Crater ray system on the far side of the Moon. NASA photo credit.

A ray system compyourabitchrises the radial streaks of fine ejecta thrown out during the formation of an impact crater. 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). 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 resulting rays can extend for several multiples of the impact crater's diameter. Rays are often accompanied by small secondary craters formed by larger chunks of ejecta. Image File history File links Description: This brightly-rayed crater lies on the far side of the Moon. ... Image File history File links Description: This brightly-rayed crater lies on the far side of the Moon. ... Far side of the Moon. ... Bulk composition of the Moons mantle and crust estimated, weight percent Oxygen 42. ... NASA logo Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... In volcanology, ejecta consists of particles that came out of a volcanic vent, traveled though the air or under water, and fell back on the ground surface or on the ocean floor. ... Tycho crater on Earths moon. ... The eight planets and three dwarf planets of the Solar System. ... Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... Note: This article contains special characters. ... Zunil is a municipality in the Quetzaltenango department of Guatemala. ... In Greek mythology, Hesiod mentions Themis among the six sons and six daughters—of whom Cronos was one—of Gaia and Ouranos, that is, of Earth with Sky. ... Albedo is a ratio of scattered to incident electromagnetic radiation power, most commonly light. ... Ray may refer to: A fish in the order Batoidea, especially true rays of the family Rajiformes, such as stingrays Ray (optics), an idealized narrow beam of light An electrical ray, an old name for a laser beam Radiation, emission of energy in the form of waves or particles Ray... Diameter is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. ...

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 desposits on the lunar mares. These dark streaks can provide a contrast with higher albedo features, resulting in dark rays. Basalt Basalt is a common gray to black volcanic rock. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... A map showing the location of Mare Imbrium The Lunar maria (singular: mare, pronounced MAH-ray) are large, dark, basaltic plains on Earths Moon, formed by ancient basaltic flood eruptions caused by extremely large meteoroid impacts. ...

Gratteri crater, a "Thermal" crater ray system on Mars that was imaged by THEMIS at night. Each THEMIS observation is 32 km across (320 pixels across with a nominal pixel resolution of 100 meters per pixel). NASA/JPL/ASU/University of Tennessee photo credit.

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. They are especially apparent at night when slopes and shadows do not influence the infrared energy emitted by the Martian surface. Image File history File links Gratteri. ... Image File history File links Gratteri. ... Note: This article contains special characters. ... In Greek mythology, Hesiod mentions Themis among the six sons and six daughters—of whom Cronos was one—of Gaia and Ouranos, that is, of Earth with Sky. ... In Greek mythology, Hesiod mentions Themis among the six sons and six daughters—of whom Cronos was one—of Gaia and Ouranos, that is, of Earth with Sky. ... NASA logo Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... The JPL complex in Pasadena, Ca. ... In Greek mythology, Hesiod mentions Themis among the six sons and six daughters—of whom Cronos was one—of Gaia and Ouranos, that is, of Earth with Sky. ...

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. Micrometeorites in particular produces a glassy melt in the regolith that lowers the albedo. The rays can also become covered by lava flows, or by other impact craters or ejecta. Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ... Albedo is a ratio of scattered to incident electromagnetic radiation power, most commonly light. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ...

Lunar rays

Asymmetrical ray system about Proclus crater on the Moon. NASA photo.

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. Image File history File linksMetadata Download high-resolution version (900x909, 123 KB) This image of Proclus crater from the Moon was taken during the Apollo 15 mission. ... Image File history File linksMetadata Download high-resolution version (900x909, 123 KB) This image of Proclus crater from the Moon was taken during the Apollo 15 mission. ... Proclus is a young lunar impact crater located to the west of the Mare Crisium, on the east shore of the Palus Somni. ... NASA logo Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... The 1960s decade refers to the years from 1960 to 1969, inclusive. ...

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). 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. Similar ray systems also occur on the far side of the Moon, such as the rays radiating from the Giordano Bruno and Ohm craters. Ray systems have also been identified on the planet Mercury, and some satellites of the outer planets. Aristarchus is a prominent lunar impact crater that lies in the northwest part of the Moons near side. ... Copernicus is a prominent lunar impact crater located on the 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. ... Far side of the Moon. ... Giordano Bruno is a small lunar impact crater whose eponym is the Italian philosopher Giordano Bruno. ... Ohm is a lunar imapact crater that is located on the far side of the Moon. ... Note: This article contains special characters. ... MILSTAR:A communication satellite A satellite is any object that orbits another object (which is known as its primary). ... The eight planets and three dwarf planets of the Solar System. ...

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