Bowl-like depression (“crater” means “cup” in Latin) on the surface of a The term "planet" originally comes from the Greek word for "wanderer" since these objects were seen to move in the sky independently from the background of fixed stars that moved together through the seasons. The IAU last defined the term planet in 2006, however the new definition has remained controversial. Click on Term to Read More, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by Igneous rock that forms from cooling magma on the surface of a planet or asteroid. activity, though some are due to Eruption of water or other liquid or vapor-phase volatiles (collectively referred to as "cryomagma"), together with gas-driven solid fragments, onto the surface of a planet or moon due to internal heating. After eruption cryomagma condenses to a solid form when exposed to the very low surrounding temperature. Cryovolcanism is not Click on Term to Read More.