Illustration of NASA's InSight lander on Mars

A Cutaway of InSight on Mars: In this illustration of NASA's InSight lander on Mars, layers of the planet's subsurface can be seen below, and dust devils can be seen in the background. Credit: IPGP/Nicolas Sarter. Download image ›

The heat probe hasn’t been able to gain the friction it needs to dig, but the mission has been granted an extension to carry on with its other science.

The heat probe developed and built by the German Aerospace Center (DLR) and deployed on Mars by NASA’s InSight lander has ended its portion of the mission. Since Feb. 28, 2019, the probe, called the “mole,” has been attempting to burrow into the Martian surface to take the planet’s internal temperature, providing details about the interior heat engine that drives the Mars’ evolution and geology. 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.

After getting the top of the mole about 2 or 3 centimeters under the surface, the team tried one last time to use a scoop on InSight’s robotic arm to scrape soil onto the probe and tamp it down to provide added friction. After the probe conducted 500 additional hammer strokes on Saturday, Jan. 9, with no progress, the team called an end to their efforts.

Part of an instrument called the Heat Flow and Physical Properties Package (HP3), the mole is a 16-inch-long (40-centimeter-long) pile driver connected to the lander by a tether with embedded temperature sensors. These sensors are designed to measure heat flowing from the planet once the mole has dug at least 10 feet (3 meters) deep.

“We’ve given it everything we’ve got, but Mars and our heroic mole remain incompatible,” said HP3’s principal investigator, Tilman Spohn of DLR. “Fortunately, we’ve learned a lot that will benefit future missions that attempt to dig into the subsurface.”

short video of InSight's mole working on Mars
InSight’s ‘Mole’ Comes to Rest: The “mole,” a heat probe that traveled to Mars aboard NASA’s InSight lander, as it looked after hammering on Jan. 9, 2021, the 754th Martian day, or sol, of the mission. After trying since Feb. 28, 2019, to bury the probe, the mission team called an end to their efforts. Full image and caption ›

While NASA’s Phoenix lander scraped the top layer of the Martian surface, no mission before InSight has tried to burrow into the soil. Doing so is important for a variety of reasons: Future astronauts may need to dig through soil to access water ice, while scientists want to study the subsurface’s potential to support microbial life.

“We are so proud of our team who worked hard to get InSight’s mole deeper into the planet. It was amazing to see them troubleshoot from millions of miles away,” said Thomas Zurbuchen, associate administrator for science at the agency’s headquarters in Washington. “This is why we take risks at NASA – we have to push the limits of technology to learn what works and what doesn’t. In that sense, we’ve been successful: We’ve learned a lot that will benefit future missions to Mars and elsewhere, and we thank our German partners from DLR for providing this instrument and for their collaboration.

Hard-Earned Wisdom

The unexpected properties of the soil near the surface next to InSight will be puzzled over by scientists for years to come. The mole’s design was based on soil seen by previous Mars missions – soil that proved very different from what the mole encountered. For two years, the team worked to adapt the unique and innovative instrument to these new circumstances.

“The mole is a device with no heritage. What we attempted to do – to dig so deep with a device so small – is unprecedented,” said Troy Hudson, a scientist and engineer at NASA’s Jet Propulsion Laboratory in Southern California who has led efforts to get the mole deeper into the Martian crust. “Having had the opportunity to take this all the way to the end is the greatest reward.”

Besides learning about the soil at this location, engineers have gained invaluable experience operating the robotic arm. In fact, they used the arm and scoop in ways they never intended to at the outset of the mission, including pressing against and down on the mole. Planning the moves and getting them just right with the commands they were sending up to InSight pushed the team to grow.

They’ll put their hard-earned wisdom to use in the future. 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.

There’s much more science to come from InSight, short for Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport. NASA recently extended the mission for two more years, to Dec. 2022. Along with hunting for quakes, the lander hosts a radio experiment that is collecting data to reveal whether the planet’s core is liquid or solid. And InSight’s weather sensors are capable of providing some of the most detailed meteorological data ever collected on Mars. Together with weather instruments aboard NASA's Curiosity rover and its new Perseverance rover, which lands on Feb. 18, the three spacecraft will create the first meteorological network on another planet.

