Mars Dunes - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 142

Fig. 12.21 HiRISE subscene of
Nili Patera barchans used to
document ripple and dune
movement. The two arrows at
right point to the edge of the dune
in an image acquired 3 years
earlier. A closeup showing ripple
movement is shown in Fig. 9.10

sampling instruments in November 2012, a sand deposit
(called 'Rocknest') was scooped repeatedly; the final sieved
portions of the sand were examined by precision chemistry
and mineralogy instruments within the body of the rover.
Olivine, plagioclase, and two pyroxenes were identified in
the sand materials\150 lm in size using the Chemistry and
Mineralogy (ChemMin) instrument, the first time that an
X-ray diffraction pattern has been obtained on another
planet (see Sect. 17.1 ) , and the Sample Analysis on Mars
(SAM) instrument confirmed the basaltic composition of the
sand. The Mars Hand Lens Imager (MAHLI) on the
movable arm of Curiosity obtained wonderful close-up
images of the surface of the Rocknest deposit, revealing a
surface coating of 1 mm-size large clasts overlying dark
sand that comprises the bulk of the deposit (Fig. 12.23 ).
This is only a 'first glimpse' of what the instruments on
Curiosity will be able to tell us about the Martian surface
materials; we are fortunate that, for engineering reasons, the
first location selected for the scooping of samples was an
aeolian sand deposit.
The small-car-sized Curiosity rover is the latest in a
series of increasingly sophisticated robotic vehicles capable
of driving across the Martian surface. In 1997, the micro-
wave-oven-sized Sojourner rover became the first space-
craft to demonstrate the great advantages of having mobility
for exploration spacecraft on Mars, as part of the Mars
Pathfinder spacecraft that also demonstrated the practical
use of airbags as a way to land instruments on Mars.

Sojourner provided images of large sand ripples that were
not visible to the cameras on the Pathfinder lander (Fig. 1.6
), as well as making the first Alpha Proton X-ray Spec-
trometer (APXS) measurements of Martian aeolian depos-
its, confirming their basaltic composition (Greeley et al.
1999). In 2004, the twin Mars Exploration Rover (MER)
spacecraft Spirit and Opportunity brought golf-cart-sized
robotic explorers to two sites on opposite sides of Mars. The
Microscopic Imager (MI) and the Panoramic Camera
(Pancam) provided numerous images of sand deposits at
both landing sites, and the AXPS on the robotic arm of both
rovers obtained dozens of chemistry measurements from
sand deposits. Spirit obtained images of cm-scale sand
ripples that visibly moved (see Fig. 16.15 ) during a 2-day
period (Sullivan et al. 2008), and Opportunity investigated
megaripples during its long drives across Meridiani Planum
(Sullivan et al. 2005).
Next we mention a few of the MER investigation sites
that have relevance to dunes:
Endurance crater, Meridiani Planum (*100 m diame-
ter). Opportunity spent nine months exploring inside this
impact crater, mostly intended to provide access to the
rocks exposed in the crater wall. However, it was also able
to drive to within a few meters of the small field of sand
dunes or ripples on the crater floor. For reasons related to
rover trafficability, Opportunity was not allowed to drive
into the dune field in Endurance, mainly because other sand
deposits had resulted in both MER rovers to become