Scientists are trying to figure out why the "mole" of InSight can not go deeper



The engineers of the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt, DLR) are busy working with an InSight Lander replica to see if they can understand what is blocking the landing module's mole.

The mole is the short name for the heat probe of the lander, which is making its way to the Martian surface. The heat probe is actually called HP3, or package of physical and heat properties. It is designed to work at a distance of up to 5 meters (16.4 feet) on the ground, where it will measure the heat that flows from inside the planet. Those measurements will tell scientists a lot about the structure of Mars and how rocky planets were formed.

But as reported last month, the probe is blocking at about 30 cm (1 foot)

Initially, the engineers thought that the mole had hit a rock. But at a DLR facility in Bremen, they are using a replica probe, in a box containing a cubic meter of sand, to investigate the situation thoroughly. They hope to find a solution, obviously, but that is a difficult proposition when you are on Earth and the mole is on Mars.

"There are several possible explanations, to which we will have to react differently."

Matthias Grott, scientist of the HP3 project.

"We are investigating and testing various possible scenarios to discover what led to the arrest of 'Mole'," explains Torben Wippermann, Test Leader at the DLR Space Systems Institute in Bremen.

The HP3 was placed on the surface of Mars on February 12, 2019. Image credit: NASA / JPL-Caltech / DLR
The HP3 was placed on the surface of Mars on February 12, 2019. Image credit: NASA / JPL-Caltech / DLR

The InSight Lander mission went well at the beginning. There was some shallow rock near the landing site, but the site itself seemed to be free of rocks. The seismometer of the landing module, SIX (Seismic Experiment for interior structure) was placed on the surface without any problem. But when the mole was placed and began its first hammering operation near the end of February, problems arose.

At first the mole advanced. But then he hit his first rock. He was able to make his way beyond that rock, but finally stopped and could not go beyond 30 cm.

The engineers are trying to understand what happened, but they do not have a lot of data to follow. They did a brief test of hammering with the mole on March 26, and they are using data from that test to get an idea of ​​the situation of the moles. They have some images, temperature data, radiometer data and recordings made by SIX during the hammering test to help them.

The InSight Lander seismometer under its protection against the wind and the heat shield. The data collected by SEIS during a hammering test will help engineers understand what stopped the mole's progress. Image credit: NASA / JPL-Caltech
The InSight Lander seismometer under its wind protection and heat shield. The data collected by SEIS during a hammering test will help engineers understand what stopped the mole's progress. Image credit: NASA / JPL-Caltech

The central question is what caused the mole to make such progress at the beginning, only to stop in its tracks. A stone is the obvious answer, but it may not be the correct one. "There are several possible explanations, to which we will have to react differently," says Matthias Grott, a planetary and scientific researcher on the HP³ project.

One possibility involves the nature of the sand itself, rather than obstructive rocks. To be able to make its way on the surface, the mole requires friction with each other and the sand in which it hammers. Engineers believe that it is possible that the mole has created a cavity around itself, denying itself the friction it needs to proceed.

When the mole was being tested on Earth, it was tested on an badog of Martian sand and was able to make its way to the ideal depth of 5 meters without problems. "So far, our tests have been done using a sand similar to Mars that is not very cohesive," explains Wippermann. Now, they are testing the replica in the Bremen laboratory on a different type of sand.

This type of sand is much more compact and they want to see if the mole has a kind of "dig its own grave", creating a cavity around itself. They will also place 10 cm rocks in the sand, to see if that can replicate what the Mars data is telling them. As they perform several tests, they will record seismic data and see if any of the results match the SEIS data.

"Ideally, we can reconstruct the processes on Mars as accurately as possible," Wippermann said in a press release.

Once scientists and engineers discover what is stopping the mole, they can try to find solutions. That's where NASA will get more involved.

The first full selfie of InSight on Mars. The selfie was taken on December 6 and is a mosaic of 11 images taken with his Instrument Implementation Camera on the elbow of his robotic arm. Image credit: NASA / JPL-Caltech
The first full selfie of InSight on Mars. The selfie was taken on December 6 and is a mosaic of 11 images taken with his Instrument Implementation Camera on the elbow of his robotic arm. Image credit: NASA / JPL-Caltech

The DLR designed and built the HP3 for the InSight Lander mission, but the lander itself was designed and built by NASA. And only NASA has an InSight landing replica at a test facility at JPL in Pasadena, California. So DLR has sent a replica of the HP3, or mole, to JPL. There, potential solutions involving the lander, the mole, the support structure and the robotic arm of the lander can be tested. It may turn out that the mole or its supporting structure can be lifted, or partially lifted, to solve the problem.

In any case, do not expect a quick solution.

"I think it will be a few weeks before more action is taken on Mars," says Grott.

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