Difference between revisions 1862529 and 1900979 on enwikiversity

[[Image:Chain of impact craters on Ganymede.jpg|thumb|right|250px|The image shows a chain of craters on Ganymede. Credit: Galileo Project, Brown University, JPL, NASA.]]
A '''crater''' may be any large, roughly circular, depression or hole in or beneath the rocky surface of a rocky object.

'''Crater astronomy''' applies the techniques of astronomy to the apparent craters observed on rocky objects in an effort to understand what they are, when they occurred, and their importance to rocky objects.
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==Astronomy==
{{main|Astronomy/Keynote lecture}}
When any effort to acquire a system of laws or knowledge focusing on an ''astr'', ''aster'', or ''astro'', that is, any natural body in the sky especially at night,<ref name=Gove>{{ cite book
|author=
|title=Webster's Seventh New Collegiate Dictionary
|publisher=G. & C. Merriam Company
|location=Springfield, Massachusetts
|yeardate=1963
|editor=Philip B. Gove
|pages=1221
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=2011-08-26 }}</ref> succeeds in discovering or exploring craters even in its smallest [[measurement]], '''crater astronomy''' is the name of the effort and the result. Once an entity, source, or object has been detected as having craters, it may be necessary to determine what the mechanism is. Usually this information provides understanding of the same entity, source, or object. Craters suggests a violent event. The formation of craters on [[Earth]] may be associated with the sense of seeing as much as hearing, what can be termed [[acoustic astronomy]]. As telescope optics transmit visual light well, [[visual astronomy]] is a field associated with crater astronomy.

For crater astronomy, the proof of concept is demonstrated by unique or novel [[Astronomy/Keynote lecture|astronomy]] in any band that explores craters to reveal knowledge, especially regarding their formation.

==Radiation==
{{main|Radiation/Keynote lecture}}
Radiation that may produce a crater is likely larger than subatomic particles. The range of size and composition of this radiation is large. Such radiation may be rocky, liquid, gaseous, or plasma, a moving galaxy cluster, down to the size of an atom, molecule, or dust.

The characteristics of the crater likely depend on the energy of impact broken down into at least angle, speed, media, and dissipation.

==Planetary geology==
{{main|Planets/Geology|Planetary geology}}
[[Image:Moon-apollo17-schmitt boulder.jpg|thumb|right|2050px|Planetary geologist and NASA astronaut Harrison "Jack" Schmitt collects lunar samples during the Apollo 17 mission. Credit: NASA.]]
'''Planetary geology''', '''astrogeology''' or '''exogeology''', is a [[planetary science]] concerned with the [[geology]] of celestial bodies such as the planets and their [[Moon/Keynote lecture|moon]]s, asteroids, comets, and [[meteorites]]. It includes determining the internal structure of the terrestrial planets, planetary volcanism and surface processes such as impact craters, fluvial and aeolian processes.
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==Minerals==
{{main|Minerals}}
[[Image:LvMS-Lvm.jpg|thumb|left|2050px|The photomicrographs show of a sand grain held in an amorphous matrix, in plane-polarized light on top, cross-polarized light on bottom. Scale box in mm. Credit: [[w:User:Qfl247|Qfl247]].]]
[[Image:820qtz.jpg|thumb|left|2050px|This is a thin section with cross-polarized kight through a sand-sized quartz grain of 0.13 mm diameter. Credit: Glen A. Izett, USGS.]]
[[Image:Suvasvesi shocked quartz.jpg|thumb|right|2050px|This is a thin section of a shocked quartz grain. Credit: Martin Schmieder.]]
Alpha-quartz (space group ''P''3<sub>1</sub>21, no. 152, or ''P''3<sub>2</sub>21, no. 154) under a high pressure of 2-3 gigapascals and a moderately high temperature of 700°C changes space group to monoclinic ''C''2/c, no. 15, and becomes the mineral coesite. It is "found in extreme conditions such as the impact craters of meteorites.

(contracted; show full)tersecting sets of shock lamellae produced by the late Eocene Chesapeake Bay bolide impact. This shocked quartz grain is from the upper part of the crater-fill deposits at a depth of 820.6 ft in the core. The corehole is located at the NASA Langley Research Center, Hampton, VA, near the southwestern margin of the Chesapeake Bay impact crater."<ref name=Izett>{{ cite book
|author=Glen A. Izett
|title=Shocked Quartz from the USGS -- NASA Langley Core
|publisher=U. S. Geological Survey
|location=
|
monthdate=September 26,⏎
|year=  2000
|url=http://geology.er.usgs.gov/eespteam/crater/shockquartz.html
|accessdate=2012-10-23 }}</ref> "Very high pressures produced by strong shock waves cause dislocations in the crystal structure of quartz grains along preferred orientations. These dislocations appear as sets of parallel lamellae in the quartz when viewed with a petrographic microscope. Bolide impacts are the only natural process known to produce shock lamellae in quartz grains."<ref name=Izett/>

(contracted; show full)|bibcode=
|doi=10.1130/​0091-7613(1993)​021<0435:CASQDI>​2.3.CO;2
|pmid=
|accessdate=2012-10-23 }}</ref>
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==Theoretical crater astronomy==
[[Image:Mount Mazama eruption timeline.PNG|thumb|right|2
050px|Example of the formation of a caldera, the pictures show Mount Mazama's eruption timeline. Credit: .]]
A "cataclysm [may] have affected the entire inner Solar System ... [when] numerous main-belt asteroids ... were driven onto high-velocity and highly eccentric orbits by the effects of the late migration of the giant planets."<ref name=Marchi>{{ cite journal
(contracted; show full)

Catenae are thought to have been formed by the impact of a body that was broken up by tidal forces into a string of smaller objects following roughly the same orbit. An example of such a tidally disrupted body that was observed prior to its impact on [[Jupiter]] is Comet Shoemaker-Levy 9.

Catenae on [[Mars]], represent chains of collapse pits associated with grabens (see, for example, the Tithoniae Catenae near Tithonium Chasma).

Crater chains seen on the [[Moon
/Keynote lecture|Moon]] often radiate from larger craters, and in such cases are thought to be either caused by secondary impacts of the larger crater's ejecta or by volcanic venting activity along a rift.<ref name=Apollo>{{ cite book
|url=http://www.hq.nasa.gov/office/pao/History/SP-362/ch5.3.htm
|title=Apollo over  the Moon - Chapter 5: Craters
|accessdate=2008-02-03 }}</ref>
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==Entities==
{{main|Radiation astronomy/Entities|Entities}}
[[Image:Vulkanbombeneinschlag.png|thumb|right|2050px|A volcanic bomb has deformed the rock strata. Credit: [[:de:User:Drucker03|Drucker03]].]]
'''Def.'''
# the study of rock layers and the layering process of stratification or
# the layering of deposits, with newer remains overlaying older ones, forming a chronology of the site

is called '''stratigraphy'''.

