Page 27 - (DK) Eyewitness - Mars

Clouds on Mars

Clouds form on the great volcanic
peaks in summertime, when
warmer air flows upward and
cools. Water or carbon dioxide
vapors form clouds over the polar
caps and also at high altitudes.
Clouds of water ice are found at
12–18 miles (19–29 km) high,
and carbon dioxide clouds are at
30 miles (48 km). Because Mars is MIST IN A LABYRINTH STREAKY CLOUDS LEE WAVE CLOUDS
dry and cold, there is never rain, but Spacecraft cameras show early These clouds may appear This photograph shows an
in winter polar clouds leave frost on morning fog in Noctis Labyrinthus, anywhere on Mars, but are example of a lee wave cloud
the ground and maybe snow. canyons at the western end of Valles most common in the Syrtis over an impact crater. Lee wave
Major highlands north of
Marineris. The Martian atmosphere
clouds form around large
holds very little water vapor, but the Hellas Planitia. Earth-based obstacles such as mountains,
combination of cold temperatures telescopes can see Martian ridges, craters, and volcanoes.
and low atmospheric pressure creates clouds, which reflect sunlight The air in such regions often
water ice clouds. and appear as bright spots. produces wavelike ripples.
Dust storms and “dust devils”

Martian winds are always at work scouring rocks and lifting dust. Clouds of dust can
become powerful storms that cover thousands of miles. Dust clouds rise 3,000 feet
(1 km) high and fill the air for weeks. Often, small whirlwinds—“convection
currents”—spin into columns that twirl across the land. Termed “dust devils,” they
can be 300 feet (100 m) tall, and are visible to orbiting spacecraft.

MARTIAN TWISTER
Sunlight gleams off a spinning dust devil
that is leaving a twisted trail behind it.
Dust devils often form in summertime on
the flat plains of Mars.

A DUST STORM GATHERS
The power of a smothering dust cloud
is recorded in these 1999 images of a
giant, swirling storm system over the
north polar region. Taken two hours
apart (from left to right), these pictures
show the storm’s rapid progress and
turbulent expansion.

Does it snow on Mars? SURPRISE SNOWFALL
An artist pictures a future astronaut
studying surface ice on Mars when a light
In autumn, dense clouds blanket the northern polar region. This snow begins to fall. The astronaut reaches
“polar hood” is difficult to see through, so scientists are not sure what out to catch the flakes.
is happening underneath. As winter sets in, the hood grows larger.
Icy vapors freeze on the dust particles in the air, becoming snowlike
crystals. When the polar hood shrinks, it leaves behind a white
coating on the ground from frost and, possibly, snow.

CONTRASTING SNOWFLAKES
A six-sided water-ice snowflake formed
in Earth’s atmosphere appears delicate
and feathery beside this gemlike
plastic model of a Martian
carbon dioxide snowflake.
Scientists know that frost
regularly forms on Mars,
but they are uncertain
about whether or not
snow occurs.
Snowflake
on Earth
Martian
snowflake

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