When the Perseverance rover finishes a drive and is exploring a new
location, you may see it create a round, shallow hole in a nearby rock. Why
does it do this, and how?
Mars rovers are robot geologists. They study the rocks around them to
understand how the area was formed. However, the environment on the
surface of Mars can dramatically change the exterior of a rock. The
unaltered rock below the surface may hold important clues to the history of
the area.
The previous rovers Spirit and Opportunity each had a Rock Abrasion Tool
(RAT), a high-speed grinder with brushes to remove that weathered outer
layer of rock and clear away dust. Perseverance creates abraded
patches that look similar to the ones Spirit and Opportunity made, but it
does so in a very different way.
Perseverance is equipped with a rotary percussive drill and a suite of
interchangeable drill bits. The sampling team had the task of being
able to collect cores, collect regolith, and create abraded patches all
using the same drill.
To do this, the abrading bits have an unusual tooth pattern: three parallel
lines of different lengths, arranged asymmetrically. When the drill
spins and hammers with an abrading bit, that tooth pattern creates
crisscrossing, well distributed impacts in the rock. This chips away
the surface and makes a smooth, flat patch of fresh rock about 2 inches (5
centimeters) in diameter.
However, the newly drilled abrasion is full of cuttings - the dust generated
by drilling. The cuttings hide what the scientists are interested in
seeing: the color and shape of individual grains in the abrasion.
Perseverance removes the cuttings using another tool on the turret called
the Gaseous Dust Removal Tool (GDRT). The GDRT has a tank of nitrogen
gas and uses four short puffs to blow the cuttings away and reveal the fresh
rock surface underneath.
The rover can then use its suite of instruments to study the abrasion.
These observations provide insight into the formation of the area, and also
help the team decide whether to take a core sample from that rock.
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Space & Astrophysics