Comments on “A high resolution Mars surface gravity grid” (Górski et al., 2018, Planetary and Space Science 160, 84–106)

Abstract

© 2019 Elsevier Ltd Górski et al. (2018, Planetary and Space Science 160, 84–106, 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, 147–154. 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 ∼20 mGal (root-mean-square) and reach amplitudes as large as ∼695 mGal in places. Górski 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 ∼40% of the signal) with the Górski 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 Górski 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.