What observational evidence supports the idea that Mercury once shrank by some 20 kilometers in radius?

Question

Quizplus · Accepted Answer

The presence of many long, tall cliffs, known as scarps, on Mercury's surface is the primary observational evidence supporting the idea that Mercury once shrank by some 20 kilometers in radius. These scarps are thought to have formed as the planet's interior cooled and contracted, causing the surface to crack and buckle. The total length of these scarps is over 5,000 kilometers, suggesting significant global-scale contraction.

What Observational Evidence Supports the Idea That Mercury Once Shrank