{{short description|Broad lava plain in the southern highlands of the planet Mars}}
{{Infobox feature on celestial object |name = Hesperia Planum |image = Hesperia Topo Map.jpg |caption = [[Mars Orbital Laser Altimeter|MOLA]] colorized relief map of Hesperia Planum region. Hesperia Planum has fewer impact craters than the surrounding [[Noachian]] highlands of [[Tyrrhena Terra]] and [[Terra Cimmeria]]. This indicates that the plain is younger than its more heavily cratered surroundings. | location = [[Mare Tyrrhenum quadrangle]], [[Mars]] | type = Lava plain |coordinates = {{coord|21|25|S|109|53|E|globe:mars_type:landmark|display=inline,title}} |coordinates_footnotes = <ref name=gpn>{{gpn|2488|Hesperia Planum}} (Center Latitude: -21.42°, Center Longitude: 109.89°)</ref> |diameter = ~1 600 km<ref name=gpn/> |eponym = Poetic ''Hesperia'' }}
'''Hesperia Planum''' is a broad [[lava plain]] in the southern highlands of the planet [[Mars]]. The plain is notable for its moderate number of [[impact crater]]s and abundant [[wrinkle ridge]]s. It is also the location of the ancient [[volcano]] Tyrrhena Mons ([[Tyrrhena Patera]]). The [[Hesperian]] time period on Mars is named after Hesperia Planum.<ref name=ScottCarr78>Scott, D.H.; Carr, M.H. (1978). Geologic Map of Mars. U.S. Geological Survey Miscellaneous Investigations Series Map I-1083.</ref><ref>Morton, 2002, p. 117.</ref> [[File:Wikiterracimmeriaboundaries.jpg|right|thumb|320px|MOLA map showing exact boundaries of it and other regions. Color indicates elevation.]]
==Name origin== [[File:PIA00182-MC-22-MareTyrrhenumRegion-19980605.jpg|left|thumb|280px|[[Viking program|Viking]] [[NASA World Wind#Extraterrestrial datasets|MDIM]] of [[Mare Tyrrhenum quadrangle]]. Hesperia is the intermediate-toned (dusky) region (left of center) lying between the darker regions Mare Tyrrhenum (left) and Mare Cimmerium (right).]] Most place names on Mars are derived from sources in the [[Bible]] or [[classical antiquity]].<ref>Hartmann, 2003, p. 12.</ref> ''[[wikt:Hesperia|Hesperia]]'' is a Greco-Latin poetic term for "lands to the west," which to the [[Ancient Greece|ancient Greeks]] and [[Ancient Rome|Romans]] meant [[Italy]], while [[Spain]] was referred as ''Hesperia Ultima''.<ref name=GPN1>{{gpn|2486|Hesperia}}</ref><ref>Simpson, D.P. (1968). ''Cassell's New Latin Dictionary;'' Funk & Wagnalls: New York, p. 275.</ref> ''Planum'' (pl. ''plana'') is [[Latin]] for plateau or high plain. It is a [[Planetary nomenclature#Descriptor terms (feature types)|descriptor term]] used in [[planetary geology]] for a relatively smooth, elevated terrain on another [[planet]] or [[Natural satellite|moon]].<ref name=GPN2>USGS Gazetteer of Planetary Nomenclature. https://planetarynames.wr.usgs.gov/DescriptorTerms.</ref>
The Hesperia region of Mars was named by Italian astronomer [[Giovanni Schiaparelli]] in 1877 for an intermediate-toned [[classical albedo features on Mars|albedo feature]] centered at lat. 20°S, long. 240°W between two darker regions.<ref name=GPN1 /><ref>Hartmann, 2003, p. 199.</ref> Believing the dark areas were bodies of water, Schiaparelli interpreted Hesperia to be a [[floodplain]] or [[marsh]] bridging two adjacent seas, the Mare Tyrrhenum and Mare Cimmerium.<ref>Sheehan, 1996, p. 223.</ref> Although the existence of seas on Mars had been discounted by the early 20th century,<ref>Moore, P. (1954). The Planet Mars in ''Realities of Space Travel: Selected Papers of the British Interplanetary Society,'' L.J. Carter, Ed.; McGraw-Hill: New York, p. 320.</ref> the true nature of the region remained obscure until the [[space age]]. In 1972, the [[Mariner 9]] spacecraft showed that Hesperia was a cratered, wind-streaked plain.<ref>Sagan, C. ''et al.'' (1972). Variable Features on Mars: Preliminary Mariner 9 Television Results. ''Icarus,'' '''17,''' 346–372.</ref> The [[International Astronomical Union]] (IAU) formally named the area Hesperia Planum in 1973.<ref name=GPN3>{{gpn|2488}}</ref> The dark areas flanking Hesperia Planum were found to be heavily cratered uplands. In 1979, the IAU designated the upland area to the west as [[Tyrrhena Terra]] and to the east as [[Terra Cimmeria]].<ref>{{cite web|publisher=USGS Gazetteer of Planetary Nomenclature |url=https://planetarynames.wr.usgs.gov/SearchResults?target=MARS&featureType=Terra,%20terrae|title=Terra, terrae}}</ref> (''Terra'' is a Latin descriptor term meaning land or continent.)
