Difference between revisions 2235894 and 2239156 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.

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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
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|last=Sublette⏎
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|first=Carey⏎
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|title=The Effects of Underground Explosions⏎
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|url=http://nuclearweaponarchive.org/Library/Effects/UndergroundEffects.html⏎
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|work=Nuclear Weapon Archive⏎
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|accessdate=21 June 2011⏎
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}}</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.
| display-authors=etal
| title=Galileo views of the geology of Callisto
(contracted; show full)
| author = Kenneth Chang
| date = 2012-11-29
| page = A3
| accessdate = 2012-11-29 }}</ref>
Sean C. Solomon was quoted in the ''New York Times'' as estimating the volume of the ice as large enough to ''"encase Washington, D.C., in a frozen block two and a half miles deep."''

A small crater named Hun Kal provides the reference point for measuring longitude. The center of Hun Kal is 20° west longitude.<ref name="usgs">{{cite book
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|url=http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html⏎
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|accessdate=22 October 2009⏎
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|title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)  ⏎
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}}</ref>

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==
(contracted; show full)|title=Callisto, In: ''Jupiter: The planet, Satellites and Magnetosphere''
|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
}}</ref>

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

The ancient surface of Callisto is one of the most heavily cratered in the Solar System.<ref name="Zahnle 1998">{{cite journal⏎
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|last=Zahnle⏎
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|first=K.⏎
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|coauthors=Dones, L.  ⏎
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|title=Cratering Rates on the Galilean Satellites⏎
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|journal=Icarus⏎
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|year=1998⏎
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|volume=136⏎
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|issue=2⏎
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|pages=202&ndash;222⏎
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|doi=10.1006/icar.1998.6015⏎
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| url=http://lasp.colorado.edu/icymoons/europaclass/Zahnle_etal_1998.pdf  ⏎
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|pmid=11878353⏎
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|bibcode=1998Icar..136..202Z⏎
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}}</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⏎
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|author=Bender, K. C.; Rice, J. W.; Wilhelms, D. E.; Greeley, R.  ⏎
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|title=Geological map of Callisto  ⏎
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|publisher=U.S. Geological Survey  ⏎
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|year=1997  ⏎
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|url=http://astrogeology.usgs.gov/Projects/PlanetaryMapping/DIGGEOL/galsats/callisto/jcglobal.htm  ⏎
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}}</ref>

Callisto's surface can be divided into several geologically different parts: cratered plains, light plains, bright and dark smooth plains, and various units associated with particular multi-ring structures and impact craters.<ref name=Greeley/><ref name="Bender 1997"/> The cratered plains constitute most of the surface area and represent the ancient lithosphere, a mixture of ice and rocky material. The light plains include bright impact craters like Burr and Lofn, (contracted; show full)
|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
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|last= Klemaszewski⏎
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|first= J.A., Greeley, R.⏎
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|title= Geological Evidence for an Ocean on Callisto  ⏎
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|date=2001⏎
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|publisher=Lunar and Planetary Science XXXI⏎
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|page=1818⏎
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|url=http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1818.pdf  ⏎
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}}</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/>
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==Europa==
{{main|Europa}}
(contracted; show full)|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
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|author=R. G. Strom and Schneider, N. M.  ⏎
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|editor=Morrison, D.  ⏎
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|title=Volcanic eruptions on Io, In: ''Satellites of Jupiter''  ⏎
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|date=1982  ⏎
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|publisher=University of Arizona Press  ⏎
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|isbn=0-8165-0762-7  ⏎
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|pages=598–633  ⏎
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}}</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">{{ci(contracted; show full)|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
  ⏎
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|url=http://planetary.org/blog/article/00000874/  ⏎
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|title=Here We Go!  ⏎
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|accessdate=2007-06-03  ⏎
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|last=Spencer  ⏎
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|first=John  ⏎
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|date=2007-02-23  ⏎
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}}</ref> This imaging has allowed scientists to monitor volcanic activity on Io, even without a spacecraft in the Jupiter system.

The ''New Horizons'' spacecraft, en route to Pluto and the Kuiper belt, flew by the Jupiter system and Io on February 28, 2007. During the encounter, numerous distant observations of Io were obtained. These included images of a large plume at Tvashtar, providing the first detailed observations of the largest class of Ionian volcanic plume since observat(contracted; show full)[[Category:Earth sciences/Lectures]]
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