The Mars Survey Survey (MRO) - summary of findings - part XNUMX

Part two of the three parts of the summary

Volcanoes

The Tharsis region is the youngest volcanic plateau on Mars and according to the accepted approach the proof of this is the low density of craters in it. The height of this volcanic plateau is 5 km above the ground. The area is covered with an almost continuous layer of cracks and dust several meters thick(24). The photographs show that the main flanks of the volcanoes in Tharsis are similar to each other with lava channels covering several underground lava tubes located there, although it should be noted that each volcano had later eruptions that differed in their pattern of action from those of the other volcanoes . Lava that flowed from fissures on the sides of the volcanoes created large lava covers that were given the name rift aprons by the researchers. rift aprons In the northernmost volcano Ascraeucs, there are most of the lava tubes that are not covered by the lava channels.

Since lava aprons are the first to form over hot spots, it is estimated that Ascraeucs was recently active. The stream at the southernmost volcano Arsia Mons has the smallest number of lava tubes, indicating that its rift aprons are older. Yes, more currents were observed in Arsia that partially cover tube currents. This trend continues along the chain of volcanoes and indicates that the rift aprons have a common origin as in the Hawaiian volcanoes and that the apron eruptions started in Arsia. The trend moved towards the north and buried older tube streams in Arsia through flow channels(25).

A study published in 2010 reported that more than 18,000 circular escarpments known as mud volcanoes were counted. These are volcanic sources that emit sediments of mud brought from the earth's condensation. Volcanic sources of this type were first noticed by the Viking spacecraft in Planitia .Acidalia. Mud volcanoes are geological structures through which a mixture of gas, liquid and fine-grained rocks are pushed to the surface from a depth of several meters or several kilometers. The diameter of the base of such volcanoes can reach tens of kilometers and they rise to a height of hundreds of meters(26).

tectonics

Photographs of the North Pole during the summer season revealed pits and fractures in the residual ice that had not been observed before. These fault lines are similar to such formations on Earth in places where the crust is pushed upwards. The conclusion is that the recently observed fault lines are new. Another possible explanation is that these fault lines were formed by collapses following the removal of subsurface material. The pits are parallel to the fault lines for two possible reasons. One reason is that material drains into underground areas parallel to the fault lines. Second reason, gases broke out through them to the surface(27).

dunes

Near the equator to the north in Planum Meridiani two types of dunes were noticed. One type is the Barachan dunes, which are 200 meters long. In the southwest direction, their slopes are steep, which indicates the direction of the winds - northeast. This direction corresponds to the direction of light streaks created by winds in a crater located near the site. These streaks are the product of intra-alveolar erosion of light sand. The second type of dunes are transverse dunes. These are long ridges of sand whose direction is perpendicular to the direction of the winds. They tend to develop when there is a large supply of sand(28).

Near the North Pole there are many dunes made of basaltic sand. In one of the photographs they resemble the Barkhan Dunes. The dunes and their surroundings are bright because they are covered with the seasonal frost of winter in the Northern Hemisphere(29).

Sand dunes were found in the Hellas Pontus area. They originate from formations of buttons and layers of table mountains (mesas) that have been eroded by strong winds. The shape of the dunes indicates that the wind direction is west-east. The dunes are of the Barhan and Seif dunes type. The latter are longitudinal dunes that are formed when their longitudinal axis is perpendicular to the direction of the wind and are characterized by sharp summit slopes(30). Examination of photographs of dunes from latitude N °65 and north for 3 years from Adimim showed that two dunes 20 meters long, one of them disappeared and a third dune shrunk by 15%. These observations indicate that not all dunes are stable over time(31). Gypsum was found in some of the dunes (32).

Large dunes observed for 30 years did not move or disappear at all. It was believed that snow and ice trapped in the depths of the dunes fixed them to their destination. It turned out that these factors are not enough. To find the additional factors, a comparison was made with Antarctica. Photographs taken in the Victoria Valley on this continent between the years 1961-2001 were taken and the rate of movement of the dunes in this area was examined. It is known that these dunes are covered with seasonal snow and that within the dunes there are layers of snow and ice. It was found that the dunes moved at a rate of 1.5 per year, very low compared to dunes in hot deserts where the rate of movement is 30-70 meters per year.

In another test, they took photographs of Mars taken in 1975 by the Viking spacecraft and compared them to their new photographs taken in 2009. It turned out that the new photographs show crusts on the surface of the dunes. A similar phenomenon is found in deserts on Earth. On these dunes, sand deposits with hardened surfaces were found. The dunes underwent a cementisation process and this was probably caused by ice or geochemical processes. Other reasons limiting the movement of dunes on Mars could be the thin atmosphere that requires high wind speeds to move sand and water frost and 2 CO covering polar regions for 70% of the Martian year(33).

