Light Rock, Dark Rock?
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With only four sols left and mission success nearly achieved, the
choices of what to do and where to go become harder and harder as
real-time events play the role of the "wild card". Scientist
John Grant explains, "On one hand, there is a strong desire to
approach a 'light rock' which may be a piece of the resistant rock that
lies throughout the region. On the other hand, the team is curious
about the mysterious 'dark rocks' that have been scattered in the
landing region. These rocks are thought to be fragments of cooled
lava, but remain unexplored and very interesting. With time running
out, one of the major decisions that looms larger and larger is which
of the two types of rocks to target. It is simply not possible to
The good news is that approaching either kind of rock and using the
Rock Abrasion Tool (RAT) to help characterize its composition is an
important unfulfilled exercise and would be a valuable learning
experience. It is also likely that either type of rock will yield its own
particular surprises. These exercises and uncertainties form important
parts of the excitement and process of exploration and discovery.
But why bother to go to "light rocks" and "dark
rocks," and why all the discussion? "It all relates to the
different stories that they may tell regarding the geology of the
region." Based on current information, some of the team members
advocate for taking a better look at the "light rocks",
suspecting they may be limestone, a type of rock that is typically
created in warm, shallow seas. Others suggest going to the
"dark rocks" in order to understand whether they are
volcanic, heavily weathered, or represent a rock layer that is
somewhere in between that of modern surfaces and ancient rock
formations on the local cliffs.
It may sound like a simple decision, but there's a catch. FIDO's most
recent traverse took it a little off the expected track and its Navcam
image coverage only reveals the view directly in front of the rover, not
the wider view up Long Valley that would have helped the team make a
decision. Additionally, the rover did not find the expected plethora of
large easily accessible "light" and "dark" rocks
at the end of the traverse. Some "light rocks" may lie on
the ground in the distance or in place, but are probably too far or
difficult to reach and sample. The "dark rocks" are widely
scattered, but are all too small to approach and scour with the RAT.
Now what? Work is underway to use FIDO's remote sensing instruments
to target the "light rocks" along the cliffs near Camelback
and should help resolve the origin of the regional cap rock and whether
a sea once was present. It is hoped that some of the questions about
the origin of the "light rock" can be resolved without
actually touching it. Hopes are also high that new the Navcam data
expected in the upcoming sol's downlink of data will reveal some
sufficiently large "dark rocks" nearby enough to be
approached in time to use the RAT and take measurements. In the
meantime, the mission clock ticks ever louder as time runs on.
As you can see in these images taken after Sol 22, the RAT is a
powerful grinder, able to create a hole 45 millimeters (about 2 inches) in
diameter and 5 millimeters (0.2 inches) deep into a rock on the
The RAT is located on the arm of the rover and weighs less than 720
grams (about 1.6 lbs). It uses three electric motors to drive rotating
grinding teeth into the surface of a rock. Two grinding wheels rotate
at high speeds. These wheels also rotate around each other at a much
slower speed so that the two wheels sweep the entire cutting area.
The RAT is able to grind through hard volcanic rock in about two hours.
Once a fresh surface is exposed, scientists can examine the abraded area in detail
using the rover's other science instruments. This means that the interior of a rock
may be very different from its exterior. That difference is important to scientists as it may
reveal how the rock was formed and the environmental conditions in which it
was altered. A rock sitting on the surface of Mars may become covered with dust and will
weather, or change in chemical composition from contact with the atmosphere.