Here’s How NASA Might Rescue InSight’s Extremely Stuck Heat Probe

NASA InSight’s robotic arm will use its scoop to pin the heat probe against the wall of its hole.
Image: NASA/JPL-Caltech

Back in February, the heat probe of NASA’s InSight lander didn’t get very far while trying to tunnel a hole into Mars. It’s been stuck ever since, but NASA has devised a plan in the hopes of getting the probe moving again.

NASA’s InSight lander arrived at Elysium Planitia, a plain near the Martian equator, back in November 2018. On February 28, 2019, the lander began an important phase of the mission: deploying its heat probe, a component of the Heat Flow and Physical Properties Package (HP3). Designed by the German Aerospace Center, the probe, or “mole,” is designed to measure the amount of heat escaping from beneath the Martian surface, and it was supposed to get as deep as 5 meters (16 feet).

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Unfortunately, the heat probe only managed to get down some 35 centimeters (14 inches) before it stopped. So little progress was made that the top of the mole is still sticking out from the hole.

In the months since, NASA has not been able to remedy the situation, and it’s been a rather big disappointment. At the time, the InSight team figured the heat probe struck a shallow rock, preventing its progress. Unfortunately, the team can’t just pull the device out and start again elsewhere; the probe is a one-and-done deal, as it’s unable to move in reverse.

Evidence gathered over the summer suggests the heat probe may not have hit a rock at all, but instead a very dense patch of material. This has now raised hopes that a solution might be found to put the probe back into action, according to a NASA release posted on Thursday.

The new plan will use the scoop on the end of InSight’s robotic arm to assist with the heat probe’s hammering. In the proposed “pinning” tactic, InSight’s arm will shove the scoop into the probe to push against the edge of the hole. As InSight engineer Ashitey Trebbi-Ollennu put it in a NASA video, “We believe we will constrain the motion of the mole more in the direction downward so we might make forward progress.”

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This plan has already been put into action, with InSight repositioning its arm this past weekend, according to NASA. The pinning maneuver will be attempted during the next few weeks.

The first signs that a plan like this might work came in June, when team members used the arm to remove a structure designed to hold the mole steady while it worked. By removing the obstruction, the team was able to peer down into the hole. Now, it’s still certainly possible that the probe met an impenetrable rock, but the new visual evidence suggested another possible culprit: a 5-to-10 centimeter (2-to-4 inch) layer of duricrust, which NASA described as “a kind of cemented soil thicker than anything encountered on other Mars missions and different from the soil the mole was designed for.”

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This is potentially good news, because progress through this dense layer may still be possible. It’s just that the heat probe needs a little help. For the probe to dig, it needs friction. The absence of dirt prevents the self-hammering action from pulling the probe further down. Without a medium to work in, the probe simply bounces in place like a useless pogo stick. Whether that bouncing is happening right now isn’t clear.

“Since we can’t bring the soil to the mole, maybe we can bring the mole to the soil by pinning it in the hole,” Tilman Spohn, HP3's principal investigator at DLR, said in the NASA press release.

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This isn’t the first time that NASA has tried to use InSight’s arm to remedy the situation. This past summer, the scoop was used to disturb the area around the hole in hopes of causing a collapse, thereby providing a medium for the probe to work in. It didn’t work, as the arm simply couldn’t exert the required pressure.

If the pinning tactic doesn’t work, there might still be other options. NASA is also working on a potential strategy that would see the scoop function in the way it was originally intended: working like a backhoe to scrape and pull dirt into the current hole.

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Trebbi-Ollennu said he’s “cautiously optimistic” that the team will get the mole working again. We’ll now have to wait and see if the pinning tactic works, but one thing’s for sure: NASA does not give up easily.

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George Dvorsky

George is a senior staff reporter at Gizmodo.