(contracted; show full)
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==Sources==
{{main|Radiation astronomy/Sources|Radiation astronomy sources|Sources}}
[[Image:Mount Tambora Volcano, Sumbawa Island, Indonesia.jpg|thumb|right|2
050px|This detailed astronaut photograph depicts the summit caldera of the Mount Tambora. Credit: NASA ISS Expedition 20 crew.]]
[[Image:Santa Ana Volcano.USAF.C-130.3.jpg|right|thumb|2050px|The crater in Santa Ana Volcano is photographed from a United States Air Force C-130 Hercules flying above El Salvador. Credit: .]]
[[Image:Karthala volcano-Comoros.jpg|thumb|left|2050px|The view is into Karthala volcano crater in November 2006 at the solidified lava lake Credit: alKomor.com.]]
[[Image:SP Crater.jpg|thumb|right|2050px|S P Crater is a cinder cone volcano in the San Francisco volcanic field. Credit: .]]
The first image at right is a "detailed astronaut photograph [that] depicts the summit caldera of the volcano. The huge caldera—6 kilometers (3.7 miles) in diameter and 1,100 meters (3,609 feet) deep—formed when Tambora’s estimated 4,000-meter- (13,123-foot) high peak was removed, and the magma chamber below emptied during the April 10 eruption. Today the crater floor is occupied by an ephemeral freshwater lake, recent sedimentary deposits, and minor lava flows and domes from the nineteenth and twentieth centuries. Layered tephra deposits are visible along the northwestern crater rim. Active fumaroles, or steam vents, still exist in the caldera."<ref name=Wiscombe>{{ cite book
|author=Warren Wiscombe
|title=Mount Tambora Volcano, Sumbawa Island, Indonesia
|publisher=NASA Earth Observatory
|location=
|monthdate=July 19,⏎
|year=  2009
|url=http://earthobservatory.nasa.gov/IOTD/view.php?id=39412
|accessdate=2013-03-30 }}</ref>

"On April 10, 1815, the Tambora Volcano produced the largest eruption in recorded history. An estimated 150 cubic kilometers (36 cubic miles) of tephra—exploded rock and ash—resulted, with ash from the eruption recognized at least 1,300 kilometers (808 miles) away to the northwest. While the April 10 eruption was catastrophic, historical records and geological analysis of eruption deposits indicate (contracted; show full)
|author=Ulrich, G E
|title=SP Mountain cinder cone and lava flow, northern Arizona
|publisher=Geological Society of American Centennial Field Guide – Rocky Mountain Section
|
yeardate=1987
|pages=385–8 }}</ref> However, there is some debate about the relationship between the cone and flow as it is not uncommon to form cinder cones during the early phase of an eruption as a magma degasses, and then to have lava push through the side of a cone during a late phase of eruption.

K/Ar dates on the lava are ~ 70 ka,<ref name=Basksi>{{cite journal
|author=Basksi  A, K
|title=K-Ar study of the S.P. flow
|journal=Canadian Journal of Earth Sciences
|year=1974
(contracted; show full)|doi=
|pmid=
|accessdate=2013-10-18 }}</ref>
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==Objects==
{{main|Radiation astronomy/Objects|Object astronomy|Objects}}
[[Image:Mare Imbrium-Apollo17.jpg|thumb|2
050px|right|Mare Imbrium (foreground) is peppered with secondary craters from the impact that formed Copernicus crater (upper center). Credit: NASA.]]
'''Def.''' a hemispherical pit, a basinlike opening or mouth about which a cone is often built up, any large roughly circular depression or hole is called a '''crater'''.

(contracted; show full)|doi=
|pmid=
|accessdate=2013-10-18 }}</ref>
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==Strong forces==
{{main|Charges/Interactions/Strong|Strong forces}}
[[Image:La Cumbre - ISS.JPG|thumb|right|2
050px|This satellite photograph is of the summit caldera on Fernandina Island in the Galapagos archipelago. Credit: .]]
[[Image:Pinatubo92pinatubo caldera crater lake.jpg|thumb|left|2050px|Mt.Pinatubo is in the Philippines. Credit: .]]
[[Image:Crater lake oregon.jpg|thumb|left|2050px|Crater Lake, Oregon, formed around 5,680 BC. Credit: .]]
[[Image:Aniakchak-caldera alaska.jpg|thumb|left|2050px|Aniakchak-caldera, Alaska shows a characteristic caldera. Credit: .]]
A '''caldera''' is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters. The word comes from Spanish ''caldera'', and this from Latin <small>CALDARIA</small>, meaning "cooking pot". In some texts the English term ''cauldron'' is also used.

(contracted; show full)ave proposed that the human race was reduced to approximately five to ten thousand people.<ref name=Supervolcano>[http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml Supervolcanoes], BBC2, 3 February 2000</ref> Whichever figure is right, the fact remains that the human race seemingly came close to extinction about 75,000 years ago.
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==Electromagnetics==
{{main|Charges/Interactions/Electromagnetics|Electromagnetics}}
[[Image:Davy Crater region hi res.jpg|thumb|right|2
050px|The Davy crater chain (arrow) is one of the most spectacular chains of craters on the Moon. Credit: NASA.]]
The image at page top right shows a chain of 13 craters (Enki Catena) on Ganymede measuring 161.3 km in length. The Enki craters formed across the sharp boundary between areas of bright terrain and dark terrain, delimited by a thin trough running diagonally across the center of this image. The ejecta deposit surrounding the craters appears very bright on the bright terrain. Even though all the cra(contracted; show full)
|author=Harold Masursky, G. W. Colton, and Farouk El-Baz
|title=APOLLO OVER THE MOON: A VIEW FROM ORBIT (NASA SP-362), Cahpter 5: Craters (3/6)
|publisher=NASA Headquarters
|location=Washington, DC USA
|
monthdate=December⏎
|year=  1978
|url=http://www.hq.nasa.gov/office/pao/History/SP-362/ch5.3.htm
|accessdate=2013-03-31 }}</ref>

“Electrical currents flow in [plasmas], punching into long filaments and then braiding themselves into ropelike structures. These long, twisted filaments are visible in solar prominences, galactic jets, and comet tails. They were detected as “stringy things” in the forty-million-kilometer-long tail of Venus last year.”<ref name=Acheson>{{ cite book
|author=Mel and Amy Acheson
|title=Thunderbolts of the Gods: Does Growing Evidence of an Electric Universe Reveal Previously Hidden Meaning in ancient Mythology?, In: ''Forbidden History Prehistoric Technologies, Extraterrestrial Intervention, and the Suppressed Origins of Civilization''
|publisher=Bear & Company
|location=Rochester, Vermont
|month=
|yeardate=2005
|editor=J. Douglas Kenyon
|pages=69-77
|url=http://books.google.com/books?hl=en&lr=&id=DBDe-vhGTR0C&oi=fnd&pg=PP1&ots=CIEnZrYfQI&sig=4waK0rG-TNNQwTqCAT9FpPp3WLI#v=onepage&f=false
|arxiv=
|bibcode=
|doi=
|pmid=
(contracted; show full)|bibcode=1988LPI....19..701L
|doi=
|pmid=
|accessdate=2013-10-18 }}</ref>

==Emissions==
{{main|Radiation astronomy/Emissions|Emission astronomy|Emissions}}
[[Image:Toba zoom.jpg|thumb|left|2
050px|Landsat captures an image of Lake Toba, on the island of Sumatra, Indonesia. Credit: .]]
[[Image:Whetstone Sulky 001.jpg|thumb|right|2050px|Rubble mound, or dome, formed by the Operation Whetstone Sulky explosion. Credit: .]]
[[Image:Callisto Har PIA01054.jpg|thumb|right|2050px|This is a Galileo image of Hár. Credit: NASA.]]
[[Image:Panum Crater.jpg|thumb|right|2050px|This is an image of Panum Crater with its central lava dome, Mono Craters, California, USA. Credit: USGS.]]
A resurgent dome forms the island of Samosir within the caldera of Lake Toba. It is 100 km/62 mi long and 30 km/19 mi wide, a caldera of the world's largest class.

