Filling the Mole Hole

The size of the mole hole is a huge surprise but is also diagnostic of the problem and indicates a (probably) workable solution. The only way to make a hole that big without actually excavating material is to compact it. In terms of materials familiar to us Earth dwellers, the soil around the mole is behaving a lot more like wet snow than it is like sand. For the mole’s self-hammering drive to work, it needs friction to keep it from just bouncing; it needs the surface to behave more like sand (or, if you’re into Minecraft, like gravel), falling into any excavated hole. If the walls of the hole are compacting rather than collapsing as the mole hammers, there’s insufficient friction, and the mole just bounces around and has no hope of penetrating. This is bad.

But. InSight has a secret weapon, a tool it wasn’t even supposed to have. It has a shovel, mounted on the end of the arm, inherited from the canceled Mars Surveyor lander mission. InSight can use the shovel to press down on the surface, tamping down the soil like you tamp dirt around a transplanted root ball, thereby enclosing the HP3 mole in sand and giving it the friction it needs to keep going. One way or another, they plan to “fill the pit,” Spohn says, and hopefully when they’ve done that the mole will be able to proceed downward.

So for the next few weeks to months, the team will keep playing in the Martian sandbox. But there’s real hope that the efforts will end with the burial of the mole, to some depth, allowing that part of InSight’s Martian experiment to begin.