Until now, Mars has generally been regarded as a desert world. But, a team of scientists has now found proof that the arid planet possesses high-level dense ice clouds which scud across its orange sky.
Using data obtained by the OMEGA spectrometer on board ESA’s Mars Express, the French scientists have found the existence of the clouds of dry ice which sometimes become so large and dense that they throw quite dark shadows on the dusty surface of the planet.
“This is the first time that carbon dioxide ice clouds on Mars have been imaged and identified from above. This is important because the images tell us not only about their shape, but also their size and density.”
“Previously, we had to rely on indirect information. However, it is very difficult to separate the signals coming from the clouds, atmosphere and surface,” lead scientist Franck Montmessin of the Service dAeronomie at University of Versailles was quoted by the ScienceDaily as saying.
Not only are the clouds surprisingly high — over 80 km above the surface — but they can be several hundred kilometres across.
They are also much thicker than expected. Instead of looking like the wispy ice clouds seen on Earth, they resemble tall convectional clouds that grow as the result of rising columns of warm air.
Even more surprising is the fact that the CO2 ice clouds are made of quite large particles — more than a micron (one thousandth of a millimetre) across — and they are sufficiently dense to noticeably dim the sun.
“The clouds imaged by OMEGA can reduce the sun’s apparent brightness by up to 40 per cent. This means that they cast quite a dense shadow and this has a noticeable effect on the local ground temperature.
Temperature
“Temperatures in the shadow can be up to 10 degree Celcius cooler than their surroundings, and this in turn modifies the local weather, particularly the winds,” Montmessin said.
Since the CO2 clouds are mostly seen in equatorial regions, the OMEGA team believes that the unexpected shape of the clouds and the large size of their ice crystals can be explained by the extreme variations in daily temperature that occur near the equator.
“The cold temperatures at night and relatively high day-time temperatures cause large diurnal waves in the atmosphere. This means there is a potential for large-scale convection, particularly as the morning sun warms the ground,” Montmessin said.