==Location and physical description== [[File:NW Hesperia PSP 010337 1650 RED.jpg|right|thumb|320px|Closeup of the surface of northwestern Hesperia Planum, as seen by [[HiRISE]] camera on [[Mars Reconnaissance Orbiter]] (MRO).]] Hesperia Planum is located along the broad northeastern rim of the giant [[Hellas Planitia|Hellas impact basin]]<ref name=Ivanovetal05>Ivanov, M. A.; Korteniemi, J.; Kostama, V.-P.; Aittola, M.; Raitala, J.; Glamoclija, M.; Marinangeli, L.; Neukum, G. (2005), "Major Episodes of the Hydrologic History in the Region of Hesperia Planum", Mars. ''J. Geophys. Res.,'' '''110,''' E12S21, {{doi|10.1029/2005JE002420}}.</ref> and is centered at lat. 22.3°S, long. 110°E in the [[Mare Tyrrhenum quadrangle]] (MC-22). A small part of this region in the south is found in the [[Hellas quadrangle]]. It has a maximum width of {{convert|1,700|km|mi|abbr=on}}<ref name=GPN3 /> and covers an area of about {{convert|2|e6km2|sqmi|abbr=unit}}.<ref name=GreggCrown05>Gregg, T. K. P.; Crown, D. A. (2005). [http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1962.pdf ''What is Hesperia Planum, Mars? An Examination of Multiple Working Hypotheses''.] (PDF) 36th Lunar and Planetary Science Conference, Abstract #1962.</ref>
At large scales (>{{cvt|100|m|ft|disp=or}}), Hesperia Planum appears smooth and level,<ref>Greeley, R. (1994). ''Planetary Landscapes,'' 2nd ed.; Chapman & Hall: New York, p. 162. {{ISBN|0-412-05181-8}}.</ref> having a relatively uniform surface elevation of {{cvt|1.2|km}} above [[Geography of Mars#Zero elevation|Mars datum]].<ref>Kostama, V.-P.; Ivanov, M. A.; Korteniemi, J.; Aittola, M.; Raitala, J.; Glamoclija, M.; Marinangeli, L.; Neukum, G.; and the HRSC Co-Investigator Team. (2005). [http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1659.pdf ''Major Episodes of the Hydrologic History of Hesperia Planum, Mars''.] (PDF) 36th Lunar and Planetary Science Conference, Abstract #1659.</ref> The plain's surface is {{cvt|200|–|800|m}} lower in elevation than the surrounding uplands of Tyrrhena Terra and Terra Cimmeria and is slightly tilted to the south, with a mean regional slope of about 0.03°.<ref name=Ivanovetal05 /> In high-resolution images (<{{cvt|19|m|ft|disp=or}}/pixel), the surface of Hesperia Planum is dominated by dust and fine-grained deposits. Few boulders or bedrock outcrops are visible. Abundant, shallow craters filled with smooth, flat-lying deposits are common. No vents or volcanic constructs are identifiable, although small (<10s meters wide) channels are present.<ref name=GreggdeSilva09 />
==Geology== Hesperia Planum is generally interpreted to be composed of [[Flood basalt|flood lavas]],<ref name= GreeleySpudis81/> although layered [[volcaniclastic]] or [[Lake|lacustrine]] (lake-bed) sediments cannot be ruled out.<ref name=GreggdeSilva09>Gregg, T. K. P.; de Silva, S. (2009). Tyrrhena Patera and Hesperia Planum, Mars: New Insights (and Old Interpretations) from High-Resolution Imagery. 40th Lunar and Planetary Science Conference, Abstract #1700. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1700.pdf.</ref> The lavas appear to partly fill a large, irregular topographic depression that existed in [[Noachian]] times. The rims of pre-existing impact craters are still visible in places, indicating that the lava deposits are 250–500 m in thickness. The volume of lavas within Hesperia Planum is comparable to that found in [[large igneous province]]s on Earth, such as the [[Columbia River Basalt Group]].<ref name=Ivanovetal05/>