When the material above the explosion is solid rock, then a mound may be formed by broken rock that has a greater volume. This type of mound has been called "retarc", "crater" spelled backwards.<ref name=nwa_effects>{{ cite book|last=Sublette|first=Carey|title=The Effects of Underground Explosions|url=http://nuclearweaponarchive.org/Library/Effects/UndergroundEffects.html|work=Nuclear Weapon Archive|accessdate=21 June 2011}}</ref>

'''Hár''' is a crater on [[Jupiter/Keynote lecture|Jupiter]]'s moon [[Callisto]]. Its name is one of the many names of Odin, the supreme god in Norse mythology. This is an example of a central dome impact crater.<ref name=Greeley>{{ cite journal
| last=Greeley| first=R.| coauthors=Klemaszewski, J.E.;Wagner L.; et al.
| title=Galileo views of the geology of Callisto
|journal=Planetary and Space Science
| year=2000
| volume=48
| issue=9
| pages=829–853
| doi=10.1016/S0032-0633(00)00050-7
|bibcode=2000P&SS...48..829G}}</ref>

"The name Panum Crater refers to a crater surrounded by [an] ejecta ring, with a dome in the middle. At Panum Crater the dome didn't completely fill the crater or overrun the ring (as often happens) providing an opportunity to explore all three structures."<ref name=Sieh>{{ cite book
|author=Kerry Sieh
|title=Long Valley Caldera Field Guide - Panum Crater
|publisher=USGS
|location=
|monthdate=January 31,⏎
|year=  2012
|url=http://volcanoes.usgs.gov/volcanoes/long_valley/long_valley_sub_page_17.html
|accessdate=2013-03-30 }}</ref>

"At Panum, a pyroclastic eruption (new magma explosively fragmented into the air) followed the phreatic (steam) eruption. During a pyroclastic eruption, the gas within the magma continues to expand and escape as the magma is thrown into the air and cools. The resulting deposits included ash (particles <2mm in size) and pumice. The pumice is frothy preserving the frozen gas bu(contracted; show full)
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==Absorptions==
{{main|Radiation astronomy/Absorptions|Absorption astronomy|Absorptions}}
[[Image:Sedan Plowshare Crater.jpg|thumb|right|2
050px|This image shows the crater created by the Sedan shallow underground nuclear test explosion. Credit: National Nuclear Security Administration, Federal Government of the United States.]]
[[Image:Stylised crater.png|thumb|left|2050px|This diagram depicts a stylized cross-section of a crater formed by a below-ground explosion. Credit: [[w:User:JBel|JBel]].]]
[[Image:Huron King Crater.jpg|thumb|right|2050px|Post-shot subsidence crater and Operation Tinderbox Huron King test chamber is from an explosion of less than 20 TNT equivalent kilotons (1980). Credit: .]]
[[Image:Callisto Tindr PIA01657.jpg|right|thumb|250px|The image shows a Galileo image of Tindr. Credit: .]]
[[Image:Elura.png|right|thumb|2050px|Sub-Level Caving Subsidence reaches surface at the Ridgeway underground mine. Credit: Rolinator.]]
[[Image:Škocjan, Divača - naravni most med Veliko in Malo dolino.jpg|thumb|left|2050px|This is the gorge where the Reka River disappears underground. Credit: [http://www.flickr.com/people/53197929@N00 Dennis Tang] from London, UK.]]
[[Image:Unterflöz 12.jpg|thumb|right|2050px|A photograph shows a collapsed mine tunnel to the west of № VI Conow adit. Credit: Bernd Triller, Bergamt Stralsund; Recherche:[[commons:User:Berginspektor|Berginspektor]].]]
[[Image:Makhtesh Hazera.jpg|thumb|left|2050px|This image is an oblique aerial photo of Makhtesh Hazera. Credit: N. Fruchter, A. Matmon, Y. Avni, and D. Fink.]]
The image at right shows the crater created by the Sedan shallow underground nuclear test explosion.

At left is a stylised cross-section of a crater formed by a below-ground explosion.

(contracted; show full)

When a drilling oil well encounters high-pressured gas which cannot be contained either by the weight of the drilling mud or by blow-out preventers, the resulting violent eruption can create a large crater which can swallow up a drilling rig. This phenomenon is called "cratering" in oil field slang.

An image of Tindr is shown at right. It is a pit crater.

'''Tindr''' is a crater on 
[[Jupiter]]'s moon Callisto. It is named after one of the ancestors of Ottar in Norse mythology. This is an example of a central pit impact crater.<ref name=Greeley/>

Removal of material and rock beneath a surface may result in a collapse of material above into the cavern below.

(contracted; show full)|accessdate=2013-10-16 }}</ref>

At lower left, the image is an oblique aerial photo of Makhtesh Hazera. The Makhtesh drainage divide is outlined by a bold black line, with both of its constituent features (the anticlinal valley and the Upper Basin) located.<ref name=Fruchter/>
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==Bands==
{{main|Radiation astronomy/Bands|Band astronomy}}
[[Image:Tycho crater on the Moon.jpg|thumb|right|2
050px|The prominent impact crater is Tycho on the Moon. Credit: NASA.]]
[[Image:Impact movie.ogg|thumb|left|2050px|A laboratory simulation of an impact event and crater formation is shown. Credit: .]]
[[Image:Craterstructure.gif|thumb|right|2050px|Impact crater structure is diagrammed. Credit: .]]
[[Image:Wells creek shatter cones 2.JPG|thumb|left|2050px|Close-up of shatter cones developed in fine grained dolomite from the Wells Creek crater, USA, are shown. Credit: .]]
[[Image:USGS Decorah crater.jpg|thumb|right|2050px|U.S. Geological Survey aerial electromagnetic resistivity map of the Decorah crater has been produced. Credit: .]]
[[Image:Crater 24.jpg|thumb|right|2050px|The image shows a crater produced by missile impact in silty sand and sandy silt, oblique view. Credit: US Army.]]
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 a larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other solid body in the [[Solar System]], formed by the hypervel(contracted; show full)

At right is a "[r]ecent airborne geophysical surveys near Decorah, Iowa [which is] providing an unprecedented look at a 470- million-year-old meteorite crater concealed beneath bedrock and sediments."<ref name=Koontz>{{ cite book
|author=Heidi Koontz and Robert McKay
|title=Iowa Meteorite Crater Confirmed
|publisher=U.S. Geological Survey
|location=12201 Sunrise Valley Dr, MS 119 Reston, Virginia 20192 USA
|
monthdate=March 5,⏎
|year=  2013
|url=http://www.usgs.gov/newsroom/article.asp?ID=3521#.UVfS467Qorc
|accessdate=2013-03-30 }}</ref>

"Capturing images of an ancient meteorite impact was a huge bonus," said Dr. Paul Bedrosian, a USGS geophysicist in Denver who is leading the effort to model the recently acquired geophysical data.<ref name=Koontz/> "These findings highlight the range of applications that these geophysical methods can address."<ref name=Koontz/>

(contracted; show full)
|author=Henry J. Moore
|title=Missile impact craters (White Sands Missile Range, New Mexico) and applications to lunar research: Contributions to astrogeology
|publisher=USGS
|location=Washington, DC USA
|
month=
|yeardate=1976
|url=http://pubs.usgs.gov/pp/0812b/report.pdf
|accessdate=2014-06-13 }}</ref>

"Craters in natural materials at White Sands Missile Range, N. Mex., were produced by the impact of high-velocity to hypervelocity missiles traveling along oblique trajectories with kinetic energies between 2.1 and 81 x 10<sup>14</sup> ergs. The oblique impacts produce craters 2 to 10 m across with morphologies and ejecta that are bilaterally symmetrical with respect to the plane of the missile trajectory. Rims are high and the amount of ejecta large in down-trajectory and lateral directions, whereas rims are low to nonexistent and ejecta thin to absent up-trajectory. Symmetry development and modifications of the symmetry are a function of target material, local topography, and angle of impact."<ref name=Moore/>
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==Mercury==
{{main|Mercury}}
[[Image:Mercury Globe-MESSENGER mosaic centered at 0degN-0degE.jpg|thumb|right|2050px|This is a composite image of Mercury taken by the MESSENGER probe. Credit: .]]
[[Image:Mariner 10.jpg|thumb|left|2050px|Mariner&nbsp;10 is the first probe to visit the innermost planet (1974–75). Credit: .]]
{{multiple image
| align = left
| direction = horizontal
| width = 230
| image1 = Caloris basin labeled.png
| caption1 = Mercury's Caloris Basin is one of the largest impact features in the Solar System
| image2 = Mercury weird terrain.jpg
| caption2 = The so-called "Weird Terrain" was formed at the point antipodal to the Caloris Basin impact
}}
[[Image:Stevenson crater (MESSENGER).png|thumb|right|2050px|This is a MESSENGER image of catena on Mercury. Credit: NASA, JPL, APL (Jet Propulsion Laboratory).]]
Mercury's surface is heavily cratered and similar in appearance to Earth's [[Moon/Keynote lecture|Moon]]. For example, an unusual crater with radiating troughs has been discovered which scientists called "the spider."<ref>{{cite newsbook
 | author=Staff | title=Scientists see Mercury in a new light
 | url=http://www.sciencedaily.com/releases/2008/02/080201093149.htm
 | publisher=Science Daily | date=February 28, 2008
 | accessdate=2008-04-07 }}</ref> ... Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that the area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity.<ref name=Spudis01>{{cite journal
(contracted; show full)

