{{Short description|Planitia on Mars}} {{Use dmy dates|date=February 2021}} {{Infobox feature on celestial object | name = Hellas Planitia | image = Hellas Planitia by the Viking orbiters.jpg | caption = [[Viking program#Viking orbiters|Viking orbiter]] image mosaic of Hellas Planitia | location = [[:Category:Hellas quadrangle|Hellas quadrangle]], [[Mars]] | coordinates = {{coord|42.4|S|70.5|E|globe:mars_type:landmark|display=inline,title}} | diameter = {{circa}} {{convert|2300|km|mi|abbr=on}} |age={{circa}} 4 billion years|imp_size={{circa}} 370 km}} [[Image:Hellas MOLA zoom 64 medium.jpg|thumb|260px|Topographic map of Hellas Planitia and its surroundings in the southern uplands, from the [[Mars Orbiter Laser Altimeter|MOLA]] instrument of ''[[Mars Global Surveyor]]''. The crater depth is {{convert|7152|m|ft|abbr=on}} below the standard topographic [[datum (geodesy)|datum]] of Mars.<ref name="stanhellas">{{cite web |title=Martian weather observation |series=[[Mars Global Surveyor]] |url=http://www-star.stanford.edu/projects/mgs/sum/s0403210230.html |publisher=[[Stanford University]] |place=Palo Alto, California |archive-url=https://web.archive.org/web/20080531235046/http://www-star.stanford.edu/projects/mgs/sum/s0403210230.html |archive-date=2008-05-31 }} MGS radio science measured 11.50 mbar at 34.4° S 59.6° E −7152 meters</ref>]]
'''Hellas Planitia''' {{IPAc-en|'|h|ɛ|l|ə|s|_|p|l|ə|'|n|ɪ|ʃ|i|ə}} is a [[Planitia|plain]] located within the huge, roughly circular [[impact basin]] '''Hellas'''{{efn|Technically, ''Hellas'' is an 'albedo feature'.<ref name = "USGS_Hellas">{{cite web | title = Hellas | website = Gazetteer of Planetary Nomenclature | publisher = [[United States Geological Survey]] | department = [[USGS Astrogeology Science Center]] | url = https://planetarynames.wr.usgs.gov/Feature/2429 | access-date = 2015-03-10}}</ref>}} located in the southern [[Sphere|hemisphere]] of the [[planet]] [[Mars]].<ref name = "USGS_Hellas_Planitia">{{cite web | title = Hellas Planitia | work = Gazetteer of Planetary Nomenclature | publisher = [[USGS Astrogeology Science Center]] | url = https://planetarynames.wr.usgs.gov/Feature/2432 | access-date = 2015-03-10}}</ref> Hellas is the fourth or [[List of largest craters in the Solar System|fifth-largest known impact crater in the Solar System]]. The basin floor is around {{convert|7152|m|ft|abbr=on}} deep, {{convert|3000|m|ft|abbr=on}} deeper than the Moon's [[South Pole-Aitken basin]], and extends about {{convert|2300|km|mi|abbr=on}} east to west.<ref name="Ref_">The part below zero datum, see [[Geography of Mars#Zero elevation]]</ref><ref name="Ref_a">{{cite web |url=http://rst.gsfc.nasa.gov/Sect19/Sect19_12.html |series=Remote sensing tutorial |title=Section 19-12 |archive-url=https://web.archive.org/web/20041030132127/http://rst.gsfc.nasa.gov/Sect19/Sect19_12.html |archive-date=2004-10-30 |publisher=NASA |url-status=dead |department=[[Goddard Space Flight Center]]}}</ref> It is centered at {{Coord|42.4|S|70.5|E|globe:mars_type:landmark|notes=.<ref name = "USGS_Hellas_Planitia"/>}} It features the [[Badwater Crater|lowest point on Mars]],<ref>{{cite web | title=Highest and Lowest Points on Mars | first=Hobart M. | last=King | website=geology.com – Geoscience news and information | url=https://geology.com/articles/highest-point-on-mars.shtml#mars-low-point | access-date=2024-12-11 }}</ref> serves as a known source of global dust storms, and may have contained lakes and glaciers.<ref name="Bleamaster & Crown 2010">{{cite web |last1=Bleamaster |first1=Leslie F. III |last2=Crown |first2=David A. |title=Geologic Map of MTM -40277, -45277, -40272, and -45272 Quadrangles, Eastern Hellas Planitia Region of Mars |website=U.S. Geological Survey Publications Warehouse |date=2010-03-19 |url=https://pubs.usgs.gov/sim/3096/ |access-date=2024-06-30}}</ref> Hellas Planitia spans the boundary between the [[Hellas quadrangle]] and the [[Noachis quadrangle]].
