Hellas Planitia

Template:Short description Template:Use dmy dates Template:Infobox feature on celestial object

CitationClass=web }} MGS radio science measured 11.50 mbar at 34.4° S 59.6° E −7152 meters</ref>

Hellas Planitia Template:IPAc-en is a plain located within the huge, roughly circular impact basin HellasTemplate:Efn located in the southern hemisphere of the planet Mars.<ref name = "USGS_Hellas_Planitia">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Hellas is the fourth- or fifth-largest known impact crater in the Solar System. The basin floor is about Template:Convert deep, Template:Convert deeper than the Moon's South Pole-Aitken basin, and extends about Template:Convert east to west.<ref name="Ref_">The part below zero datum, see Geography of Mars#Zero elevation</ref><ref name="Ref_a">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is centered at Template:Coord It features the lowest point on Mars,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> serves as a known source of global dust storms, and may have contained lakes and glaciers.<ref name="Bleamaster & Crown 2010">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Hellas Planitia spans the boundary between the Hellas quadrangle and the Noachis quadrangle.

DescriptionEdit

With a diameter of about Template:Convert,<ref name="Schultz1990">Template:Cite journal</ref> it is the largest unambiguous well-exposed impact structure on the planet; the obscured Utopia Planitia is slightly larger (the 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, approximately 4.1 to 3.8 billion years ago, when a protoplanet or large asteroid, suggested to be around Template:Convert in diameter, hit the surface.<ref name="Acuna1999">Template:Cite journal</ref><ref>Template:Cite journal</ref>

The altitude difference between the rim and the bottom is over Template:Convert. 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>Template:Cite journal</ref> The crater's depth of Template:Convert<ref name="stanhellas"/> below the topographic datum of Mars explains the atmospheric pressure at the bottom: 12.4 mbar (1240 Pa or 0.18 psi) during winter, when the air is coldest and reaches its highest density.Template:Efn 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 liquid phase could be present under certain conditions of temperature, pressure, and dissolved salt content.<ref name="Ref_c">Template:Cite press release</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.<ref name="Heldmann2005">Template:Cite journal – page 2, para 3: Martian Gullies Mars#References</ref>

Hellas Planitia is antipodal to Alba Patera.<ref name = "Peterson">Template:Cite journal </ref><ref name = "Williams"> Template:Cite journal </ref><ref name = "Williams2"> Template:Cite journal </ref> It and the somewhat smaller Isidis Planitia together are roughly antipodal to the Tharsis Bulge, with its enormous shield volcanoes, while Argyre Planitia is roughly antipodal to 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

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

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MOLA map showing boundaries of Hellas Planitia and other regions
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Geographic context of Hellas
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This elevation map shows the surrounding elevated ring of ejecta
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Apparent viscous flow features on the floor of Hellas, as seen by HiRISE.
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Twisted terrain in Hellas Planitia (actually located in Noachis quadrangle).
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Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
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Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program These twisted bands are also called "taffy pull" terrain.

Discovery and namingEdit

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 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 Anthony Proctor in 1867 in honor of Sir Joseph Norman Lockyer, an English astronomer who, using a Template:Convert refractor, produced "the first really truthful representation of the planet" (in the estimation of E. M. Antoniadi).<ref name="William">Template:Cite book</ref>

Possible glaciersEdit

Template:Multiple image Radar images by the Mars Reconnaissance Orbiter (MRO) spacecraft's SHARAD radar sounder suggest that features called lobate debris aprons 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">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The buried ice in these craters as measured by SHARAD is about Template:Convert thick on the upper crater and about Template:Convert and Template:Convert 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 glaciers, 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">Template:Cite journal</ref>

Select analysis of landforms in eastern Hellas Planitia<ref name="Glacier2">Template:Cite journal</ref> suggests that the detected ice deposits are remnants of a 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"/>

Honeycomb terrainEdit

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">Template:Cite journal</ref> The geologic process responsible for creating these features remains unresolved.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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>Template:Cite journal</ref><ref>Template:Cite journal</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.

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Honeycomb terrain, as seen by HiRISE under HiWish program
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Close, color view of honeycomb terrain, as seen by HiRISE under HiWish program
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Close view of honeycomb terrain, as seen by HiRISE under HiWish program
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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.

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Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
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Floor features in Hellas Planitia, as seen by HiRISE under HiWish program
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Floor features in Hellas Planitia, as seen by HiRISE under HiWish program

LayersEdit

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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.
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Wide view of layers, as seen by HiRISE under HiWish program
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Close view of layered deposit in crater, as seen by HiRISE under HiWish program
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Layered formation, as seen by HiRISE under HiWish program
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Close view of layers from previous image, as seen by HiRISE under HiWish program

In popular cultureEdit

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.
In Planet-Size X-Men #1, the X-Men terraform Mars, turning the basin into Lake Hellas and building the Lake Hellas Diplomatic Ring, where galactic ambassadors can meet within the Sol system.