Difference between revisions 2117901 and 2235894 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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'''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
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| first=R.⏎
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| coauthors=Klemaszewski, J.E.;Wagner L.; ⏎
| display-authors=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⏎
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}}</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=
|date=January 31, 2012
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|author=Craig Glenday
|date=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
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, ''⏎
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(contracted; show full)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 book
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|last=Moore⏎
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|title=Callisto, In: ''Jupiter: The planet, Satellites and Magnetosphere''⏎
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|  url=http://lasp.colorado.edu/~espoclass/homework/5830_2008_homework/Ch17.pdf  ⏎
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}}</ref>

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

(contracted; show full)|publisher=Academic Press
|date=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
 ''⏎
|display-authors=et  al.''
|pages=140–74
|volume=169
|issue= 1
|year=2004
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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 |author=R. G. Strom and Schneider, N. M. |editor=Morrison, D. |title=Volcanic eruptions on Io, In: ''Satellites of Jupiter'' |date=1982 |publisher=University of Arizona Press |isbn=0-8165-0762-7 |pages=598–633 }}</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 ⏎
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|last=Perry ⏎
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|editor=Lopes, R. M. C.; and Spencer, J. R. ⏎
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|title=A Summary of the Galileo mission and its observations of Io, In: ''Io after Galileo'' ⏎
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|publisher=Springer-Praxis ⏎
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|isbn=3-540-34681-3 ⏎
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|pages=35–59 ⏎
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}}</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 ⏎
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| author=C. C. Porco ''⏎
|display-authors=et  al.'' ⏎
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|title=Cassini imaging of Jupiter's atmosphere, satellites, and rings ⏎
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|journal=Science ⏎
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}}</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 ⏎
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| last=Marchis ⏎
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|first=F. |co⏎
|display-authors=''et  al.'' ⏎
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|title=Keck AO survey of Io global volcanic activity between 2 and 5 μm ⏎
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|journal=Icarus ⏎
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|volume=176 ⏎
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|issue= 1⏎
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|pages=96–122 ⏎
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|year=2005 ⏎
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|url= ⏎
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|bibcode=2005Icar..176...96M⏎
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}}</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 |date=2007-02-23 |publisher= |pages= }}</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 observations of Pele's plume in 1979.<ref name="Spencer2007">{{cite journal ⏎
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|title=Io Volcanism Seen by New Horizons: A Major Eruption of the Tvashtar Volcano ⏎
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|journal=Science ⏎
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|last=Spencer ⏎
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|first=J. R. |co⏎
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|doi=10.1126/science.1147621 ⏎
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|pmid=17932290⏎
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|bibcode = 2007Sci...318..240S ⏎
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}}</ref> ''New Horizons'' also captured images of a volcano near Girru Patera in the early stages of an eruption, and several volcanic eruptions that have occurred since ''Galileo''.<ref name="Spencer2007"/>

Images from the ''Galileo'' spacecraft revealed that many of Io's major lava flows, like those at Prometheus and Amirani, are produced by the build-up of small breakouts of lava flows on top of older flows.<ref name="Keszthelyi2001">{{ cite journal ⏎
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|title=Imaging of volcanic activity on Jupiter's moon Io by Galileo during the Galileo Europa Mission and the Galileo Millennium Mission ⏎
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}}</ref> Larger outbreaks of lava have also been observed on Io. For example, the leading edge of the Prometheus flow moved 75 to 95 km (47 to 59 mi) between ''Voyager'' in 1979 and the first ''Galileo'' observations in 1996. A major eruption in 1997 produced more than {{convert|3500|km2|sqmi|sigfig=2|abbr=on}} of fresh lava and flooded the floor of the adjacent Pillan Patera.<ref name="Mcewen1998b">{{ cite journal ⏎
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}}</ref>

The discovery of plumes at the volcanoes Pele and Loki were the first sign that Io is geologically active.<ref name="Morabito1979">{{cite journal ⏎
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|first=L. A. |co⏎
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|bibcode = 1979Sci...204..972M  ⏎
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}}</ref>

The global distribution of mountains appears to be opposite that of volcanic structures; mountains dominate areas with fewer volcanoes and vice versa.<ref name="McKinnon2001">{{cite journal ⏎
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| last=McKinnon ⏎
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|first=W. B. |co⏎
|display-authors=''et  al.'' ⏎
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|title=Chaos on Io: A model for formation of mountain blocks by crustal heating, melting, and tilting ⏎
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|journal=Geology ⏎
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|volume=29 ⏎
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|issue= 2 ⏎
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|pages=103–106 ⏎
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|year=2001 ⏎
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|doi=10.1130/0091-7613(2001)029<0103:COIAMF>2.0.CO;2 ⏎
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|bibcode=2001Geo....29..103M ⏎
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}}</ref>
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==Mimas==
{{main|Mimas}}
[[Image:Mimas moon.jpg|thumb|right|250px|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.
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