==Description== With a [[diameter]] of about {{convert|2300|km|mi|abbr=on}},<ref name="Schultz1990">{{cite journal |last1=Schultz |first1=Richard A. |last2=Frey |first2=Herbert V. |year=1990 |title=A new survey of multi-ring impact basins on Mars |journal=Journal of Geophysical Research |volume=95 |pages=14175–14189 |url=http://www.agu.org/pubs/crossref/1990/JB095iB09p14175.shtml |doi=10.1029/JB095iB09p14175 |bibcode=1990JGR....9514175S |access-date=16 November 2008 |archive-date=30 March 2012 |archive-url=https://web.archive.org/web/20120330073904/http://www.agu.org/pubs/crossref/1990/JB095iB09p14175.shtml |url-status=dead |url-access=subscription }}</ref> it is the largest unambiguous well-exposed impact structure on the planet; the obscured [[Utopia Planitia]] is slightly larger (the [[North Polar Basin (Mars)|Borealis Basin]], if it proves to be an impact crater, is considerably larger). Hellas Planitia is thought to have been formed during the [[Late Heavy Bombardment]] period of the [[Solar System]], between 4.1-3.8 billion years ago, when a protoplanet or large asteroid, suggested to be around {{Convert|370|km}} in diameter, hit the surface.<ref name="Acuna1999">{{cite journal |last=Acuña |first=M. H. |display-authors=etal |date=1999 |title=Global Distribution of Crustal Magnetization Discovered by the Mars Global Surveyor MAG/ER Experiment |journal=Science |volume=284 |issue=5415 |pages=790–793 |doi=10.1126/science.284.5415.790 |url= https://zenodo.org/record/1231157|pmid=10221908 |bibcode = 1999Sci...284..790A }}</ref><ref>{{Cite journal |last1=Branco |first1=Hely C. |last2=Miljkovic |first2=Katarina |last3=Plesa |first3=Ana-Catalina |date=April 2024 |title=New Numerically Derived Scaling Relationships for Impact Basins on Mars |journal=Journal of Geophysical Research: Planets |language=en |volume=129 |issue=4 |doi=10.1029/2023JE008217 |issn=2169-9097|doi-access=free |bibcode=2024JGRE..12908217B }}</ref>
The altitude difference between the [[rim (craters)|rim]] and the bottom is over {{convert|9000|m|ft|abbr=on}}. Despite being deeper than the Moon's [[South Pole-Aitken basin]], Hellas's rim peaks are significantly less prominent. This may be because large Martian impacts such as Hellas induced global hot rainfall and meltwater flows that degraded crater rims, including their own.<ref>{{cite journal | last1 = Head | first1 = J.W. | last2 = Palumbo | first2 = A.M. | year = 2018 | title = Impact cratering as a cause of climate change, surface alteration, and resurfacing | journal = Meteoritics & Planetary Science | volume = 53, Nr4 | pages = 687–725 | doi = 10.1111/maps.13001 | url = https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.13001| url-access = subscription }}</ref> The crater's depth of around {{convert|7152|m|ft|abbr=on}}<ref name="stanhellas"/> below the topographic [[Geodetic datum|datum]] of Mars explains the atmospheric pressure at the bottom: 12.4 mbar (1,240 Pa or 0.18 psi) during winter, when the air is coldest and reaches its highest density.{{efn| "... the maximum surface pressure in the baseline simulation is only 12.4 mbar. This occurs in the bottom of the Hellas basin during northern summer."