View source for Solar System, technical/Ganymede

[[Image:Ganymede g1 true 2.jpg|thumb|left|200px|A true color image of Ganymede is acquired by the Galileo spacecraft on June 26, 1996. Credit: NASA/JPL.]]
{{halfway}}
"If '''Ganymede''' rotated around the Sun rather than around Jupiter, it would be classified as a planet."<ref name=Jonsson>{{ cite web
|author=Bjorn Jonsson and Steve Albers
|title=Ganymede (Jupiter moon)
|publisher=NOAA
|location=
|date=October 17, 2000
|url=http://sos.noaa.gov/Datasets/dataset.php?id=247
|accessdate=2012-07-01 }}</ref>
{{experimental}}
The ''Galilean Moons'' is a "name given to Jupiter's four largest moons, Io, Europa, Callisto & Ganymede. They were discovered independently by Galileo Galilei and Simon Marius."<ref name=Aravind V R>{{ cite journal
|author=[[User:Aravind V R|Aravind V R]]
|title=Astronomy glossary
|journal=Wikiversity
|month=April 17,
|year=2012
|volume=
|issue=
|pages=1
|url=http://en.wikiversity.org/wiki/Astronomy_glossary
|bibcode=
|doi=
|pmid=
|accessdate=2013-06-22 }}</ref>
{{secondary}}
{{tertiary}}
{{research}}
{{article}}
{{lecture}}
{{astronomy}}
==Notation==

'''Notation''': let the symbol '''Def.''' indicate that a definition is following.

'''Notation''': let the symbols between [ and ] be replacement for that portion of a quoted text.

==Universals==

To help with definitions, their meanings and intents, there is the learning resource [[theory of definition]].

'''Def.''' evidence that demonstrates that a concept is possible is called '''proof of concept'''.

The proof-of-concept structure consists of
# background,
# procedures,
# findings, and
# interpretation.<ref name=Lehrman>{{ cite journal
|author=Ginger Lehrman and Ian B Hogue, Sarah Palmer, Cheryl Jennings, Celsa A Spina, Ann Wiegand, Alan L Landay, Robert W Coombs, Douglas D Richman, John W Mellors, John M Coffin, Ronald J Bosch, David M Margolis
|title=Depletion of latent HIV-1 infection in vivo: a proof-of-concept study
|journal=Lancet
|month=August 13,
|year=2005
|volume=366
|issue=9485
|pages=549-55
|url=http://www.sciencedirect.com/science/article/pii/S0140673605670985
|arxiv=
|bibcode=
|doi=10.1016/S0140-6736(05)67098-5
|pmid=
|pdf=http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1894952/
|accessdate=2012-05-09 }}</ref>

The findings demonstrate a statistically systematic change from the status quo or the [[control group]].

==Planetary science==
[[Image:Moon Ganymede by NOAA.jpg|thumb|right|200px|This is global pictoral map of Ganymede. Credit: National Oceanic and Atmospheric Administration/USGS.]]
"Ganymede has a very distinct surface with bright and dark regions. The surface includes mountains, valleys, craters and lava flows. The darker regions are more heavily littered with craters implying that those regions are older. The largest dark region is named Galileo Regio and is almost 2000 miles [3200 km] in diameter. The lighter regions display extensive series of troughs and ridges, thought to be a result of tectonic movement."<ref name=Jonsson/>

"A notable attribute of the craters on Ganymede is that they are not very deep and don’t have mountains around the edges of them as can normally be seen around craters on other moons and planets. The reason for this is that the crust of Ganymede is relatively soft and over a geological time frame has flattened out the extreme elevation changes."<ref name=Jonsson/>
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==X-ray astronomy==

