Joulaud M., Allemand P., Flahaut J., Füri E.
Planetary and Space Science, Article n°106338, Volume 282, November 2026
Voir en ligne : https://doi.org/10.1016/j.pss.2026.106338
Mercury’s surface is covered by regolith produced by meteoritic bombardment, recording the planet’s impact and geological history. In this study, we assess the regolith thickness of the Borealis Planitia region (−72°E, 66°N), within two hermean terrain types: the smooth plains and the older intercrater plains. The regolith thickness is estimated using the highest resolution imagery available from MESSENGER’s Mercury Dual Imaging System Narrow Angle Camera (MDIS NAC) and the small crater morphology method. A total of 3546 craters (<400 m in diameter) presenting a specific morphology (i.e., central mound, flat-bottomed or concentric) were identified and characterized. In addition, 855 bowl-shaped craters (BSC) are mapped and their depth, derived from a depth-to-diameter law, is used to estimate a lower boundary of the regolith thickness, as BSC form solely in regolith. The estimated regolith thickness is highly variable laterally within the two units, with, on average, thicker regolith in the smooth plains (median: 4.6 m) and a thinner regolith in the intercrater plains (3.7 m). No correlation between regolith thickness and surface age can be established, highlighting a possible difference in the bedrock properties of the two units. The hermean regolith is generally thicker than on the Moon, as expected, because the higher impact energy due to the Sun’s proximity leads to more regolith production. While our study provides one of the first estimates of regolith thickness in Mercury’s volcanic units, further quantitative analyses of the hermean regolith thickness at a global scale are needed for comparison and assessment of the physical structure of Mercury’s surface, especially in the absence of in situ data.