<ref name=Haberle>{{cite journal |journal=Journal of Geophysical Research |volume=106 |issue=EL0 |pages=23,317–23,326 |date=October 25, 2001 |title=On the possibility of liquid water on present-day Mars |first1=Robert M. |last1=Haberle |first2=Christopher P. |last2=McKay |first3=James |last3=Schaeffer |first4=Nathalie A. |last4=Cabrol |first5=Edmon A. |last5=Grin |first6=Aaron P. |last6=Zent |first7=Richard |last7=Quinn|doi=10.1029/2000JE001360 |bibcode=2001JGR...10623317H |doi-access=free }}</ref>}} This is 103% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar, or 0.09 psi) and above the [[triple point]] of [[water]], suggesting that the [[phase (matter)|liquid phase]] could be present under certain conditions of temperature, pressure, and dissolved salt content.<ref name="Ref_c">{{cite press release |url=https://science.nasa.gov/science-news/science-at-nasa/2000/ast29jun_1m/ |title=Making a splash on Mars |publisher=[[NASA]] |date=29 June 2000 |access-date=12 July 2017 |archive-date=1 May 2017 |archive-url=https://web.archive.org/web/20170501032128/https://science.nasa.gov/science-news/science-at-nasa/2000/ast29jun_1m |url-status=dead }}</ref> It has been theorized that a combination of glacial action and [[explosive boiling]] may be responsible for gully features in the crater.
Some of the low elevation outflow channels extend into Hellas from the volcanic [[Hadriacus Mons]] complex to the northeast, two of which [[Mars Orbiter Camera]] images show contain gullies: [[Dao Vallis]] and [[Reull Vallis]]. These gullies are also low enough for liquid water to be transient around Martian noon, if the temperature were to rise above 0° Celsius.<!-- Heldmann cite talks of equatorial regions, not the 34 degree latitude region. Pathfinder at 19 degrees North found maximum of -8 degrees. --><ref name="Heldmann2005">{{cite journal |last=Heldmann |first=Jennifer L. |display-authors=etal |date=2005 |title=Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions |journal=Journal of Geophysical Research |volume=110 |issue=E5 |pages=E05004 |doi=10.1029/2004JE002261 |bibcode=2005JGRE..110.5004H |citeseerx=10.1.1.596.4087 |s2cid=1578727 }} – page 2, para 3: Martian Gullies [[Mars#References]]</ref>
Hellas Planitia is antipodal to [[Alba Mons|Alba Patera]].<ref name = "Peterson">{{cite journal | last = Peterson | first = J. E. | title = Antipodal Effects of Major Basin-Forming Impacts on Mars | journal = Lunar and Planetary Science | volume = IX | pages = 885–886 | date = March 1978 | bibcode=1978LPI.....9..885P }} </ref><ref name = "Williams"> {{cite journal | last1 = Williams | first1 = D.A. | last2 = Greeley | first2 = R. | year = 1991 | title = The Formation of Antipodal-Impact Terrains on Mars | journal = Lunar and Planetary Science | volume = XXII | pages = 1505–1506 | url = http://www.lpi.usra.edu/meetings/lpsc1991/pdf/1748.pdf | access-date = 2012-07-04 }} </ref><ref name = "Williams2"> {{cite journal | last1 = Williams | first1 = D.A. | last2 = Greeley | first2 = R. | date = August 1994 | title = Assessment of Antipodal-Impact Terrains on Mars | journal = [[Icarus (journal)|Icarus]] | volume = 110 | issue = 2 | pages = 196–202 | doi = 10.1006/icar.1994.1116 |bibcode=1994Icar..110..196W }} </ref> It and the somewhat smaller [[Isidis Planitia]] together are roughly [[Antipodal point|antipodal]] to the [[Tharsis Bulge]], with its enormous shield volcanoes, while [[Argyre Planitia]] is roughly antipodal to [[Elysium (volcanic province)|Elysium]], the other major uplifted region of shield volcanoes on Mars. Whether the shield volcanoes were caused by antipodal impacts like that which produced Hellas, or if it is mere coincidence, is unknown.
