The probe, made up of a spike and a sensor-studded tether, is designed to burrow nearly 16 feet into the surface. That’s deeper than previous instruments have gone “on any other planet, moon, or asteroid,” according to NASA (excluding Earth, of course). The tether was supposed to follow the spike down and measure the heat coming from the planet’s interior. The machine only made it 12 inches. “It initially was making fabulous progress, and then just abruptly stopped moving forward,” Smrekar said.

The team was stunned. Maybe the instrument had hit a rock, they thought. The scientists and engineers of the InSight mission had prepared for such a scenario; during testing before launch, the heat probe, which they call “the mole,” had shown it could break some rocks and even maneuver around others. The team instructed the mole to keep hammering, in case the force shattered the obstacle, but that didn’t help.

Scientists now suspect another culprit: the Martian soil itself. As the probe hammered, loose dirt was supposed to swirl around it, providing friction for its back-and-forth movements. But the soil might have clumped together instead and moved away from the instrument. Eventually, a moat of empty space could have emerged between them. “Some friction is essential for the mechanism to work, as the recoil produced by the mechanism during hammering needs to be absorbed,” says Matthias Grott, a scientist at the German Aerospace Center’s Institute of Planetary Research, which provided the instrument to NASA. Without that friction, the probe just bounces in place.

Spacecraft have never encountered such difficult soil on Mars before, and the probe wasn’t designed to handle it. Scientists have since recreated these conditions back on Earth, with a replica of the heat probe and stickier sand; the experiment, in an outcome that is both reassuring and disheartening, showed that the probe could indeed become stuck like this.

The circumstances are certainly unexpected, but not insurmountable. The team could generate some friction by using a scoop on the robotic arm to drop some soil into the space around the probe or apply pressure to the ground.

If only they could see anything.

InSight’s cameras can take pictures of its surroundings to send home, but they don’t have eyes on the problem. The probe arrived in a cylindrical case that holds it steady until it drills itself free, but only made it out so far before becoming stuck. The case now blocks InSight’s view of the probe and the surrounding regolith.

So the InSight team has devised a rather clever plan. They will use the robotic arm to lift the case, little by little, to get a better look at the probe beneath.

It’s a risky operation. If they end up pulling the probe out of the ground, they can’t stick it back in. InSight’s robotic arm was designed to clutch the case, not handle the probe. So they will command the spacecraft to move carefully, like a stop-motion animator adjusting clay after every take: Lift a little, back off, take a picture, beam it home. The spacecraft is scheduled to attempt this maneuver for the first time tomorrow, raising the case a mere five inches. More attempts are planned for next week. With a better view, the team can confirm the problem and determine a fix.