Ice Clouds on Mars
Up to now, Mars was thought of as a desert world–dry, boring, arid, and where nobody would want to be. But now the Omega Visible and Infrared Minerological Mapping Spectrometer instrument, on ESA’s Mars Express, has shown that the dry planet has high-level clouds that are dense enough to cast a shadow on the surface. On the flanks of the giant Martian volcanoes clouds of water ice particles can be found.
There may also be higher wispy clouds that are made up of carbon dioxide (CO2) in crystals. This is possible because the thin Martian atmosphere is composed of carbon dioxide, and temperatures often fall well below the “freezing point” of carbon dioxide. That these clouds of dry ice do exist has been shown by a group of French scientists. It is thought that they can be so large and dense as to throw dark shadows on the dusty surface.
“This is the first time that carbon dioxide ice clouds on Mars have been imaged and identified from above”, said Frank 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 the 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”. Data showed that any high altitude clouds are not very thick and made up of
much smaller particles, but the CO2 detcted by OMEGA are very different. Aside from being very high - more than 80 km above the surface - but they can be several
hundred kilometres across. Rather than looking like wispy ice clouds on Earth, the clouds look like tall convectional clouds that grow as the result of rising columns of warm air.
The CO2 ice clouds are made up of rather large particles and their density can dim
the Sun. “The clouds imaged by OMEGA can reduce the Sun’s apparent brightness by up to 40 percent”‘ 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 th
Even though CO2 clouds are usually seen in equatorial regions, team members believe that the unexpected shape of the clouds and large size of their ice crystals are because of the extreme variations in daily temperature that happen near the equator. Large thermal waves in the atmosphere are caused by cold temperatures at night and relatively high day-time temperatures. As the morning Sun warms the ground bubbles of warm gas above the surface and when they reach high levels they become cold enough for CO2 to condense. Latent gas is released by this process , while causing gas and the ice particles to rise even further. Present conditions help to understand the role that such high level clouds could have played in the global warming of Mars.
This entry was posted on Monday, February 4th, 2008 at 4:51 am and is filed under Space Agency 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.
