P53A-2098
Basin Formation and Cratering on Mercury Revealed by MESSENGER
Friday, 18 December 2015
Poster Hall (Moscone South)
Clark R Chapman1, Caleb Fassett2, Simone Marchi3, William J Merline1, Lillian Rose Ostrach4 and Louise M Prockter5, (1)Southwest Research Institute, Boulder, CO, United States, (2)Mount Holyoke College, Department of Astronomy, South Hadley, MA, United States, (3)Southwest Research Institute Boulder, Boulder, CO, United States, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States
Abstract:
Mercury has been bombarded by asteroids and comets throughout its history. The resulting craters and basins are the dominant topographic features on the planet. Although visible basins contain some of the most interesting tectonic features, plains, and evidence of vertical stratigraphy, they fall far short of saturating the surface. Nevertheless, Mercury has a greater spatial density of peak-ring basins and protobasins than any other Solar System body, partly because these morphologies begin at smaller sizes than on most bodies. Cratering at approximately three times the cratering rate on the Moon, combined with likely plains-forming volcanism, prevents recognition of surface features older than 4.0 to 4.1 Ga. Severe losses of craters <50 km in diameter (<20 km in some places) are ascribed to extensive formation of intercrater plains. Estimates of the cratering chronology of Mercury suggest that most plains formation ended about 3.6 to 3.7 Ga, though activity has continued in a few small regions until much more recently (e.g., inside the Rachmaninoff basin). Mercury, compared with other terrestrial bodies, is struck by projectiles impacting at much higher velocities, which is probably responsible for the formation of abundant secondary craters that dominate the numbers of craters <10 km diameter on older plains surfaces. The history of high-velocity bombardment has resulted in the production of abundant impact melts and has churned and processed the regolith, and eroded older topography, more thoroughly than on other Solar System bodies. Although the possible role of Mercury-specific impactors (“vulcanoids”) cannot be excluded, imaging searches by MESSENGER have revealed no remaining vulcanoids and no other evidence suggests that Mercury has been bombarded by anything other than the same populations of asteroids and comets that have impacted the Moon and other terrestrial planets from the end of the period of heavy bombardment 3.8 to 3.9 Ga to the present.
