It's been a long road for InSight & # 39; s Mole. InSight landed on Mars almost two years ago, in November 2018. While the lander's other instruments are working flawlessly and returning scientific data, the mole has struggled to find its way into the planet's surface.
After a lot of hard work and a lot of patience, the mole finally managed to bury itself in the Marian regolith.
But the drama doesn't end there.
The mole is a 16-inch long thermal probe that pounds deep into the surface. The maximum depth is 5 meters below the surface and that is the ideal operating depth. But it can also collect useful scientific data at shallower depths of around 3 meters. As it is now, the mole is nowhere deep enough to practice any science.
But after two years this is still the deepest it has ever been.
The real name of the mole is HP3 (Heat Flow and Physical Properties Package). It was designed to measure the heat coming from inside Mars. The cable that connects it to the InSight lander contains thermal sensors along its length. InSight stands for interior exploration with seismic investigations, geodesy and heat transport. The heat transfer part of the mission is the job of the mole.
There have been problems since using the instrument. The mole enters by slowly hammering itself into the ground. However, this hammer movement is due to friction between the mole and the sides of its hole. Without this friction, the instrument will simply spring back out of the hole.
The InSight thermal probe (HP3) emerged from its hole shortly after being deployed. Photo credit: NASA / JPL-Caltech
The problem is what is known as duricrust. It is a hardened surface layer that forms in dry areas. And Mars is definitely dry. The duricrust around the mole prevents soil from falling into the mole's hole when hammering, and removes the friction necessary from the instrument to hammer its way into Mars.
While InSight is primarily a NASA mission, the pier was designed and built by the DLR (German Aerospace Center). They worked with NASA's JPL, which has a technical version of the mole on a test bed. There they tried to overcome these challenges.
You tried to apply side pressure on the mole with the shovel at the end of the InSight instrument arm, hoping to get the friction required. They have also tried pushing on the mole while carefully avoiding the delicate leash. And they tried to pick up loose material with the shovel and put it in the hole of the mole.
The shovel on the InSight instrument arm puts pressure on the mole. Photo credit: NASA / DLR
Today NASA announced that the mole was finally buried in the dirt. This is kind of a win, but there is still a long way to go. Now that it is buried, the InSight team will continue to shovel more soil onto the instrument and push it down before it continues pounding.
But it all takes time.
"I'm very happy that we were able to recover from the unexpected 'pop-out' event we witnessed and get the mole deeper than ever," said Troy Hudson, the scientist and Engineer at NASA's Jet Propulsion Laboratory who led the work to dig the mole. "But we're not quite done yet. We want to make sure that there is enough soil on the mole so that it can dig on its own without the help of the arm," said Hudson in a press release.
It will take months to scoop and tamp the soil. NASA says the hammering is unlikely to resume until January 2021. Part of what hinders operation is the buildup of dust on InSight's solar panels. This reduces the power available for the entire mission.
One of Mars InSight's two 2.2 meter wide solar panels was imaged by the lander's Instrument Deployment Camera attached to the elbow of its robotic arm. The accumulated dust on the panels reduced the power available for the mission. Credits: NASA / JPL-Caltech
Tilman Spohn is scientific director for the mole at DLR. He wrote a blog about the effort to get the mole up and running. In today's post from October 16, 2020, Spohn spoke about the next steps and how they are working towards another "Free Mole Test". The free mole test consists in the mole trying to hammer its way below the surface without the help of the shovel.
"After some discussion of the next steps, we decided to perform two parallel paddle movements on Saturday October 17th (Sol 659)," he wrote.
The mole is now buried under the surface of Mars, but has not yet cleared all the hurdles. On October 17th, the instrument arm shovel will make two parallel movements to put more soil over the mole. Photo credit: NASA / DLR
"Then a thermal conductivity measurement is carried out, which should also give us indirect information about the filling," writes Spohn. “Then the filling is squeezed to compress the sand and press down on the mole. Depending on the outcome of the backfill, further actions to fill the pit will be planned before further hammering, and later another free mole test will take place. "
On Earth, it would be easy to use a drill to get below the surface. However, drills are heavy, requiring a lot of strength and stability to keep them from rotating instead of drilling. That's just not possible on Mars. A drill would weigh way too much and use a lot more strength than the mole. The mole is only 2.7 cm (1 inch) in diameter and about 40 cm (16 inches) long. It had to be both light and small enough to fit within the confines of the mission.
Hopefully the mole will eventually reach its working depth. In the meantime, InSight's other tools are working and returning data. Thanks to the SEIS (Seismic Experiment for Interior Structure) we know that Mars is a seismically active planet.
But without the mole and its heat transfer properties, the InSight lander will never do its mission justice.