Peak ring crater

In an impact with more energy than one that makes a central peak crater, the central peak opens into a ring.

The central ring is a stage of crater development that does not depend on the properties of the planet. This is the largest kind of complex crater. The ring may be continuous or broken into small peaks. The transition between central peak and ring forms is gradual.

The crater size at which the ring first appears depends on three things. These are the gravity of the body, the energy of the impact (which depends on the mass of the impactor and the impact speed) and the material of the target rock. On Venus, rings begin to form at a crater diameter of 33 km (Baker et al. 2011).

Barton, shown on the plate, is 52 km across. One side of the crater is straight, which gives it an irregular shape. This may be linked to cracks in the bedrock or to the angle of impact. Lachappelle is 36 km across. Here the central peak is no longer focused at the centre but “scattered” across the crater floor. Yet it does not form a ring.

The figure shows the stages in which the ring opens.