Hellas Planitia

Hellas Planitia is a plain located within the huge, roughly circular impact basin Hellas located in the southern hemisphere of the planet Mars. Hellas is the third- or fourth-largest known impact crater in the Solar System. The basin floor is about deep, deeper than the Moon's South Pole-Aitken basin, and extends about east to west.The part below zero datum, see Geography of Mars#Zero elevation It is centered at Hellas Planitia spans the boundary between the Hellas quadrangle and the Noachis quadrangle.

Description

With a diameter of about , it is the largest unambiguous 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 hit the surface.

The altitude difference between the rim and the bottom is over . The crater's depth of 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. 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. 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. – page 2, para 3: Martian Gullies Mars#References

Hellas Planitia is antipodal to Alba Patera.

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.

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.

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 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 refractor, produced "the first really truthful representation of the planet" (in the estimation of E. M. Antoniadi).

Possible glaciers

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. The buried ice in these craters as measured by SHARAD is about thick on the upper crater and about and 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.

Also, 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.

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. The geologic process responsible for creating these features remains unresolved. 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. 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.

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.

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

Layers

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

Interactive Mars map

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''.
*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.

See also

* Argyre Planitia
* Atmosphere of Mars e.g. pressure at floor of Hellas Planitia
* Dune
* Gale crater
* Geography of Mars
* Glaciers on Mars
* Groundwater on Mars
* List of plains on Mars
* Water on Mars

Notes

References

Further reading

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External links

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* – centered on Hellas
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Hellas quadrangle
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Noachis quadrangle
Plains on Mars