[[File:Hellas and SP-A basins.png|thumb|Elevation profiles along south to north transects across Mars's Hellas basin and the Moon's South Pole-Aitken basin, created with Lunar Quickmap and Mars Quickmap]]
<gallery class="center" widths="190px" heights="180px"> Wikiterracimmeriaboundaries.jpg|MOLA map showing boundaries of Hellas Planitia and other regions Hellas basin topo.jpg|Geographic context of Hellas Image:False color of Hellas Planitia.jpeg|This elevation map shows the surrounding elevated ring of ejecta Image:Twisted Ground in Hellas.jpg|Apparent viscous flow features on the floor of Hellas, as seen by HiRISE. Image:Twisted Terrain in Hellas Planitia.jpg|Twisted terrain in Hellas Planitia (actually located in [[Noachis quadrangle]]). File:ESP 055080 1425twistedbands.jpg|Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program File:ESP 055212 1420taffypull.jpg|Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program These twisted bands are also called "taffy pull" terrain.
</gallery>
==Discovery and naming== Due to its size and its light coloring, which contrasts with the rest of the planet, Hellas Planitia was one of the first Martian features discovered from [[Earth (planet)|Earth]] by [[telescope]]. Before [[Giovanni Schiaparelli]] gave it the name Hellas (which in Greek means ''[[Greece]]''), it was known as '''Lockyer Land''', having been named by [[Richard A. Proctor|Richard Proctor]] in 1867 in honor of Sir [[Norman Lockyer|Joseph Lockyer]], an English astronomer who, using a {{convert|16|cm|in|abbr=on}} [[Refracting telescope|refractor]], produced "the first really truthful representation of the planet" (in the estimation of [[Eugène Michel Antoniadi|E. M. Antoniadi]]).<ref name="William">{{cite book |first=William |last=Sheehan |year=1996 |title=The Planet Mars: A history of observation and discovery |at=Chapter 4 |publisher=[[University of Arizona Press]] |place=Tucson, AZ |isbn=9780816516414 |url=http://www.uapress.arizona.edu/onlinebks/mars/chap04.htm |access-date=2021-02-19}}</ref>
==Possible glaciers== {{multiple image | align = right | direction = vertical | width = 260 | image1 = Tongue23141.jpg | caption1 = Tongue-shaped glacier in Hellas Planitia. Ice may still exist there beneath an insulating layer of soil. | image2 = Tongue23141close.jpg | caption2 = Close-up of glacier with a resolution of about 1 meter. The patterned ground is believed to be caused by the presence of ice. }} Radar images by the [[Mars Reconnaissance Orbiter]] (MRO) spacecraft's [[SHARAD]] radar sounder suggest that features called [[lobate debris apron]]s in three craters in the eastern region of Hellas Planitia are actually glaciers of water ice lying buried beneath layers of dirt and rock.<ref name="Nasa">{{cite web |url=http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia11433 |title=PIA11433: Three craters |access-date=2008-11-24 |publisher=[[NASA]]}}</ref> The buried ice in these craters as measured by SHARAD is about {{convert|250|m|ft|abbr=on}} thick on the upper crater and about {{convert|300|m|ft|abbr=on}} and {{convert|450|m|ft|abbr=on}} on the middle and lower levels respectively. Scientists believe that snow and ice accumulated on higher topography, flowed downhill, and is now protected from sublimation by a layer of rock debris and dust. Furrows and ridges on the surface were caused by deforming ice.
