Topographic map of Hellas Planitia and its surroundings in the southern uplands, from theMOLA instrument ofMars Global Surveyor. The crater depth is 7,152 m (23,465 ft) below the standard topographicdatum of Mars.[1]
With adiameter of about 2,300 km (1,400 mi),[8] it is the largest unambiguous well-exposed impact structure on the planet; the obscuredUtopia Planitia is slightly larger (theBorealis Basin, if it proves to be an impact crater, is considerably larger). Hellas Planitia is thought to have been formed during theLate Heavy Bombardment period of theSolar System, approximately 4.1 to 3.8 billion years ago, when a protoplanet or large asteroid, suggested to be around 370 kilometres (230 mi) in diameter, hit the surface.[9][10]
The altitude difference between therim and the bottom is over 9,000 m (30,000 ft). Despite being deeper than the Moon'sSouth 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.[11]The crater's depth of 7,152 m (23,465 ft)[1] below the topographicdatum 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.[b] This is 103% higher than the pressure at the topographical datum (610 Pa, or 6.1 mbar, or 0.09 psi) and above thetriple point ofwater, suggesting that theliquid phase could be present under certain conditions of temperature, pressure, and dissolved salt content.[13] It has been theorized that a combination of glacial action andexplosive boiling may be responsible for gully features in the crater.
Some of the low elevation outflow channels extend into Hellas from the volcanicHadriacus Mons complex to the northeast, two of whichMars Orbiter Camera images show contain gullies:Dao Vallis andReull 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.[14]
Hellas Planitia is antipodal toAlba Patera.[15][16][17] It and the somewhat smallerIsidis Planitia together are roughlyantipodal to theTharsis Bulge, with its enormous shield volcanoes, whileArgyre Planitia is roughly antipodal toElysium, 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.
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
MOLA map showing boundaries of Hellas Planitia and other regions
Geographic context of Hellas
This elevation map shows the surrounding elevated ring of ejecta
Apparent viscous flow features on the floor of Hellas, as seen by HiRISE.
Twisted terrain in Hellas Planitia (actually located inNoachis quadrangle).
Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program These twisted bands are also called "taffy pull" terrain.
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 fromEarth bytelescope. BeforeGiovanni Schiaparelli gave it the name Hellas (which in Greek meansGreece), it was known asLockyer Land, having been named byRichard Anthony Proctor in 1867 in honor of Sir Joseph Norman Lockyer, an English astronomer who, using a 16 cm (6.3 in)refractor, produced "the first really truthful representation of the planet" (in the estimation ofE. M. Antoniadi).[18]
Tongue-shaped glacier in Hellas Planitia. Ice may still exist there beneath an insulating layer of soil.
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 theMars Reconnaissance Orbiter (MRO) spacecraft'sSHARAD radar sounder suggest that features calledlobate 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.[19] The buried ice in these craters as measured by SHARAD is about 250 m (820 ft) thick on the upper crater and about 300 m (980 ft) and 450 m (1,480 ft) 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 ofglaciers, 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.[20]
Select analysis of landforms in eastern Hellas Planitia[21] suggests that the detected ice deposits are remnants of acomplex 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.[21]
These relatively flat-lying "cells" appear to have concentric layers or bands, similar to a honeycomb. Thishoneycomb terrain was first discovered in the northwestern part of Hellas.[22] The geologic process responsible for creating these features remains unresolved.[23] 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.[24][25][22] When one substance moves up through another denser substance, it is called adiapir. 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.
Honeycomb terrain, as seen by HiRISE underHiWish program
Close, color view of honeycomb terrain, as seen by HiRISE under HiWish program
Close view of honeycomb terrain, as seen by HiRISE under HiWish program
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.
Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
Floor features in Hellas Planitia, as seen by HiRISE under HiWish program
Floor features in Hellas Planitia, as seen by HiRISE under HiWish program
Layers in depression in crater, as seen by HiRISE under HiWish program A special type of sand ripple calledTransverse aeolian ridges, TAR's are visible and labeled.
Wide view of layers, as seen by HiRISE under HiWish program
Close view of layered deposit in crater, as seen by HiRISE under HiWish program
Layered formation, as seen by HiRISE under HiWish program
Close view of layers from previous image, as seen by HiRISE under HiWish program
Hellas Basin was a primary location in the 2017 video gameDestiny 2. The location is part of the second game'sWarmind downloadable content.
It is also featured as a main location in the 2016 Bethesda video game rebootDoom.
InPlanet-Size X-Men #1, theX-Menterraform Mars, turning the basin into Lake Hellas and building the Lake Hellas Diplomatic Ring, where galactic ambassadors can meet within the Sol system.
^ "... 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."[12]
^Peterson, J. E. (March 1978). "Antipodal Effects of Major Basin-Forming Impacts on Mars".Lunar and Planetary Science.IX:885–886.Bibcode:1978LPI.....9..885P.
^Weiss, D.; Head, J. (2017). "Hydrology of the Hellas basin and the early Mars climate: Was thehoneycomb terrain formed by salt or ice diapirism?".Lunar and Planetary Science.XLVIII: 1060.
^Weiss, D.; Head, J. (2017). "Salt or ice diapirism origin for thehoneycomb terrain in Hellas basin, Mars?: Implications for the early martian climate".Icarus.284:249–263.Bibcode:2017Icar..284..249W.doi:10.1016/j.icarus.2016.11.016.
Secosky, Jim.Martian ice (video lecture). 16th Annual International Mars Society Convention.Archived from the original on 21 December 2021 – via YouTube.
Cabrol, Nathalie.Lakes on Mars (video lecture). SETI Talks.Archived from the original on 21 December 2021 – via YouTube.
