{{About|the crater on Mars|the lunar crater|Slipher (lunar crater)}} {{Infobox crater data | titlecolor = #FA8072 | title = Slipher Crater | image = SlipherMartianCrater.jpg | caption = Topographic location map of Slipher Crater. | coordinate_title = [[Mars#Geography|Coordinates]] | globe = Mars | coordinates = {{coord|47.3|S|84.6|W|globe:mars_type:landmark|display=inline,title}} | diameter = {{cvt|127|km}} | eponym = [[Vesto Slipher|Vesto]] and [[Earl Slipher|Earl]] Slipher }}
'''Slipher''' is an [[impact crater]] in the [[Thaumasia quadrangle]] of [[Mars]], located at 47.3°S latitude and 84.6°W longitude. It measures {{convert|127|km}} in diameter and was named after American astronomers [[Vesto Slipher|Vesto]] and [[Earl Slipher]]. The naming was approved by IAU's [[Working Group for Planetary System Nomenclature]] in 1973.<ref>{{cite web|url=https://planetarynames.wr.usgs.gov/Feature/5600 |title=Slipher on Mars |work=Gazetteer of Planetary Nomenclature |author=[[International Astronomical Union]] (IAU) Working Group for Planetary System Nomenclature (WGPSN) |publisher=US Geological Survey |access-date=2 February 2021}}</ref>
== Description == Gullies are visible on the walls of a crater that is on the rim of Slipher. They can be seen in the pictures below. [[Gullies on Mars|Martian gullies]] are small, incised networks of narrow channels and their associated downslope [[sediment]] deposits, found on the planet of Mars. They are named for their resemblance to terrestrial [[gully|gullies]]. First discovered on images from [[Mars Global Surveyor]], they occur on steep slopes, especially on the walls of craters. Usually, each gully has a [[Dendritic drainage#Drainage patterns|dendritic]] ''alcove'' at its head, a [[Alluvial fan|fan-shaped]] ''apron'' at its base, and a single thread of incised ''channel'' linking the two, giving the whole gully an hourglass shape.<ref name="Malin, M. 2000">Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and [[surface runoff]] on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research.
As soon as gullies were discovered,<ref name="Malin, M. 2000"/> researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.<ref>Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.</ref> Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water.<ref>Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.</ref><ref>McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.</ref><ref>Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.</ref> With continued observations many more changes were found in Gasa Crater and others.<ref>NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. www.sciencedaily.com/releases/2014/03/140322094409.htm</ref>
With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.<ref>{{Cite web|url=http://www.jpl.nasa.gov/news/news.php?release=2014-226|title=NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars|website=[[Jet Propulsion Laboratory]]}}</ref><ref>{{Cite web|url=http://hirise.lpl.arizona.edu/ESP_032078_1420|title=HiRISE | Activity in Martian Gullies (ESP_032078_1420)}}</ref><ref>{{Cite web|url=http://www.space.com/26534-mars-gullies-dry-ice.html|title = Gullies on Mars Carved by Dry Ice, Not Water|website = [[Space.com]]|date = 16 July 2014}}</ref> In some years frost, perhaps as thick as 1 meter.
<gallery heights="180px" mode="packed"> File:Slipher crater 053A56.jpg|[[Viking program|Viking Orbiter 1]] image with Slipher crater at bottom File:Wikislipher.jpg|Slipher crater on Mars, as seen by [[Mars Reconnaissance Orbiter|MRO]]'s CTX camera File:Wikisliphergullies.jpg|Gullies in crater on the rim of Slipher. This is an enlargement of the previous image. File:Pedestal crater in Slipher crater F04 037244 1323 XN 47S085W.jpg|The small pedestal crater in the northwestern floor of Slipher </gallery>
== See also == * [[List of craters on Mars]]
== References == {{reflist}}
{{Geography of Mars}}
[[Category:Thaumasia quadrangle]] [[Category:Impact craters on Mars]]