{{short description|Martian valley}} {{Infobox feature on celestial object |name = Niger Vallis |image = [[Image:Dao Niger and Harmakhis Vallis PIA02810.jpg|250px]] |caption = Niger Vallis is the middle of the three channels pictured, joining Dao Vallis in the upper center of the image. The direction of water flow was toward the bottom of the image. |coordinates = {{coord|35.4|S|267.8|W|globe:mars_type:landmark|display=inline,title}} |length = 333.0 km |naming = River in Africa. }}
'''Niger Vallis''' is a valley on [[Mars]] that appears to have been carved by water. It has been identified as an [[outflow channel]].<ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> It merges with [[Dao Vallis]] which runs southwestward into [[Hellas Planitia]] from the volcanic [[Hadriacus Mons]].<ref name="a">{{cite journal|title=Geologic Evolution of Dao Vallis, Mars|author=Crown, D. A.|author2=Bleamaster, L. F.|author3=Mest, S. C.|journal=AGU Fall Meeting Abstracts |publisher= American Geophysical Union, Fall Meeting 2003, abstract #P11B-1035|date=December 2003|volume=2003 |bibcode=2003AGUFM.P11B1035C}}</ref> Like Dao, it was formed around the Late Noachian and Early Hesperian [[Geology of Mars#Crater density timeline|Epoch]]s.<ref name="a" /> It is named after the [[Niger River]] in [[Africa]].
== Ice-rich mantle == Much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.<ref>Head, J. et al. 2003. Recent ice ages on Mars. Nature:426. 797-802.</ref> This ice-rich mantle, a few yards thick, smooths the land, but in places it has a bumpy texture, resembling the surface of a basketball. Because there are few craters on this mantle, the mantle is relatively young. An image below shows a good view of this smooth mantle around Niger Vallis, as observed with [[HiRISE]].
Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.<ref>MLA NASA/Jet Propulsion Laboratory (2003, December 18). Mars May Be Emerging From An Ice Age. ScienceDaily. Retrieved February 19, 2009, from https://www.sciencedaily.com/releases/2003/12/031218075443.htmAds{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes }} by GoogleAdvertise</ref>
<gallery> Image:Niger Vallis hirise.JPG|Niger Vallis with features typical of this latitude, as seen by [[HiRISE]]. Click on image to see chevron pattern and mantle.
</gallery>
==Notes== {{reflist|1}}
==External links== * [https://www.google.com/mars/#lat=-36.102376&lon=91.076660&zoom=6&q=niger%20vallis Google Mars map centred on Niger Vallis]. {{Geography of Mars}} {{Portal bar|Solar System}}
[[Category:Valleys and canyons on Mars]] [[Category:Hellas quadrangle]]