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How fast do objects usually travel when they strike a planet and form impact craters?

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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.

When an asteroidal or cometary object strikes a planetary surface to form an impact crater, it typically travels at velocities of several tens of kilometres per second. This extreme speed is referred to as a hypervelocity impact.1

For comparison, the average impact velocity for Earth-crossing asteroids is approximately 15 km per second, while long-period comets strike Earth at much higher average velocities, typically around 51.7 km per second. These objects do not slow down appreciably as they pass through the atmosphere, allowing them to strike the surface with immense kinetic energy and create a crater.23

It is important to note that smaller meteoroids that do not form craters are often slowed significantly by the atmosphere, eventually falling to the ground at much lower velocities—typically between 100 and 200 metres per second—in a process known as dark flight.4