Small view (135 KBytes)
Large view (370 KBytes)
One of the benefits of the Mars Global Surveyor (MGS) Mars Orbiter
Camera (MOC) Extended Mission is the opportunity to observe how the
planet’s weather changes during a second full martian year. This
picture of Arsia Mons was taken June 19, 2001; southern spring equinox
occurred the same day. Arsia Mons is a volcano nearly large enough to
cover the state of New Mexico. On this particular day (the first day
of Spring), the MOC wide angle cameras documented an unusual
spiral-shaped cloud within the 110 km (68 mi) diameter
caldera–the summit crater–of the giant volcano. Because the
cloud is bright both in the red and blue images acquired by the wide
angle cameras, it probably consisted mostly of fine dust grains. The
cloud’s spin may have been induced by winds off the inner slopes of
the volcano’s caldera walls resulting from the temperature differences
between the walls and the caldera floor, or by a vortex as winds blew
up and over the caldera. Similar spiral clouds were seen inside the
caldera for several days; we don’t know if this was a single cloud
that persisted throughout that time or one that regenerated each
afternoon. Sunlight illuminates this scene from the left/upper left.