Overall, about 15 impact basins have been identified on the imaged part of Mercury. A notable basin is the 400&nbsp;km wide, multi-ring Tolstoj Basin which has an ejecta blanket extending up to 500&nbsp;km from its rim and a floor that has been filled by smooth plains materials. Beethoven Basin has a similar-sized ejecta blanket and a 625&nbsp;km diameter rim.<ref name="Spudis01" /> Like the [[Moon
/Keynote lecture|Moon]], the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts.<ref name=Denevi>{{ cite journal
 | title=Albedo of Immature Mercurian Crustal Materials: Evidence for the Presence of Ferrous Iron
 | journal=Lunar and Planetary Science | volume=39 | year=2008 | page=1750
 | last=Denevi | first=B. W. | coauthors=Robinson, M. S.
 | bibcode=2008LPI....39.1750D
 | last2=Robinson }}</ref>

(contracted; show full)Mariner&nbsp;10 provided the first close-up images of Mercury's surface, which immediately showed its heavily cratered nature

At right is an example of catena on Mercury.
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==Venus==
{{main|Venus}}
[[Image:Mgn p39146.png|thumb|right|2
050px|Impact craters on the surface of Venus (image reconstructed from radar data) are shown. Credit: NASA.]]
The absence of evidence of lava flow accompanying any of the visible caldera remains an enigma. The planet has few impact craters.

After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne.<ref>{{ cite book
|url=http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html
(contracted; show full)|volume=112
|issue=1
|pages=253–281
|doi=10.1006/icar.1994.1180
|bibcode=1994Icar..112..253H }}</ref> Incoming projectiles less than 50 meters in diameter will fragment and burn up in the atmosphere before reaching the ground.<ref name=Morrison>{{ cite book
|title = The Planetary System
|author = David Morrison
|
yeardate = 2003
|publisher = Benjamin Cummings
|isbn = 0-8053-8734-X }}</ref>
{{clear}}

==Earth==
{{main|Earth}}
[[Image:Barringer Crater aerial photo by USGS.jpg|thumb|left|2050px|This is an aerial view of the Barringer Meteor Crater about 69 km east of Flagstaff, Arizona USA. Credit: D. Roddy, U.S. Geological Survey (USGS).]]
[[Image:Meteor Crater - Arizona.jpg|thumb|right|2050px|This is a Landsat image of the Barringer Meteor Crater from space. Credit: National Map Seamless Server, NASA Earth Observatory.]]
[[Image:Canyon-diablo-meteorite.jpg|thumb|right|2050px|This is an image of the Canyon Diablo iron meteorite (IIIAB) 2,641 grams. Credit: Geoffrey Notkin, Aerolite Meteorites of Tucson, [[w:User:Geoking42|Geoking42]].]]
[[Image:Meteor Crater 08 2010 151.JPG|thumb|right|2050px|The Holsinger meteorite is the largest discovered fragment of the meteorite that created Meteor Crater and it is exhibited in the crater visitor center. Credit: [[commons:User:Mariordo|Mariordo]] Mario Roberto Duran Ortiz.]]
[[Image:Yucatan chix crater.jpg|thumb|right|1250px|The Chicxulub impact crater is outlined. Credit: NASA/JPL-Caltech, modified by [[w:User:David Fuchs|David Fuchs]].]]
[[Image:Aurora Borealis.jpg|thumb|right|2050px|Aurora Borealis is photographed by NASA astronaut Donald R. Pettit. Credit: NASA.]]
[[Image:392171ab.eps.2.gif|thumb|right|300px|The figure shows a reconstruction of the North American (Laurentian) and Eurasian plate positions in the Northern Hemisphere of Earth 214 Myr ago (Mercator projection), with the locations of the five impact structures marked. Credit: John G. Spray, Simon P. Kelley & David B. Rowley.]]
[[Image:Tundra thaw crater.jpg|left|thumb|2050px|This is one of the giant craters discovered on the Yamal Peninsula. Credit: Vasily Bogoyavlensky/AFP/Getty Images.{{tlx|fairuse}}]]
In the image at left is an aerial view of the Barringer Meteor Crater about 69 km east of Flagstaff, Arizona USA. Although similar to the aerial view of the Soudan crater, the Barringer Meteor Crater appears angular at the farthest ends rather than round.

(contracted; show full)

"More recently, a huge explosion was heard in June [2017] in the Yamal Peninsula. Reindeer herders camped nearby saw flames shooting up with pillars of smoke and found a large crater left in the ground. Melting permafrost was again suspected, thawing out dead vegetation and erupting in a blowout of highly flammable methane gas."<ref name=Plester>{{ cite book
|author=Jeremy Plester
|title=All hell breaks loose as the tundra thaws
|publisher=The Guardian
|location=
|
monthdate=20 July⏎
|year=  2017
|url=https://www.theguardian.com/environment/2017/jul/20/hell-breaks-loose-tundra-thaws-weatherwatch#img-1
|accessdate=2017-07-31 }}</ref>

"Over the past three years, 14 other giant craters have been found in the region, some of them truly massive – the first one discovered was around 50m (160ft) wide and about 70m (230ft) deep, with steep sides and debris spread all around."<ref name=Plester/>

(contracted; show full)"When [permafrosts] release carbon, it will accelerate the rate of warming in the future."<ref name=Henderson/>

"All these hypotheses [on how the craters are formed], though, use the fact that temperature in the region is increasing."<ref name=Romanovsky>{{ cite book
|author=Vladimir Romanovsky
|title=Mysterious craters blowing out of Russia could mean trouble for the whole planet
|publisher=Yahoo News
|location=
|
monthdate=30 July⏎
|year=  2017
|url=https://www.yahoo.com/news/m/da88ff71-92f7-3f97-a8c7-705d13f80680/mysterious-craters-blowing.html?.tsrc=daily_mail&uh_test=2_04
|accessdate=2017-07-31 }}</ref>

"There is no estimate for how much methane is released into the atmosphere because we don't know how [to measure it]."<ref name=Romanovsky/>

"People in permafrost regions rely on frozen ground for their infrastructure. As the ground melts, the railway collapses, the roads fall apart, the buildings sink into the ground … It's happening already."<ref name=Henderson/>
{{clear}}

