MARS AT OPPOSITION

These NASA Hubble Space Telescope views provide the most
detailed complete global coverage of the red planet Mars
ever seen from Earth.  The pictures were taken on February
25, 1995, when Mars was at a distance of 65 million miles
(103 million km).

To the surprise of researchers, Mars is cloudier than seen
in previous years. This means the planet is cooler and
drier, because water vapor in the atmosphere freezes out to
form ice-crystal clouds. Hubble resolves Martian surface
features with a level of detail only exceeded by planetary
probes, such as impact craters and other features as small
as 30 miles (50 kilometers) across.

[Tharsis region] - A crescent-shaped cloud just right of
center identifies the immense shield volcano Olympus Mons,
which is 340 miles (550 km) across at its base.  Warm
afternoon air pushed up over the summit forms ice-crystal
clouds downwind from the volcano.  Farther to the east
(right) a line of clouds forms over a row of three extinct
volcanoes which are from north to south:  Ascraeus Mons,
Pavonis Mons, Arsia Mons.  It's part of an unusual,
recurring "W"-shaped cloud formation that once mystified
earlier ground-based observers.

[Valles Marineris region] - The 16 mile-high volcano
Ascraeus Mons pokes through the cloud deck along the
western (left) limb of the planet.  Other interesting
geologic features include (lower left) Valles Marineris, an
immense rift valley the length of the continental United
States.  Near the image center lies the Chryse basin made
up of cratered and chaotic terrain. The oval-looking Argyre
impact basin (bottom) appears white due to clouds or
frost.

[Syrtis Major region] - The dark "shark fin" feature left
of center is Syrtis Major.  Below it the giant impact basin
Hellas.  Clouds cover several great volcanos in the Elysium
region near the eastern (right) limb.  As clearly seen in
the Hubble images, past dust storms in Mars' southern
hemisphere have scoured the plains of fine light dust and
transported the dust northward.  This leaves behind a
relatively coarser, and less reflective sand in,
predominantly, the southern hemisphere.

The pictures were taken with Hubble's Wide Field Planetary
Camera 2.

Credit:  Philip James (University of Toledo),
         Steven Lee (University of Colorado),
         NASA