MAPPING MERCURY’S TECTONIC FEATURES AT THE TERMINATOR: IMPLICATIONS FOR RADIUS CHANGE ESTIMATES AND THERMAL HISTORY MODELS.

Prior to the MESSENGER mission only 45% of the Mercury’s surface was imaged by Mariner 10. By using the latter data for mapping tectonic features it was suggested that the detected compressional structures can account for a planetary radius contraction of less than 1 km (0.43-0.64 km). These results have been slightly revised by recent studies using images acquired during the three MESSENGER flybys. In fact, several previously unobserved compressional features (including the longest known to date on Mercury) have been discovered, increasing the total number of known contractional features by approximately one third and thus bringing the amount of estimated radius contraction to 0.8 km. However, these estimates yet appear too low with respect to the amount of radius contraction (up to 5-6 km) predicted by the most accredited studies based on thermo-mechanical evolution models.