+ An InSight Team Member's Perspective

Written by Troy Hudson, a JPL scientist and engineer who led efforts to get the mole deeper into the Martian crust

Following repositioning of the robotic arm's scoop on sol 734 in December, 2020, the mole was commanded to hammer 500 strokes on January 9, 2021 (Sol 754). The goal of this final “Free Mole Test” was to see if the mole (no longer in direct contact with the arm) made any significant downward progress following the scrape and tamp activities of the last two months. Though not all images from the “movie” taken during the test have been sent back from Mars, we have enough to conclude that there was no perceptible downward motion of the mole and thus the test was not successful.

After two years and amidst a variety of constraints, this test was our line in the sand.

Despite heroic efforts on the part of those involved at every stage of the process, and even though the mole shows all signs of remaining fully functional, Mars remains a jealous guardian of its secrets.

We do observe significant slumping of regolith [soil] on the margins of the pit at side-piles from previous scraping activities. Also seen are lateral motion of the mole tether, a very slight change in mole orientation (it became 1 - 2 degrees more vertical), and what appears to be a “fountaining” of regolith out of the ground around the back of the mole and from under the scoop. But no “in” or “out” motion is apparent, judging from various markers on the tether itself.

In order to continue to use the mole as a probe of regolith thermal conductivity in response to seasonal atmospheric pressure changes, we hope that the mole remains covered in regolith.

Our next steps are to retract the robotic arm and do imaging of the site to confirm this and garner further information about soil / mole behavior. Should it be the case that the recent hammering exposed the mole, there may be final scraping steps to bring in more soil to ensure complete burial. Otherwise, the arm will be free to perform any other activities deemed desirable by the project.

On today’s team call, many folks had the chance to express their thoughts as we turn to the epilogue of the mole’s story.

I cannot do justice to all of their feelings, nor even capture all of my own emotions in words. But I think we all agree on these points:

  • InSight is a FAMILY. We have bonded so closely over the years and trials, and would all relish the chance to work together again. Indeed, InSight is the grandest-scale cooperative effort I’ve ever had the privilege to be involved with. And it has been the greatest learning opportunity for me in all aspects of robotic planetary exploration.

  • The mole works! HP3 as a whole, and the mole in particular, are marvels of engineering. And through tireless work, from early prototypes to operations, we created something unique (i.e., without any true heritage) that remains robustly healthy – even after nearly two full years exposed on the surface of Mars and over 10,000 on-site hammer strokes.

  • Sand is hard. What we have lived through as part of this anomaly resolution process is the “best” kind of problem one could have: the device behaved exactly as designed… it was MARS that defied our expectations. We have learned much that will inform future drilling attempts on this and other worlds. The value of this pathfinding (literally groundbreaking) knowledge can’t be overstated.

  • We got to try. There were many points where things could have gone sideways and stopped our efforts. Instead, we actually had the chance to try *everything* in our severely limited arsenal from millions of miles away, and deployed them in a logical, risk-aware way that both built on the knowledge accumulated and was ever-cognizant of the unknowns before us.

For two years I’ve been approaching this as dispassionately as possible. Focused on facts, data, and constraints, I didn’t really let my emotions about it come through. Now that the results are in, there’s finally room for me to start processing the whole experience. The emotions ebb and flow like tides.

Everyone has been incredibly supportive and have offered very valuable perspectives, and for this you have my most profound thanks.

I vastly prefer cooperation over competition. I would rather help someone paint their house than play a game of cards. I like to work together to build something. InSight has been the greatest and grandest endeavor it has ever been my joy to take part in.

More About the Mission

JPL manages InSight for NASA’s Science Mission Directorate. InSight is part of NASA’s Discovery Program, managed by the agency’s Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space in Denver built the InSight spacecraft, including its cruise stage and lander, and supports spacecraft operations for the mission.

A number of European partners, including France’s Centre National d’Études Spatiales (CNES) and the German Aerospace Center (DLR), are supporting the InSight mission. CNES provided the Seismic Experiment for Interior Structure (SEIS) instrument to NASA, with the principal investigator at IPGP (Institut de Physique du Globe de Paris). Significant contributions for SEIS came from IPGP; the Max Planck Institute for Solar System Research (MPS) in Germany; the Swiss Federal Institute of Technology (ETH Zurich) in Switzerland; Imperial College London and Oxford University in the United Kingdom; and JPL. DLR provided the Heat Flow and Physical Properties Package (HP3) instrument, with significant contributions from the Space Research Center (CBK) of the Polish Academy of Sciences and Astronika in Poland. Spain’s Centro de Astrobiología (CAB) supplied the temperature and wind sensors.

News Media Contacts
Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.

Alana Johnson / Grey Hautaluoma
NASA Headquarters, Washington
202-672-4780 / 202-358-0668 /

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