NASA has officially terminated the InSight mission's HP3 heat flux sensor—affectionately nicknamed the 'mole'—following repeated failures to penetrate deep into Mars' soil.
The InSight lander touched down successfully on Mars in November 2018, with its primary goal to detect subtle seismic waves from the planet's interior, revealing insights into its composition and structure.
Among its suite of instruments was the Heat Flow and Physical Properties Package (HP3), developed by the German Aerospace Center (DLR). This 40-centimeter tube was designed to burrow up to five meters into the Martian subsurface, earning its 'mole' moniker. A tungsten mass, propelled by springs and an electric motor, drove the penetration to measure heat flow and unlock clues about Mars' geological past.
As the lander's most complex instrument, HP3 faced significant hurdles from the outset of deployment in March 2019.
The mole initially burrowed three-quarters of its length but stalled due to unexpectedly compact surface soil. Friction proved insufficient to prevent rebounding after each impact, as the soil didn't collapse back into the hole.
This marked the first attempt at such subsurface penetration on Mars, so NASA and DLR teams couldn't fully predict the soil's behavior. Multiple innovative strategies were tested over time, but none succeeded. Ultimately, principal investigator Tilman Spohn of DLR declared, "We gave it everything we had, but Mars and our heroic mole remain incompatible."
Despite this setback, InSight's primary mission persists at least through 2022. The SEIS seismometer continues detecting marsquakes, RISE analyzes the planet's iron-rich core via rotation data, and the weather station monitors atmospheric conditions.
Though the mole fell short, its challenges provide invaluable lessons for future Mars excavations—critical for astronauts seeking subsurface water ice or signs of ancient life.