==Moon==
{{main|Wanderers/Moon|Moon/Keynote lecture}}
[[Image:Carte Lune mers crateres.jpg|thumb|right|2050px|The image is a map in French of the Moon showing the maria and the major craters. Credit: additions made to Lune22h27septembre2004.jpg created by Yves under GFDL by Eric Gaba ([[commons:User:Sting|Sting]] - fr:Sting).]]
[[Image:Full moon.jpeg|thumb|2050px|left|Composite image of the Moon is taken by the Galileo spacecraft on 7 December 1992. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision. Credit: NASA/JPL/USGS.]]
[[Image:Moon names.svg|thumb|right|2050px|Lunar nearside, major maria and craters are labeled. Credit: [[commons:User:Peter Freiman|Peter Freiman]], [[commons:User:Cmglee|Cmglee]], and background photograph by Gregory H. Revera.]]
[[Image:Moon South Pole.jpg|thumb|left|250px|alt=Twenty degrees of latitude of the Moon's disk, completely covered in the overlapping circles of craters. The illumination angles are from all directions, keeping almost all the crater floors in sunlight, but a set of merged crater floors right at the south pole are completely shadowed. Mosaic image of the lunar south pole as taken by ''Clementine'': note permanent polar shadow. Credit: NASA/JPL-Caltech.]]
[[Image:The Moon's North Pole.jpg|thumb|right|2050px|The Moon's north pole is shown during the summer. Credit: NASA/GSFC/Arizona State University.]]
[[Image:Moon Farside LRO.jpg|thumb|right|2050px|This full disk is nearly featureless, a uniform grey surface with almost no dark mare. There are many bright overlapping dots of impact craters. Credit: NASA/GSFC/ASU LRO.]]
[[Image:MoonTopoLOLA.png|thumb|left|2050px|Topography of the [[Moon]] measured from the Lunar Orbiter Laser Altimeter on the Lunar Reconnaissance Orbiter mission, referenced to a sphere of radius 1737.4&nbsp;km. Credit: Mark A. Wieczorek.]]
[[Image:Water Around Fresh Moon Crater.jpg|thumb|right|2050px|These images show a very young lunar crater on the side of the moon that faces away from Earth. Credit: ISRO/NASA/JPL-Caltech/USGS/Brown Univ.]]
[[Image:GRAIL's gravity map of the moon.jpg|thumb|right|2050px|This image shows the variations in the lunar gravity field as measured by NASA's Gravity Recovery and Interior Laboratory (GRAIL) during the primary mapping mission from March to May 2012. Credit: NASA/JPL-Caltech/MIT/GSFC.]]
[[Image:Davy_crater.png|right|thumb|2050px|Lunar crater Davy is at top and Catena Davy below, as seen from Apollo 12. Credit: NASA.]]
[[Image:Small crater in Daguerre crater AS16-P-4511.jpg|left|thumb|250px|Oblique view is facing south of a small, fresh impact crater within the larger Daguerre crater, Mare Nectaris, the moon. Credit: James Stuby.{{tlx|free media}}]]
Lunar craters "are pits or depressions in the surface of the Moon, produced by great impacts of gigantic meteoroids which mostly took place billions of years ago. They range in size from huge walled plains more than a hundred miles across to microscopic pits. The smallest craters which can be glimpsed through ordinary binoculars are about twenty miles across. These craters are most common in the light-colored Lunar highlands. They are named after historical figures, mostly scientists."<ref name=FountainsofBrynMawr>{{ cite book
|author=Fountains of Bryn Mawr
|title=Skygazing
|monthdate=October 30,⏎
|year=  2008
|url=http://en.wikiversity.org/w/index.php?title=Skygazing&oldid=367815
|accessdate=2013-03-30 }}</ref>

"During its flight, the Galileo spacecraft returned images of the Moon. The Galileo spacecraft took these images on December 7, 1992 on its way to explore the Jupiter system in 1995-97. The distinct bright ray crater at the bottom of the image is the Tycho impact basin. The dark areas are lava rock filled impact basins: Oceanus Procellarum (on the left), Mare Imbrium (center left), Mare Serenitatis and Mare Tranquillitatis (center), and Mare Crisium (near the right edge). This picture contains images through the Violet, 756 nm, 968 nm filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision."<ref name=Nelson>{{ cite book
|author=Jon Nelson
|title=Earth's Moon
|publisher=NASA/JPL/USGS
|location=
|monthdate=June 8,⏎
|year=  1998
|url=http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00405
|accessdate=2012-09-26 }}</ref>

The dark irregular mare lava plains are prominent in the fully illuminated disk. A single bright star of ejecta, with rays stretching a third of the way across the disk, emblazons the lower centre: this is the crater Tycho on the Near side of the Moon. But, on the far side, the full disk is nearly featureless, a uniform grey surface with almost no dark mare. There are many bright overlapping dots of (contracted; show full)
|title = The Biggest Hole in the Solar System|last = Taylor|first = G.J.
|date = 17 July 1998
|publisher = Planetary Science Research Discoveries, Hawai'i Institute of Geophysics and Planetology
|accessdate =12 April 2007 }}</ref> The highest elevations are found just to its north-east, and it has been suggested that this area might have been thickened by the oblique formation impact of South Pole – Aitken.<ref name=Schultz>{{cite journal
|last=Schultz|first=P. H.
|date=
03/March 1997
|page=1259
|volume=28
|title=Forming the south-pole Aitken basin – The extreme games|journal=Conference Paper, 28th Annual Lunar and Planetary Science Conference
|bibcode=1997LPI....28.1259S }}</ref> Other large impact basins, such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims.<ref name="Spudis1994">{{ cite journal
| doi = 10.1126/science.266.5192.1848
| last = Spudis
| first = Paul D.
(contracted; show full)er [M<sup>3</sup>] on the Indian Space Research Organization's Chandrayaan-1 spacecraft. On the left is an image showing brightness at shorter infrared wavelengths. On the right, the distribution of water-rich minerals (light blue) is shown around a small crater. Both water- and hydroxyl-rich materials were found to be associated with material ejected from the crater."<ref name=Wilson>{{ cite book
|author=Jim Wilson
|title=Water Around a Fresh Crater
|publisher=NASA
|location=
|
monthdate=September 24,⏎
|year=  2009
|url=http://www.nasa.gov/topics/moonmars/features/clark3.html
|accessdate=2012-09-26 }}</ref>

"Very precise microwave measurements between two spacecraft, named Ebb and Flow, were used to map gravity with high precision and high spatial resolution. The field shown [at right] resolves blocks on the surface of about 12 miles (20 kilometres) and measurements are three to five orders of magnitude improved over previous data. Red corresponds to mass excesses and blue corresponds to mass deficiencies. The map shows more small-scale detail on the far side of the moon compared to the nearside because the far side has many more small craters."<ref name=Greicius>{{ cite book
|author=Tony Greicius
|title=GRAIL's Gravity Map of the Moon
|publisher=NASA/JPL-Caltech/MIT/GSFC
|location=
|monthdate=December 6,⏎
|year=  2012
|url=http://www.nasa.gov/mission_pages/grail/multimedia/zuber4.html
|accessdate=2012-12-15 }}</ref>

"Crystallized spheres of orange glass from Shorty Crater at the Apollo 17 site are ... the characteristic ingredient of the dark mantling deposit of the Taurus-Littrow region."<ref name=Adams>{{ cite journal
|author=John B. Adams, Carle Pieters, and Thomas B. McCord
(contracted; show full)y is a linear string of 23 tiny craters [that] runs from the midpoint of Davy Y towards the walled basin Ptolemaeus, following a slightly curving course to the east-northeast. It is located at selenographic coordinates 11.0° S, 7.0° W, and has a diameter of 50&nbsp;km. It is not radial to a suitable source crater. High resolution images have demonstrated that the craters formed at about the same time since the ejecta from each crater does not overlay neighboring craters.
{{clear}}

==Mars==
{{main|Mars
/Keynote lecture}}
[[Image:PIA15038 Spirit Lander and Bonneville Crater in Color.jpg|thumb|right|2050px|Near the lower left corner of this view of Bonneville Crater is the three-petal lander platform that NASA's Mars Exploration Rover Spirit drove off in January 2004. Credit: NASA/JPL-Caltech/Univ. of Arizona.]]
[[Image:Olympus Mons alt.jpg|thumb|right|2050px|This is a top down view of Olympus Mons, the Solar system's largest known volcano. Credit: ]]
[[Image:Mars rampart crater.jpg|thumb|left|2050px|This is an image of the Rampart Crater. Credit: NASA.]]
"Near the lower left corner of this view [at right] is the three-petal lander platform that NASA's Mars Exploration Rover Spirit drove off in January 2004. The lander is still bright, but with a reddish color, probably due to accumulation of Martian dust."<ref name=HiRise>{{ cite book
|author=HiRise
|title=PIA15038: Spirit Lander and Bonneville Crater in Color 
|publisher=NASA/JPL
|location=Pasadena, California USA
|monthdate=February 8,⏎
|year=  2012
|url=http://photojournal.jpl.nasa.gov/catalog/PIA15038
|accessdate=2013-03-31 }}</ref>

