Here is the heat probe of NASA’s InSight lander – nicknamed the “mole” – on October 3, 2020, when the peak-like mole was still trying to bury itself in the red Martian soil. The copper ribbon attached to the mole has sensors to measure the heat flow of the planet. Now, NASA engineers have called for this part of the mission to be stopped. Image by NASA / JPL-Caltech.
A key aspect of NASA’s InSight mission to Mars unfortunately ended last week. NASA has announced that InSight’s HP3 heat probe – aka the mole – has failed to gain the friction it needs to dig as deep as planned on the surface of Mars. Now, mission engineers have finally completed attempts, NASA said, to make the probe sink deeper into the ground. However, there is also good news. The mission was given an extension, giving it more time on the surface of Mars to complete its other tasks.
The mole – officially known as heat flux and the package of physical properties – was designed to dig up to 5 meters. The goal was to take measurements of Mars’ internal temperature, providing vital clues as to how active Mars is and how much heat it still holds inside.
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The problem was that the mole needed friction from the surrounding soil to be able to dig deeper. As it turns out, the soil on that side of Mars was more crowded than expected, which means less friction. The mole would penetrate about two inches or so, less than an inch, and then it would tend to come back again. Finally, the mission team began trying to push the mole further down with the spoon on the robot arm of the lander. The ground was scraped on the mole, and then the shovel was used to clog it with “hammer blows”, hoping to provide more friction. This worked to some extent for a while, but it still wasn’t enough to cause the mole to continue digging deeper on its own.
By January 9, 2021, more than 500 such knocks had been struck to no avail. At that moment, the mission team called for an end to the effort.
It’s unfortunate, but – as you can imagine – unexpected problems often arise when exploring worlds hundreds of millions of miles away. According to Tilman Spohn of the German Aerospace Center (DLR), who built the mole:
We gave him everything we have, but Mars and our heroic mole remain incompatible. Fortunately, I learned many things that will benefit future missions trying to dig underground.
The mission team used the scoop at the end of the robotic arm to try to collide the heat probe deeper into the ground. The attempts failed, however, due to the lack of friction in the soil due to congestion. Image by NASA / JPL-Caltech.
The artist’s conception of NASA’s InSight lander on Mars, with a cropped view of the basement. Image via PGP / Nicolas Sarter / JPL-Caltech.
Other landers and rovers used spoons to dig into the surface layers of the soil to obtain samples, but the InSight mole was meant to bury them significantly deeper. The failure to dig deep enough is disappointing, but it has certainly not been for lack of attempts and is still a success in other ways. As Thomas Zurbuchen, associate administrator for science at NASA, said.
We are so proud of our team that they worked hard to bring the InSight mole deeper into the planet. It was amazing to see them troubleshooting millions of miles away. This is why we take risks at NASA, we have to push the limits of technology to find out what works and what doesn’t. In this regard, we have been successful: we have learned many things that will benefit future missions to Mars and elsewhere, and we thank our German DLR partners for providing this tool and for their collaboration.
So what went wrong?
The Earth was surprising, as testing the instrument back on Earth was based on the properties of the Martian soil seen by previous missions to Mars. But the ground at the InSight landing site in the Elysium Planitia proved to be different from that observed at any other landing site. According to Troy Hudson, a scientist and engineer at NASA’s Jet Propulsion Laboratory (JPL):
The mole is a legacy device. What we tried to do – dig so deep with such a small device – is unprecedented. Having had the opportunity to complete this is the greatest reward.
InSight has many different scientific tools. The heat sink, shown to the right, was to be buried about five feet into the ground. Image by NASA / JPL-Caltech.
Heat flow probe diagram. Image via DLR / InSight Project / Spaceflight 101.com.
All is not lost, however. The counterattack gave the mission team more experience using the robotic arm, as well as the chance to learn more about the ground at this location. What makes it busier?
Another task in the near future will be to use the robotic arm to bury the link that connects the seismometer instrument – called the Seismic Experiment for Internal Structure (SEIS) – to the lander. It is hoped that this will reduce the amount of cracking and popping sounds heard in seismic data due to temperature changes.
SEIS takes the “pulse” of Mars, listening to seismic activity below the surface and has so far recorded over 480 earthquakes. By far the majority are very small, but they tell scientists how active Mars is beneath the surface. So far, it appears to be somewhere between Earth and the moon. Some of the seismic activity detected by InSight comes from still-active fault regions and ancient volcanoes, suggesting that Mars may have been volcanically active to some extent, at least below the surface.
The Lander itself continues to be in excellent general health, which is good news, and the mission has been extended for another two years, until December 2022. This means that there is still much more science that can be done with all the other InSight tools.
InSight’s mission is primarily to study the interior of Mars and determine if the planet is still geologically active. Image by NASA / JPL-Caltech.
The overall mission of InSight is to study the interior of Mars, to determine how geologically active the planet is and how it has formed and changed in the last billions of years. An onboard radio experiment called the Rotation and Interior Structure Experiment (RISE) is designed to find out if the core of Mars is still liquid or solid and what its overall composition is, including iron.
InSight also monitors Martian weather above the surface, with some of the most advanced weather sensors ever sent to the planet. The Curiosity rover also monitors the atmosphere and weather, as does the Perseverance rover when it lands next month, on February 18th. All three together will create the first meteorological network on another planet, another huge achievement.
The mole may not dig anymore, but the mission is far from over, with a lot of good science to come!
Bottom line: The mission team for the InSight land on Mars has canceled any additional attempt to try to dig deep into the ground with the heat probe instrument called the “mole.” The rest of the mission continues, however, with an extension until December 2022.
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