Hellas Planitia is a

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

located within the huge, roughly circular impact basin Hellas located in the southern hemisphere of the

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. Hellas is the fourth- or fifth-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 It features the lowest point on Mars, serves as a known source of global dust storms, and may have contained lakes and glaciers. Hellas Planitia spans the boundary between the Hellas quadrangle and the Noachis quadrangle.

Description

With a

diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

of about , 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 The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

, approximately 4.1 to 3.8 billion years ago, when a protoplanet or large asteroid, suggested to be around in diameter, hit the surface. The altitude difference between the rim and the bottom is over . 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. The crater's depth of below the topographic

datum Data ( , ) are a collection of discrete or continuous value (semiotics), values that convey information, describing the quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols t ...

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 In thermodynamics, the triple point of a substance is the temperature and pressure at which the three Phase (matter), phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at ...

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, 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 Elysium (), otherwise known as the Elysian Fields (, ''Ēlýsion pedíon''), Elysian Plains or Elysian Realm, is a conception of the afterlife that developed over time and was maintained by some Greek religious and philosophical sects and cult ...

, 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. Hellas and SP-A basins

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 Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. Before Giovanni Schiaparelli gave it the name Hellas (which in Greek means ''

Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

''), 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. The shapes of many features in Hellas Planitia and other parts of Mars are strongly suggestive of

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

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. Select analysis of landforms in eastern Hellas Planitia 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.

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

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 The X-Men are a superhero team in American comic books published by Marvel Comics. Created by writer/editor Stan Lee and artist/co-plotter Jack Kirby, the team first appeared in Uncanny X-Men, ''The X-Men'' #1 (September 1963). Although initial ...

terraform Mars, turning the basin into Lake Hellas and building the Lake Hellas Diplomatic Ring, where galactic ambassadors can meet within the Sol system.

Notes

References

External links

* * – centered on Hellas * * {{Authority control Hellas quadrangle # Noachis quadrangle Plains on Mars