"Apart from the [[Sun (star)|Sun]], the known X-ray emitters now include planets ([[Venus]], [[Earth]], [[Mars]], [[Jupiter]], and [[Saturn]]), planetary satellites ([[Moon]], [[Io]], [[Europa]], and Ganymede), all active comets, the Io plasma torus, the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere."<ref name=Bhardwaj>{{ cite journal
|author=Anil Bhardwaj, Ronald F. Elsner, G. Randall Gladstone, Thomas E. Cravens, Carey M. Lisse, Konrad Dennerl, Graziella Branduardi-Raymont, Bradford J. Wargelin, J. Hunter Waite Jr., Ina Robertson, Nikolai Østgaard, Peter Beiersdorfer, Steven L. Snowden, Vasili Kharchenko
|title=X-rays from solar system objects
|journal=Planetary and Space Science
|month=June
|year=2007
|volume=55
|issue=9
|pages=1135-89
|url=http://www.sciencedirect.com/science/article/pii/S0032063306003370
|arxiv=
|bibcode=
|doi=10.1016/j.pss.2006.11.009
|pmid=
|pdf=http://web.ift.uib.no/~nikost/papers/Solar_System_X-rays_PSS_review_revised_paper.pdf
|accessdate=2013-05-23 }}</ref>

==Violet astronomy==
[[Image:Ganymede-moon.jpg|thumb|right|200px|In this image of Ganymede's trailing side, the colors are enhanced to emphasize color differences. Credit: NASA/JPL/DLR.]]
"In this global view of Ganymede's trailing side, the colors are enhanced to emphasize color differences. The enhancement reveals frosty polar caps in addition to the two predominant terrains on Ganymede, bright, grooved terrain and older, dark furrowed areas. Many craters with diameters up to several dozen kilometers are visible. The violet hues at the poles may be the result of small particles of frost which would scatter more light at shorter wavelengths (the violet end of the spectrum). Ganymede's magnetic field, which was detected by the magnetometer on NASA's Galileo spacecraft in 1996, may be partly responsible for the appearance of the polar terrain. Compared to Earth's polar caps, Ganymede's polar terrain is relatively vast. The frost on Ganymede reaches latitudes as low as 40 degrees on average and 25 degrees at some locations. For comparison with Earth, Miami, Florida lies at 26 degrees north latitude, and Berlin, Germany is located at 52 degrees north."<ref name=Lavoie99>{{ cite web
|author=Sue Lavoie
|title=PIA01666: Ganymede's Trailing Hemisphere
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|date=January 18, 1999
|url=http://photojournal.jpl.nasa.gov/catalog/PIA01666
|accessdate=2013-06-22 }}</ref>

"North is to the top of the picture. The composite, which combines images taken with green, violet, and 1 micrometer filters, is centered at 306 degrees west longitude. The resolution is 9 kilometers (6 miles) per picture element. The images were taken on 29 March 1998 at a range of 918000 kilometers (570,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft."<ref name=Lavoie99/>
{{clear}}

