NASA Pulls Plug On InSight Lander’s Mars Mole

NASA has pulled the plug on its InSight lander’s Mars mole, more than two years after the lander touched down at Elysium Planitia. The German-built Mars mole heat probe could simply never penetrate the hard exterior surface of its landing site in order to make the kind of measurements necessary to give planetary scientists the first real clues as to the makeup of the Martian interior.

For nearly two years, the InSight, short for Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport’s mole probe has been attempting to burrow into the Martian surface to take the planet’s internal temperature, says NASA. But the soil’s unexpected tendency to clump deprived the spike-like mole of the friction it needs to hammer itself to a sufficient depth, the team notes.

Part of the spacecraft’s Heat Flow and Physical Properties Package (HP3), the mole was intended to be a self-hammering probe that would burrow down to almost 16 feet (five meters) below Mars’ surface. This would have enabled planetary scientists to better understand whether Mars’ interior is radically different from Earth or our own Moon.

“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.”

The mole itself is a 16-inch-long spike designed to drag with it a ribbonlike tether that extends from the spacecraft, says NASA.  The idea was that Temperature sensors are embedded along the tether to measure the planet’s interior heat.

But InSight landed in an area with an unusually thick duricrust, or a layer of cemented soil, NASA reports.  Rather than being loose and sandlike, as expected, the dirt granules stick together, says the agency.

Unfortunately, to work properly, the mole needs friction from the soil in order to travel downward. Without it, says NASA, recoil from its self-hammering action causes it to simply bounce in place.  Paradoxically, it’s loose soil, not this cement-like duricrust that InSight has encountered at its landing site, that would ideally provide the needed friction as it falls around the mole.

The landing site at Elysium Planitia, a broad, equatorial volcanic plain, was selected in part because it has so few visible rocks, implying few large subsurface rocks.  Designed to measure heat flowing from the planet once the mole has dug at least 10 feet deep, the mole is strong enough to nudge small rocks out of its way, says NASA.   

But after repeated attempts to aid the mole in its actions over a two year period using the spacecraft’s robotic arm in ways that it was never intended, the team realized that they were in a no-win situation.

Meanwhile, the rest of InSight’s instruments are functioning and taking data. In fact, NASA says that the mission intends to employ the robotic arm in burying the tether that conveys data and power between the lander and InSight’s seismometer, which has recorded more than 480 marsquakes. Burying it will help reduce temperature changes that have created cracking and popping sounds in seismic data, the team notes.

The InSight mission itself has been recently extended to late next year. Along with hunting for marsquakes, the lander hosts a radio experiment that is collecting data to reveal whether the planet’s core is liquid or solid, says NASA. And InSight’s weather sensors are capable of providing some of the most detailed meteorological data ever collected on Mars, says the agency. Together with weather instruments aboard NASA’s Curiosity rover and the Perseverance rover, which lands on Feb. 18th, the team says that the three spacecraft will create the first meteorological network on another planet.

Could the problem simply be an ordinary rock?

“We don’t know for sure, because we can’t see underground,” Spohn said in a statement.  “[But] there’s also the possibility that we’ve hit a rock.”