article_snippet: Regolith is a term that refers to a soil that is lacking organic material.
article_snippet: As the fresh soil grains sit on the surface, the fresh soil grains are exposed to radiation and slowly become darker and redder.
article_snippet: This is largely caused by a reduction of iron in minerals to iron metal – reverse of rusting that happens on Earth.
article_snippet: This slow change in reflectance and colour is generally referred to as space weathering; fresh soil is referred to as immature, and weathered soil is mature.