Here is the heat probe from NASA’s InSight lander – nicknamed “the mole” – on October 3, 2020, when the spike-like mole was still trying to bury itself in the Martian red soil. The copper-colored tape attached to the mole has sensors to measure the heat flow from the planet. Now NASA engineers have stopped this part of the mission. Image via NASA / JPL-Caltech.
A key aspect of NASA’s InSight mission to Mars sadly ended last week. NASA announced that InSight’s HP3 heat probe, also known as the mole, has not achieved the friction it needs to dig as deep as planned on the surface of Mars. Now mission engineers have put an end to attempts, NASA said, to get the probe buried deeper into the ground. However, there is also good news. The mission has been granted an extension, giving more time to the surface of Mars to carry out its other tasks.
The mole, officially known as the heat flow package and 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 Mars is still geologically active and how much heat it still retains inside.
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The problem was that the mole needed friction from the surrounding soil in order to continue digging deeper. It turns out that the ground in that part of Mars was thicker than expected, that is, less friction. The mole would penetrate a couple of inches or so, less than an inch, and then tend to reappear. Eventually, the mission team began trying to push the mole down with the ball of the lander’s robotic arm. The ground would be scraped over the mole, and then the spoon was used to be pounded with “hammer blows,” hoping to provide more friction. This worked to some extent, for a while, but it still wasn’t enough to get the mole to continue deepening on its own.
By January 9, 2021, more than 500 hammer blows had already been made, to no avail. At that moment, the mission team called for an end to the effort.
It is unfortunate, however, as you can imagine, unexpected problems often arise when exploring worlds hundreds of millions of miles away. As stated by Tilman Spohn of the German Aerospace Center (DLR), who built the mole:
We have given him everything we have, but Mars and our heroic mole remain incompatible. Fortunately, we have learned many things that will benefit future missions that will attempt to delve deeper into the subsoil.
The mission team used the ball at the end of the robotic arm to try to hammer the heat probe deeper into the ground. Attempts failed, however, due to lack of friction on the ground due to mass. Image via NASA / JPL-Caltech.
NASA’s InSight landing artist concept on Mars, with a cropped view of the subsoil. Image via PGP / Nicolas Sarter / JPL-Caltech.
Other landers and rovers have used balls to dig into the surface layers of the soil to obtain samples, but the mole of InSight was intended to dig significantly deeper. The inability to dig deep enough is disappointing, but it was certainly not for lack of attempts and yet it is a success in other ways. As Thomas Zurbuchen, associate science administrator at NASA, said:
We are very proud of our team who have worked hard to get the InSight mole to get deeper into the planet. It was amazing to see them fix problems millions of miles away. That’s why we take risks at NASA, we have to push the boundaries of technology to learn 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 instrument and their collaboration.
What went wrong, then?
The density of the soil was surprising, as the test of the instrument on Earth was based on the properties of the Martian soil that saw missions before Mars. But the ground at the InSight landing site, at Elysium Planitia, proved to be different from what was seen at any other landing site. According to Troy Hudson, a scientist and engineer at NASA’s Jet Propulsion Laboratory (JPL):
The mole is a device without heritage. What we tried to do, deepen with such a small device, is unprecedented. Having had a chance to get it to the end is the biggest reward.
InSight has many different scientific instruments. The heat flow probe, shown on the right, was supposed to fall about five feet to the ground. Image via NASA / JPL-Caltech.
Schematic of the heat flow probe. Image via DLR / InSight Project / Spaceflight 101.com.
All is not lost, however. The setback provided the mission team with more experience with the robotic arm, as well as the opportunity to learn more about the ground at this location. What makes it more rude?
Another task in the near future will be to use the robotic arm to bury the rope that connects the seismometer instrument (called Seismic Experiment for Indoor Structures) to the lander. Doing so is expected to reduce the amount of sounds heard in seismic data due to temperature changes.
SEIS takes the “dust” of Mars, listening for seismic activity below the surface, and has so far recorded more than 480 earthquakes. Most are, by far, very small, but tell scientists how Mars is active below the surface. So far it seems to be somewhere between the Earth and the moon. Some of the seismic activity detected by InSight comes from regions with still-active faults and ancient volcanoes, suggesting that Mars may still be volcanically active to some extent, at least below the surface.
The lander itself continues to maintain excellent overall health, which is good news, and the mission has been extended for two more years, until December 2022. This means that there is still much more science that can be done. with all other InSight instruments.
InSight’s mission is primarily to study the interior of Mars and determine if the planet is still geologically active. Image via NASA / JPL-Caltech.
InSight’s overall mission is to study the interior of Mars, determine the geological state of the planet, and how it has formed and changed in the last billion years. An onboard radio experiment called the Inner Structure and Rotation Experiment (RISE) is designed to find out if the core of Mars is still liquid or if it is solid and what its overall composition is, including iron.
InSight also monitors Martian climate on 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, February 18th. All three together will create the first weather network on another planet, another huge success.
Maybe the mole is no longer digging, but the mission is far from over, and there is still a lot of good science to come.
Bottom line: NASA’s InSight landing mission team to Mars has called off any other 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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