"The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded this view on Jan. 29, 2012, providing the first image from orbit to show Spirit's lander platform in color. The view covers an area about 2,000 feet (about 600 meters) wide, dominated by Bonneveille Crater. North is up. A bright spot on the northern edge of Bonneville Crater is a remnant of Spirit's heat shield."<ref name=HiRise/>

The shield volcano, Olympus Mons [shown in the second image at right] (''Mount Olympus''), at 27&nbsp;km is the second highest known mountain in the Solar System.<ref name="glenday09">{{cite book
|author=Craig Glenday
|yeardate=2009
|page=12
|title=Guinness World Records
|publisher=Random House, Inc.
|isbn=0-553-59256-4 }}</ref> It is an extinct volcano in the vast upland region Tharsis, which contains several other large volcanoes. Olympus Mons is over three times the height of Mount Everest, which in comparison stands at just over 8.8&nbsp;km.<ref name="scsdes49">{{cite journal
|author=Junyong Chen, ''et al''.
(contracted; show full)ller ones are only found in the high latitudes where ice is predicted to be close to the surface. It seems that the impact has to be powerful enough to penetrate to the level of the subsurface ice. Since ice is thought to be close to the surface in latitudes far from the equator, it does not take too strong of an impact to reach the ice level.<ref name="Kieffer1992">{{ cite book
|author=Hugh H. Kieffer
|title=Mars
|url=http://books.google.com/books?id=NoDvAAAAMAAJ
|accessdate=7 March 2011
|
yeardate=1992
|publisher=University of Arizona Press
|isbn=978-0-8165-1257-7 }}</ref> So, based on images from the Viking program in the 1970s, it is generally accepted that rampart craters are evidence of ice or liquid water beneath the surface of Mars. The impact melts or boils the water in the subsurface producing a distinctive pattern of material surrounding the crater.
{{clear}}

==Vesta==
{{main|Wanderers/Vesta|Vesta}}
"The [NASA's Dawn spacecraft] Framing Camera (FC) discovered enigmatic orange material on [[Vesta]]. FC images revealed diffuse orange ejecta around two impact craters, 34-km diameter Oppis, and 30-km diameter Octavia, as well as numerous sharp-edge orange units in the equatorial region."<ref name=Corre>{{ cite journal
|author=L Le Corre, V Reddy, KJ Becker
|title=Nature of Orange Ejecta Around Oppia and Octavia Craters on Vesta from Dawn Framing Camera
|journal=American Astronomical Society, DPS meeting
|month=October
|year=2012
|volume=
|issue=44
(contracted; show full)ght to have evolved predominantly under the influence of impacts.<ref name=Greeley/> Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters (''catenae'') and associated scarps, ridges and deposits.<ref name=Greeley/> At a small scale, the surface is varied and consists of small, bright frost deposits at the tops of elevations, surrounded by a low-lying, smooth blanket of dark material.<ref name=Moore2004>{{cite 
encyclopediabook|last=Moore|first=Jeffrey M.|coauthors=, Chapman, Clark R.; Bierhaus, Edward B. et al. |title=Callisto|encyclopedia=, In: ''Jupiter: The planet, Satellites and Magnetosphere|year''|date=2004|publisher=Cambridge University Press|editor=Bagenal, F.; Dowling, T.E.; McKinnon, W.B.| url=http://lasp.colorado.edu/~espoclass/homework/5830_2008_homework/Ch17.pdf|format=PDF  }}</ref>

Many fresh impact craters like Lofn also show enrichment in carbon dioxide.<ref name=Hibbitts1998>{{ cite book|last=Hibbitts |first=C.A.|coauthors=McCord, T. B.; Hansen, G.B.|title=Distributions of CO<sub>2</sub> and SO<sub>2</sub> on the Surface of Callisto|yeardate=1998|publisher=Lunar and Planetary Science XXXI|url=http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1908.pdf|page=1908|format=PDF  }}</ref>

The ancient surface of Callisto is one of the most heavily cratered in the Solar System.<ref name="Zahnle 1998">{{cite journal|last=Zahnle|first=K.|coauthors=Dones, L. |title=Cratering Rates on the Galilean Satellites|journal=Icarus|year=1998|volume=136|issue=2|pages=202&ndash;222|doi=10.1006/icar.1998.6015| url=http://lasp.colorado.edu/icymoons/europaclass/Zahnle_etal_1998.pdf|format=PDF  |pmid=11878353|bibcode=1998Icar..136..202Z}}</ref> In fact, the crater density is close to saturation: any new crater will tend to erase an older one. ... The impact craters and multi-ring structures—together with associated fractures, scarps and deposits—are the only large features to be found on the surface.<ref name=Greeley/><ref name="Bender 1997">{{ cite journal|author=Bender, K. C.; Rice, J. W.; Wilhelms, D. E.; Greeley, R. |title=Geological map of Callisto |publisher=U.S. Geological Survey |year=1997 |url=http://astrogeology.usgs.gov/Projects/PlanetaryMapping/DIGGEOL/galsats/callisto/jcglobal.htm }}</ref>

(contracted; show full)ve central domes, which are thought to result from central tectonic uplift after an impact;<ref name=Greeley/> examples include Doh and Hár craters. A small number of very large&mdash;more 100&nbsp;km in diameter&mdash;and bright impact craters show anomalous dome geometry. These are unusually shallow and may be a transitional landform to the multi-ring structures, as with the Lofn impact feature.<ref name=Greeley/> Callistoan craters are generally shallower than those on the [[Moon
/Keynote lecture|Moon]].

The largest impact features on the Callistoan surface are multi-ring basins.<ref name=Greeley/><ref name="Bender 1997"/> Two are enormous. Valhalla is the largest, with a bright central region 600&nbsp;kilometers in diameter, and rings extending as far as 1,800&nbsp;kilometers from the center (see figure).<ref name="Map 2002">{{ cite book
|title=Controlled Photomosaic Map of Callisto JC 15M CMN |publisher=U.S. Geological Survey |edition=2002 |url=http://geopubs.wr.usgs.gov/i-map/i2770/}}</ref> The second largest is Asgard, measuring about 1,600&nbsp;kilometers in diameter.<ref name="Map 2002"/> Multi-ring structures probably originated as a result of a post-impact concentric fracturing of the lithosphere lying on a layer of soft or liquid material, possibly an ocean.<ref name=Klemaszewski2001>{{ cite book|last= Klemaszewski|first= J.A.|coauthors= Greeley, R.|title= Geological Evidence for an Ocean on Callisto |yeardate=2001|publisher=Lunar and Planetary Science XXXI|page=1818|url=http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1818.pdf|format=PDF  }}</ref> The catenae&mdash;for example Gomul Catena&mdash;are long chains of impact craters lined up in straight lines across the surface. They were probably created by objects that were tidally disrupted as they passed close to Jupiter prior to the impact on Callisto, or by very oblique impacts.<ref name=Greeley/>
{{clear}}

==Europa==
{{main|Europa}}
[[Image:Europa Pwyll.jpg|thumb|right|2050px|This enhanced color image is of the region surrounding the young impact crater Pwyll on Jupiter's moon Europa. Credit: NASA/Jet Propulsion Lab.]]
The image at page top right shows the prominent crater in the lower right, Pwyll.

