{{Short description|Planitia on Mars}} {{Infobox feature on celestial object |name = Acidalia Planitia |image = Acidalia planitia topo.jpg |caption = Topographic map of Acidalia Planitia |coordinates = {{coord|49.76|N|339.26|E|globe:mars_type:landmark|display=inline,title}} |diameter = 3362.97 km |type = Plains }} '''Acidalia Planitia''' is a [[plain]] on [[Mars]], between the [[Tharsis]] volcanic province and [[Arabia Terra]] to the north of [[Valles Marineris]], centered at {{coord|49.8|339.3|globe:Mars}}.<ref name = "USGS_Acidalia_Planitia"> {{cite web | title = Acidalia Planitia | work = Gazetteer of Planetary Nomenclature | publisher = [[USGS Astrogeology Science Center]] | url = https://planetarynames.wr.usgs.gov/Feature/38 | access-date = 2015-03-10 | archive-url = https://archive.today/20160601131028/http://planetarynames.wr.usgs.gov/Feature/38 | archive-date = 2016-06-01 | url-status = dead }} </ref> Most of this region is found in the [[Mare Acidalium quadrangle]], but a small part is in the [[Ismenius Lacus quadrangle]]. The plain contains the famous [[Cydonia (Mars)|Cydonia]] region at the contact with the heavily cratered highland terrain.
The plain is named after a corresponding [[albedo feature]] on a map by [[Giovanni Schiaparelli]], which was in turn named after the mythological [[Venus (mythology)#Epithets|fountain of Acidalia]]. Some places in Acidalia Planitia show cones, which some researchers have suggested are mud volcanoes. The scientific community is divided over whether an ancient [[ocean]] existed on the plain and other parts of the northern lowlands.<ref>{{Cite web|url=https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19796|title=The Martian, Part 1: Acidalia Planitia|website=www.jpl.nasa.gov|access-date=2017-04-10|archive-date=2017-04-05|archive-url=https://web.archive.org/web/20170405045809/https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19796|url-status=live}}</ref>
== Geological history == [[File:MOLA_Map.png|thumb|363x363px|Topographical map generated from MOLA data including feature boundaries. Acidalia Planitia is the central, northernmost feature characterized by dark blue, low elevation land.]]There are several hypotheses regarding the geological history of Acidalia Planitia based on evidence from satellite data.
=== Springs and steam vents === Acidalia Planitia was once covered by ancient crust. Its surface eroded into knobs of iron/magnesium [[phyllosilicates]] during the [[Amazonian (Mars)|Amazonian]].<ref name=":0">{{Cite journal|last=Pan|first=L.|last2=Ehlmann|first2=B. L.|date=2014-03-28|title=Phyllosilicate and hydrated silica detections in the knobby terrains of Acidalia Planitia, northern plains, Mars|journal=Geophysical Research Letters|language=en|volume=41|issue=6|pages=1890–1898|doi=10.1002/2014GL059423|issn=1944-8007|bibcode=2014GeoRL..41.1890P|url=https://authors.library.caltech.edu/53021/1/grl51515.pdf|doi-access=free|access-date=2019-09-19|archive-date=2018-07-23|archive-url=https://web.archive.org/web/20180723045218/https://authors.library.caltech.edu/53021/1/grl51515.pdf|url-status=live}}</ref> Sediments filled the empty plain, leaving the phyllosilicate knobs as protrusions through the surface. The spatial density of these knobs is consistent with the ancient crust that was once above Acidalia Planitia.<ref name=":0" />
Hydrated silica materials surround the phyllosilicate knobs and the sides of rocky slopes. Rather than covering the entire surface, these features are localized.<ref name=":0" /> This indicates that the plain was once home to springs and steam vents not extensive bodies of water such as oceans or [[glacier]]s.<ref name=":0" />
=== Oceans === [[Utopia Planitia]] is a similar plain at the same latitude as Acidalia Planitia.<ref>{{Cite web|url=https://planetarynames.wr.usgs.gov/Feature/38;jsessionid=9B11820B35648760AF2DDFB459362740|title=Planetary Names: Planitia, planitiae: Acidalia Planitia on Mars|website=planetarynames.wr.usgs.gov|language=en|access-date=2017-04-10|archive-date=2017-04-21|archive-url=https://web.archive.org/web/20170421093910/https://planetarynames.wr.usgs.gov/Feature/38;jsessionid=9B11820B35648760AF2DDFB459362740|url-status=live}}</ref> Etched flows in its terrain suggest that mud flowed into Utopia Planitia creating a large reservoir of water and mud in the deepest part of the basin, about 1000 km across. This may have been the remnants of a more extensive ocean that covered all of the northern lowlands including Acidalia Planitia.