QUESTION: 
Are there any type of clouds in the Mars atmosphere?
 
ANSWER from Mary Urquhart on May 2, 1997:
Clouds on Mars are rare compared with clouds on the Earth (which always has a 
substantial amount of clouds, so that even if it's clear where you live it's 
very cloudy someplace else) and are very thin.  Most clouds on Mars are clouds 
of water ice, although some are probably made of frozen carbon dioxide (dry ice). 

Because the clouds are made of ice, they are different from most clouds on the 
Earth. Most clouds on the Earth are made of droplets of liquid water. However, 
some such as cirrus clouds are made of water ice, and are more like the clouds 
on Mars.  Sometimes, the clouds on Mars are close to the ground, or even touch 
the ground and become fog just like on the Earth. You can see a painting of 
clouds on Mars based on images taken by the Viking spacecraft at: 

http://cass.jsc.nasa.gov/images/sred/sred_S18.gif

And an image of fog in canyons on Mars (in the western end of the giant Martian 
canyon Valles Mariner is at:

http://cass.jsc.nasa.gov/images/sred/sred_S19.gif 

You can also see clouds in pictures taken by the Hubble Space Telescope such as 
the image at:

http://oposite.stsci.edu/pubinfo/jpeg/Mars95.jpg

(The caption for this image is at: 
http://oposite.stsci.edu/pubinfo/gif/Mars95.txt)