Mars: Landing Site Geology, Mineralogy and Geochemistry 345
FIGURE 21 Images of Meridiani outcrops acquired by the
Opportunityrover. (A) Pancam image of Guadalupe in Eagle
crater, after RAT grinding. Notice slightly redder, dustier surface
around the circular RAT hole and small hematite spherules
protruding from the outcrop. (B) Microscopic image of
Guadalupe RAT hole, showing blueberries (dark circles) and
tabular voids produced by dissolution of soluble minerals. (C)
Pancam image of Ontario in Endurance crater, after RAT
grinding (circular smooth area). (D) Mosaic of microscopic
images of Ontario, showing fine laminations, tabular voids, and a
few blueberries (dark circles).
Two oddball rocks at theOpportunitysite deserve spe-
cial mention. Bounce Rock, so named because the lander
bounced on it as it rolled to a stop, was discovered on the
Meridiani plains as the rover exited Eagle crater. Its chem-
ical composition, as measured by APXS, is remarkably like
the compositions of a group of Martian basaltic meteorites
FIGURE 22 MI image mosaic of the Upper Dells in Eagle
crater showing fine sand-sized particles making up the
laminations, blueberries, and cuspate or curved cross laminations
that indicate the sand-sized particles were deposited by running
water.
FIGURE 23 Color image mosaic of evaporite outcrop of Burns
Cliff at the rim of Endurance crater. The lower unit exposed in
the lower left shows steeply dipping layers that are truncated by
a middle-layered unit with shallow dipping beds. Uppermost
unit is lighter toned. The lowermost unit has been interpreted as
eolian cross beds that are truncated by the flatter beds of a sand
sheet. The uppermost layer is interpreted as the unit deposited
in running water of an ephemeral playa or salt water lake.called shergottites (Fig. 13). Its mineralogy is dominated
by pyroxenes and plagioclase, as are shergottites. This rock
is obviously not in place and may have been lofted in as
ejecta from a large impact crater to the south. Heat Shield
Rock, named for its proximity to the heat shield discarded
during descent of theOpportunitylander, is likewise an
interloper in this terrain. TheOpportunityinstruments re-
vealed that it is an iron meteorite, composed of iron–nickel
alloys, similar to some iron meteorites that fall to Earth.
[SeeMeteorites.]5.2 Soils
In addition to numerous soil analyses by the Mars
Pathfinder,Spirit, andOpportunityrovers, we have soils
collected by scoops and analyzed at the twoVikinglanding
sites. As defined by soil scientists on Earth, “soil” usually
contains a component of organic matter formed by decayed
organisms. Soils on Mars do not contain measurable organic
materials, but the term “soil” is nonetheless commonly used
in planetary science (“regolith” may be a more accurate
term, meaning the surface layer formed by the destruction
of rocks).
It is not easy to distinguish between soil and dust on
Mars. Soil, normally dark, represents deposited materials,
commonly of sand or silt grains (Fig. 17). Bright reddish
dust is much finer grained (several micrometers in size) and
can either be suspended in the atmosphere or deposited on
the ground. The top surface of soil is usually a thin layer