The shapes of many features in Hellas Planitia and other parts of Mars are strongly suggestive of [[glacier]]s, as the surface looks as if movement has taken place. Advances in orbital and climatic modelling have supported earlier arguments that viscous flow features present in the mid-latitudes of Mars like Hellas Planitia are related to geologically recent ice ages.<ref name="Glacier1">{{cite journal |last1=Forget |first1=F. |last2=Haberle |first2=R. M. |last3=Montmessin |first3=F. |last4=Levrard |first4=B. |last5=Head |first5=J. W |title=Formation of Glaciers on Mars by Atmospheric Precipitation at High Obliquity |journal=Science |date=20 January 2006 |volume=311 |issue=5759 |pages=368–371 |doi=10.1126/science.1120335 |pmid=16424337 |bibcode=2006Sci...311..368F |url=https://www.science.org/doi/10.1126/science.1120335 |access-date=19 March 2025|url-access=subscription }}</ref>
Select analysis of landforms in eastern Hellas Planitia<ref name="Glacier2">{{cite journal |last1=Brough |first1=S. |last2=Hubbard |first2=B. |last3=Souness |first3=C. |last4=Grindrod |first4=P. M. |last5=Davis |first5=J. |title=Landscapes of polyphase glaciation: eastern Hellas Planitia, Mars |journal=Journal of Maps |date=2015 |volume=12 |issue=3 |pages=530–542 |doi=10.1080/17445647.2015.1047907 |url=https://www.tandfonline.com/doi/full/10.1080/17445647.2015.1047907 |access-date=19 March 2025|url-access=subscription }}</ref> suggests that the detected ice deposits are remnants of a [[Water on Mars#Ice ages|complex history of glaciation]] and that the region has undergone at least two and possibly three, phases of glaciation. The presence of multiple overlapping glacial units indicates episodes of ice accumulation and flow, interrupted by periods of stagnation and burial under debris. Evidence recorded in the lobate debris aprons suggests that the region underwent a wider glacial period, while analysis of several glacier-like forms with several distinct structures indicative of flow and transportation of mass down-slope suggest additional subsequent more localised glaciation.<ref name="Glacier2"/> {{Clear}}
==Honeycomb terrain== These relatively flat-lying "cells" appear to have concentric layers or bands, similar to a honeycomb. This ''honeycomb terrain'' was first discovered in the northwestern part of Hellas.<ref name="ReferenceB">{{cite journal | last1 = Bernhardt | first1 = H. | display-authors = etal | year = 2016 | title = The honeycomb terrain on the Hellas basin floor, Mars: A case for salt or ice diapirism: Hellas honeycombs as salt / ice diapirs | journal = J. Geophys. Res. | volume = 121 | issue = 4 | pages = 714–738 | doi=10.1002/2016je005007 | bibcode = 2016JGRE..121..714B | doi-access = free }}</ref> The geologic process responsible for creating these features remains unresolved.<ref>{{Cite web | url=http://www.uahirise.org/ESP_049330_1425 | title=HiRISE {{pipe}} to Great Depths (ESP_049330_1425)}}</ref> Some calculations indicate that this formation may have been caused by ice moving up through the ground in this region. The ice layer would have been between 100 m and 1 km thick.<ref>{{cite journal |last1=Weiss |first1=D. |first2=J. |last2=Head |year=2017 |title=Hydrology of the Hellas basin and the early Mars climate: Was the ''honeycomb terrain'' formed by salt or ice diapirism? |journal=Lunar and Planetary Science |volume=XLVIII |page=1060}}</ref><ref>{{cite journal | last1 = Weiss | first1 = D. | last2 = Head | first2 = J. | year = 2017 | title = Salt or ice diapirism origin for the ''honeycomb terrain'' in Hellas basin, Mars?: Implications for the early martian climate | journal = Icarus | volume = 284 | pages = 249–263 | doi=10.1016/j.icarus.2016.11.016 | bibcode=2017Icar..284..249W}}</ref><ref name="ReferenceB"/> When one substance moves up through another denser substance, it is called a [[diapir]]. So, it seems that large masses of ice have pushed up layers of rock into domes that were subsequently eroded. After erosion removed the top of the layered domes, circular features remained.
<gallery class="center" widths="380px" heights="360px"> ESP 049330 1425honeycomb.jpg|Honeycomb terrain, as seen by HiRISE under [[HiWish program]]
ESP 049330 1425honeycombcolor.jpg|Close, color view of honeycomb terrain, as seen by HiRISE under HiWish program
49330 1425honeycombcubes.jpg|Close view of honeycomb terrain, as seen by HiRISE under HiWish program
49330 1425honeycombcubesclose.jpg|Close view of honeycomb terrain, as seen by HiRISE under HiWish program This enlargement shows material breaking up into blocks. Arrow indicates a cube-shaped block.
