Encyclopedia of the Solar System 2nd ed

338 Encyclopedia of the Solar System

FIGURE 7 Color mosaic of theViking 2landing site showing
flat rocky and dusty plain. Pitted rocks in foreground suggest
they are volcanic basalts, and the angular homogeneous rock
field suggests they are distal ejecta from the fresh crater Mie to
the east of the landing site. Lighter toned trough in the middle of
the image, in front of the large rocks, has been interpreted to
result from the freezing and thawing of subsurface ground ice.

was expected to be the roughest at all three of these length
scales, which agrees with the undulating ridge and rough
terrain and the more distant streamlined islands visible from
the lander. The other three landing sites are in between
these extremes at the three length scales, withViking 2
(Fig. 7) and portions of Gusev (Fig. 9) fairly smooth at the
100 m and 1 km scale,Viking 1slightly rougher at all three
length scales, andViking 2and portions of Gusev (like the

FIGURE 8 Color mosaic of theMars Pathfinderlanding site
showing undulating, ridge–trough moderately dusty and rocky
plain. Large rocks in the middle left of the image appear stacked
or imbricated on a ridge with a trough behind it that trends
toward the northeast. Streamlined hills on the horizon, the
ridge–trough topography, and angular to subrounded boulders
are consistent with depositional plains deposited by catastrophic
floods as expected from the setting of the site downstream from
the mouth of Ares Valles outflow channel. Note dust coating the
tops of rocks.

FIGURE 9 Color mosaic of theSpiritlanding site on the

cratered plains of Gusev. Note the soil-filled hollows that are

impact craters filled in by sediment. Dark angular blocks are

consistent with ejecta, and the pebble-rich surface is similar to a

desert pavement in which the sand-sized particles have been

moved by the wind leaving a lag deposit. The landing site is in a

dust devil track explaining its lower albedo and less dusty surface.

The plain is relatively flat with Grissom Hill in the background.

Note dark wind tails behind rocks in lower middle foreground.

Columbia Hills) in between in roughness at the several me-

ter length scale. All these observations are consistent with

the relief observed at the surface.

The close correspondence between surface character-

istics inferred from orbital remote sensing data and that

found at the landing sites argues that future efforts to select

safe landing sites will be successful. Linking the five landing

sites to their remote sensing signatures suggests that they

span many of the important surfaces available for landing

on Mars. Such surfaces that have moderate to high ther-

mal inertia with low to high albedo (but not low albedo and

low thermal inertia) constitute almost 80% of the planet,

suggesting that to first order most of Mars is likely safe for

suitably engineered landers. These results show that basic

FIGURE 10 Color mosaic of the eastern part of Bonneville

crater showing dusty and rocky surface of this part of the

cratered plains. Note that wall of the crater is composed of dark

rubble, suggesting that it formed in a regolith of basalt ejecta.

This location is not in a dust devil track and so is much dustier

with much higher albedo, consistent with inferences made from

orbital images. Hills in the background are the Columbia Hills,

which are 90 m high and composed of older rocks.Spirit

traversed the cratered plains and climbed to the top of the

Columbia Hills (highest peak shown is Husband Hill).