In 2018, NASA launched the Insight mission to Elysium Planitia, Mars, to probe the interior of Mars and answer key questions about its early formation and current tectonic activity. One of InSight’s main instruments is the Heat Flow and Physical Properties Package (HP3) developed and built by the German Aerospace Center (DLR). HP3 was designed to burrow up to approximately 5 meters below the martian surface and measure the heat that is coming from the martian interior. Measuring the internal heat flow of Mars would help scientists learn more about the evolution of the planet and the extent to which it is similar to Earth and the Moon.
Unfortunately, on January 14, the heat probe on the HP3 instrument, informally named the “mole,” ended its journey. The mole was designed as a spike that burrows into the surface propelled by repeated “hammer” strokes. Since the initial deployment of the mole on February 28, 2019, it has not been able to gain the friction required to dig due to the soil’s unexpected tendency for clumping. After 500 hammer strokes, the deepest the mole managed to penetrate was 2 to 3 centimeters. This included an attempt to use a scoop on InSight’s robotic arm to scrape soil onto the probe and tamp it down to generate more friction.
The mole was designed to burrow into soils encountered by previous Mars missions, so the fact that it was unable to burrow into the soil at Elysium Planitia suggests that the soil properties there are somehow different. Future robotic or human exploration missions that may attempt to dig into the subsurface to understand the habitability of the subsurface for microorganisms or in search of resources such as water ice that can be used by astronauts will benefit from lessons learned from the mole. Although the mole has been decommissioned, InSight continues to operate on the surface of Mars, collecting seismic data from marsquakes, measuring the wobble of the martian north pole as it orbits the Sun, and providing valuable information on tectonic activity, meteorite impacts, and the size of the martian core. READ MORE