==Infrared astronomy==
[[Image:Hubble Spies Jupiter Eclipses.jpg|thumb|right|200px|Jupiter appears in pastel colors in this photo because the observation was taken in near-infrared light. Credit: NASA, ESA, and E. Karkoschka (University of Arizona).]]
The image at right shows Jupiter in the near infrared. "Five spots -- one colored white, one blue, and three black are scattered across the upper half of the planet. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons -- [[Io]], Ganymede, and [[Callisto]] -- across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. Io's shadow is located just above center and to the left; Ganymede's on the planet's left edge; and Callisto's near the right edge. Only two of the moons, however, are visible in this image. Io is the white circle in the center of the image, and Ganymede is the blue circle at upper right. Callisto is out of the image and to the right. ... [[Jupiter]] appears in pastel colors in this photo because the observation was taken in near-infrared light. Astronomers combined images taken in three near-infrared wavelengths to make this color image. The photo shows sunlight reflected from Jupiter's clouds. In the near infrared, methane gas in Jupiter's atmosphere limits the penetration of sunlight, which causes clouds to appear in different colors depending on their altitude. Studying clouds in near-infrared light is very useful for scientists studying the layers of clouds that make up Jupiter's atmosphere. Yellow colors indicate high clouds; red colors lower clouds; and blue colors even lower clouds in Jupiter's atmosphere. The green color near the poles comes from a thin haze very high in the atmosphere. Ganymede's blue color comes from the absorption of water ice on its surface at longer wavelengths. Io's white color is from light reflected off bright sulfur compounds on the satellite's surface. ... In viewing this rare alignment, astronomers also tested a new imaging technique. To increase the sharpness of the near-infrared camera images, astronomers speeded up Hubble's tracking system so that Jupiter traveled through the telescope's field of view much faster than normal. This technique allowed scientists to take rapid-fire snapshots of the planet and its moons. They then combined the images into one single picture to show more details of the planet and its moons."<ref name=DavisMay>{{ cite web
|author=Phil Davis
|title=Triple Eclipse
|publisher=National Aeronautics and Space Administration
|location=Washington, DC USA
|date=May 3, 2011
|url=http://solarsystem.nasa.gov/multimedia/display.cfm?Category=Planets&IM_ID=3083
|accessdate=2012-07-20 }}</ref>
{{clear}}
==Atmospheric astronomy==
[[Image:Hubblesite 1995 36.jpg|thumb|right|200px|NASA's Hubble Space Telescope found ozone's spectral "fingerprint" during observations of Ganymede made by Keith Noll and colleagues at the Space Telescope Science Institute in Baltimore, Maryland. Credit: NASA.]]
"Though ozone may be diminishing on Earth, it is being manufactured one-half billion miles away, on Jupiter's largest satellite, Ganymede."<ref name=Davis>{{ cite web
|author=Phil Davis
|title=Hubble Finds Ozone on Jupiter's Moon Ganymede
|publisher=NASA
|location=Washington, DC USA
|date= 
|url=http://solarsystem.nasa.gov/multimedia/display.cfm?Category=Planets&IM_ID=1863
|accessdate=2013-06-22 }}</ref>

"NASA's Hubble Space Telescope found ozone's spectral "fingerprint" during observations of Ganymede made by Keith Noll and colleagues at the Space Telescope Science Institute in Baltimore, Maryland. These Hubble Faint Object Spectrograph results were presented at the American Astronomical Society's 27th Annual Meeting of the Division of Planetary Sciences in Kona, Hawaii."<ref name=Davis/>
{{clear}}

==Crater astronomy==
[[Image:Chain of impact craters on Ganymede.jpg|thumb|right|200px|The image shows a chain of craters on Ganymede. Credit: Galileo Project, Brown University, JPL, NASA.]]
[[Image:Craters on Ganymede.jpg|thumb|right|200px|The craters [[w:Gula (crater)|Gula]] and [[w:Achelous (crater)|Achelous]] (bottom) are shown in the grooved terrain of Ganymede, with [[w:ejecta blanket|ejecta]] "[[w:pedestal crater|pedestals]]" and [[w:rampart crater|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.]]
The image at right shows a chain of 13 craters ([[w:Enki Catena|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 craters formed nearly simultaneously, it is difficult to discern any ejecta deposit on the dark terrain."<ref name=EnkiCatena>{{ cite journal
|title=Enki Catena
|journal=Wikipedia
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|month=December 8,
|year=2012
|url=http://en.wikipedia.org/wiki/Enki_Catena
|accessdate=2013-02-16 }}</ref>

"Cratering is seen on both types of terrain [third image at right], but is especially extensive on the dark terrain: it appears to be saturated with impact craters and has evolved largely through impact events.<ref name=Showman1999>{{ cite journal
|author=Adam P. Showman, Renu Malhotra
|title=The Galilean Satellites
|year=1999
|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]], 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 web
|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 web
|publisher=Lunar and Planetary Institute
|title=Ganymede
|year=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  [[w:Palimpsest (planetary astronomy)|palimpsest]].<ref name="nineplanets.org-Ganymede"/>"<ref name=GanymedeMoon>{{ cite journal
|title=Ganymede (moon)
|journal=Wikipedia
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|month=June 22,
|year=2013
|url=http://en.wikipedia.org/wiki/Ganymede_(moon)
|accessdate=2013-06-22 }}</ref>

