Up-Close Look at a Martian Rock That Refused to Release Curiosity’s Arm

NASA’s Curiosity had spent years gradually ascending the slopes of Mount Sharp inside Gale Crater. On April 25, the rover drilled into a rock known as Atacama, which was about a foot and a half across and six inches thick, weighing over thirty pounds. The drill sank in neatly enough to collect the sample the scientists need. The rover then pulled its arm back. The entire rock came with it.

Instead of remaining on the Martian surface, Atacama rose directly out of the ground and remained securely attached to the fixed sleeve that encircled the rotating drill bit. Nobody had ever seen anything like this. Previous drills had split rock layers and left fragments behind, but nothing had ever ridden the sleeve like a tenacious passenger.

Engineers at NASA’s Jet Propulsion Laboratory discovered the problem almost immediately from the photographs Curiosity sent home. Distance made everything deliberate; radio messages take more than half an hour each way, so every command had to travel 140 million miles before the rover could answer. The squad couldn’t just reach out and shake the arm free. They needed to plot each move, send it, wait for confirmation, and then adapt.

They first instructed the rover to vibrate the drill, as the rock was tightly packed. A few days later, they changed the arm position and tried the vibration again. Small granules of sand slipped away, but Atacama remained in place. Days passed while the rover remained immobile on the crimson hill, its arm extended and the rock still dangling. On May 1, the engineers tested a more vigorous sequence. They slanted the drill farther than before, then coupled rotation, vibration, and bit spin. They planned to repeat the steps numerous times if necessary. One cycle proved sufficient. The rock released go, fell to the ground, and broke into pieces upon impact.

Images sent back thereafter show the broken remains surrounding the drill site, as well as the now-empty sleeve. The drill’s sample material gathered inside Atacama scattered during the fall, so the crew will need to find a more stable rock for the next try. Curiosity resumed its usual regimen of atmosphere checks, dust monitoring, and the plodding journey further up Mount Sharp.
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