Mars is an icy planet
|Series: From the acid clouds of Venus through the hurricane hell of Neptune to the icy Pluto desert|
This magnificent photo of our neighboring red planet was taken on June 26, 2001 by the Hubble Space Telescope. It is considered to be the sharpest photo of Mars ever taken from Earth. You can see two storm systems brewing together: One is revealed by the white cloud formations in the north polar region, the other by the yellow-brown dust veil on the right edge of the southern hemisphere of the planet. A few weeks later, the dense dust clouds of a global mega-hurricane enveloped the entire planetary disk in a cloudy, reddish light.
Hardly any other planet in our solar system is as similar to Earth as Mars. With a diameter of almost 6,800 kilometers, our neighbor is significantly smaller than the earth, but it also has a shell-shaped, inner structure with a solid core, a partly glowing mantle and a solid rock crust with a rocky surface. On the red planet there are strongly structured landscapes with partly volcanic mountains, valleys, basins and wide plains. In addition, there are seasons and changing weather processes with clouds, wind and even water ice. The most important building block of life as we know it, liquid water, was largely lost to our red neighbor in space a long time ago.
In the beginning there was the water. Even on Mars. Water flowed over its surface, in rivers and lakes, yes, even filled entire ocean basins - planetary researchers now have little doubt about that. Because countless traces of erosion point to the existence of a humid age in Mars history shortly after the formation of the planet. The warm and humid climate regime presumably lasted for several hundred million years, but came to an abrupt end around 4 billion years ago. Although there are indications that in the more recent history of Mars, at least intermittently and regionally, water has flowed again and again or has led to the formation of glaciers in the form of snow, but such temporary events are likely to be related to the primordial, planet-wide, humid climate never have come back.
In those days, huge volcanoes, in addition to lava and dust, also spat vast amounts of carbon dioxide and water vapor into the then dense and warm Martian atmosphere. When the planet had cooled down sufficiently, the water vapor condensed into clouds like on Earth, and rivers fed by heavy rains formed valleys, ravines and basins in the surface of the young planet. For several hundred million years there was an abundance of water. Snowfalls caused glaciers to form in the polar regions and on the flanks of the mountain ranges.
Unlike the more massive Earth, however, the young Mars was unable to maintain its atmosphere, which was fed by volcanic eruptions and asteroid impacts, so that part of its gas envelope was permanently escaping into space. When the volcanism subsided and the supply of gases and water came to a standstill, a chain reaction set in with devastating consequences: the atmosphere became thinner and more and more water began to evaporate.
With the inexorably escaping atmosphere, the greater part of the water vapor gas was gradually lost and the warming greenhouse effect weakened more and more. This in turn meant that it got colder and colder until the last remnants of water had frozen to ice and the planet finally turned into the dry dusty desert that we know it today.
However, the last remnants of that former water resource can still be found today on and above all under the surface of Mars. Some of them have entered into chemical compounds, but others are also hidden under the surface of the planet in the form of embedded layers of ice, where they are well preserved covered by dust and debris and largely protected from evaporation through sublimation.
It cannot be completely ruled out that somewhere deep under the surface of Mars, in addition to layers of materials containing water ice, veins of liquid water could also survive. The radar probes by Mars Express and the Mars Reconnaissance Orbiter could soon provide clarity about the structure of the deeper Martian soil layers.
Regardless of its dramatic climatic history, which has transformed the planet into a hostile dust desert after losing almost all of its water, some climatic cycles and weather processes that we also know on earth were able to assert themselves on Mars. There, as here, there are changing seasons, which can be seen in the advancement and retreat of the polar ice caps, which are covered by both dry ice and remnants of water ice.
The cause of the seasons on Mars is the already mentioned inclination of its axis to the orbit plane by currently around 25 degrees, so that in the polar regions of the two hemispheres - as on Earth - the midnight sun and polar night alternate. If summer is in the northern hemisphere, it is winter in the southern hemisphere and vice versa. And because Mars needs almost two earth years to orbit the sun, its seasons are almost twice as long as on earth: One Mars year corresponds to 687 earth days and thus about 22 ½ months.
The Martian temperatures are anything but comfortable. The annual mean temperature is minus 55 ° C, which is around 70 ° below that of our earth. The reason for such low values is the almost missing greenhouse effect. The thin atmosphere consists of 97 percent carbon dioxide, but the small, absolute amount of CO2 can only raise Mars temperatures by 5 ° C. On the other hand, the greenhouse effect is currently causing a temperature increase of 35 ° C. Without greenhouse gases, the mean temperature of the earth would only be minus 20 ° C, which would freeze the oceans and endanger the most important prerequisites for life.
Of all meteorological phenomena, the wind is by far the most important, because wind, in interaction with received solar energy, is the engine of all weather events on all planets that have an atmosphere. On Mars, too, it compensates for differences in air pressure and temperature caused by different levels of solar radiation, thus ensuring a constant change in the state of the atmosphere. Depending on regional conditions and the season of the year, it only blows as a gentle, barely perceptible breath or it chases away as a thundering hurricane and can change entire landscapes through the dust that is always carried along.
Under the thin Martian atmosphere, the friction of the wind with the surface of the planet is significantly less than on Earth and due to the low force of gravity, which is only about a third of the earth's gravity, dust particles can be blown up by the wind to great heights and transported over long distances . Even with longer periods of calm weather, the finest dust particles always float in the atmosphere and give the marsh sky its typical, dull reddish shimmer even in completely cloudless weather.
Despite the low temperature level, the differences between mild, cold and extremely cold at the end of the long winter on one hemisphere and at the end of summer on the other are enormous. In addition, the seasonal carbon dioxide sublimation reaches its maximum at this time and also creates large differences in air pressure. This creates ideal conditions for huge balancing storms to form, which can affect the entire planet. The masses of dust thrown up by such mega-storms then often cover the entire Martian sphere with dense, reddish clouds for weeks, sometimes even months.
© by NASAJ. Bell, M. Wolff and STScI / AURA
The starting regions for such gigantic storms are the areas near the poles, in which, as the autumn cooling begins, carbon dioxide sublimes from the atmosphere and precipitates as dry ice on the water ice caps. As a result, the atmosphere contracts, the air pressure drops by more than 25 percent and a huge, atmospheric low pressure area is created. - Exactly the opposite processes take place at the opposite pole: Here the winter dry ice sublimates back into the atmosphere with the spring warming, whereby the air envelope expands and the air pressure balance compared to the warmer, equatorial areas is out of balance due to a pressure increase of more than 25 percent device. This creates a huge high pressure area over the South Pole region, at the edges of which cold air begins to flow out.
The pressure equalization storms that develop in the course of the seasonal carbon dioxide sublimation in high latitudes are also subject to the distracting influence of the Coriolis force on Mars, as a result of which the air mass boundaries form into wide curved streaks and frontal arches with elongated cloud bands. These weather fronts, characterized by clouds of dust and ice, move - like on Earth - in the northern hemisphere against and in the southern hemisphere clockwise around the controlling low.
If the seasonal storm formations coincide with particularly intense radiation weather in the equatorial zones when the planet is close to the sun, the increased radiation supply further intensifies the global air pressure gradient. As a result, the initially only regional storm zones at higher latitudes can easily penetrate the planetary wind system and build up into a global mega-storm. At the end of such a development, there are pressure equalization storms that last for weeks every few years, the dust clouds of which reduce solar radiation on the entire planet until the air pressure and temperature structure has stabilized again.
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