NASA’s mole failed to dig deep into Mars failed. And after? | Space



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Animation of robot arm repeatedly hitting dusty red ground.

Here is the thermal probe from NASA’s InSight lander – dubbed “the mole” – on October 3, 2020, as the spike-shaped mole still tried to burrow into the red Martian soil. The copper-colored tape attached to the mole has sensors to measure the heat flux of the planet. NASA engineers have now ended this part of the mission. Image via NASA / JPL-Caltech.

A key aspect of NASA’s InSight mission to Mars sadly came to an end last week. NASA announced that InSight’s HP3 thermal probe – aka the mole – failed to get the friction needed to dig as deep into the surface of Mars as expected. 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 got an extension, giving it more time on the surface of Mars to complete its other tasks.

The mole – officially known as the “Heat Flow and Physical Properties Package” – was designed to dig up to 16 feet (5 meters). The goal was to take measurements of the internal temperature of Mars, providing vital clues to the degree of geological activity of Mars and the amount of heat it still retains inside.

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The problem was, the mole required friction from the surrounding soil in order to continue digging deeper. It turns out that the ground in this part of Mars was more lumpy than expected, which means less friction. The mole would penetrate a few inches or so, less than an inch, and then it would tend to move up. Eventually, the mission team began trying to push the mole lower with the shovel on the lander’s robotic arm. Dirt would be scraped off the mole and then the shovel would be used to tamp it down with “hammer blows”, hopefully providing more friction. It worked to some extent, for a while, but still wasn’t enough to keep the mole digging deeper on its own.

As of January 9, 2021, more than 500 hammer blows of this type had been carried out, to no avail. At that point, the mission team ended the effort.

It’s unfortunate, but – as you can imagine – unexpected issues often arise when exploring worlds hundreds of millions of miles away. As Tilman Spohn of the German Aerospace Center (DLR), who built the mole, said:

We’ve given him 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 underground.

Long metallic cylindrical arm with shovel at the end, on reddish ground.

The mission team used the shovel at the end of the robotic arm to try and drive the heat probe deeper into the ground. The attempts were unsuccessful, however, due to the lack of friction in the soil due to the formation of lumps. Image via NASA / JPL-Caltech.

Robotic lander on a planetary surface, with a sectional view of the subsoil.

Artist’s concept of NASA’s InSight lander on Mars, with a sectional view of the basement. Image via PGP / Nicolas Sarter / JPL-Caltech.

Other landers and rovers used shovels to dig into the top layers of the soil to obtain samples, but InSight’s mole was intended to dig much deeper. Not digging deep enough is disappointing, but it’s certainly not for lack of trying and it’s always a success in other ways. As Thomas Zurbuchen, Associate Administrator for Science at NASA, said:

We are very proud of our team who have worked hard to bring the InSight mole deeper into the planet. It was amazing to watch them help out 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 succeeded: we have learned a lot that will benefit future missions to Mars and elsewhere, and we thank our German DLR partners for providing this instrument and for their collaboration.

So what is wrong?

The agglomeration of the soil was surprising, as the instrument’s testing on Earth was based on the properties of Martian soil seen during previous missions to Mars. But the ground at InSight’s landing site at Elysium Planitia turned out to be different from that seen at any other landing site. According to Troy Hudson, scientist and engineer at NASA’s Jet Propulsion Laboratory (JPL):

The mole is a device without inheritance. What we have attempted to do – dig so deep with such a small device – is unprecedented. To have had the opportunity to go all the way is the greatest reward.

Robotic lander with solar panels and other instruments, on a reddish floor with parts labeled.

InSight has many different scientific instruments. The heat flow probe, shown at right, was supposed to burrow about five meters (16 feet) into the ground. Image via NASA / JPL-Caltech.

Schematic drawing of the mole with the parts labeled.

Schematic of the heat flow sensor. Image via DLR / InSight Project / Spaceflight 101.com.

However, all is not lost. The setback allowed the mission team to gain more experience using the robotic arm and learn more about the ground there. What makes it lumpier?

Another task in the near future will be to use the robotic arm to bury the tether that connects the seismometer instrument – called the Seismic Experiment for Interior Structure (SEIS) – to the lander. It is hoped that this will reduce the amount of crackles and pops heard in the seismic data due to temperature changes.

SEIS takes the “pulse” of Mars, listens for seismic activity below the surface, and has so far recorded more than 480 earthquakes. Most are very small by far, but they tell scientists how active Mars is below the surface. So far it appears to be somewhere between Earth and 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 be in excellent health overall, which is good news, and the mission has been extended for two years, until December 2022. This means there is still a lot more science. to do with all other InSight instruments.

Reddish planet cut in half showing inner layers offered in orange, yellow and white.

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 is still, and how it has formed and changed over the past billions of years. An onboard radio experiment called the Rotation and Interior Structure Experiment (RISE) is designed to find out whether the core of Mars is still liquid or whether it is 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 18. All three will together create the first weather network on another planet, another great achievement.

The mole may not be digging anymore, but the mission is far from over, with a lot of good science to come!

Bottom line: NASA’s InSight Mars lander mission team canceled any further attempts to try and dig deep into the ground with the thermal probe instrument called “the mole”. The rest of the mission continues, however, with an extension until December 2022.

Via JPL

Paul Scott Anderson

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