Snow-covered dunes in the northern hemisphere of Mars
Photo: HANDOUT/ AFP
There are not only seasons on Earth, summer and winter also exist on Mars.
The red planet's axis of rotation is tilted more than 25 degrees.
For comparison: Our earth is a good 23 degrees.
This means that during one orbit of the respective planet around the sun, one polar region is in the light for a long time and later in the dark – and cold – for just as long.
In the case of Mars, however, a season lasts about twice as long as ours, because the planet takes two years to orbit the sun.
An international team, which included experts from the Technical University of Berlin, the German Aerospace Center (DLR) and institutions from other European countries, the USA, Japan and Russia, has now been able to show impressively how much Mars has changed in the Change of seasons changed.
Among other things, the group presents evidence in the "Journal of Geophysical Research - Planets" that winter in the polar regions causes additional ice and snow thicknesses of up to four meters over huge areas.
Then the temperature can drop to values of minus 125 degrees Celsius and lower.
At the poles there is "an enormous volume if you add up the additional snow and ice masses of the winter," says Haifeng Xiao from the Institute for Geodesy and Geoinformation Technology at the Technical University of Berlin.
His co-author Alexander Stark from the DLR Institute for Planetary Research in Berlin estimates that almost ten trillion cubic meters of mainly frozen carbon dioxide, but also snowflakes and ice crystals are also bound to the permanent polar caps.
"That's almost the volume of Lake Superior on the border between Canada and the USA, the second largest freshwater lake on earth with a volume of twelve trillion cubic meters," says Stark.
Or more than two hundred times the content of Lake Constance.
600 million laser pulses
That Mars has thick ice caps is not new.
The one at the South Pole was discovered in 1672 by the Dutch astronomer Christiaan Huygens.
And in 1704, the Italian Giacomo Filippo Maraldi sighted the ice at the North Pole for the first time.
So far, however, the areas have usually been measured on the respective polar day because they are well lit then.
With the help of the laser measurement data from NASA's "Mars Global Surveyor" space probe from 1999 to 2001 - which has actually been known for many years - the team has now calculated the extent in winter as well.
Because the laser signals naturally do not mind the darkness.
In total, the measured values of 600 million laser pulses and 8000 laser profiles were evaluated.
It was to be expected that the volume of ice and snow cover would be highest towards the end of winter.
The expansion was different.
This was already at its greatest at the winter solstice, i.e. about six Earth months earlier.
By the end of winter she had already lost a lot of weight.
"This discrepancy can possibly be explained by the fact that carbon dioxide ice at the edge of the polar caps sublimes earlier in winter, i.e. changes from the solid back to the gaseous state and is then part of the atmosphere," says Xiao.
At the same time, CO2 ice condenses from the atmosphere outside of the permanent polar ice caps and is deposited further north.
This is how the ice volume increases until the end of winter.
At the same time, almost a third of the atmosphere disappears - because it turns to ice.
At the south pole of Mars, the seasonal growth on the up to 1,500 meter thick, permanent ice layers of CO2 ice is highest at two and a half meters.
At the North Pole, with its much thicker permanent ice cover consisting mostly of water ice, the height of the additional ice and snow cover is only 1.3 meters at most.
Interestingly, it reaches its maximum value 500 to 800 kilometers further south, on the large dunes of the vast, almost 500,000 square kilometer Olympia Undae desert.
There, the white layer can be up to four meters thick.