Here’s the heat probe from NASA’s InSight lander – nicknamed “the mole” – on Oct. 3, 2020, when the spike-like mole was still settling in the red Martian soil. The copper-colored ribbon attached to the mole has sensors to measure the planet’s heat flow. Now NASA engineers have put an end to this part of the mission. Image via NASA / JPL-Caltech.
An important aspect of NASA’s InSight mission to Mars, sadly, came to an end last week. NASA announced that InSight’s HP3 heat probe – also known as the mole – has not been able to get the friction needed to dig as deep into the surface of Mars as planned. Now mission engineers have finally put an end to attempts, NASA said, to dig the probe deeper into the ground. However, there is also good news. The mission has been extended, giving it more time on the surface of Mars to complete its other tasks.
The mole – known officially as the Heat Flow and Physical Properties Package – is designed to dig up to 16 feet (5 meters). Its purpose was to take measurements of the internal temperature of Mars, to provide vital clues as to how geologically active Mars still is and how much heat it still retains inside.
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The problem was that the mole needed friction from the surrounding soil to keep digging deeper. It turned out that the soil on that part of Mars was lumpier than expected, meaning less friction. The birthmark would penetrate an inch or so, less than an inch, and then it would tend to pop up again. Finally, the mission team tried to push the mole further down with the shovel on the lander’s robotic arm. The soil would be scraped on the mole, and then the shovel would be used to pound it with “hammering strokes,” hopefully for more friction. That worked to some extent for a while, but wasn’t enough to keep the mole digging on its own.
By January 9, 2021, more than 500 such hammering blows had been performed to no avail. At that point, the mission team called 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. As Tilman Spohn of the German Aerospace Center (DLR), which built the mole, stated:
We’ve given everything we have, but Mars and our heroic mole remain incompatible. Fortunately, we learned a lot that will benefit future missions that try to dig underground.
The mission team used the shovel on the end of the robotic arm to attempt to drive the heat probe deeper into the ground. However, the attempts were unsuccessful due to the lack of friction in the soil due to lumpiness. Image via NASA / JPL-Caltech.
Artist’s concept of NASA’s InSight lander on Mars, with an exploded view of the subsurface. Image via PGP / Nicolas Sarter / JPL-Caltech.
Other landers and robbers have used shovels to dig into the surface layers of the soil to obtain samples, but InSight’s mole was intended to dig significantly deeper. The failure to dig deep enough is disappointing, but it certainly wasn’t because of a lack of trying, 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 who have worked hard to move InSight’s birthmark deeper into the planet. It was great to see them solve 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 sense, we have been successful: we have learned much 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 lumpiness of the ground was surprising, as the testing of the instrument on Earth was based on properties of the soil of Mars seen during previous missions to Mars. But the ground at InSight’s landing site, in Elysium Planitia, turned out to be different from that 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 with no inheritance. What we’ve tried to do – dig so deep with such a small device – is unprecedented. Having had the chance to bring this all the way to the end is the greatest reward.
InSight has many different scientific tools. The heat flow probe, shown on the right, should burrow about five meters into the ground. Image via NASA / JPL-Caltech.
Diagram of the heat flow probe. Image via DLR / InSight Project / Spaceflight 101.com.
However, everything is not lost. The setback gave the mission team more experience with the robotic arm and the opportunity to learn more about the soil at this location. What makes it more lumpy?
Another task in the near future will be to use the robotic arm to bury the cable connecting the seismometer instrument – called the Seismic Experiment for Interior Structure (SEIS) – to the lander. It is hoped that this will reduce the amount of crackling and popping noises in the seismic data due to temperature changes.
SEIS records the “pulse” of Mars, listening for subsurface seismic activity, and has recorded more than 480 quakes so far. Most of them are very small, but they tell scientists how active Mars is below the surface. So far it appears to be somewhere between the Earth and the Moon. Some of the seismic activity detected by InSight comes from areas of 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 is still in excellent health, which is good news, and the mission has been extended for an additional two years, until December 2022. That means a lot more science can be done with all the 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 to determine how geologically active the planet still is, and how it has formed and changed over the past billions of years. An onboard radio experiment called Rotation and Interior Structure Experiment (RISE) is designed to find out if Mars’ core is still liquid or solid, and what its overall composition is, including iron.
InSight also monitors Mars’s weather above the surface, with some of the most advanced weather sensors ever sent to the planet. The Curiosity rover will also monitor the atmosphere and weather, as will the Perseverance rover when it lands next month, February 18. All three together will create the first meteorological network on another planet, another huge achievement.
The mole may not be digging anymore, but the mission is far from over and there is still a lot of good science to come!
In short, the mission team for NASA’s InSight lander on Mars has called off all further efforts to attempt to dig deep into the ground with the heat probe instrument called “the mole.” However, the remainder of the mission will continue with an extension until December 2022.
Via JPL