Regarding dunes in the North Pole and which were observed at W ° 233.2 – N ° 84 covering 845,000 km, it was estimated that they are static in nature and that they were formed a long time ago when the winds were stronger than today. New photographs show that the morphology of these dunes undergoes significant changes over the course of one Adamic year. A seasonal layer of 2 CO that covers the area in winter and sublimates in spring is what causes annual erosion in the polar dunes. The escape of the gas causes the sand to lose its stability and because of this avalanches are formed and channels and aprons of dunes develop. Dunes that have been thoroughly surveyed at high latitudes have been shown to be devoid of rigid or ice-cemented crusts. The extent of the debris found was greater than expected. In several places, hundreds of cubic meters of sand fell along the dune slopes. On Earth, water ice is recognized as a cause of landslides and sand flows in the dunes of Antarctica. The erosion of CO2 on Mars seems to be unique to the dunes of this planet(34).

Alolim-  dust devils                     

Towards the end of July 2007 the MRO photographed dust devils near Hellas Planitia. On Mars, dust devils are usually formed in the afternoon. This is because sunlight needs enough time to heat the surface. The photo was taken at 3:08 in the afternoon Madimi time, the width of the dust devils was 200 meters, although at the base it is narrower and 500 meters high (35).

holes

The Odyssey spacecraft and the Mars Global Surveyor discovered openings in the form of circles with a diameter of 100-250 meters troychol, which may be openings to underground spaces. In a photograph taken by the MRO, such a hole was found in the Arsia Mons volcano. This hole penetrates through the lava flow in one of the flanks of the volcano. Similar ones are found in the volcanoes of Hawaii and they are called pit craters. In the photographs taken in infrared it became clear that there are temperature differences during the day, in the afternoon and before dawn. The temperatures of the holes vary day and night by 1/3 as much as the temperature in their surroundings. They are colder than their surroundings during the day and warmer at night. This group of holes received the name "Seven Sisters". They seem to have been formed when pressures around the volcano caused fractures to widen and create cavities under the ground(36,37).

erosion

In the photo taken in Candor Chasma, you see layers of rock that have undergone folding and taken the shape of an elliptical dome. The upper parts of these folds have been removed by erosion and concentric patterns of layers and step formations have been exposed. The dark shade of the material is a layer of sand material that was transported by winds and trapped in the steps(38).

Stratigraphy

Layers in the Martian soil were discovered for the first time by the Mariner 9 spacecraft and the Vikings, and we can learn from them about the places where materials were deposited and their origins. From all places they were removed and deposited by water, winds or volcanic activity. A place about which there were differences of opinion as to their formation is Candor Chasma. The question that arose was whether the layers were formed before or after the chasm in the ground opened. Thanks to the great resolution of the MRO it is possible to carry out meticulous studies of the Martian layers(39). In one of the photos you can see in detail the material of layers, sand and dust from which the North Pole dome is made. Layers with a length of up to 960 km were discovered. 4 regions of ice and dust layers separated by only a thick layer of water ice were discovered. According to the researchers, this pattern of thick layers without water ice indicates climatic cycles on the scale of a million years(40).

In the Boreale Chasma, a large valley that enters the ice cap in the North Pole, layers are visible and it is possible to notice changes in the composition of the soil in them and some ice mixed with soil. A layer below contains little ice and below it is an ice-rich layer similar to the upper layers. The very ability to distinguish between the ice layers and layers with less ice indicates different periods of deposition of material(41). To illustrate, the thickness of one of the observed layers is 500 meters (42).

In the Gale Crater which is 152 km in diameter and located at E 138 S °5, hundreds of layers as high as the Rockies in the USA were found. You can learn from them about the environmental changes that took place on Mars billions of years ago. These findings are consistent with the accepted assumption regarding ancient Mars. Layers where clay minerals are found at the bottom of the stratigraphic section indicate a humid environment when they were formed. Above them is a layer that has a mixture of clay and sulfate minerals. Sulfates are formed in a humid environment and are deposited when the water in them evaporates. In the next layers there are sulfates without clay and in the uppermost layers there are minerals without water. Such an exposure of layers as in the Gale Crater is found in another place and a group of researchers in Paris made a proposal to date the geological periods of Mars based on the presence of clay minerals and sulfate minerals(43). In the western flank of the Arsia Mons volcano there are many layers that indicate different lava flows and these provide information about the nature of the volcanic eruptions(44).

water

After Earth, among the inner planets, Mars has the largest amount of water. The main component of the Antarctic ice cap is water. The amount of silica from the totality of the material found in the polar cap is only 15% and the density of the ice is 1.22. A large part of the ice is covered with dust(45). It is estimated that the amount of water at the poles of Mars is 2-3 million cubic kilometers. For comparison, this amount is 100 times greater than the amount of water in the Great Lakes in the USA (46).