<ref name=":1">{{Cite journal|last=Ivanov|first=M. A.|last2=Hiesinger|first2=H.|last3=Erkeling|first3=G.|last4=Reiss|first4=D.|date=2015-03-01|title=Evidence for large reservoirs of water/mud in Utopia and Acidalia Planitiae on Mars|journal=Icarus|volume=248|pages=383–391|doi=10.1016/j.icarus.2014.11.013|bibcode=2015Icar..248..383I}}</ref> The [[Vastitas Borealis|Vastitas Borealis Formation]] (VBF) stretched across both Utopia and Acidalia Planitiae and delineated the threshold for an ancient ocean. The two segments of the VBF at Utopia and Acidalia have congruent ages, reliefs, crater frequencies, [[albedo]]s, thermal properties, and [[Law of superposition|superpositions]] of geological features. This suggests that the Acidalia Planitia may have once been covered by a large Martian ocean.<ref name=":1" />
=== Glaciers === Craters on Acidalia Planitia are asymmetrical. [[Mars Orbiter Laser Altimeter|Mars Orbital Laser Altimeter]] (MOLA) data revealed that the slopes of the pole-facing crater walls are shallower than the equator-facing slopes.<ref name=":3">{{Cite journal|last=Conway|first=Susan J.|last2=Mangold|first2=Nicolas|date=2013-07-01|title=Evidence for Amazonian mid-latitude glaciation on Mars from impact crater asymmetry|journal=Icarus|volume=225|issue=1|pages=413–423|doi=10.1016/j.icarus.2013.04.013|bibcode=2013Icar..225..413C|url=https://hal-insu.archives-ouvertes.fr/insu-02276810/file/HAL_Conway_Icarus_2013.pdf|access-date=2019-09-26|archive-date=2019-09-26|archive-url=https://web.archive.org/web/20190926153558/https://hal-insu.archives-ouvertes.fr/insu-02276810/file/HAL_Conway_Icarus_2013.pdf|url-status=live}}</ref> Other studies show the opposite asymmetry to be true. The two theories indicate either biased glacial deposition during the Amazonian era or long-term creep of hundreds of meters of ice-rich [[regolith]] beneath the surface, respectively.<ref name=":3" />
== Geological features == [[File:24951gullyclose.jpg|left|thumb|274x274px|A gully found in the Bamberg Crater, which resides in Acidalia Planitia]]
===Gullies=== 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 are 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.
=== Mud volcanoes === [[File:Possible_mud_volcano_on_Acidalia_Planitia_by_HiRISE.jpg|thumb|Possible mud volcano in Acidalia Planitia]] Cone-shaped features with higher albedo than surrounding rocks litter the surface of Acidalia Planitia. The most similar terrestrial feature to these formations are [[mud volcano]]es.<ref name=":2">{{Cite journal|last=Oehler|first=Dorothy Z.|last2=Allen|first2=Carlton C.|date=2010-08-01|title=Evidence for pervasive mud volcanism in Acidalia Planitia, Mars|journal=Icarus|volume=208|issue=2|pages=636–657|doi=10.1016/j.icarus.2010.03.031|bibcode=2010Icar..208..636O}}</ref> On Mars, mud volcanoes have an average diameter of ~1 km and a relief of 10 to 180 meters. Their higher albedo is a result of more crystalline [[Iron(III) oxide|iron oxides]] than the rest of Acidalia Planitia.<ref name=":2" /> Mud volcanoes erupt sediments from deep beneath the surface and change the rising rocks very minimally. These rocks are used to analyze organic matter as mud volcanoes also create subterranean conduits for ancient ground water that may have hosted [[microbiota]].<ref name=":2" />
== In popular culture == In the 2011 novel ''[[The Martian (Andy Weir)|The Martian]]'' by Andy Weir, and [[The Martian (film)|its 2015 film adaptation]], Acidalia Planitia is the landing site of the Ares III mission, where the protagonist is stranded following a dust storm.<ref>{{cite book|last=Weir|first=Andy|title=The Martian|year=2014|location=[[New York City|New York]]|publisher=[[Crown Publishers]]|isbn=978-0-8041-3902-1|title-link=The Martian (Andy Weir)}}</ref>
==See also== *[[Geography of Mars]] *[[List of plains on Mars]] *[[Martian Gullies]] *[[North Polar Basin (Mars)|Martian North Polar Basin]]
== References == {{Reflist}}
== External links == {{Commons category}} *[http://www.google.com/mars/#lat=44&lon=-21&q=Acidalia%20Planitia%20albedo Google Mars zoomable map centered on Acidalia Planitia]
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[[Category:Plains on Mars]] [[Category:Mare Acidalium quadrangle]] [[Category:Ismenius Lacus quadrangle]]