Rockglaciers from Mars !!!

"No one would have believed in the last years of the 20th century that this world was being watched keenly and closely by intelligences other than martians's and yet as mortal as his own. Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this mars with envious eyes, and slowly and surely drew their plans against us. "

From all planets and minor objects of the solar system, most similarities to features of periglacial regions on Earth can be found on the red neighbour - Mars.
The term periglacial refers here to immediate results of frost as climatic factor acting on soil substrat/detritus (geologic component).

Even if the terminus is mostly debated and in part imprecise, he can be summarized as “conditions, processes and landforms associated with cold, nonglacial environment”.

Permafrost – perennially frozen soil- is one diagnostic criteria for a periglacial environment, that can, but mustn’t contain ground ice. In the last case it can be called “dry permafrost”, but it plays a minor role in the development of characteristics or spectacular landforms of the periglacial realm.
The most spectacular forms of permafrost imply the presence of water and ice. Pingos (or hydrolaccolith), literally small mountains, contain a core of pure ice, and can reach up to 50m high. Other features that imply frozen water are ice-wedges or ice-lens and bodies.
Important macroscale features of permafrost are rockglaciers. Rockglaciers can best be defined by their morphology, saying that a rockglacier is “an accumulation of angular rock debris that contains either interstitial ice or an ice core and shows evidence of movement through creep and deformation of the ice-part”.

The presence of ice on Mars was never questioned. Even the first modern geographical maps by american astronomer Richard Antony Proctor from 1867 located two huge icecaps on both the poles. Today we know that the polar ice caps of Mars contain at least a part of water-ice, but it seemed not so extraordinary much, in ever case lesser, then some author speculated needed for a civilisation on Mars.

The question still remaining –even today- is, how much ice, and so water exist on Mars, and where else it can be found, in an atmosphere with so less pressure that it is prohibiting that water can exist in liquid form (at least for a longer period)? Models showed that a cover of detritus could prevent the ice to sublimate, so allowing in theory in some regions great amounts of subsurface ice, and maybe even liquid water. But how to prove the existence of this modelled ice?

Landforms indicative of ground ice on Mars have known since the first flyby missions of the 1960s. Images from Viking orbiters provided an overwhelming list of permafrost and ground ice indicators.
Mars resembles an astounding variety of landforms that on Earth can found in recent glacier covered, and/or in past glaciated areas, like patterned ground, thermokarst, mass movement phenomena, cirques and horns, grooves and valley troughs filled with morain-like material. On earth they are declared to prove glacial to periglacial conditions and glacier ice. On the other side, on Mars there exist a lot of forms that have no counterpart on Earth.

The most recent space probes measured the emission of neutrons from the surface of Mars. Water ice adsorbs more neutrons that dry detritus, so mapping the amount can be used to map and estimate the presumed water ice content of the first meters of the surface detritus, the so called regolith.

Fig.1. Watercontent in percent of weigth of the martian regolith, ranging from 3% (light blu) to 11% (dark blue). The presence of water ice is correlated with latitude, radiation and elevation/temperature. Red zones are areas with dense numbers of "debris aprons" (after KERR 2003).

The Phoenix Mission finally discovered subsurface ice covered only by centimeters of some dust and detritus on the high latitude (ca. 70°N) of the northern hemisphere. But still they prove only an ice content up to 6-11% in the first 1 to 2 meters of the regolith.

On Mars there are different types of features whose morphology certainly indicate the presence of deep buried ground ice - rampart craters, debris flows, lobate debris aprons, terrain softening and collapsing and patterned or polygonal terrain.

Many martian craters have a unique morphology - they are surrounded by lobes or tongues with layered ejecta, terminating in a low ridge or escarpment. This “rampart craters” are unique for Mars in our solar system, and probably represents refrozen ejecta from an impact that melted the subsurface ice-rocks mixture.

Most curious and debated are very large features, up to hundreds of kilometres long, that shows ridges and furrows on their surface, and seem to flow along rock walls and follow valleys.

Three main forms can be distinguished

- linear valley fills – long features, that resembles lava flows that fill the valleys

- pancake-like crater fills (like found in the hourglass crater)

- and lobate to tonguelike shorter mass movements, that initiate from a rock wall, shows a pronounced ridge and furrow morphology, and end with a gently slope on flat terrain.