In the middle latitudes between ° 60 – ° 30 North and South, large amounts of glaciers were found under fields of rock fragments. It seems that these fragments came from hills located at a distance of 20 km from their current location. It should be noted that there is a debate as to the origin of these glaciers. Some researchers claim that particles from the ice are actually condensation of water vapor from the atmosphere that reached the ground as rain and turned into ice. This ice served as lubrication for the rocky material and allowed it to move down the hills. Other researchers claim that the rock fragments cover large glaciers. In the eastern part of the Hellas Crater there is a layer of glaciers 800 meters thick and the amount of ice covers an area of ​​28,000 square kilometers (47).

Light-colored deposits were found in different channels. Each of these channels has its own typical mineralogy and therefore the geological processes are local. Different types of clays and sulfates have been identified in small basins that are 30-100 km long each. In one channel dozens of layers with different thicknesses, colors and erosive structures were found. Mixtures of sulfates and clays were found in the deposits. Which indicates different levels of acidity (pH) in the complex of acidic and alkaline conditions. One of the channels is buried several meters under the sediments (eposits) of spirits and is only exposed in its upper part. Several kilometers elsewhere are outcrops of hydrated silicates and calcium sulfate. The great diversity of deposits and minerals indicates a complex hydrological history. It is possible that volcanic activity created water by melting ice or that underground hydrothermal processes resulted in water rising to the surface that filled some of the small basins(48).

One of the main evidences of water flow in the past and probably also in the present is the phenomenon of gullies. The Mars Global Surveyor found key evidence made in 2004. Tens of thousands of gullies have been found on the inner slopes of craters and other depressions. Most of the gullies are found in latitudes of 30° and above (in the northern hemisphere and the southern hemisphere). The first report on this was given in 2000 by Michael Malin and his team of senior Martian researchers. Two craters that have recently (and I mean the last few years) flowed water are found in Terra Sirenee and Centauri Monts. in the southern hemisphere. The fresh deposits found in them raise the possibility that in several places water bursts out of the ground and flows for a short period until it evaporates. The questions that arise in light of these findings are: how will water remain liquid under the ground, to what distance is it common in these places and is there a humid environment there that allows life to exist(49). Additional evidence of current water flow was found in the changes that occurred in the gullies between 2000-2006. The changes were found when a comparison was made between the Global Surveyor Mars photographs taken in 2000 and 2006. The photographs from these years show sudden events where water appears on the ground following eruptions from the sides of craters and flows down along the slopes.

As for Terra Sirenum, deposits of light material covering the bottom of gullies that were observed in April 2005 were not found in December 2001. The same for the crater in Centauri Monts. Differences were found between the photographs in 8.1999 and 2.2004. According to Michael Malin's assessment, some of the salty or acidic, or semi-melted water breaks out of the soil thickener under the gullies and leaves their traces. Quite similar to the type of mud flows that you see on Earth after heavy rains or sudden streams(50).

Photographs of equatorial regions showed hills made of alternating dark and light-dark colored layers crossed by dark sand dunes. In these layers you see a series of linear cracks called joints surrounded by "halos". These rock layers are clear and according to the researchers, they are proof of water flow in the past. Minerals that moved in the water passed through these layers and acted like cement, strengthening and bleaching these layers. The hardened rocks are more resistant to wind erosion than other formations found on the sides of the canyons. On Earth, the bleaching of rocks surrounding rocks is evidence of chemical interaction between currents moving within cracks(39).

Many gullies are also solid evidence of water flow in the last millions of years but probably in different climatic cycles. Some of these areas, during these climatic cycles were warmer than others. The MRO images show clear signs of water flow. Formations of alluvial fan deposits around several craters contribute to this evidence(51). In Promethei Crater, a gully drift fan was found for the first time and the researchers were able to date it. It was formed 1.25 million years ago. In the gullies system, 4 layers were found made of water sediments that reached the crater floor downstream and were deposited in the alluvial fan. The length of the western and eastern channels of the gully from the place of their formation (alcove) to the drift fan is less than 1 km. The width of the alluvial fan is hundreds of meters. Inside the fan itself, 4 lobes were found and each one was deposited separately. Ice and snow deposits formed in alcoves. When the axis of Mars was very tilted (during the last ice age of Mars) the ice accumulated in middle latitudes(52).