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 web
|author=Sue Lavoie
|title=PIA01609: Fresh Impact Craters on Ganymede
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|date=July 15, 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 web
|author=Sue Lavoie
|title=PIA02577: Bright-Dark terrain boundary, Ganymede
|publisher=NASA's Office of Space Science
|location=Washington, DC USA
|date=December 16, 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/>
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==Gravity astronomy==

In the general case only planets (with their sattelites) and stars could be considered "as free, as possible" to be used as some "antenna" to the [[w:gravitational wave|gravitational wave]]s detection. Spherical megascopic bodies have the folloving characteristic impedance:
:<math>\rho_{GS} = \frac{v_cr_s}{3m_s}, \ </math>
where 
::<math>v_c \ </math> is the equatorial velocity, 
::<math>r_s \ </math> spherical body radius and 
::<math>m_s \ </math> body mass.

{| class="prettytable"
!width="20%" style="background:#efefef;" | Body name
!width="15%" style="background:#efefef;" | Body radius, m
!width="15%" style="background:#efefef;" | Equator velocity, m/s
!width="20%" style="background:#efefef;" | Body mass, kg
!width="15%" style="background:#efefef;" | Body impedance
!width="15%" style="background:#efefef;" | <math>\rho_G/\rho_{G0} \ </math>
|-
| [[Moon]]
| <math>1.738\cdot 10^7 </math>
| 4.36
| <math>7.35\cdot 10^{22} </math>
| <math>3.437\cdot 10^{-17} </math>
| <math>1.23\cdot 10^{1} </math>
|-
| [[Titan]]
| <math>2.44\cdot 10^7 </math>
| 276.8
| <math>1.37\cdot 10^{23} </math>
| <math>1.643\cdot 10^{-15} </math>
| <math>5.875\cdot 10^{2} </math>
|-
| Ganymede
| <math>2.6\cdot 10^7 </math>
| 1116
| <math>1.54\cdot 10^{23} </math>
| <math>6.28\cdot 10^{-15} </math>
| <math>12.245\cdot 10^{3} </math>
|-
| [[Callisto]]
| <math>2.36\cdot 10^6 </math>
| 252.7
| <math>9.5\cdot 10^{22} </math>
| <math>2.092\cdot 10^{-17} </math>
| <math>7.48\cdot 10^{2} </math>
|}
Satellite data are taken from the textbook<ref name = Allen>Allen C.W.(1973). Astrophysical quantities. 3-d edition. University of London, The Athlone Press.</ref> As may be seen from the table, only the [[Moon]] has the closest value of characteristic impedance about 12-times greater than for free space.

==Astroglaciology==
[[Image:PIA00081 Ganymede Voyager 2 mosaic.jpg|thumb|200px|left|''[[w:Voyager 2|Voyager 2]]'' image mosaic of Ganymede's anti-Jovian hemisphere. The ancient dark area of [[w:Galileo Regio|Galileo Regio]] lies at the upper right. It is separated from the smaller dark region of Marius Regio to its left by the brighter and younger band of [[w:Uruk Sulcus|Uruk Sulcus]]. Fresh ice ejected from the relatively recent [[w:List of craters on Ganymede|Osiris Crater]] created the bright rays at the bottom. Credit: .]]
"Ganymede is composed of approximately equal amounts of [[w:silicate|silicate rock]] and water ice."<ref name=GanymedeMoon/>

