Difference between revisions 2239252 and 2240732 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.

(contracted; show full)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
|pages=1350–1356
|volume=11 }}</ref> but are considered unreliable because of excess Ar<ref name=Duffield>{{ cite journal
|author=Duffield, Wendell A
; ⏎
|author2=Riggs, Nancy; ⏎
|author3=Kaufman, Darrell; ⏎
|author4=Champion, Duane; ⏎
|author5=Fenton, Cassandra; ⏎
|author6=Forman, Steven; ⏎
|author7=McIntosh, William; ⏎
|author8=Hereford, Richard; ⏎
|author9=Plescia, Jeffrey; ⏎
|author10=Ort, Michael
|title=Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona
|journal=Geological Society of America Bulletin
|volume=118
|issue=3-4
|pages=421-9
|year= 2006 }}</ref> and the un-weathered young appearance of the cone.

(contracted; show full)
|title=Landscapes from the ancient and eroded lunar far side 
|publisher=esa 
|url=http://www.esa.int/esaSC/SEMDWNWALPE_index_0.html 
|accessdate=15 February 2010 }}</ref>

The topography of the Moon has been measured with laser altimetry [using the sodium D2 line in the yellow] and stereo image analysis.<ref name=Spudis>{{ cite journal
|title=Topography of the South Polar Region from Clementine Stereo Imaging
|author=Spudis, Paul D.
; Cook, A.; Robinson, M.; Bussey, B.; ⏎
|author2=Cook, A.
|author3=Robinson, M.
|author4=Bussey, B.
|author5=Fessler, B.
| bibcode=1998nvmi.conf...69S
|journal=Workshop on New Views of the Moon: Integrated Remotely Sensed, Geophysical, and Sample Datasets
|page=69
|date=01/1998
(contracted; show full)
| url=http://lasp.colorado.edu/icymoons/europaclass/Zahnle_etal_1998.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.
; ⏎
|author2=Rice, J. W.; ⏎
|author3=Wilhelms, D. E.; ⏎
|author4=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>

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