</gallery> <gallery class="center" widths="380px" heights="360px"> File:ESP 055080 1425twistedbands.jpg|Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
File:ESP 055001 1425honeycomb.jpg|Floor features in Hellas Planitia, as seen by HiRISE under HiWish program
File:ESP 055067 1420ridgenetwork.jpg|Floor features in Hellas Planitia, as seen by HiRISE under HiWish program
</gallery>
==Layers== <gallery class="center" widths="190px" heights="180px"> Esp 037147 1430layers.jpg|Layers in depression in crater, as seen by HiRISE under HiWish program A special type of sand ripple called [[Transverse aeolian ridges]], TAR's are visible and labeled ESP 045507 1470layers.jpg|Wide view of layers, as seen by HiRISE under HiWish program ESP 045507 1470layeredcrater.jpg|Close view of layered deposit in crater, as seen by HiRISE under HiWish program 45507 1470layerswhite.jpg|Layered formation, as seen by HiRISE under HiWish program 45507 1470layerswhiteclose.jpg|Close view of layers from previous image, as seen by HiRISE under HiWish program </gallery>
== In popular culture == * Hellas Basin was a primary location in the 2017 video game ''[[Destiny 2]]''. The location is part of the second game's ''Warmind'' downloadable content. * It is also featured as a main location in the 2016 Bethesda video game reboot ''[[Doom (2016 video game)|Doom]]''. *In ''Planet-Size X-Men #1'', the [[X-Men]] [[terraforming|terraform]] Mars, turning the basin into Lake Hellas and building the Lake Hellas Diplomatic Ring, where galactic ambassadors can meet within the Sol system.
==See also== {{div col|colwidth=25em}} * [[Argyre Planitia]] * [[Atmosphere of Mars]] e.g. pressure at floor of Hellas Planitia * [[Dune]] * [[Gale (crater)|Gale crater]] * [[Geography of Mars]] * [[Glaciers on Mars]] * [[Groundwater on Mars]] * [[List of plains on Mars]] * [[Water on Mars]] {{Div col end}}
==Notes== {{Notelist}}
==References== {{Reflist|colwidth=25em}}
==Further reading== * {{cite magazine |last=Antoniadi |first=E.M. |title=The hourglass sea on Mars |magazine=Knowledge |date=July 1897 |pages=169–172}} * {{cite book |editor-last1=Grotzinger |editor-first1=J. |editor-first2=R. |editor-last2=Milliken |year=2012 |title=Sedimentary Geology of Mars |publisher=SEPM}} * {{cite journal |last=Lockyer |first=J.N. |title=Observations on the planet Mars |type=abstract |journal=[[Monthly Notices of the Royal Astronomical Society]] |year=1863 |volume=23 |page=246|doi=10.1093/mnras/23.8.246 |bibcode=1863MNRAS..23..246L |doi-access=free }}
==External links== {{Commons category|Hellas Planitia}} * {{cite news |url=http://www.spacedaily.com/news/mars-water-science-00i8.html |title=The Hellas of catastroph |first=Peter |last=Ravenscroft |date=2000-08-16 |website=Space Daily}} * {{cite web |url=http://www.google.com/mars/#lat=-42.7&lon=70 |title=Mars scrollable map}} – centered on Hellas * {{cite AV media |url=https://www.youtube.com/watch?v=_sUUKcZaTgA |archive-url=https://ghostarchive.org/varchive/youtube/20211221/_sUUKcZaTgA |archive-date=2021-12-21 |url-status=live|title=Martian ice |first=Jim |last=Secosky |type=video lecture |publisher=16th Annual International Mars Society Convention |via=YouTube}}{{cbignore}} * {{cite AV media |url=https://www.youtube.com/watch?v=DGBbke1wJRk |archive-url=https://ghostarchive.org/varchive/youtube/20211221/DGBbke1wJRk |archive-date=2021-12-21 |url-status=live|title=Lakes on Mars |first=Nathalie |last=Cabrol |publisher=SETI Talks |via=YouTube |type=video lecture}}{{cbignore}}
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[[Category:Hellas quadrangle]] [[Category:Impact craters on Mars|#]] [[Category:Noachis quadrangle]] [[Category:Plains on Mars]]