"The average [[w:density|density]] of Ganymede, 1.936&nbsp;[[w:gram|g]]/cm<sup>3</sup>, suggests a composition of approximately equal parts rocky material and water, which is mainly in the form of ice.<ref name=Showman1999/> The [[w:mass fraction (chemistry)|mass fraction]] of ices is between 46–50%, slightly lower than that in Callisto.<ref name=Kuskov2005>{{cite journal|last=Kuskov|first=O.L.|author2=Kronrod, V.A.|title=Internal structure of Europa and Callisto|year=2005|volume=177|issue=2|pages=550&ndash;369|doi=10.1016/j.icarus.2005.04.014| bibcode=2005Icar..177..550K | journal = Icarus}}</ref> Some additional volatile ices such as [[w:ammonia|ammonia]] may also be present.<ref name=Kuskov2005/><ref name=Spohn2003>{{cite journal |last=Spohn|first=T.|author2=Schubert, G.|title=Oceans in the icy Galilean satellites of Jupiter?|journal=Icarus|year=2003|volume=161 |issue=2|pages=456&ndash;467|doi=10.1016/S0019-1035(02)00048-9| url=http://lasp.colorado.edu/icymoons/europaclass/Spohn_Schubert_oceans.pdf|format=PDF|bibcode=2003Icar..161..456S}}</ref>"<ref name=GanymedeMoon/>

"Water ice seems to be ubiquitous on the surface, with a mass fraction of 50–90%,<ref name=Showman1999>{{cite journal|last=Showman |first=Adam P.|author2=Malhotra, Renu|title=The Galilean Satellites|year=1999|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|format=PDF|pmid=10506564|issue=5437}}</ref> significantly more than in Ganymede as a whole. [[w:Near-infrared|Near-infrared]] [[w:spectroscopy|spectroscopy]] has revealed the presence of strong water ice [[w:absorption band|absorption band]]s at wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0&nbsp;[[w:micrometre|μm]].<ref name=Calvin1995>{{cite journal|last=Calvin|first=Wendy M.|author2=Clark, Roger N.
|author3=Brown, Robert H.
|author4=Spencer John R.|title=Spectra of the ice Galilean satellites from 0.2 to 5 µm: A compilation, new observations, and a recent summary|journal=J.of Geophys. Res.|year=1995|volume=100|issue=E9|pages=19,041&ndash;19,048| bibcode=1995JGR...10019041C|doi=10.1029/94JE03349}}</ref> The grooved terrain is brighter and has more icy composition than the dark terrain.<ref name="RESA">{{cite web|url=http://www.resa.net/nasa/ganymede.htm|archiveurl=http://web.archive.org/web/20071202132022/http://www.resa.net/nasa/ganymede.htm|archivedate=2007-12-02|title=Ganymede: the Giant Moon|work=Wayne RESA|accessdate=2007-12-31}}</ref>"<ref name=GanymedeMoon/>

"The forces that caused the strong stresses in the ganymedian ice [[lithosphere]] necessary to initiate the tectonic activity may be connected to the [[w:tidal heating|tidal heating]] events in the past, possibly caused when the satellite passed through unstable [[w:orbital resonance|orbital resonance]]s.<ref name=Showman1999/><ref name=Showman1997b>{{cite journal|last=Showman|first=Adam P.|author2=Stevenson, David J.
|author3=Malhotra, Renu|title=Coupled Orbital and Thermal Evolution of Ganymede|journal=Icarus|year=1997|volume=129|issue=2|pages=367&ndash;383|doi=10.1006/icar.1997.5778| url=http://www.lpl.arizona.edu/~showman/publications/showman-etal-1997.pdf|format=PDF|bibcode=1997Icar..129..367S}}</ref> The tidal flexing of the ice may have heated the interior and strained the lithosphere, leading to the development of cracks and [[w:horst and graben|horst and graben]] faulting, which erased the old, dark terrain on 70% of the surface.<ref name=Showman1999/><ref name=Bland2007>{{cite journal|last=Bland|first=|author2=Showman, A.P.
|author3=Tobie, G.|title=Ganymede's orbital and thermal evolution and its effect on magnetic field generation|journal=Lunar and Planetary Society Conference|date=March 2007|volume=38|page=2020| url=http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2020.pdf|format=PDF|bibcode=2007LPI....38.2020B|last2=Showman|last3=Tobie}}</ref> The formation of the grooved terrain may also be connected with the early core formation and subsequent tidal heating of the moon's interior, which may have caused a slight expansion of Ganymede by 1&ndash;6% due to [[w:phase transition|phase transition]]s in ice and [[w:thermal expansion|thermal expansion]].<ref name=Showman1999/>"<ref name=GanymedeMoon/>

