The Heat Flow and Physical Properties Package (HP3) is one sophisticated experiment of NASA’s InSight Mission. Nicknamed the “Mole” it's a self-hammering probe designed to dig beneath the surface to study the interior temperature of Mars. But since the mission landed on Mars, there’s been an issue; the Mole can’t dig deep enough.
The soil where InSight landed appears to be different from previously explored locations making the design of the Mole unable to do its job. To the rescue has come the robotic scoop of InSight. Over the last few months, the scoop has been used to push down on the Mole. This was considered a risky move, though, as that’s where the cables that tether the probe are located.
This gamble has paid off and the Mole is now to be almost fully in the soil. As reported in a blog post by Dr Tilman Spohn, Principal Investigator of HP3, the Mole went from 7 centimeters (2.8 inches) above the surface on March 11 (Sol 458) to the scoop now touching the surface on May 30 (Sol 536). The Mole digs using friction, but the regolith (extraterrestrial soil) at this site has not provided enough to grip for the Mole not to bounce back, which is why the scoop is being used to hold it down.
This approach seems to have worked so far, but the team has had to be very careful not to rush it. Besides the danger of damaging the experiment, this attempt at pushing had to be done without disturbing the other experiments too much. It was carried out in six sessions every other week. Now, it has reached the point of truth: The next session will be the “free-Mole” test, where the little experiment will try to dig all by itself.
“The next step, the free-Mole test, will be very exciting. But what if the Mole is just not deep enough in for sufficient friction?" Dr Spohn ponders. "We then have two options, either fill the pit to provide more friction and push on the regolith, or use the scoop to push at the back-cap again, but this time with its tip rather than with its flat bottom surface. This would be a somewhat more difficult operation but doable, as the Instrument Deployment Arm (IDA) team thinks.“
If all goes well, over the next several weeks, the Mole might finally reach the point of digging all by itself.