![Fresh impact crater HiRise 2013](https://upload.wikimedia.org/wikipedia/commons/c/c8/Fresh_impact_crater_HiRise_2013.jpg)
A ray system comprises radial streaks of fine ''
ejecta
Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma ...
'' thrown out during the formation of an
impact crater, looking somewhat like many thin spokes coming from the hub of a wheel. The
rays may extend for lengths up to several times the
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
of their originating crater, and are often accompanied by small secondary craters formed by larger chunks of ejecta. Ray systems have been identified on the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
,
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
(
Kamil Crater),
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
, and some
moons of the outer planets. Originally it was thought that they existed only on
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s or moons lacking an
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, but more recently they have been identified on
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
in infrared images taken from orbit by ''
2001 Mars Odyssey
''2001 Mars Odyssey'' is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectr ...
''s
thermal imager.
Rays appear at visible, and in some cases infrared wavelengths, when ejecta are made of material with different reflectivity (i.e.,
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
) or thermal properties from the surface on which they are deposited. Typically, visible rays have a higher albedo than the surrounding surface. More rarely an impact will excavate low albedo material, for example
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic-
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
deposits on the
lunar maria. Thermal rays, as seen on Mars, 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 useful as an indicator of the relative age of the impact crater, because over time various processes obliterate the rays. On non-atmosphered bodies such as the Moon,
space weathering from exposure to
cosmic ray
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
s and
micrometeorites causes a steady reduction of the differential between the ejecta's albedo and that of the underlying material. Micrometeorites in particular produce a glassy melt in the
regolith that lowers the
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
. Rays can also become covered by
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
flows (such as those of
Lichtenberg on the moon), or by other impact craters or ejecta.
![Kuiper crater EW1065899876G](https://upload.wikimedia.org/wikipedia/commons/3/32/Kuiper_crater_EW1065899876G.jpg)
Lunar rays
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.
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
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
(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
Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formulated ...
,
Kepler
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...
,
Proclus
Proclus Lycius (; 8 February 412 – 17 April 485), called Proclus the Successor ( grc-gre, Πρόκλος ὁ Διάδοχος, ''Próklos ho Diádokhos''), was a Greek Neoplatonist philosopher, one of the last major classical philosophers ...
,
Dionysius
The name Dionysius (; el, Διονύσιος ''Dionysios'', "of Dionysus"; la, Dionysius) was common in classical and post-classical times. Etymologically it is a nominalized adjective formed with a -ios suffix from the stem Dionys- of the name ...
,
Glushko, and
Tycho. Smaller examples include
Censorinus
Censorinus was a Roman grammarian and miscellaneous writer from the 3rd century AD.
Biography
He was the author of a lost work ''De Accentibus'' and of an extant treatise ''De Die Natali'', written in 238, and dedicated to his patron Quintus ...
,
Stella
Stella or STELLA may refer to:
Art, entertainment, and media Comedy
*Stella (comedy group), a comedy troupe consisting of Michael Showalter, Michael Ian Black and David Wain
Characters
*Stella (given name), including a list of characters with th ...
, and
Linné
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
. Similar ray systems also occur on the
far side
''The Far Side'' is a single-panel comic created by Gary Larson and syndicated by Chronicle Features and then Universal Press Syndicate, which ran from December 31, 1979, to January 1, 1995 (when Larson retired as a cartoonist). Its surrealis ...
of the Moon, such as the rays radiating from the craters
Giordano Bruno
Giordano Bruno (; ; la, Iordanus Brunus Nolanus; born Filippo Bruno, January or February 1548 – 17 February 1600) was an Italian philosopher, mathematician, poet, cosmological theorist, and Hermetic occultist. He is known for his cosmologic ...
,
Necho,
Ohm
Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm.
Ohm or OHM may also refer to:
People
* Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm''
* Germán Ohm (born 1936), Mexican boxer
* Jörg Ohm (b ...
,
Jackson,
King
King is the title given to a male monarch in a variety of contexts. The female equivalent is queen, which title is also given to the consort of a king.
*In the context of prehistory, antiquity and contemporary indigenous peoples, the tit ...
, and the small but prominent
Pierazzo.
Most lateral transport of primary ejecta from impact craters is limited to a distance of a few crater radii, but some larger impacts, such as the impacts that made the
Copernicus
Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formulated ...
and
Tycho craters, launched primary ejecta halfway around the moon.
North Ray and
South Ray craters, each with a clear ray system, were observed from the ground by the astronauts of
Apollo 16
Apollo 16 (April 1627, 1972) was the tenth crewed mission in the United States Apollo space program, administered by NASA, and the fifth and penultimate to land on the Moon. It was the second of Apollo's " J missions", with an extended sta ...
in 1972.
Image:AS15-94-12836.jpg, Asymmetrical ray system about the lunar crater Proclus
Proclus Lycius (; 8 February 412 – 17 April 485), called Proclus the Successor ( grc-gre, Πρόκλος ὁ Διάδοχος, ''Próklos ho Diádokhos''), was a Greek Neoplatonist philosopher, one of the last major classical philosophers ...
(Apollo 15
Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the United States' Apollo program and the fourth to Moon landing, land on the Moon. It was the first List of Apollo missions#Alphabetical mission types, J mission, with a ...
image)
Image:Pierazzo crater Clementine mosaic.jpg, Pierazzo crater (Mosaic of Clementine images)
File:Giordano Bruno crater rays AS11-44-6665HR.jpg, The rays of Giordano Bruno
Giordano Bruno (; ; la, Iordanus Brunus Nolanus; born Filippo Bruno, January or February 1548 – 17 February 1600) was an Italian philosopher, mathematician, poet, cosmological theorist, and Hermetic occultist. He is known for his cosmologic ...
extend for hundreds of kilometers from the small crater (Apollo 11
Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon. Commander Neil Armstrong and lunar module pilot Buzz Aldrin landed the Apollo Lunar Module ''Eagle'' on July 20, 1969, at 20:17 UTC, an ...
image)
File:South Ray crater AS16-P-4618 ASU.jpg, South Ray (Apollo 16
Apollo 16 (April 1627, 1972) was the tenth crewed mission in the United States Apollo space program, administered by NASA, and the fifth and penultimate to land on the Moon. It was the second of Apollo's " J missions", with an extended sta ...
image)
See also
*
List of craters with ray systems
This is a list of craters with ray systems. In the following tables, the listed coordinates and the diameter are for the crater.
Mercury
The following craters on Mercury possess ray systems.
Mars
The following craters on Mars possess ray syst ...
*
Reiner Gamma
Reiner Gamma (γ) is a geographical feature of the Moon known as a lunar swirl. It is one of the most visible lunar swirls from Earth, visible from most telescopes. It was originally thought to be a lunar highland, but scientists eventually reali ...
References
Citations
Sources
* Martel, L.M.V. (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)
{{The Moon, state=collapsed
Impact craters