"Ganymede also has polar caps, likely composed of water frost. The frost extends to 40° latitude.<ref name="The Grand Tour">{{cite book |title=The Grand Tour: A Traveler's Guide to the Solar System|last= Miller|first= Ron|authorlink= Ron Miller (artist and author)|author2=William K. Hartmann|date=May 2005|pages=108&ndash;114|publisher= Workman Publishing|location=Thailand|edition=3rd|isbn=0-7611-3547-2}}</ref> These polar caps were first seen by the [[w:Voyager program|''Voyager'']] spacecraft. Theories on the caps' formation include the migration of water to higher latitudes and bombardment of the ice by plasma. Data from ''Galileo'' suggests the latter is correct.<ref name="Polar caps">{{cite journal|last=Khurana|first=Krishan K.|author2=Pappalardo, Robert T.
|author3=Murphy, Nate
|author4=Denk, Tilmann|year=2007|title=The origin of Ganymede's polar caps|journal= Icarus|volume=191|issue=1|pages=193&ndash;202|doi=10.1016/j.icarus.2007.04.022|bibcode= 2007Icar..191..193K}}</ref>"<ref name=GanymedeMoon/>

"Additional evidence of the oxygen atmosphere comes from spectral detection of gases trapped in the ice at the surface of Ganymede. The detection of [[w:ozone|ozone]] (O<sub>3</sub>) bands was announced in 1996.<ref name=Noll1996>{{cite journal |last= Noll|first= Keith S.|date=July 1996|title=Detection of Ozone on Ganymede |journal= Science|volume=273|issue=5273|pages=341&ndash;343|url=http://www.sciencemag.org/cgi/content/abstract/273/5273/341|accessdate= 2008-01-13|doi=10.1126/science.273.5273.341|pmid=8662517|bibcode = 1996Sci...273..341N |author-separator= , |author2= Johnson |author3= Robert E. |display-authors= 2 |last4= Domingue |first4= D. L. |last5= Weaver |first5= H. A. }}</ref> In 1997 spectroscopic analysis revealed the [[w:Dimer (chemistry)|dimer]] (or [[w:diatomic|diatomic]]) absorption features of [[w:molecular oxygen|molecular oxygen]]. Such an absorption can arise only if the oxygen is in a dense phase. The best candidate is molecular oxygen trapped in ice. The depth of the dimer absorption bands depends on [[w:latitude|latitude]] and [[w:longitude|longitude]], rather than on surface [[w:albedo|albedo]]&mdash;they tend to decrease with increasing latitude on Ganymede, while O<sub>3</sub> shows an opposite trend.<ref name=Oxygen97>{{cite journal|last=Calvin|first=Wendy M.|author2=Spencer, John R.|date=December 1997|title=Latitudinal Distribution of O2 on Ganymede: Observations with the Hubble Space Telescope|journal=Icarus|volume=130 |issue=2|pages=505–516|doi=10.1006/icar.1997.5842|bibcode=1997Icar..130..505C}}</ref> Laboratory work has found that O<sub>2</sub> would not cluster or bubble but dissolve in ice at Ganymede's relatively warm surface temperature of 100 K.<ref>{{cite journal|last=Vidal|first=R. A.|author2=Bahr, D.|year=1997|title=Oxygen on Ganymede: Laboratory Studies |journal=Science|volume=276| issue=5320|pages=1839&ndash;1842|bibcode=1997Sci...276.1839V| doi=10.1126/science.276.5320.1839|pmid=9188525|display-authors=1}}</ref>"<ref name=GanymedeMoon/>

