Mars is a dirty place. We know from Viking and Pathfinder that many martian rocks are covered with dust.
Also, martian rocks might have been weathered by long-term exposure to the planet's atmosphere. If
weathering has occurred, the surface of even a dust-free rock may not have the same composition as
the rock's interior. And it's what's inside the rocks that matters most.
In order to look at the interior of rocks, a field geologist on Earth uses a rock hammer. On the
Athena payload, the job of a rock hammer is done by the RAT —
the Rock Abrasion Tool. The RAT is
positioned against a rock by the rover's instrument arm, and uses a grinding wheel to remove dust
and weathered rock, exposing fresh rock underneath. The RAT exposes an area nearly 5 cm (2 inches)
in diameter, and grinds down to a depth of about 5 mm (0.2 inches).
Credit: NASA/JPL/Cornell/Honeybee Robotics
Opportunity's Pancam camera shows the rover's rock abrasion tool before
and after it ground into a rock at the region dubbed "El Capitan." The
image on the left was taken on the 29th sol of Opportunity's mission,
and the image on the right on the 31st sol. (released March 5, 2004)
Credit: NASA/JPL/Cornell/Honeybee Robotics
Opportunity's rock abrasion tool generated a significant amount of
reddish dust when it drilled into a target called "Guadalupe" within the
"El Capitan" region of the rock outcrop at Meridiani Planum. This image
is an enhanced color composite generated from three different Pancam
camera filters. (released March 5, 2004)
