High-Level Clouds Observed Around Mars
“This is the first time that carbon dioxide ice clouds on Mars have been imaged and identified from above”, said Franck Montmessin of the Service d’Aeronomie, University of Versailles (UVSQ), lead author of the paper in the Journal of Geophysical Research. “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-for example, from the SPICAM instrument on board Mars Express-to find out what the clouds are made of. However, it is very difficult to separate the signals coming from the clouds, the atmosphere and the surface.”
It is not likely that an astronaut on Mars, the 4th planet from the sun, would be able to observe clouds in a Martian sky, especially since the planet has been thought of as a desert world. However, the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer instrument on board ESA’s Mars Express has found evidence that the dry planet has high-level clouds that are dense enough to cast a shadow on the surface.
It has been observed that the flanks of the giant Martian volcanoes have clouds of water ice particles, as well as the possibility of much higher, wispy clouds made up of carbon dioxide (CO2) ice crystals. All of this is totally possible since the Martian atmosphere is thin and made up of carbon dioxide, in addition to temperatures which drop below the freezing point of carbon dioxide. Clouds of dry ice do exist as shown by a team of French scientists. They also found that some clouds are so large and dense that they throw dark shadows on the dusty surfaces.
High altitude clouds are composed of much smaller particles and are not very thick are data from the SPICAM Ultraviolet and Infrared Atmospheric Spectrometer. Omega detected CO2 clouds are very different as they are very high, more than 80 km above the surface and much thicker than previously thought. Unlike earth’s wispy icy clouds, these clouds are tall convectional clouds that grow as the result of rising columns of warm air. Surprisingly, the CO2 ice clouds consist of large particles-more than a micron (one thousandth of a millimeter) across. They are dense enough to dim the sun. “The clouds imaged by OMEGA can reduce the Sun’s apparent brightness by up to 40 per cent”, said Montmessin. “This means that they cast quite a dense shadow and this has a noticeable effect on the local ground temperature. Temperatures in the shadow can be up to 10A*C cooler than their surroundings, and this in turn modifies the local weather, particularly the winds.”
The OMEGA team thinks that the large size of ice crystals and unexpected shape of the clouds can be explained by the extreme variations in daily temperature near the equator, since the CO2 clouds are mostly seen in equatorial regions. “This discovery is important when we come to consider the past climate of Mars”, said Montmessin. “The planet seems to have been much warmer billions of years ago, and one theory suggests that Mars was then blanketed with CO2 clouds. We can use our studies of present-day conditions to understand the role that such high level clouds could have played in the global warming of Mars.”
This entry was posted on Friday, January 18th, 2008 at 6:33 am and is filed under Mars News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
