Regolith (noun, “RAY-go-lith”)
Regolith is the layer of loose rocks and dust on the surface of moons, asteroids and rocky planets — including Earth.
This blanket of fine material comes from forces that break down or transform rock. On Earth, wind and water break rocks down into smaller and smaller particles, such as pebbles and sand. Volcanoes — on Earth and other planets — also create ash and lava fragments. These too become regolith. Meteorites crashing into moons, asteroids and planets can blast bedrock into tiny particles as well.
Different celestial bodies have different kinds of regolith. For example, Martian regolith contains high levels of iron oxide. This is what gives the “Red Planet” its distinctive hue. But the moon’s regolith is made of lots of silicates. These compounds include the element silicon. Heat from meteorite collisions has melted some of these silicates. This has resulted in lunar regolith that consists of tiny pieces of glass.
In the coldest reaches of our solar system, regolith may consist of grains of frozen hydrocarbons, such as methane. Or even water. Ice grains cover the surface of Saturn’s moon Titan. In Titan’s frigid temperatures, ice behaves more like stone. So, scientists consider Titan’s icy granules to be Titan’s regolith.
In a sentence
Scientists managed to sprout some scrawny seedlings in lunar regolith samples.
