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Is Mercury still geologically active beneath its surface?

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Messenger: Mercury — Mercury Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.

Whether Mercury is geologically active is a subject of ongoing scientific study, as the planet presents a complex picture of internal versus surface activity.

Evidence suggests that Mercury’s interior remains warm and partially molten. The presence of a dipolar magnetic field indicates that a magnetohydrodynamic dynamo is currently operating, which requires an electrically conducting fluid—likely a molten outer iron-sulfur core—to generate the field. Furthermore, measurements of the planet's gravitational field support the conclusion that at least the outer portion of the core remains in a molten state.12

However, surface activity is a different matter. While the planet appears to be "geologically alive" in its interior, most evidence suggests that large-scale volcanic surface activity ceased long ago. The primary exception involves lobate scarps, which are cliffs formed by thrust faults. Because some of these scarps appear to be geologically young and have altered fresh impact craters, they indicate that the planet is still slowly contracting as its interior cools. Thus, while Mercury is not volcanically active on its surface, it remains geologically dynamic through ongoing global contraction.13