Fig.2. Infrared MOC-image, east of the Hellas-basin, Mars. A typical association of debris aprons, debris tongues and crater fills. Note the superimposed features in the center of image. Scale in 100 kilometers.

Interpretations range from lavaflows, that some features resemble, to vast mass-movements and rockfalls deposits.
The huge aureole deposits, that form a ring extending up to 1.000km around the basal escarpment of Olympus Mouns, were also interpreted to represent immense submarine landslides.

Studies on (primarily mentioned) terrestrial rockglaciers and debris-covered glaciers in recent years offered a new explanation – the rockglacier like features on Mars are - according to the duck test … rockglaciers.

Fig.3. Terrestrial rockglaciers, Alps. Scale in 100 of meters. Showing a tongue like rockglaciers, and two "lobate debris aprons".

A rockglacier can be active - containing enough ice to show creep and deformation, inactive – still containing ice, but to less to show movement, and relictic – containing no more ice, but still displaying the morphology of past movement

Under modern climatic conditions on Mars, and assuming a behaviour comparable with terrestrial rockglaciers in Antarctica, the rockglaciers on Mars can possibly be active containig both water as CO2-ice in a belt stretching approximately on the 30° latitude (Fig.4).

Fig.4. Martian rockglaciers. Mean elevation data map (blu - deep, red - high) showing areas with high density of lobate debris aprons, like east of the Hellas basin, the chaotic terrain from Deuteronilus and Protonilus Mensae, the west escarpment of Olympus Mons and the Argyre basin.

MOC (Mars Global Surveyor Camera) Orbiter images of lineated valley fills and lobate debris aprons show that the surface of this features are practically uncratered, indicating likely emplacement and formation within the past several million years. With this method, the lobes of Olympus Mons were dated to be polygenetic with ages ranging between 280-130, 60-20, and -surprisingly- 4 million years and younger.

Fig.5. The west escarpment of Olympus Mons, with pronounced lobes (note the ridges)expanding for more then 200 km (scale) - some authors interpreted the morphology as deposits from glaciers, or remanents of debris covered glaciers. It is unclear however if they still contain ice.

However at current Mars surface temperatures, and very low accumulation rates of material, flow rates large ice masses would be so slow, that they could not be younger then 1 to 10 millions of years, but still much older then the crater counting let conclude. But assuming higher past temperatures in geologically speaking recent times, a young age became more convincing.
Overlapping tongues seen on some lobes even let assume that they were periodically active, implying possibly glacial and interglacial periods on Mars, driven by the steep tilted axis of Mars (15-35°).

The distribution of the presumed activ and relict rockglaciers seem to support this hypothesis, they only occur in a narrow belt of 30 to 50° of latitude on both hemisphere, region that in past “passed trough” the climatic zone that enables the formation of great amounts of ice and activity of rockglaciers (Fig.4.).

Discovery of microbial activity inside of active terrestrial rockglaciers give room for speculation that rockglaciers on Mars can be a habitat for primitive live forms. Pressure of the overlaying rockdetritus, with an average thickness calculated from thermodynamic constrictions of 200 up to 300 meters, maybe melt some waterice, or some water pentrates from deeper zones of the martian crust on the base of the formations and create pockets of liquid water.

And so we are (re) arrived to new frontiers...

P.S.

Until today, rockglaciers are only known from Earth and Mars. Mercury and Venus are much to hot to possess water, or even ice. The gas giants lack a surface, and the minor objects in the solar system seemed to small or to cold to enables creep and deformation of material.
But the Voyager in 1979, and the Cassini-Galileo in 1997 mission have provided some images from one of the moons of Jupiter, Callisto.

The high resolution image from the Galileo space probe shows a crater with a lobate deposit, protruding from the craterrim to the centre for 3 to 3.5 kilometers.

The nature of this morphology is still unknown, possible interpretation includes landslides or creep of ice-detritus mixture. The morphology, tonguelike to lobate with a low surface angle and a steep escarpment at the end resemble a rockglacier. But the very low temperature on the surface of Callisto of -180°C does not support creep of water ice. Alternately a different ice component, like methane or other gases, maybe is still capable to deform and so creep along the inner craterrim.

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