Impact gardening is the process by which

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or ...

s stir the outermost crusts of moons and other celestial objects with no

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

s. In the particular case of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, this is more often known as lunar gardening. Planetary bodies lacking an atmosphere will generally also lack any

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

al processes, with the possible exception of

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...

, and as a result impact debris accumulates at the object's surface as a rough "soil," commonly referred to as

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...

. Subsequent impacts, especially by

micrometeorite A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. T ...

s, stir and mix this soil. It had long been estimated that the top centimeter of the lunar surface is overturned every 10 million years. However a 2016 analysis by the LRO satellite of impact ejecta coverage puts the figure closer to 80,000 years.

References

Further reading