Los Angeles ? Scientists fixed a glitch that froze the robotic arm on the Mars rover Opportunity and then prepared the robot explorer to dig a narrow trench in the Martian soil, NASA said Saturday.

Scientists hoped the patch of soil, dubbed “Hematite Slope,” would prove to be rich in the iron-bearing mineral, which typically forms in water.

Opportunity’s explorations had been delayed Friday because the rover failed to properly stow its robotic arm. Engineers sent instructions to the rover that fixed the problem, mission manager Jim Erickson said Saturday.

The glitch occurred because scientists had instructed Opportunity to perform what could have been an unsafe movement with the robotic arm. Faced with the conflict between that instruction and its safety instructions, the rover stopped with its robotic arm still extended until scientists revised the commands.

“The rover is sometimes smarter than we are,” said Erickson. “The trick is to catch these on the ground and resequence them correctly before we send them up.”

With that problem solved, scientists wanted Opportunity to dig four inches or so into the soil, using one of its front wheels as an excavator. They hoped the move would expose minerals that could reveal whether Mars ever was wet enough to support life.

Opportunity’s twin rover, Spirit, was on the other side of the planet inspecting two rocks nicknamed “Stone Council” and “Mimi,” and the surrounding soil before resuming its trip toward a crater 1,100 feet away.

“Spirit is still moving out, but it’s stopping to smell the roses along the way,” Erickson said.