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published on 5 October 2006 in space

Mars

Martial explorations
Thera are a lot of missions, in the present and in the past, on Mars. One of these missions, the Mars Express probe, has to cartography the topography and  the mineral composition of the planet. This job is carried out with accuracy that once upon a time  was possible just on Earth, in fact in the past ten years we entered the third big martial exploration era. In the XIX century we were busy with telescope observations, in the sixties and seventies with probe recognitions, while nowadays studies let us relieve  the planet’s characteristics, to determine the mineral composition, to obtain surface images with details that let us interpret the geological processes and to compare orbital data and closer soil observations.
The MARSIS radar on the European probe Mars Express started to work since July, realized  by Alenia Spazio for the Italian Spatial Agency directed by scientist from the Sapienza di Roma University. The aim is to understand if under Mars surface there are subterranean lakes or oceans, or better water extensions in the liquid estate. The radar technique  is very similar to the one used on Earth  for the petrol beds through the echo analysis  of the radio waves reflection that is different for every kind of ground structure (such as dry, iced firn or humid). The low frequency signals penetrate until 5 kilometers deep, then they are converted into a digital form and electronically elaborated to give us a water and ice distribution map that exist in the Mars superior layers underground. Marsis has two thin “antennas” that are 20 meters long and analyze  the ionosphere.
SHARAD is another Italian radar who is ready for a new mission, that will observe the same areas studied by Marsis but with an higher resolution.

A surprising planet
Scientists have discussed  for years what characteristics Mars has and if once upon a time the weather was hot or humid , cold or dry or completely desolated such as the Moon. Although Mars has the most important interesting and rich story of all the solar system, we can still discover new things by gaining and analyzing the rock’s data, it’s minerals  and the surface morphology, the same way researchers did to understand the geological history of the World. This way it has been discovered  that there were many different types of environments determined by different processes and conditions on Mars: arid landscapes, others totally humid, others covered up with snow and ice.
Let’s not forget about the morphology and the characteristics of a landscape that are given by it’s structure (rocks and minerals that compose it), from processes that shape this structure and the time these take to operate on it. On the long run the mountainous relives  and the hills fret: the slopes decrease while the rock debris are deposited in the most depressed parts  (that are called  sediment basin). This erosive action is caused continuously exogenous agents such as water.
Taking into consideration  this bizarre landscape diversity  that characterize Mars, scientist start asking themselves new questions: for how long and where did these cold and hot periods happen? These diversities created different environments so are there any that can give hospitality to any kind of form of life?

Different landscapes
The rover Spirit and Opportunity studied two different places a thousand kilometres distant one from the other and characterized by completely different landscapes: one similar to the arid desert and the other to a plain, interrupted by many lakes. Why? Which processes formed them?
The Gusev crater
The rover Spirit explored a site that initially was disappointing  because the rocks that had olivine and pyroxenes didn’t leave trace to a possible past water existence; in fact olivine and pyroxenes are minerals who dissolve with water. In a second moment plenty sulphur salt was discovered and that was supposedly formed by a water percolation through volcanic rocks that were full of olivine and pyroxenes. Researchers deduced that in the past billion years water a secondary role for modifying this passage even if the images taken from the scope show a valley that teminates in the Gusav crater, as if once upon a time it was a lake.
The Meridian Earth plains
The Meridian Earth, explored by Opportunity, is characterized by a landscape completely flat  such as a laky bed or a small isolated sea  and  circled by many crater in the south and west part that probably were other separated lakes. This is accredited by hematite deposits, ferric oxide that are constituted by processes for water presence. These rocks enriched with hematite are organized in a certain way to form easy erosion layers over a more antique surface, such as a sedimentary deposit that formed in a aqueous environment. In this case they would fill up depressions, bays and channels that characterized the antecedent landscape.
Besides, the sedimentary stratified rocks that have abundance in sulphates have been created thanks to water evaporation with a big sulphur quantity.
Other scientists instead evaluated the rocks alterations caused by rich sulphur vapours that escaped from the volcanic ashes deposits; as a consequence the region could result as a typical volcanic zone of North America, Hawaii or Europe.

