What happened to NASA’s ‘mole’? Mars digger intended to take planet’s temperature declared dead by scientists
The probe was attempting to burrow into the Martian surface since February 28, 2019
NASA’s InSight lander ‘mole’ – which the agency describes as a 16-inch-long (40-centimeter-long) pile driver and heat probe deployed on Mars – was declared dead after it failed to burrow deep into the Red Planet to take its temperature. It has not 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 traveled to Mars aboard the InSight lander. Part of an instrument called the Heat Flow and Physical Properties Package (HP3), the mole is 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.
Since February 28, 2019, the probe 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 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, explain scientists.
After getting the top of the mole about two or three 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 January 9, 2021, with no progress, the team called an end to their efforts and the end of the mole’s journey on Mars.
“We’ve given it everything we’ve got, but Mars and our heroic mole remain incompatible. Fortunately, we’ve learned a lot that will benefit future missions that attempt to dig into the subsurface,” says HP3’s principal investigator, Tilman Spohn of DLR.
NASA’s Phoenix lander scraped the top layer of the Martian surface, but no mission before InSight has tried to burrow into the soil. According to researchers, doing so is critical for many reasons: Future astronauts may need to dig through the soil to access water ice, while scientists want to study the subsurface’s potential to support microbial life.
The mole’s design was based on soil seen by previous Mars missions. For two years, the team worked to adapt the unique instrument to these new circumstances. But the soil did not behave as expected. “The mole is a device with no heritage. What we attempted to do – to dig so deep with a device so small – is unprecedented. Having had the opportunity to take this all the way to the end is the greatest reward,” notes 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.
The Insight mission
Short for Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport, the InSight mission was recently extended for two more years, to December 2022. “Studying Mars’ interior structure answers key questions about the early formation of rocky planets in our inner solar system – Mercury, Venus, Earth, and Mars - more than 4 billion years ago, as well as rocky exoplanets. InSight also measures tectonic activity and meteorite impacts on Mars today,” notes NASA.
According to researchers, Mars is neither too big nor too small when compared to the other terrestrial planets. “This means that it preserves the record of its formation and can give us insight into how the terrestrial planets formed. It is the perfect laboratory from which to study the formation and evolution of rocky planets. Scientists know that Mars has low levels of geological activity. But a lander like InSight can also reveal just how active Mars really is,” they add.
The InSight spacecraft touched down November 26, 2018, on Mars to study the planet’s deep interior. A little more than one Martian year later, the stationary lander has detected more than 480 quakes and collected what NASA describes as the “most comprehensive weather data of any surface mission sent to Mars.”
The mission has been to help scientists to compare Earths and Mars. Studying what the depths of Mars is made of, how that material is layered, and how quickly heat seeps out of it could help scientists better understand how a planet’s starting materials make it more or less likely to support life, say experts.
While there's more science to come from InSight, a key finding is the lack of quakes larger than magnitude 4, considering how frequently the Red Planet shakes due to smaller quakes. Scientists propose that it could be that Mars is just more static than anticipated, or that InSight landed in an especially quiet period.
“It’s a little surprising we haven't seen a bigger event. That may be telling us something about Mars, or it may be telling us something about luck,” emphasizes seismologist Mark Panning of NASA's Jet Propulsion Laboratory in Southern California, which leads the InSight mission.
Once InSight started detecting quakes, they became so regular that, at one point, they were happening every day. But in late June 2020, the detections stopped. Only five quakes have been detected since then, all of them since September 2020. Experts believe Mars’ wind is responsible for these seismically blank periods: the planet entered the windiest season of the Martian year around June.
“InSight’s extended mission will focus on producing a long-duration, high-quality seismic dataset. Continued operation of its weather station and burial of the seismic tether using the spacecraft’s Instrument Deployment Arm (IDA), will contribute to the quality of this seismic dataset,” states the agency.