Impact garening is the process by which impact events stir the outer most crust of moons and other celestial objects with no atmosphere. In the particular case of the moon, this is more often known as lunar gardening. Planetary bodies lacking an atmosphere will generally also lack any erosional process, with the possible except of volcanism, and as a result impact debris accumulates at the object's surface as a rough "soil". Subsequent impacts, especially by micrometeorites, stir and mix this soil. It is estimated that the top centimeter of the lunar surface is overturned every 10 million years.