Hints from a volcano world
In spring 2004, the Mars Express probe confirmed a big feldspar, olivine and pyroxene distribution which are typical minerals from basaltic rocks. Basalt is a igneous rock diffuse on the Earth too that comes from magma consolidation erupted from volcanoes such as Etna, from the Hawaii volcanoes and from the mid-oceanic ridge.
What was really surprising though was to find andesite, a rock that has more silicates than ferrum and it forms when water gathered in a subsidence tectonic plate mixes up  with underground melted rocks.
Mars’ volcanoes have gigantic dimensions and are incredibly complex. Studies researchers did on the Syrtis Major volcano, for example, which is located next to the martial equator has 1100 kilometres diameter and many calderas at the summit. The volcano past many succeeding development phases: slopes with peaks, cones and vitric lava flows and enriched in silica (dacite)  are characteristic.
Magma  cools off by moving away from the magma chamber, at first ferrum and magnesium start to crystallize (olivine and pyroxene), than a bit later siliceous  and aluminium start to constitute dacite. Some peaks are made of granite in which the percent of silica is higher and was created thanks to crystal separation or to the most antique basalt rocks reflowing.
To comprehend the geological evolution  of a planet it is necessary to understand the motives some minerals or rocks are almost or completely absent. Quartz, for example, is very rare on Mars such as minerals that compose metamorphic rocks, created by the influence high pressure and temperature on sedimentary and igneous rocks has. So researchers deduced there aren’t tectonic processes on the planet able to transport rocks deep enough to be affected by metamorphic transformations.
Analogously carbonate rocks deposits  haven’t been individuated but were supposed to exist if we suppose  there was hot and humid weather in the past. So probably martial oceans were cold or impermanent, covered up with ice and the small quantities of carbonates found in dust all over the planet, probably formed by a direct interaction with the atmosphere water vapour. Clay minerals are rare too, and they can form in contact with water.

Visible lakes from the orbit
Recent studies show that researchers have the proof martial water was present and stable in isolated regions and for short periods. From the mineral mapping it is possible to see an antique surface, a very little bit altered by water; in fact the basaltic sand of Meridian Earth are overlapped on laky sediments  that prove it has been arid since 2 or 3 billion years. It is possible that water was under a solid state and it would melt in very little occasions and freeze again.
In the Valles Marineris’ lower part  there are rocks with a high percent of hematite and are generally deposited in stagnant water. In places such as the equatorial band, lakes probably faced different phases like floods, evaporation or congealment. Other regions are engrave crisscross grip channels, that seem to be created by surface water flowage, whilst a few scientists, after  the picture observations and topography analyses, were able to define the coast line and the depth so they deduced there used to be big Oceans on Mars.
Rock layers  with hematite  were found in the Aram Chaos crater where the water was gathered in a small lake in the crater  following a catastrophic water outflow from underground.
Scientists started to ask themselves some questions: from where does this martial water come from?
Anyway most of the people agree on a recent geological activity on Mars where some craters come from eruptions not long ago. Mars has gotten colder  so volcanism is very rare. There are occasional eruptions but scientists  didn’t find the hot spots.

Mars climatic variations
The novelty is the solid water storage discovery on Mars that changes position on the planet  depending on the climate variations. On the poles, an area which is twice Arizona, was found ice deposits or rich ice sediments many kilometres thick. The THEMIS measurements found water ice come up to the surface in many spots. In the past instead it was thought that boreal ice cap was made of water ice, whilst the austral one ice was made of carbon dioxide.
The instrumentations on Mars Odyssey discovered ice in the subsoil: in the belt between the poles and sixty degrees latitude, water constitutes more than 50 percent of the soil and it comes from snow or rime deposits only  cause it is very abundant. The landscape morphology study of these areas, noticed fractures along the ground that can form as an ice evaporation consequence caused by heating or small channels with very little water source or from ice founding or from melting ice deposits.
All of these observations and data put together make people think that Mars could have been characterized by glaciation cycles.
Can you remember the hypothesis that want to explain the glaciation causes on Earth? In the same way  scientists tried to explain a glaciation cycle possibility on Mars and got some considerations.
Mars axis inclination oscillates twenty degrees in 125000 years: when the inclination is small, the poles are the coldest places, more snow falls than evaporation and ice accumulates. Instead the poles heat up damaging the mid latitudes when the inclination grows and accumulates snow in the equatorial regions; when snow melts, water can carve channels and model typical landscapes. In this moment the snowy cover almost vanished completely because the middle latitudes are heating up, but if the models are correct , the snow should show up within the next 25000 – 50000 years.

Written by Elisabetta Monistier

With the sponsorship of the Italian Ministry of Education, Universities and Research
 
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