14 DAY TRIAL // Most of the popular science articles and documentaries published over the years imprinted in our imagination a picture of Mars dominated by a massive desert of red sand constantly bayed in sunlight. Recent findings, however, tell a different story. ESA's Mars Express spacecraft revealed the presence of clouds of water ice particles, mostly around elevated surface structures such as the flanks of inactive volcanoes.
Previously, clouds of carbon dioxide ice crystals were detected in Mars' atmosphere, nothing too special considering the fact that the Red Planet's atmosphere is composed mostly of carbon dioxide gas. Carbon dioxide frozen of the planet's surface is routinely being evaporated during the periods of time when the Sun illuminates the surface. The evaporated gas freezes in the cold Martian atmosphere, forming carbon dioxide ice crystal that are packed into relatively large clouds.
Though Mars doesn't have a great deal of water on its surface, the same process might be available for this substance as well. A team of scientists have shown that as these dry clouds move above the surface of the planet, they cast large dark shadows, some capable of cooling the dusty surface to a few degrees bellow the temperature of the surrounding areas, and could in fact affect the local weather.
Nevertheless, the clouds recently found by the Mars Express spacecraft seem to have slightly different characteristics. They hover at extremely high altitudes, some reaching up to 80 kilometers above the surface of the planet. Furthermore, they are much thicker and larger than any such structure previously observed on Mars. They form through a process similar to that of convectional clouds that grow as large columns of hot air rise towards the upper layers of the atmosphere.
During the cloud formation, some particles of dry ice could reach sizes more than a micron in diameter, which would create a cloud dense enough to cast dark shadows over the surface of Mars, reducing the brightness by about 40 percent.
The so-called OMEGA team, which conducted the study, argues that the formation of large dry ice particles is mostly due to the wide variation in temperatures, in the equatorial regions of the planet. The process results in the formation of such large ice particles is still uncertain. On Earth, water condenses mostly around dust particles to form either larger water droplets, or in cooler conditions large water ice particles
It is generally believed that the thin Martian atmosphere permits micrometeorites to reach distances relatively small in relation to the surface, thus providing a base for the nucleation process that forms the large dry ice particles.