===Impact cratering and age=== [[File:Viking 418S39 Hesperia.jpg|left|thumb|280px|[[Viking program|Viking orbiter]] view of [[wrinkle ridge]]s in Hesperia Planum. North is at upper left. Image is about {{convert|107|km|mi|abbr=on}} across.<ref>Boyce, 2008, p. 89.</ref>]] The moderate amount of cratering on Hesperia Planum indicates that the plain has an intermediate age in Martian history. In [[planetary geology]], the number density of impact craters is a measure of the [[relative dating|relative age]] of a planetary surface. Heavily cratered surfaces are old, and sparsely cratered surfaces are young. Hesperia Planum is the [[Type locality (geology)|type locality]] for the [[Hesperian]] System and time period. The lavas making up Hesperia Planum define the base of the Hesperian [[System (stratigraphy)|System]].<ref>Tanaka, K.L. (1986). The Stratigraphy of Mars. ''J. Geophys. Res.,'' Seventeenth Lunar and Planetary Science Conference Part 1, '''91'''(B13), E139–E158.</ref> They erupted at the beginning of the Hesperian Period around 3700 million years ago.<ref>[[Stephanie C. Werner|Werner, S.C.]] (2009). The Global Martian Volcanic Evolutionary History. ''Icarus,'' '''201,''' 44–68.</ref> (Mars itself, along with the other planets, formed about 4500 million years ago.) Hesperian lavas are younger than the rocks in the heavily cratered [[Noachian]] terrains but older than rocks formed during the more recent Amazonian Period. (See [[Geology of Mars#Crater density timescale|Geology of Mars]].)
===Wrinkle ridges=== Wrinkle ridges are long, linear [[topography|topographic]] highs with a distinctive morphology that consists of a low, broad arch topped by a narrow crenulated ridge (pictured left). They are common features on the Moon where they occur exclusively within lava flow plains (the lunar [[Lunar mare|maria]]).<ref>Carr, 2006, p. 89.</ref> Their occurrence on Mars is thought to reflect a similar volcanic association. Thus, areas on Mars with abundant wrinkle ridges are interpreted as plains formed by very fluid basaltic lava ([[flood basalt]]s). The ridges themselves are believed to be the surface expression of [[thrust fault]]s formed after the lava flows were emplaced.<ref>Golombek, M.P.; Anderson, F.S.; Zuber, M.T. (2001). Martian Wrinkle Ridge Topography: Evidence for Subsurface Faults from MOLA. ''J. Geophys. Res.,'' '''106'''(El0), 23,811–23,821.</ref><ref>Montési, L. G. J.; Zuber, M.T. (2003). Clues to the Lithospheric Structure of Mars from Wrinkle Ridge Sets and Localization Instability. ''J. Geophys. Res.,'' '''108'''(E6), 5048, {{doi|10.1029/2002JE001974}}.</ref> They are not volcanic features, but secondary, [[tectonics|tectonic]] structures that form in dense, competent rocks (such as layered basalts) that have undergone compressional stress. Hesperian-aged "ridged plains" like Hesperia Planum cover about 30% of the Martian surface.<ref name=GreeleySpudis81>Greeley, R.; Spudis, P. (1981). Volcanism on Mars. ''Rev. Geophys. Space Phys.''''', 19'''(1), 13–41.</ref>