"This enhanced color image of the region surrounding the young impact crater Pwyll on Jupiter's moon Europa was produced by combining low resolution color data with a higher resolution mosaic of images obtained on December 19, 1996 by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. This region is on the trailing hemisphere of the satellite, centered at 11 degrees South and 276 degrees West, and is about 1240 kilometers across. North is toward the top of the image, and the sun illuminates the surface from the east."<ref name=Lavoie03061998>{{ cite book
|author=Sue Lavoie
|title=PIA01211: Pwyll Crater on Europa
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|monthdate=March 6,⏎
|year=  1998
|url=http://photojournal.jpl.nasa.gov/catalog/PIA01211
|accessdate=2013-06-24 }}</ref>

"The 26 kilometer diameter impact crater Pwyll, just below the center of the image, is thought to be one of the youngest features on the surface of Europa. The diameter of the central dark spot, ejecta blasted from beneath Europa's surface, is approximately 40 kilometers, and bright white rays extend for over a thousand kilometers in all directions from the impact site. These rays cross over many different terrain types, indicating that they are younger than anything they cross. Their bright white color may indicate that they are composed of fresh, fine water ice particles, as opposed to the blue and brown tints of older materials elsewhere in the image."<ref name=Lavoie03061998/>

"Also visible in this image are a number of the dark lineaments which are called "triple bands" because they have a bright central stripe surrounded by darker material. Scientists can use the order in which these bands cross each other to determine their relative ages, as they attempt to reconstruct the geologic history of Europa."<ref name=Lavoie03061998/>
{{clear}}

==Ganymede==
{{main|Ganymede}}
[[Image:Chain of impact craters on Ganymede.jpg|thumb|right|2050px|The image shows a chain of craters on Ganymede. Credit: Galileo Project, Brown University, JPL, NASA.]]
[[Image:Craters on Ganymede.jpg|thumb|right|2050px|The craters Gula and Achelous (bottom) are shown in the grooved terrain of Ganymede, with ejecta "pedestals" and ramparts. Credit: NASA/JPL/Brown University.]]
[[Image:Ganymede terrain.jpg|thumb|250px|right|A sharp boundary divides the ancient dark terrain of Nicholson Regio from the younger, finely striated bright terrain of Harpagia Sulcus. Credit: NASA/JPL/DLR.]]
(contracted; show full)
|journal=Science
|volume=286
|pages=77&ndash;84
|doi=10.1126/science.286.5437.77
| url=http://www.lpl.arizona.edu/~showman/publications/showman-malhotra-1999.pdf
|pmid=10506564
|issue=5437 }}</ref> The brighter, grooved terrain contains many fewer impact features, which have been only of a minor importance to its tectonic evolution.<ref name=Showman1999/> The density of cratering indicates an age of 4&nbsp;billion years for the dark terrain, similar to the highlands of the [[Moon
/Keynote lecture|Moon]], and a somewhat younger age for the grooved terrain (but how much younger is uncertain).<ref name=Zahnle1998>{{ cite journal
|author=K. Zahnle, L. Dones
|title=Cratering Rates on the Galilean Satellites
|journal=Icarus
|year=1998
|volume=136
|issue=2
|pages=202&ndash;22
|doi=10.1006/icar.1998.6015
| url=http://lasp.colorado.edu/icymoons/europaclass/Zahnle_etal_1998.pdf
|pmid=11878353
|bibcode=1998Icar..136..202Z }}</ref> Ganymede may have experienced a period of heavy cratering 3.5 to 4&nbsp;billion years ago similar to that of the Moon.<ref name=Zahnle1998/> If true, the vast majority of impacts happened in that epoch, while the cratering rate has been much smaller since.<ref name="nineplanets.org-Ganymede">{{ cite book
|publisher=nineplanets.org
|title=Ganymede
|date=October 31, 1997
|url=http://www.nineplanets.org/ganymede.html
|accessdate=2008-02-27 }}</ref> Craters both overlay and are crosscut by the groove systems, indicating that some of the grooves are quite ancient. Relatively young craters with rays of ejecta are also visible.<ref name="nineplanets.org-Ganymede"/><ref name="Ganymede">{{ cite book
|publisher=Lunar and Planetary Institute
|title=Ganymede
|yeardate=1997
|url=http://www.lpi.usra.edu/resources/outerp/gany.html }}</ref> Ganymedian craters are flatter than those on the Moon and Mercury. This is probably due to the relatively weak nature of Ganymede's icy crust, which can (or could) flow and thereby soften the relief. Ancient craters whose relief has disappeared leave only a "ghost" of a crater known as a  palimpsest.<ref name="nineplanets.org-Ganymede"/>

The second image at right is an "[o]blique view of two fresh impact craters in bright grooved terrain near the north pole of Jupiter's moon, Ganymede. The craters postdate the grooved terrain since each is surrounded by swarms of smaller craters formed by material which was ejected out of the crater as it formed, and which subsequently reimpacted onto the surrounding surface. The crater to the north, Gula, which is 38 kilometers (km) in diameter, has a distinctive central peak, while the crater to the south, Achelous, (32 km in diameter) has an outer lobate ejecta deposit extending about a crater radius from the rim. Such images show the range of structural details of impact craters, and help in understanding the processes that form them."<ref name=Lavoie98>{{ cite book
|author=Sue Lavoie
|title=PIA01609: Fresh Impact Craters on Ganymede
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|monthdate=July 15,⏎
|year=  1998
|url=http://photojournal.jpl.nasa.gov/catalog/PIA01609
|accessdate=2013-06-22 }}</ref>

"North is to the top of the picture and the sun illuminates the surface from the right. The image, centered at 62 degrees latitude and 12 degrees longitude, covers an area approximately 142 by 132 kilometers. The resolution is 175 meters per picture element. The images were taken on April 5, 1997 at 6 hours, 33 minutes, 37 seconds Universal Time at a range of 17,531 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft."<ref name=Lavoie98/>

In the third image at right "[t]he ancient, dark terrain of Nicholson Regio (left) shows many large impact craters, and zones of fractures oriented generally parallel to the boundary between the dark and bright regions of Jupiter's moon Ganymede. In contrast, the bright terrain of Harpagia Sulcus (right) is less cratered and relatively smooth."<ref name=Lavoie2000>{{ cite book
|author=Sue Lavoie
|title=PIA02577: Bright-Dark terrain boundary, Ganymede
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|monthdate=December 16,⏎
|year=  2000
|url=http://photojournal.jpl.nasa.gov/catalog/PIA02577
|accessdate=2013-06-22 }}</ref>

"The nature of the boundary between ancient, dark terrain and younger, bright terrain, the two principal terrain types on Ganymede, was explored by NASA's Galileo spacecraft on May 20, 2000. Subtle parallel ridges and grooves show that Harpagia Sulcus's land has been smoothed out over the years by tectonic processes."<ref name=Lavoie2000/>

"North is to the top of the picture. The Sun illuminates the surface from the left. The image, centered at ?14 degrees latitude and 319 degrees longitude, covers an area approximately 213 by 97 kilometers (132 by 60 miles.) The resolution is 121 meters (about 250 feet) per picture element. The images were taken on May 20, 2000, at a range of 11,800 kilometers (about 7,300 miles)."<ref name=Lavoie2000/>
{{clear}}

==Io==
{{main|Io}}
[[Image:Io highest resolution true color.jpg|thumb|right|2050px|This is a true-color image of Io taken by the ''Galileo'' probe. Credit: NASA.]]
[[Image:Io VGR South polar color mosaic.jpg|thumb|left|2050px|This mosaic of ''Voyager 1'' images covers Io's south polar region. The view includes two of Io's ten highest peaks, the Euboea Montes at upper extreme left and Haemus Mons at bottom. Credit: .]]
[[Image:PIA01667-Io's Pele Hemisphere After Pillan Changes.jpg|thumb|right|2050px|This global view of Io, is obtained from the tenth orbit of Jupiter by NASA's Galileo spacecraft. Credit: NASA.]]
[[Image:Iosurface.jpg|thumb|300px|right|Changes in surface features in the eight years between ''Galileo'' and ''New Horizons'' observations are shown. Credit: .]]
[[Image:Tvashtarvideo.gif|left|thumb|2050px|Five-image sequence of ''New Horizons'' images showing Io's volcano Tvashtar spewing material 330&nbsp;km above its surface. Credit: .]]
The dark spot just left of center [in the image at right] is the erupting volcano Prometheus. Whitish plains on either side of it are coated with volcanically emplaced sulfur dioxide frost, while yellower regions are encrusted with a higher proportion of sulfur.

