Page 44 - (DK) Eyewitness - Mars

Dunes on Mars

As fine, wind-blown dust rises into the
Martian atmosphere, the heavier particles
settle to the surface to fill gullies and craters.
Some particles pile up into dunes that are
shaped and sculpted by the winds. Sand and
dust are whipped into amazing, changing
forms that are captured in photographs from DUNE GULLIES WIND OR WATER EROSION
In this photo, the floor of southern
This Mars Global Surveyor image
orbiting spacecraft. Most Martian dunes are shows mysterious gullies that Auqakuh Vallis—an ancient
dark, composed of ground-up volcanic rock. stripe sand dunes of Russell Crater valley—is covered by ripple-like
forms made by the wind. This site,
in the southern highlands. How
Their patterns are especially fascinating in these gullies were formed is in Arabia Terra, might have been
spring, when carbon dioxide frost on the unknown. They occur mostly on carved out by flowing water that
south-facing slopes.
has long since vanished.
dunes begins to melt. Seen from high above,
the withdrawing ice creates fantastic designs
that cover hundreds of miles of surface. Since
Martian gravity is only a third of Earth’s,
dunes can grow twice as high as those on
Earth. The largest dunes on Mars surround
the northern polar ice field in a great ring
80 feet (24 m) high.

SCOURED AND TANGLED FROST ON THE SAND
Wind-scoured sand dunes in This springtime photo shows
central Herschel Crater were eroded dunes covered by carbon
imaged by the Mars Orbiter dioxide frost that is beginning to
Camera of Mars Global Surveyor. “sublime” away, or evaporate into
These dunes appear to be the air. Retreating frost often
cemented solidly into twisted, leaves streaks on dunes, that look
ribbonlike shapes. like works of abstract art.