InSight’s heat probe hasn’t lived up to its moniker “the mole.” It began burrowing itself into Mars’ surface back in February but hit a snag at a depth of about 14 inches. That’s a fraction of the nearly 16 feet NASA was expecting it to reach.
What happened? An unexpected rock was the worst-case scenario. But back in June, the InSight team removed a support structure meant to keep the mole steady in the hopes of getting a glimpse at what the problem could be. InSight’s camera quickly noticed something else that could be the issue – a two to four inch layer of duricrust.
NASA describes the duricrust as “a kind of cemented soil thicker than anything encountered on other Mars missions and different from the soil the mole was designed for.”
That’s a big problem because of the way the heat probe works. It needs friction from the surrounding soil in to drill through. When the thicker dirt doesn’t fall back around it, the probe just bounces in place.
Over the summer, the team used InSight’s arm to try and collapse the soil around the heat probe to give it friction it needs to keep going. Unfortunately, that didn’t pan out.
The team needed to position the heat probe as far away as possible so the spacecraft’s shadow didn’t affect any of its temperature readings. That also meant the outstretched robotic arm couldn’t press down as hard.
“We’re asking the arm to punch above its weight,” said Ashitey Trebi-Ollennu, the lead arm engineer at JPL. “The arm can’t push the soil the way a person can. This would be easier if it could, but that’s just not the arm we have.”
But NASA isn’t tossing in the towel yet on the robotic arm. Two different techniques will be tried soon. First, the team will pin the scoop at the end of the arm against one edge of the heat probe to help generate the friction it needs. If that doesn’t work, InSight engineers will use the scoop as it was intended and scrape soil into the hole and hope that it fills in around the heat probe’s hammer.
“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,” says Tilman Spohn, the heat probe’s principal investigator.
Trebi-Ollennu says the team is “cautiously optimistic” they can get the mole hammering again.
It’s rough seeing InSight make the long, dangerous journey from Earth to Mars only to run into a snag like this. The good news is, there are other instruments on InSight. The SEIS, a super-sensitive seismometer has already been delivering plenty of intriguing data.
Toss on some headphones, and listen to a pair of marsquakes recorded earlier this summer. The first one measured 3.7 in magnitude, and the second was 3.3.
The folks parsing through the SEIS data also have to account for other seismic signals including wind gusts, InSight’s robotic arm, and even vibrations within the seismometer itself.
InSight is 303 sols into a planned 709 sol mission (728 days).