NASA’s latest Mars lander is having problems with one of its main instruments — a self-hammering probe that just can’t seem to hammer itself into the interplanetary dirt. Over the weekend, the probe was attempting to dig itself into the Martian soil when it popped out of the ground unexpectedly. Now, NASA engineers are trying to troubleshoot to see if they can get this instrument to burrow underneath Mars’ surface as intended.

The probe belongs to NASA’s InSight lander, a robot the size of a small car that landed on Mars in November of 2018. InSight’s goal is to figure out what Mars’ insides are made of, and the lander has two primary tools that it uses to “peer inside” the planet. Its main instrument is a seismometer, tuned to listen for marsquakes or vibrations in the crust of Mars. These quakes act a bit like ultrasounds; the waves pass through the core of the planet, carrying details about what kinds of materials are trapped inside. So far, InSight’s seismometer has detected about 100 vibration events, 21 of which are suspected to be quakes.

InSight’s second main instrument is the heat probe — nicknamed the mole. It’s supposed to hammer down into the ground just next to InSight and take Mars’ temperature. If it works as planned, it could give scientists more information about how much heat is leaving the planet’s interior. But the mole hasn’t had as much luck as the seismometer. In fact, it pretty much started having problems as soon as InSight got to the Red Planet. Since it started digging at the end of February, it hasn’t been able to travel more than 14 inches (35 centimeters), even though it’s designed to dig up to 16 feet (5 meters).

The InSight team thinks that the soil surrounding the mole may be to blame. While it digs, the mole needs the soil to fall around the probe uniformly, providing friction that allows the instrument to hammer farther underground. Otherwise, it’d just bob up and down in one place, according to NASA. But testing has indicated that the soil in this particular spot is unlike soil encountered by previous landers on Mars. It’s clumping around the probe and not providing any friction. That may explain the slow movement.

Mars continues to surprise us. While digging this weekend the mole backed about halfway out of the ground. Preliminary assessment points to unexpected soil properties as the main reason. Team looking at next steps. #SaveTheMole #Teamwork pic.twitter.com/UURvU8VTwZ — NASA InSight (@NASAInSight) October 27, 2019

To get the mole tunneling like it’s supposed to, NASA engineers decided to use InSight’s robotic arm to press against the mole as it tried to dig. The idea was to pin the mole up against the side of the hole it created, providing the necessary friction it seems to be lacking. It seemed to be working for the last few weeks, but then this weekend, images from the InSight lander showed that the probe had partially backed out of its hole. Once again, NASA is blaming “unusual soil conditions.”

Now the InSight team is trying to figure out what to do next. If it’s safe, they may try to move the lander’s robotic arm away from the mole to better figure out what’s going on with the probe. If the worst-case scenario does become reality and the probe cannot dig underground, it’s not the end of the world for the InSight mission. The lander’s main goal is to learn more about the core of Mars by listening for marsquakes, which it’s successfully doing. While getting a good temperature reading of the Martian interior would help characterize the planet’s innards, it’s not essential to the overall mission.