Io has over 400 active volcanoes<ref name=Lopes2006>{{cite book
|title=Encyclopedia of the Solar System
|chapter=Io: The Volcanic Moon
|author=Rosaly MC Lopes
|publisher=Academic Press
|yeardate=2006
|editor=Lucy-Ann McFadden, Paul R. Weissman, Torrence V. Johnson
|pages=419–431
|isbn=978-0-12-088589-3 }}</ref><ref name="Lopes2004">{{ cite journal
|title=Lava lakes on Io: Observations of Io’s volcanic activity from Galileo NIMS during the 2001 fly-bys
|journal=Icarus
|author=R. M. C. Lopes ''et al.''
|pages=140–74
|volume=169
|issue= 1
|year=2004
|doi=10.1016/j.icarus.2003.11.013
|bibcode=2004Icar..169..140L}}</ref>

Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km (300 mi) above the surface.

Seven of the nine plumes observed in March were still active in July 1979, with only the volcano Pele shutting down between flybys [of Voyager 1 then Voyager 2].<ref name="Strom1982">{{cite book |last=Strom |first=R. G. | coauthors=author=R. G. Strom and Schneider, N. M. |editor=Morrison, D. |title=Volcanic eruptions on Io, In: ''Satellites of Jupiter |year'' |date=1982 |publisher=University of Arizona Press |isbn=0-8165-0762-7 |pages=598–633 |chapter=Volcanic eruptions on Io }}</ref>

Distant imaging of Io was acquired for almost every orbit during the primary mission, revealing large numbers of active volcanoes (both thermal emission from cooling magma on the surface and volcanic plumes), numerous mountains with widely varying morphologies, and several surface changes that had taken place both between the ''Voyager'' and ''Galileo'' eras and between ''Galileo'' orbits.<ref name="IobookChap3">{{cite book |last=Perry |first=J.; ''et al.'' |editor=Lopes, R. M. C.; and Spencer, J. R. |title=A Summary of the Galileo mission and its observations of Io, In: ''Io after Galileo |year'' |date=2007 |publisher=Springer-Praxis |isbn=3-540-34681-3 |pages=35–59 |chapter=A Summary of the Galileo mission and its observations of Io }}</ref> Observations during these encounters revealed the geologic processes occurring at Io's volcanoes and mountains, excluded the presence of a magnetic field, and demonstrated the extent of volcanic activity.<ref name="IobookChap3"/> In December 2000, the ''Cassini'' spacecraft had a distant and brief encounter with the Jupiter system en route to [[Saturn]], allowing for joint observations with ''Galileo''. These observations revealed a new plume at Tvashtar Paterae and provided insights into Io's aurorae.<ref name="Porco2003">{{cite journal | last=Porco |first=C. C. |authorlink=Carolyn Porco |coauthors=author=C. C. Porco ''et al.'' |title=Cassini imaging of Jupiter's atmosphere, satellites, and rings |journal=Science |volume=299 |issue= 5612|pages=1541–1547 |year=2003 |url= |doi=10.1126/science.1079462 | pmid=12624258 |bibcode = 2003Sci...299.1541P }}</ref>

New observations of Io's volcanism came from Earth-based telescopes. In particular, adaptive optics imaging from the Keck telescope in Hawaii and imaging from the Hubble telescope have allowed astronomers to monitor Io's active volcanoes.<ref name="Marchis2005">{{ cite journal | last=Marchis |first=F. |coauthors=''et al.'' |title=Keck AO survey of Io global volcanic activity between 2 and 5 μm |journal=Icarus |volume=176 |issue= 1|pages=96–122 |year=2005 |url= |doi=10.1016/j.icarus.2004.12.014 |bibcode=2005Icar..176...96M}}</ref><ref name="SpencerBlog02232007">{{cite book |url=http://planetary.org/blog/article/00000874/ |title=Here We Go! |accessdate=2007-06-03 |last=Spencer |first=John |coauthors= |date=2007-02-23 |year= |month= |work= |publisher= |pages= }}</ref> This imaging has allowed scientists to monitor volcanic activity on Io, even without a spacecraft in the Jupiter system.

(contracted; show full) areas with fewer volcanoes and vice versa.<ref name="McKinnon2001">{{cite journal | last=McKinnon |first=W. B. |coauthors=''et al.'' |title=Chaos on Io: A model for formation of mountain blocks by crustal heating, melting, and tilting |journal=Geology |volume=29 |issue= 2 |pages=103–106 |year=2001 |doi=10.1130/0091-7613(2001)029<0103:COIAMF>2.0.CO;2 |bibcode=2001Geo....29..103M }}</ref>
{{clear}}

==Mimas==
{{main|Mimas}}
[[Image:Mimas moon.jpg|thumb|right|2
050px|Herschel Crater on Saturn's moon Mimas is shown in the image. Credit: .]]
The Herschel Crater on Saturn's moon Mimas is shown in the image at right.
{{clear}}

==Titan==
{{main|Titan}}
[[Image:Titancrater.jpg|thumb|right|2050px|This radar image of Titan shows a semi-circular feature that may be part of an impact crater. Credit: NASA/JPL-Caltech/ASI.]]
"This radar image [at right] of Titan shows a semi-circular feature that may be part of an impact crater. Very few impact craters have been seen on Titan so far, implying that the surface is young. Each new crater identified on Titan helps scientists to constrain the age of the surface."<ref name=Lavoie02162007>{{ cite book
|author=Sue Lavoie
|title=PIA09175: A New Crater on Titan?
|publisher=NASA/JPL
|location=Pasadena, California USA
|monthdate=February 26,⏎
|year=  2007
|url=http://photojournal.jpl.nasa.gov/catalog/PIA09175
|accessdate=2013-06-13 }}</ref>
{{clear}}

==Comets==
{{main|Comets}}
[[Image:Tempel Impactor 150Km.jpg|thumb|right|2050px|The impactor close-up image is taken shortly before impact. Credit: NASA.]]
'''''Deep Impact''''' is a NASA space probe launched on January 12, 2005. It was designed to study the composition of the comet interior of 9P/Tempel, by releasing an impactor into the comet. At 5:52 UTC on July 4, 2005, the impactor successfully collided with the comet's nucleus. The impact excavated debris from the interior of the nucleus, allowing photographs of the impact crater. The photographs showed the comet to be more dusty and less icy than had been expected. The impact generated a large and bright dust cloud, which unexpectedly obscured the view of the impact crater.
{{clear}}

==Hypotheses==
{{main|Hypotheses}}
# There is at least one key clue or ingredient that allows the differentiation of craters by their origins or causative factors.⏎
{{seealso|Control groups|Proof of concept|Proof of technology}}

==See also==
{{div col|colwidth=12em}}
* [[Meteor astronomy]]
* [[Meteorites]]
{{Div col end}}

(contracted; show full)
* [http://www.springerlink.com/ SpringerLink]
* [http://www.tandfonline.com/ Taylor & Francis Online]
* [http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/convcoord/convcoord.pl Universal coordinate converter]
* [http://onlinelibrary.wiley.com/advanced/search Wiley Online Library Advanced Search]
* [http://search.yahoo.com/web/advanced Yahoo Advanced Web Search]

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