Crater ray system on the far side of the Moon. Far Side of the Moon, in original French, La face cachée de la lune, is a 2003 film by Robert Lepage. NASA photo credit. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program

A ray system comprises the radial streaks of fine ejecta thrown out during the formation of an impact crater. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body Ray systems were once thought to be only found on planetary bodies that lack an atmosphere, but have since been discovered on Mars (see Zunil) in infrared images taken from orbit by the Thermal Emission Imaging System (THEMIS). A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Zunil is a Municipality in the Quetzaltenango department of Guatemala with surface area of 92 sq For other uses see Themis (disambiguation. In Greek mythology, Hesiod mentions Themis (Θέμις among the six sons and six daughters of Gaia Ray ejecta material have different reflectivities (i. e. , albedo), compositions, or thermal properties than the surface on which it is deposited, so that the rays form visible and, in some cases, infrared patterns. The albedo of an object is the extent to which it diffusely reflects light from the sun The resulting rays can extend for several multiples of the impact crater's diameter. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the Rays are often accompanied by small secondary craters formed by larger chunks of ejecta.

Typically visible rays have a higher albedo than the surrounding surface. They stand out as brighter features that can form streaks and patterns across the surface. More rarely an impact will excavate low albedo material, such as basaltic-lava deposits on the lunar maria. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures The lunar maria (singular mare, two syllables are large dark Basaltic plains on Earth 's Moon, formed by ancient Volcanic eruptions These dark streaks can provide a contrast with higher albedo features, resulting in dark rays.

Gratteri crater, a "Thermal" crater ray system on Mars that was imaged by THEMIS at night. For other uses see Themis (disambiguation. In Greek mythology, Hesiod mentions Themis (Θέμις among the six sons and six daughters of Gaia Each THEMIS observation is 32 km across (320 pixels across with a nominal pixel resolution of 100 meters per pixel). For other uses see Themis (disambiguation. In Greek mythology, Hesiod mentions Themis (Θέμις among the six sons and six daughters of Gaia NASA/JPL/ASU/University of Tennessee photo credit. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program

Thermal rays, as seen in thermal infrared images and like the ones discovered on Mars with the THEMIS infrared imager, have contrasting temperatures with their surroundings. For other uses see Themis (disambiguation. In Greek mythology, Hesiod mentions Themis (Θέμις among the six sons and six daughters of Gaia They are especially apparent at night when slopes and shadows do not influence the infrared energy emitted by the Martian surface.

The layering of rays across other surface features can be an indicator of the relative age of the impact crater. Over time these rays can also become obliterated due to various processes, providing additional clues for determining the geologic age. On non-atmosphered bodies, such as the Moon, Space weathering from exposure to cosmic rays and micrometeorites causes a steady reduction of the differential between the ejecta's albedo and that of the underlying material. Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on Micrometeorites in particular produces a glassy melt in the regolith that lowers the albedo. Regolith ( Greek: "blanket rock" is a layer of loose Heterogeneous material covering solid rock. The albedo of an object is the extent to which it diffusely reflects light from the sun The rays can also become covered by lava flows, or by other impact craters or ejecta. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures

Lunar rays

Asymmetrical ray system about Proclus crater on the Moon. Proclus is a young lunar Impact crater located to the west of the Mare Crisium, on the east shore of the Palus Somni. NASA photo. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program

The physical nature of lunar rays has historically been a subject of speculation. Early hypotheses suggested that they were deposits of salt from evaporated water. Later they were thought to be deposits of volcanic ash or streaks of dust. After the impact origin of craters became accepted, Eugene Shoemaker suggested during the 1960s that the rays were the result of fragmented ejecta material. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969

Recent studies suggest that the relative brightness of a lunar ray system is not always a reliable indicator of the age of a ray system. Instead the albedo also depends on the portion of iron oxide (FeO). Altogether there are sixteen known Iron Oxides and oxyhydroxides Low portions of FeO result in brighter materials, so such a ray system can retain its lighter appearance for longer periods. Thus the material composition needs to be factored into the albedo analysis to determine age.

Among the lunar craters on the near side with pronounced ray systems are Aristarchus, Copernicus, Kepler, Proclus, and Tycho. Aristarchus is a prominent lunar Impact crater that lies in the northwest part of the Moon's near side Copernicus is a prominent lunar Impact crater located in eastern Oceanus Procellarum. Kepler is a young lunar Impact crater that lies between the Oceanus Procellarum to the west and Mare Insularum in the east Proclus is a young lunar Impact crater located to the west of the Mare Crisium, on the east shore of the Palus Somni. Tycho is a prominent lunar Impact crater located in the southern lunar highlands named after the Danish Astronomer Tycho Brahe. Similar ray systems also occur on the far side of the Moon, such as the rays radiating from the Giordano Bruno and Ohm craters. Far Side of the Moon, in original French, La face cachée de la lune, is a 2003 film by Robert Lepage. Giordano Bruno is a small lunar Impact crater on the far side of the Moon, just beyond the northeastern limb Ohm is a lunar Impact crater that is located on the far side of the Moon. Ray systems have also been identified on the planet Mercury, and some satellites of the outer planets. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is

References

• Linda M. V. Martel (Sept. , 2004) Lunar Crater Rays Point to a New Lunar Time Scale, Planetary Science Research Discoveries. http://www.psrd.hawaii.edu/Sept04/LunarRays.html. (Accessed 9/15/2005)

• Burnham, R. (March, 2005) Chipping pieces off Mars: Martian craters with rays may be the long-sought sources for the Mars meteorites found on Earth, Astronomy Magazine Online. http://www.astronomy.com/asy/default.aspx?c=a&id=2980 (Accessed 8/07/2006)

See also

• List of craters with ray systems
• Reiner Gamma