===Tyrrhenus Mons=== [[File:Tyrrhena Mons.jpg|right|thumb|320px|[[Thermal Emission Imaging System|THEMIS]] daytime IR mosaic image of Tyrrhenus Mons. This ancient, eroded volcano was nicknamed the Dandelion when first seen in [[Mariner 9]] images.<ref>Morton, 2002, p. 103.</ref>]] Tyrrhenus Mons ([[Tyrrhena Patera]]) is an eroded, low-lying volcano in the western part of Hesperia Planum. It is one of the oldest large central-vent volcanoes on the planet<ref name=GreeleyCrown90>Greeley, R.; Crown, D.A. (1990). Volcanic Geology of Tyrrhena Patera, Mars. ''J. Geophys. Res.,'' '''95'''(B5), 7133–7149.</ref> and a member of a class of volcanoes called [[Volcanism on Mars#Highland Paterae|highland paterae]], which erupted mainly in the Late [[Noachian]] and Early [[Hesperian]].<ref name=Crownetal07>Crown, D. A.; Berman, D. C.; Gregg, T. K. P. (2007). Geologic Diversity and Chronology of Hesperia Planum, Mars. 38th Lunar and Planetary Science Conference, Abstract #1169. http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1169.pdf.</ref> Tyrrhenus Mons stands only 1.5 km above the surrounding plains. At its center lies a 40 km diameter depression, or [[caldera]], from which radiate numerous flat-floored valleys and ridges that suggest the volcano has been highly eroded. The low relief of Tyrrhenus Mons combined with its degraded state indicate the volcano consists largely of [[friable]] and easily eroded material such as [[volcanic ash]]. The ash was likely derived from the interaction of [[magma]] with [[groundwater]] or ice.<ref>Carr, 2006, pp. 69, 74, Fig. 3.33.</ref>
===Dunes=== <gallery class="center" widths="190px" heights="180px"> ESP 045822 1680dunes.jpg|Dunes, as seen by HiRISE under HiWish program 45822 1680dunesclose.jpg|Close view of dunes, as seen by HiRISE under HiWish program 45822 1680color.jpg|Close, color view of dunes as seen by HiRISE under HiWish program Ripples are visible on dune surface. </gallery>
==References== {{reflist|colwidth=30em}}
==Bibliography and recommended reading== * Boyce, Joseph, M. (2008). ''The Smithsonian Book of Mars;'' Konecky & Konecky: Old Saybrook, CT, {{ISBN|978-1-58834-074-0}} * Carr, Michael, H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, {{ISBN|978-0-521-87201-0}}. * Hartmann, William, K. (2003). ''A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet;'' Workman: New York, {{ISBN|0-7611-2606-6}}. * Morton, Oliver (2003). ''Mapping Mars: Science, Imagination, and the Birth of a World;'' Picador: New York, {{ISBN|0-312-42261-X}}. * Sheehan, William (1996). ''The Planet Mars: A History of Observation & Discovery;'' University of Arizona Press: Tucson, AZ, {{ISBN|0-8165-1640-5}}. http://www.uapress.arizona.edu/onlinebks/MARS/CONTENTS.HTM {{Webarchive|url=https://web.archive.org/web/20090601041317/http://www.uapress.arizona.edu/onlinebks/MARS/CONTENTS.HTM |date=2009-06-01 }}.
==External links== {{commons category|Hesperia Planum}} * [https://pubs.usgs.gov/sim/3245/ Geologic Map of Reull Vallis Region of Mars], includes a portion of southern Hesperia Planum, by Astrogeology Science Center, U.S. Geological Survey
{{Geography of Mars|topography}} {{Portal bar|Solar System}}
[[Category:Lava fields]] [[Category:Plains on Mars]] [[Category:Extraterrestrial plateaus]] [[Category:Mare Tyrrhenum quadrangle]] [[Category:Hellas quadrangle]]