations from both models differ by similar to 20 mGal (root-mean-square) and reach amplitudes as large as similar to 695 mGal in places. Gorski et al. (2018) suggest that some aspects of the MGM2011 modelling algorithm are in error, but without substantiating this claim nor verifying their model. In this communication, we present results from our validation experiments using alternative gravity modelling techniques, all showing a close fit with MGM2011, while being in clear disagreement (to a level of similar to 40% of the signal) with the Gorski et al. (2018) model. We discuss and narrow down the origin of the mismatches to a scale-factor of square-root (2), apparently included in their high-frequency modelling. As a general conclusion, our experiments indicate that the Gorski et al. (2018) model should be treated with some caution, especially over rugged topography so long as the underlying modelling techniques are not comprehensively validated.