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Why do complex crater features appear in smaller craters on Mercury than on the Moon?

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four impact craters — Meteorite crater Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.

Complex crater features, such as central peaks, slumped walls, and flattened floors, appear in smaller craters on Mercury than on the Moon primarily due to differences in surface gravity.1

Mercury’s surface gravity is more than twice that of the Moon. This higher gravitational acceleration creates a greater pressure difference between the crater floor and the surrounding surface. This pressure gradient plays a significant role in driving the collapse process—known as the modification stage—that transforms a simple bowl-shaped depression into a complex crater. Because this collapse occurs more readily under higher gravity, the threshold for forming complex features is lower on Mercury (approximately 10 km in diameter) compared to the Moon (approximately 19 km in diameter).123

In essence, the diameters of the smallest complex craters decrease in inverse proportion to a body's surface gravity, meaning that higher-gravity environments facilitate the transition to complex structures at smaller scales.2