"[H]eavy ions continuously precipitate on the polar surface of the moon, [[w:sputtering|sputtering]] and darkening the ice.<ref name=Paranicas1999>{{cite journal|last=Paranicas|first=C.|title=Energetic particles observations near Ganymede|journal=J.of Geophys. Res.|year=1999|volume=104|issue=A8|pages=17,459&ndash;17,469| doi=10.1029/1999JA900199|bibcode=1999JGR...10417459P|author2=Paterson, W.R.|last3=Cheng|first3=A.F.|display-authors=2|last4=Mauk|first4=B. H.|last5=McEntire|first5=R. W.|last6=Frank|first6=L. A.|last7=Williams|first7=D. J.}}</ref>"<ref name=GanymedeMoon/>
{{clear}}

==Astromathematics==
[[Image:Galilean moon Laplace resonance animation.gif|right|thumb|365px|The [[w:Laplace resonance|Laplace resonance]]s of Ganymede, [[Europa]], and [[Io]] is illustrated. Credit: User:Matma Rex.]]
"[A]n orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. The physics principle behind orbital resonance is similar in concept to pushing a child on a swing, where the orbit and the swing both have a natural frequency, and the other body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances greatly enhance the mutual gravitational influence of the bodies, i.e., their ability to alter or constrain each other's orbits. In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of [[Jupiter]]'s moons '''Ganymede''', [[Europa]] and [[Io]], and the 2:3 resonance between [[Pluto]] and [[Neptune]]. Unstable resonances with [[Saturn]]'s inner moons give rise to gaps in the rings of Saturn. The special case of 1:1 resonance (between bodies with similar orbital radii) causes large [[Solar System]] bodies to eject most other bodies sharing their orbits; this is part of the much more extensive process of clearing the neighbourhood, an effect that is used in the current definition of a planet."<ref name=OrbitalResonance>{{ cite journal
|title=Orbital resonance
|journal=Wikipedia
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|month=March 12,
|year=2013
|url=http://en.wikipedia.org/wiki/Orbital_resonance
|accessdate=2013-05-16 }}</ref>
{{clear}}

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

==References==
{{reflist|2}}

==Further reading==

==External links==
* [http://www.ajol.info/ African Journals Online]
* [http://www.bing.com/search?q=&go=&qs=n&sk=&sc=8-15&qb=1&FORM=AXRE Bing Advanced search]
* [http://books.google.com/ Google Books]
* [http://scholar.google.com/advanced_scholar_search?hl=en&lr= Google scholar Advanced Scholar Search]
* [http://www.iau.org/ International Astronomical Union]
* [http://www.jstor.org/ JSTOR]
* [http://www.lycos.com/ Lycos search]
* [http://nedwww.ipac.caltech.edu/ NASA/IPAC Extragalactic Database - NED]
* [http://nssdc.gsfc.nasa.gov/ NASA's National Space Science Data Center]
* [http://www.osti.gov/ Office of Scientific & Technical Information]
* [http://www.ncbi.nlm.nih.gov/pccompound PubChem Public Chemical Database]
* [http://www.questia.com/ Questia - The Online Library of Books and Journals]
* [http://online.sagepub.com/ SAGE journals online]
* [http://www.adsabs.harvard.edu/ The SAO/NASA Astrophysics Data System]
* [http://www.scirus.com/srsapp/advanced/index.jsp?q1= Scirus for scientific information only advanced search]
* [http://cas.sdss.org/astrodr6/en/tools/quicklook/quickobj.asp SDSS Quick Look tool: SkyServer]
* [http://simbad.u-strasbg.fr/simbad/ SIMBAD Astronomical Database]
* [http://simbad.harvard.edu/simbad/ SIMBAD Web interface, Harvard alternate]
* [http://nssdc.gsfc.nasa.gov/nmc/SpacecraftQuery.jsp Spacecraft Query at NASA.]
* [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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