WASHINGTON — A probe on NASA’s InSight Mars lander that has been stuck for months is moving deeper into the surface again thanks to an assist from the lander’s robotic arm.

NASA’s Jet Propulsion Laboratory said Oct. 17 that the probe, or “mole,” for the Heat Flow and Physical Properties Package instrument on the lander had moved about two centimeters deeper into the surface since Oct. 8. That marks the first movement into the surface since the mole got stuck about 30 centimeters below the surface in early March.

The mole is equipped with an internal mechanism to hammer into the surface. The lack of progress led engineers to conclude that a lack of friction with the surrounding the soil was causing the mole to simply bounce in place. However, the lack of movement could also be explained if the mole had run into a rock.

That alternative explanation is now ruled out. “Seeing the mole’s progress seems to indicate that there’s no rock blocking our path,” said Tilman Spohn, principal investigator for the instrument at the German space agency DLR, in a statement. “That’s great news! We’re rooting for our mole to keep going.”

In the last few months, engineers used the robotic arm on InSight, originally intended to place the heat flow probe and a separate seismic instrument on the surface, to remove the support structure surrounding the probe and try to compress the surface around it in an unsuccessful effort to increase the friction around the probe.

More recently, the project decided to use the arm itself to pin the mole to one side of the hole with its scoop, providing the additional friction needed to go into the surface. That technique appears to have worked, at least so far. “The plan will be continuing to use the scoop to provide ‘grip’ as long as the mole is sticking out,” Spohn wrote in an Oct. 18 blog post on DLR’s website.

However, the mole will eventually go far enough below the surface that the arm will no longer be able to help. If the mole gets stuck again, other options are being studied, JPL said, including using the arm to move soil on top of the mole to increase its mass or even press down on top of it to produce additional friction. The goal is to get the mole as deep as five meters into the surface.

“The mole still has a way to go, but we’re all thrilled to see it digging again,” Troy Hudson, a JPL engineer and scientist who led the effort to get the instrument moving again, said in a statement. He said it was “crushing” when the mole got stuck. “Right now, I’m feeling giddy.”