The Impressive Rays of Mercury's Hokusai Crater

This mosaic of images taken on Oct. 6, 2008, by NASA's MESSENGER spacecraft shows an impact crater on Mercury named Hokusai. The crater has an impressive system of rays, which extend out more than 600 miles (about 1,000 kilometers) across the planet. Rays form when something impacts the surface of a celestial body. Material is kicked up from beneath the surface, and thrown outward from the crater. Mercury and other airless planetary bodies are being constantly bombarded with micrometeoroids and energetic ions, producing an effect known as space weathering. Craters with bright rays are thought to be relatively young because the rays are still visible, indicating that they have had less exposure to such weathering processes than craters that lack rays. Hokusai crater is named for Japanese artist Katsushika Hokusai (1760–1849).