Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK
18.2
Since north is at the top of the photograph, the orientation of
these barchanoidal transverse dunes indicates that prevail-
ing winds are southwesterly. These winds are moving the
dunes in a northeasterly direction toward the upper right
of the photograph. The backslopes face the direction from
which the winds are coming, whereas the slip faces lie in
the shadows. The presence of these dunes indicates that
the available sand supply is relatively low, causing distinct
dunes to form rather than a sand sea.
D i s c o v e r…
SAND DUNES ON MARS
You may know that a very active research program exists to
learn about the environment and geologic history of Mars.
The reason for this interest is that Mars and Earth are about
the same size, are relatively close to one another, and are
about the same age. Evidence suggests that flowing wa-
ter once existed on Mars, which means that the planet may
have had an atmosphere somewhat similar to Earth's at one
time. It also means that some form of primitive life may have
once existed there, or may still exist in some obscure place.
One of the ways that Mars is being studied is with satel-
lite remote sensing. This program is revealing much about
the character and history of Mars, including what you can
see in this image. Do you recognize these features? They are
barchan dunes. These dunes mean that wind blows sand
on the planet, just as it does on Earth. It also means that
the amount of sand available to blow is somewhat limited.
Of particular interest regarding these dunes are the randomly
spaced dark patches. If these dunes were on Earth, you might
assume that these spots are patches of vegetation. But, of
course, vegetation does not exist on Mars. So what are they?
The best current hypothesis is that the dunes are covered with
a light frost in the Martian winter and that the spots represent
places where the frost sublimates (turns to vapor) as summer
approaches. Fascinating, yes?
