Living Reference Work Entry

Encyclopedia of Planetary Landforms

pp 1-4

Date: Latest Version

Degraded Basin

  • Ross PotterAffiliated withCenter for Lunar Science and Exploration, USRA – Lunar and Planetary Institute Email author 


Modified impact basin.


Basins represent the largest impact craters, which, when fresh, have ring structures. Some of the large ancient basins show no obvious or only partial evidence of ring structures. These basins may have had multiple rings when they formed, but these have become subdued over time.


  1. (1)

    Relaxation: Basins may degrade over time as a result of viscous relaxation (flow of material) and isostatic (density differences) readjustment which can smooth out topography as well as subsurface features, such as the crust/mantle boundary, beneath the basin. This process is proposed for the icy satellites (palimpsest, penepalimpsest); Mercury (Fassett et al. 2012) and discussed for Venus (Solomon et al. 1982).

  2. (2)
    1. (2.1)

      Cratering: densities of heavily cratered surfaces on the Moon and Mercury are consistent with their having been cratered to saturation equilibrium. As a consequence, craters and even large basins had been degraded to and beyond the lim ...

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