Dust Storms
Wind Pattern and Temperatures on Mars
The atmosphere on Mars never clears completely. It is clearest
during the northern spring and summer, but even the sky photographed by
the Viking landers had the pinkish-yellow color of sunlight scattered off
suspended particles in Mars' atmosphere. In the northern fall and winter
(southern spring and summer), sharp rises in opacity mark the arrival of
global dust storms. Such storms are so intense that dust particles are lifted
to heights in excess of 4
0 kilometers
and surface features become totally obscured. Since there is no precipitation
on Mars to clean out the atmosphere, the dust may remain suspended for weeks
even months. The dust cycle on Mars was charted by the Viking 1 lander by
measuring the degree to which sun light was attenuated in passing through
the atmosphere as seen in the diagram (right). The more dust in the atmosphere
the greater the opacity. The Martian atmosphere never clears completely.
The broken segment represents a time when only a lower limit on the opacity
was obtained
On Mars, dust storms
are not a rare occurrence. They are much like a fine mist or fog being swirled
around by 100 plus mph winds. In contrast, on Earth in the Sahara and Mojave
Deserts, the sand is much thicker and coarser and can do more damage. Mars
Pathfinder has found that the Martian soil is finer than talcum powder.
So terrestrial sand storms are more serious than the Martian ones. Above
is a partial map of wind patterns and temperature on Mars (courtesy CMEX
Laboratories). Martian dust storms usually start in the southern hemisphere,
during summer time. In the summer, heat escapes from the surface very rapidly.
Since the southern hemisphere is closest to the sun during the summer, it
receives the most direct heat. The storms usually work their way up to the
north. Occasionally a dust storm will go global. During
the Viking missions the landers both experienced many dust storms. The following
series of images on the left were taken during the Viking 1 lander mission.
They show regular days and nights, as well as harsh dust storm conditions
on Sol. 1742. (sol 1742 means the 1742 solar cycle or day) In the Fall of 1996 (Martian spring) a dust storm raged at the
north pole of Mars while Earth had the Hubble Space Telescope pointed towards
it. It captured these spectacular images (to get a bigger view click on
the image). It shows the curly wisps of dust and sand. This image gave the
Mars Pathfinder team a small scare, in that the dust storm was lingering
very close to the Pathfinder landing site, and landing might have been delayed.
Every year there are hundreds of dust storms. From Earth based observations
we only see the long ones or the global ones that occur 3 or 4 times a year. |
