A fault surface exposed on Mercury. (July 2021) - Pegg, D.L.
Abstract: Mercury's tectonic history has been dominated by global contraction as the planet shrinks and cools. Previously, fault dips have been indirectly estimated by measuring offsets to the rims of craters displaced by fault movement. Here we present the first observations of a fault surface exposed in three dimensions, in this case within a volcanic vent. We use shadow measurements to determine the depth of the vent and have measured the dip of the fault as 28° ±5. This is towards the shallower end of previous dip estimates used to estimate global contraction. If it is representative, it suggests global contraction at the higher end (5.7–7.1 ​km) of previously published estimates. Highlights: We report the first direct observation of a fault dip on Mercury. The dip of fault surface is measured at 28° ​± ​5. Faults crossing vents are excellent targets for future orbital observations. Abstract : Plain language Summary: The surface Mercury is covered in wrinkles caused by the shrinking of the planet as it cools. We have found the first example where one of the faults beneath these wrinkles is exposed inside a big hole in the ground blasted by an explosive volcano. This location allows us to measure the angle at which the fault dips underground, providing us with a new clue as to how much the planet has shrunk.