The Heat Flow and Physical Properties Package (HP3) aka the “Mole” has stopped digging, and this time is for the last time. The important instrument on NASA’s lander InSight had troubles from the beginning of the mission, and almost two years on, the team has decided to pull the plug.
The instrument was a self-hammering probe, designed to burrow deep into the Martian soil. Its goal was to study the interior temperature of the Red Planet once it had dug for at least three meters (10 feet). However, it never managed to drill much more than its length, which stands at 40 centimeters (16 inches).
The design of the mole was based on the previous studies of the Martian soil from the many robotic missions that visited the planet. The soil underneath InSight is like no other on the planet, and the scientists only found out once it started digging. Instead of lowing around the probe, it clumped up, providing a hard barrier for the mole to overcome.
Since February 2019, when the first attempt happened, the team had to be creative with the lander’s robotic arm to help the mole dig more and more. It recently got completely into the ground, giving hope that it could finally burrow down.
On January 9, the robotic arm was used to pour more soil on to the mole and press down onto it to provide friction. The mole conducted 500 hammer strokes. But unfortunately, it didn’t go deeper. The team decided that there was no other solution but to stop trying to make the mole dig.
“We’ve given it everything we’ve got, but Mars and our heroic mole remain incompatible,” HP3’s principal investigator, Tilman Spohn of DLR, said in a statement. “Fortunately, we’ve learned a lot that will benefit future missions that attempt to dig into the subsurface.”
It is an enormous pity that the mole was not able to conduct its scientific mission, but do not think that this is a story of defeat. It is a story of innovation. There has not been a device like it before, it was a completely new approach to study an alien world. It will be influential even without scientific data.
The legacy of the mole is already being employed. The last 23 months saw the team of engineers pushing the capabilities of the lander's robotic arm to the limit. This hard-earned experience will be employed to use the arm to completely bury the tether between InSight and its seismometer, which has already recorded over 480 marsquakes. This will improve the quality of the data during InSight’s extended mission.