Often during Halloween ghost stories are told. Phantoms from the past linger in the present trying to tell us about some previous horror. We know that there are ghosts on Mercury.
Mercury is small, smaller than the moons Titan and Ganymede. Small bodies lose heat quickly and don’t generate as much internal heat as larger planets. That that is not to say that it was never hot, in the past Mercury would have been much hotter, and with that volcanically active. The planet’s surface has been covered over and reworked by volcanic activity often multiple times.
We see evidence of volcanoes on Mercury from Lava filled craters, and lava flows flowing out of them, bright spots on the surface which represent fire fountains and pyroclastic deposits. Smooth plains cover over much older crater marked surfaces.
Molten rock will follow weaknesses in the rock in order to find the easiest route, on Mercury, these are often found in impact craters, filling them up like bowls. As the bowls of lava cool, they contract the top starts to wrinkle, like the skin on custard. These wrinkles form long bands of hills imaginatively called wrinkle ridges.
In some places lava flows are very extensive forming planes which completely cover craters, concealing the scar left by an impact on the planet’s surface. because the lava is thinner at the rim of the crater and so cools and shrinks at different amounts to the lava surrounding this. The differential shrinking leads to the formation of either wrinkles or in some cases faults forming. The crater, completely buried by lava, becomes apparent, traced out on the surfacece of the lava. The outlines in the lava are known as ghost craters.