The image at the left shows dry ground in the desert on Earth.
Click on image for full size version (828K JPG).
Images from: NASA/JPL.
The image at the right shows tundra.
Click on image for full size version (128K JPG).
Images from: University of California at Berkeley.
There are many different kinds of soils on the surface of the Earth.
The desert ground shown here is just one kind of soil. Soils in a
desert are depleted of water. Tundra is a soil type that includes frozen
water, and is seen at high latitudes on Earth. In addition, many soils on
Earth include plentiful organic matter, due to the presence of life.
The image at left shows soils of Mars from the Viking 2 landing
site, Utopia Planitia. Click on image for full size version
(140K GIF). Image from: NASA/JPL.
The right image shows patterned ground at the south pole of Mars. Click on
image for full size version (1M GIF). Image from:
Though the soils of much of Mars seem to be depleted of water and can be
compared to a terrestrial desert, studies of the surface have
found the presence of water in the soils and atmosphere, in both
solid and vapor form. The patterned ground shown at the right is found
near the south pole of Mars. The patterns in the soil are thought to be
due to the presence of frozen water in the soil. To see the patterns,
click to see the full size (spectacular) image.
One of the objectives of the Mars Pathfinder mission was to study the
composition and structure of the soil. Everywhere the Rover passed, it
disturbed the soil, and the soil underneath turned out to be a darker
red-brown soil than its surroundings. The Rover found that much of the
ground is made of dust, possibly deposited during the dust storms that
periodically surround the planet. The reddish color of the soil is caused
by rust (iron oxide).
Martian soils were studied by Venera, by the Viking lander, and by Mars
Pathfinder. Before the Viking Mission to Mars, knowledge of the kinds of
rocks present on Mars was based on the Martian meteorites. The first analysis
of Mars soil from Viking landers found no evidence of life, instead showing
that organic molecules are even more scarce than on the Earth's moon.